FFR_chap10.txt

CHAPTER 10
HOMOGENEOUS REACTOR COST STUDIES*

10-1. INTRODUCTION

10-1.1 Relation between cost studies and reactor design factors. The
power cost associated with a reactor station may be subdivided into fixed
charges, operating and maintenance costs, and fuel costs. Fixed charges
include interest on investment, depreciation, and taxes; labor, supervision,
and maintenance are included in the operating and maintenance costs;
fuel costs include both variable and fixed chemical processing costs,t cost
of feed materials, and inventory charges. Because of the uncertainty of
these items, it is impossible to determine absolute costs for nuclear power
until large nuclear plants have been built and operated. However, it is
important that a reasonable effort be made to evaluate the cost in order to
compare several fuel or reactor systems of equal technological development,
to point out areas where substantial improvements are required, and to
provide a basis for determining whether economical power can ever be
produced.

Aqueous homogeneous reactors have certain features, such as high neu-
tron economy and continuous fission-product removal, which make them
appear to be potential economic power producers. However, as with all
water-moderated reactors, to attain steam temperatures corresponding to
thermal efficiencies of 25 to 30%, circulating aqueous systems require
operating pressures between 1000 and 2000 psia. Since thermal efficiency
increases relatively slowly with increasing operating pressure, while reactor
costs rise relatively sharply above pressures of about 1500 psi, it is unlikely
that reactors will be operated at pressures above 2000 psia. In addition,
icreasing the reactor temperature tends to decrease the breeding ratio,
which adversely affects fuel costs. Nearly all reactor systems considered
have therefore heen assumed to operate at pressures between 1500 and
2000 psia.

In order to optimize the design of a homogeneous reactor of a given
power output and pressure, it is necessary to know how both the fixed and
operating costs vary with the dimensions of the reactor core and pressure
vessel. In this regard, one must take into consideration that the maximum
diameter of the pressure vessel will be limited by fabrication problems, and
the minimum diameter of the core vessel will be limited by corrosion

*By P. R. Kasten, Oak Ridge National Laboratory.
TThe fixed costs in a chemical processing plant are those due to plant investment;
variable costs are due to materials, labor, ete.

514
10-1] INTRODUCTION 515

problems. For each combination of core- and pressure-vessel diameters
within these limits, there will be a mmimum fuel cost resulting from a
balance of inventory costs, processing costs, and tuel-feed costs; these latter
costs are determined by the breeding ratio, which is a function of fuel con-
centration and processing rate.

Although the fuel-fluid temperature influences power costs, this is nor-
mally limited by the properties of the fuel system or by the above-mentioned
pressure limitations, rather than by economic considerations. However,
the temperature range established on this basis is also close to that which
gives minimum fuel costs. In addition, the power level of the reactor is
usually assumed to be constant, although it is realized that this is a very
important factor influencing the cost of power, since plant investment
charges per unit power constitute a large fraction of the power cost and
change appreciably with power level. The effect of power level on capital
costs 1s discussed in Section 10-8, and on fuel costs in sections as noted.

The operating and maintenance costs, as well as plant investment costs,
are a funetion of reactor type and method of maintenance. However, the
exact form of some of the interrelations between design variables is not
known at the present time. For example, the plant investment and main-
tenance costs are undoubtedly different for a burner-type reactor than for
a breeder-type reactor; a cost difference would also exist between one- and
two-region systems. However, because of the lack of information, most
economic studies do not consider such differences, but assume investment
and maintenance charges to be determined primarily by the reactor power
level. The results of such studies are still significant if they are considered
in the light of the assumptions used; as more cost data are accumulated,
the results can be modified as required.

With respect to the fuel eycle costs, established Atomic Energy Commis-
sion prices for thorium, natural uranium, U232 and Pu®*, and the schedule
of charges for urantum of varying enrichments [1] provide a basis for cost
calculations. Charges for various chemical conversion steps and for proe-
essing spent fuel in a multipurpose chemical plant have also been an-
nounced [2]. Although these charges are applicable to the processing of
aqueous fuels, the possibility of including on-site processing facilities as part
of the homogeneous reactor complex must also be considered, since this
would have an effect on the reactor design.

10-1.2 Parametric cost studies at ORNL. The homogeneous reactor
systems considered include one- and two-region reactors, breeders, con-
verters, and burners. Although no one fuel or type of reactor shows a
marked advantage in power cost over all the others, the superior fuel
utilization of a thorium breeder system suggests that it is potentially the
most economical one for power production. Much effort has been devoted
516 HOMOGENEOUS REACTOR COST STUDIES [cHAP. 10

to two-region systems primarily because of the relatively high breeding
ratio and low fuel inventory obtainable.

Economic evaluations discussed in this chapter are for the most part
based on a three-reactor station generating a total of 375 Mw of elec-
tricity, where the required chemical processing facilities are shared by the
three reactors. The present choice of reactor dimensions for a given power
capability must be based on engineering judgment and the results of fuel-
cost studies. Based on fuel-cost studies, one-region reactors must be large
(14- to 15-ft diameter) in order to obtain good neutron economy; two-
region systems can have good neutron economy in relatively small sizes
(9- to 10-ft over-all diameter) but require high concentrations (1000 g/liter)
of fertile material in the blanket region. Iistimates of near-optimum reactor
sizes for different homogeneous systems are based on fuel-cost studies in
which highly enriched fissionable fuel 1s valued at $16/g and inventory
charges are 4%,. In all cases it is assumed that the particular fuel system is
technologically feasible.

In computing the cost of power, the fixed charges on capital investment
of depreciating items are assumed to be 159 /yr, including depreciation,
interest, return on investment, insurance, and taxes. Iixed charges on
nondepreciating items are assumed to be 49, /yr. Tuel, D20, and fertile
materials are assumed to be nondepreciating materials.

10-2. Bases ForR Cost CALCULATIONS

10-2.1 Fuel costs. The fuel costs associated with electrical power pro-
duced from reactors include those charges which are due to replacement of
conventional fuels with nuclear fuel. The fuel cost is considered to be the
sum of the net cost of nuclear-fuel feed; inventory charges for fertile mate-
rial, heavy water, and fuel; material losses; variable fuel-processing
charges; and fixed charges for fuel processing. Fuel-cost studies are pri-
marily for the purpose of investigating the economic importance of the
several parameters; of these parameters the most important are core
diameter, blanket thickness, fertile-material concentrations in core and
blanket, fuel concentration in the blanket, and poison fraction in the core.
In studying fuel costs, aqueous homogeneous power reactors are generally
considered to operate at a temperature of 280°C, a pressure 1500 to 2000
psia, an 809, load factor, and a net thermal-to-electrical efficiency of about
259,. The thermal power level per reactor i1s considered to be 450 to 500
Mw. Thorium (as oxide) i1s valued at $5/Ib with no significant charge for
making ThO2-D.0 slurry. Heavy water is valued at $28/Ib and highly
enriched figsionable uranium at $16/g. The amount of heavy water re-
quired 1s estimated on the basis of the total reactor-system volume and the
room-temperature density of heavy water. The makeup rate is taken as
10-2] BASES FOR COST CALCULATIONS 517

5%, vr. The volume of the core circulating system is taken as the volume
of the core plus an external volume of 1 liter for each 20 kw generated n
the core. The blanket external volume (in two-region reactors) is caleu-
lated on the basis of 1 liter for each 14 kw generated in the blanket. The
cost. of natural uranium 1s taken as $40/kg U either as UQy3 or U030y,
The cost of uranium of various enrichments in U39 13 obtained essentially
from the ALC price schedule or the equations for an ideal gaseous-diffusion
plant {3-5].

Fuel costs are dependent upon the value assigned to plutonium and U233,
In a power-only economy the value of these fissionable materials can be
no more or less than their fuel value; in these studies their value was taken
to be the same as that for U35 or $16/g. However, it U3 and/or plu-
tonium are assigned different values, the fuel costs can be significantly
affected. Thiz is shown m the results given for plutonium producers, in
which a plutonium value of $40/g was assumed (this value is consistent
with the ability of homogeneous reactors to produce plutonium containing
less than 29, Pu®*, and the AEC guaranteed fair price schedule for plu-
tonium extending until June 30, 1963).

The fuel values used in these studies are slightly different from those
announced by the AEC; the main difference is associated with the value
used for plutonium. However, the effect of various plutonium values on
fuel cost is indicated in the section on plutonium producers. The AEC-
announced prices for nuclear materials are given in Table 10-1.

Since the rate of fuel burnup is small with respect to the inventory of
fuel required for criticality, the investment and inventory charge for fuel
materials can be appreciable. Unless otherwise specified, inventory charges
for uranium, thorium, plutonium, and heavy water are assumed to be 4%,
of their value per year.

An economic consideration in the design of nuclear power plants is the
chemical processing requirement of the spent nuclear fuel. Aqueous
homogeneous reactor fuels can be processed by either the Purex or the
Thorex process. Both involve solvent extraction and require that the
fuels be separated from the D»0O for economical processing. The Purex
process is used for separating plutonium, uranium, and fission-product
poisons, while the Thorex process is used for the separation of thorium,
uranium, and fission products. Since investment costs in chemical process-
ing plants are presently high, a single processing plant for one good-sized
reactor is not economical. Rather, central processing facilities which serve
many reactors are usually assumed to be available. In the fuel-cost studies
given here, however, the chemical processing plant is considered to serve
a single three-reactor station generating about 1440 thermal Mw (total).
For this size processing plant, the fixed charges (based on 159, of invest-
ment per year) are estimated to be about $5500/day for either Purex or
518 HOMOGENEOUS REACTOR COST STUDIES [cHar. 10

TaBLE 10-1

U.S. AEC OrriciaL PrRICE SCcHEDULE FOR
NvUcLEAR MATERIALS [1]

 

(a) Price schedule of U235 as a function of enrichment

 

 

 

7 141 T235
W t(fdl;a%;?:) v $/kg total U $/gm U235 content
0.0072 40.50 5.62
0.010 75.75 &.09
0.020 220.00 11.00
0.030 375.50 12.52
0.10 1,529.00 15.29
0.20 3,223 00 16.31
0.90 15,361.00 17.07

 

 

 

(b) Price schedule of Pu as a function of Pu?#0 content

 

 

 

9 Pu20 ‘ Pu price, $/gm
2 1 41.50
4 38.00
6 34 .50
>8.6 30.00

 

(¢) Chemical conversion costs

 

Conversion Cost, $/kg

 

 

Uranyl nitrate = Ul

(U containing 59, or less by weight of T239) 5.60
Uranyl nitrate = UFg

(U containing greater than 59 by weight of U235) 32.00
Plutonium nitrate —- metal buttons 1,500.00
UFs (natural U) to oxide Zer0

 

(d) Valite of U233 (high purity) $15/g

 

 

 

 
10-2] BASES FOR COST CALCULATIONS 519

Thorex (complete decontamination) [6,11]. This corresponds to a power
cost due to chemical plant investment of 0.76 mill/kwh (based on a 375-Mw
net electrical capacity and an 809, load factor), which will be independent
of the amount of material processed daily.

The variable processing charges arising from labor, materials, and other
factors dependent on the throughput of fuel and fertile material are repre-
sented by Egs. (10-1) and (10-2) for processing thorium-uranium mixtures
and uranium-plutonium mixtures, respectively.

Thorex process

Variable daily processing cost = $3.00 Wy, 4+ 0.50 wy + 0.35 rp,o. (10-1)
Purex process

Variable daily processing cost = $3.50 Wy + $1.00 wp, + 0.35 vp,0. (10-2)
In the above equations:

vp,0 = liters D20 recovered/day,

wpy = ¢ Pu handled separately from U per day,
wy = g U processed per day,

W = kg Th processed per day,

Wy = kg U completely decontaminated per day.

Thus, for Thorex, the variable processing charge is considered to be
$3.00 'kg of thorium processed, plus $0.50/g total uranium processed
(U highly enriched in U233 4+ U23%), plus $0.35/liter of D20 recovered.

Note that Eqs. (10-1) and (10-2) take into consideration the effect of
throughput of fissionable material as well as fertile material on the variable
processing charges in a chemical plant of fixed size. This information Is
necessary in determining the optimum concentrations of fissionable and
fertile material in a reactor of specified dimensions.

The total processing cost in an on-site chemical plant, such as that
described above, will be 0.76 mills 'kwh plus the variable processing charges
and minus the credit for any net fissionable material produced. Thus the
chemical-plant investment costs exert a strong influence on the fuel costs.
These costs are lower if a large multipurpose chemical plant is available to
handle the fuel instead of the on-site plant. Fuel processing charges [2]
have been announced by the United States Atomic Energy Commission
for processing in such a multipurpose plant. These charges amount to
$15,300 per day, and apply to a plant having a daily capacity of 1 ton if
slightly enriched uranium (less than 3% U23% by weight) is processed, or a
daily capacity of 88 kg if highly enriched uranium is considered. In terms
of cost per gram of U2 processed, the above processing charges are
H20) HOMOGENEOUS REACTOR COST STUDIES [cHar. 10

equivalent to $2.15 per gram of U232 for natural uranium, $0.51 per gram
of U3 for uranium of 3% enrichment, and $0.37 per gram of U235 for
uranium of 479 enrichment. These values can be compared with those
considered previously, namely: $0.50 per gram of total uranium processed
(the enrichment of the uranium in the highly enriched systems is about
5090), and $3.50 per kilogram of natural or slightly enriched uranium
(equivalent to $0.50 per gram of U23% in natural uranium) plus $1.00 per
gram of plutonium. Thus, in most cases, the AEC total processing charges
amount to less than the variable processing charges considered here. In
case of a central processing plant, however, it would be necessary to in-
clude fuel-shipping charges and charges associated with preparing the
processing plant for the specific fuel.

In studying the poisoning effect of fission fragments, three groups of
fission-product poisons are considered. The first group consists of gases;
the second, nongaseous fission fragments having high microscopic cross
sections (greater than ~10,000 barns); and the third is composed of non-
gaseous fission fragments having low microscopic cross sections, and which
transmute to nuclides having the same low cross section. For processing
rates which do not cause excessive variable processing costs, only the third
group of poisons is affected by chemical processing; the first group is re-
moved by means other than Thorex or Purex, while the second group at-
tains equilibrium through neutron capture.

In processing U-Pu systems, a 20-day cooling period takes place hefore
processing 1 a Purex plant. Following complete decontamination, the
uranium is permitted to cool 100 more days before being re-enriched in a
diffusion plant. This 120-day holdup and also a 30-day feed supply are
considered in calculating inventory charges. In processing thoria slurries
(core region), the holdup time prior to processing i1s considered to be 95
days, to permit about 909 of the Pa233 to decay to U233, The processed
material is then held for an additional 110 days to permit the remaining
Pa233 to decay. For thoria slurries in blanket regions, an initial holdup of
55 days is assumed prior to processing, with an additional 150-day holdup
to permit the Pa23? to decay to U233, Thus the protactinium is held up for
205 days, in which time only about 0.5% has not yet decayed. This holdup
time and a 30-day feed supply are considered in caleulating material in-
ventories. Protactinium is valued as uranitum when outside the reactor,
but no inventory charge is placed against the amount contained in the
reactor system. This procedure is used to take into account that period of
reactor operation between startup and near-equilibrium conditions. Unless
otherwise indicated, the results are based on the assumption that equilib-
rium exists with respect to the nuclei concentrations. The isotope and
fuel concentrations are established by means of material-balance equations
and the critical equation.
10-3] FUEL COSTS IN THO2-UQ3 D20 SYSTEMS 521

In nearly all cases, fuel concentrations required for criticality are ob-
tained using the two-group model [7], in which all fissions are assumed to
oceur in the thermal group [see Eqs. (2-7) through (2-10)]. Resonance
capture is assumed to occur only in fertile material and only when neutrons
are transferred from the fast to the slow group. For the one-region U-Pu
systems, a six-group model is used in the nuclear calculations to allow for
the resonance absorptions in uranium and plutonium. Unless otherwise
specified, the thermal values for the various etas are n(U233) = 2.25,
n(U23%) = 2,08, n(Pu??) = 1.93, and n(Pu?*!) = 2.23.

10-2.2 Investment, operating, and maintenance costs. The costs con-
sidered here involve capital investment, and those associated with main-
taining and operating the nuclear power plant. Becau=e of the lack of
knowledge and experience in design, construction, and operation of nuclear
power systems, it is difficult to evaluate these costs, and most estimates
are based on the expectation that nuclear reactor plants will have lifetimes
about as long as those of conventional power plants. A 20-year depreciation
rate is assumed for permanent facilities and a 10-year depreciation rate for
all equipment associated with the reactor proper. Preparing a realistic
estimate of the cost and the required maintenance of a large homogeneous
reactor ig particularly difficult, since the equipment must handle large
amounts of radioactive material. Little experience has been obtained in
manufacturing the required equipment, and generally the costs are based
upon estimates by manufacturers. These estimated costs of equipment for
a specific reactor power are scaled according to the reactor power raised
to the 0.6 power to obtain the variation of investment cost with power
level. The annual operating and maintenance charges have been estimated
by roughly applying the corresponding charges (based on percentage of
:apital investment) in conventional steam plants; however, these estimates
cannot be considered realistic until considerable experience has been ob-
tained by operating actual reactors. These estimates correspond to 3%
of the total capital investment per year.

10=3. Errect oF DEsioN VARIABLES oN THE FueL Costs
N THO2-UO3-D20 SysteEMms [8-10]

10-3.1 Introduction. Fuel costs are given here for spherical two-region
reactors with UZ303—ThOs D»0O slurry employed in both the core and
blanket regions. Results are also given for the case of no thorium in the
core and also for one-region reactors. In addition, some results are given
for two-region reactors having cylindrical geometry. In the two-region
systems, materials from the core and blanket are assumed to be fed to a
Thorex plant for chemical processing. Thoria can be returned to both
522 HOMOGENEOUS REACTOR COST STUDIES [cuaP. 10

Feed D,O Makeup Thorium Feed

30 Days
Feed D20 Supply on Supply ofl
Storage Thorium
‘ Core -— Core Blanket —={ Blanket

Reactor u External External
System e
Volume g - Volume

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    

   
    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Core *Poison Hydroclone Separation
Rem'ovcl of Fission Products
D50
Recovery I DZO Evaporation ——
Pre-Chemical o Core Blanket Holdup,
p i and Initial
r:cnla:smg ;'lo|dup, Additional Processing
oldup 5 Days Holdup, 55 Days
150 Days Pa
________________ U_ — - —-——
] Y
Core Blanket
Chemical Chemical
Chemical Processing ~__Processing
Processing u I Poisons Poisons U Th {

 

 

 

 

 

Products Fission Products Net Uranium
Production

High Purity y233

Fig. 10-1. Schematic fuel-processing flowsheet for a two-region homogeneous
thorium breeder reactor.

regions and fuel is returned to the core as needed to maintain criticality;
the fissionable material produced in excess of that required is considered
to be sold. The fuel product is computed to be a mixture of U233 235
and other uranium isotopes, as determined by the isotope equations and
the critical equation. The system is assumed to operate under equilibrium
conditions. A schematic flowsheet of the chemical processing cycles for a
two-region reactor having a solution-type core region is given in I'ig. 10-1.
The flowsheet for the one-region system would be similar to that for the
blanket of the two-region system, except that processed fuel and thoria
would be returned to the single region.

In the processing cycle shown in Fig. 10-1, essentially two methods of
removing fission-product poisons are considered. One is the removal of
precipitated solids by hydraulic cyclones (hydroclones); by this means
the insoluble fission products are removed from the reactor in a cycle time
of about a day. The second is the removal of essentially all fission produects
10-3] FUEL COSTS IN THO2-U03-D20 SYSTEMS 523

by processing tne fluid in a Thorex-processing plant. Processing by hydro-
clones can he done only with solution fuels; the associated cyele time 1s so
short that fission products removed by this method ean be considered to
he removed from the reactor as soon as they are formed. Thorex processing,
although removing all fission products that pass through Thorex, 18 much
more costly than hydroclone processing. Because of this, the associated
cyele time 18 usually several hundreds of days.  In what follows, unless
specified otherwise, the term fuel processing applies only to Thorex or
Purex processing,

The essential difference between the processing eycele shown m Fig., 10-1
and that for solid-fuel reactors 1s assoctated with the continuous removal
of fission-product gases and of insoluble fission products (in solution re-
actors). I‘uel and fertile material processed by Thorex would undoubtedly
be removed from the reactor on a semibatch basis.

The three groups of fission-product poisons considered previously are
not all affected by Thorex processing; group-1 poisons (the fission-product
gases) are assumed to be physically removed before processing, while
group-2 poisons (nongaseous nuclei having high cross sections) are effec-
tively removed by neutron capture within the reactor system (¢, of these
nuclel 1s of the order of 10,000 barns). The macroscopic cross section of
these two groups of poisons is taken as 1.897 of the fission cross section.
Of this, 0.89, is due to nongaseous high-cross-section nuclel, while 144 is
due to the gaseous high-cross-section nuclei. The concentrations of low-
cross-section nuclei (third group) are affected hy Thorex processing (how-
ever, for reactors containing a fuel solution, the nonsoluble group-3 poisons
are assumed to be removed by hydroclone separation). The charge for
hydroclones operating on a olie-day cycle is taken as 0.03 mill,/'kwh, based
upon a charge of $75/day per reactor. Ior these solution reactors it 1s
assumed that 759, of the group-3 poisons are insoluble and removed by
hydroclones; in these circumstances only 259; of the generated group-3
poisons are removed by the Thorex process. With slurry-core reactors, all
group-3 poisons which are removed are removed by Thorex processing.

The parameter ranges covered in the spherical reactor calculations are
given in Table 10-2. Values used for n*? and resonance escape probability
are presently accepted values; however, in a few cases they were varied in
order to estimate how the results are affected by these changes. In the
following sections the influence of specific parameters upon fuel cost is
discussed.

10-3.2 Two-region spherical reactors [8]. (1) Concentration of U™3 in
blanket and core poison fraction. The optimum values of these variables are
found to be largely independent of other parameters; moreover, there is
little change in fuel cost with changes in either blanket U233 concentration
524 HOMOGENEOQUS REACTOR COST STUDIES [cmaP. 10

 

e ' | T

 

Net Fuel Cost
{mills/kw-hn

 

 

 

Blanket Thickness (f)

F1c. 10-2. Fuel cost as a function of blanket thickness for various blanket
thorium concentrations. Power per reactor = 480 Mw (heat), core diameter = 5 ft,
core thorium = 200 g/liter, core poison fraction = 0.08, blanket U233 = 4.0 g/kg
Th, 523 = 2.25,

or core poison fraction. For all slurry-core systems, the optimum poison
fraction is about 0.08, independent of the other design parameters. The
optimum poison fraction for the solution core is about 0.07. The lowest
fuel cost occurs at a blanket U233 concentration of about 4.0 g/kg thorium.

TaBLE 10-2

PArRaMETER VALUES UseED IN SLURRY REACTOR STUDIES

 

 

 

 

 

Two-region reactors | One-region reactors

Core diameter, ft 8-15 8-20
Blanket thickness, ft -3
Core thorium concentration,

g/liter 0-300 0-400
Core poison fraction, 9; 3-20 4-12
Blanket thorium concentration,

g/liter 500-2000
Blanket U233 concentration,

g/kg thorium 1-7

 

 

 

(2) Blanket thickness and blanket thortum conceniration. An example of
the effects of these parameters on fuel cost is presented in Fig. 10-2 for a
slurry-core reactor. Here it is noted that the blanket thorium concentra-
tion has relatively little effect on the minimum fuel costs. The blanket
thickness giving the lowest fuel cost lies between 2 and 2.5 ft. As is ex-
pected, higher thorium loadings are desirable if thin blankets are necessary
on the basis of other considerations. Systems having low concentrations of
thorium in the core require more heavily loaded blankets to minimize fuel
costs. For solution cores, still heavier and thicker blankets are desirable,
particularly if the core diameters are small.
10-3] FUEL COSTS IN THO2-UO3-D20 SYSTEMS 525

 

[ | |

   
 

Core Thorium|
{g/liter}

- —

-
-l
_____

Net Fuel Cost (mills /kw-hr)
i
3

 

 

 

4(2.5) 5{2) 612) 712}
Core Diameter (Blanket Thickness) (f8)

F1c. 10-3. Fuel cost as function of core diameter and core thorium concentration,
Power per reactor = 480 Mw (heat), blanket thorium = 1000 g/liter, blanket U233
= 4.0 g/kg Th, core poison fraction = 0.08, 23 = 2.25.

(3) Core thorium and core diameter. The effects of these variables upon
fuel costs are shown in Fig. 10-3. These results indicate (on the basis of
fuel cost alone) that the small solution-core reactors (ThOs core concen-
tration equal to zero) have a slight advantage over the slurry reactors.
However, the power density at the core wall is between 160 and 300 kw/liter
for such reactors operating at the given power level of 480 thermal Mw. If
larger cores are required because of power-density limitations, the fuel-cost
advantage moves to the slurry core. The slurry-core systems yield higher
outputs of generated fuel, although all the reactors shown have breeding
ratios greater than unity (see Chapter 2). As illustrated in Fig. 10-3, the
minimum fuel cost is about 1.2 mills/kwh, independent of core diameter.
The fuel cost associated with a core thorium concentration of zero is lower
than that associated with a core thorium concentration of 50 g/liter; this
is due to the ability to use hydroclones to remove fission products only
when a fuel solution is used. The hydroclone installation adds only
0.03 mill/kwh investment cost to the system, while the variable Thorex
processing cost is reduced by two-thirds; this results in the decrease in fuel
costs as shown. The relative flatness of the optimum net fuel cost curve in
Fig. 10-3 is due to compensating factors; i.e., changes in processing charges
and yield of product are offset by accompanying changes in the fuel in-
ventory charge. Similar compensating effects account for the insensitive-
ness of fuel costs to changes in other design parameters.

Table 10-3 presents a breakdown of costs for some typical reactors hav-
ing low fuel costs. The changes which occur when thorium-oxide slurry is
526 HOMOGENEOUS REACTOR (OST STUDIES [cHAP. 10

Tasri 10-3

Cost BrEAKDOWN FOR SoME Typican REACTORS

 

Core diameter, ft 6 5 4 6 14
Blanket thickness, ft 2 2 24 2 i
Core thoriuin concentration,

g/liter 200 100 0 0 250
Blanket thorium concentration,

g /liter 1000 1000 1000 1000
Blanket U232 concentration,

g/kg thorium 4 4 4 4
Core poison fraction 0.08 0.08 0.08 0.08 0.08
Critical concentration,

g U238 liter 9.4 |64 |41 14 |68
Net breeding ratio 1,102 | 1.081 | 1.089 | 1.045 | 1.012
Core wall power density, kw/liter | 53 91 170 80
Core cycle time, days 637 418 884 342 1094
Blanket cvcle time, days 265 205 176 210

Inventory of U2 and U235 kg | 368 272 200 148 522
Inventory of heavy water, Ib 96,100 | 87,400 @ 89,600 | 99,500 | 157,000
Net U2 and U235 production,

o/day 49 39 43 21 6
Grams of U233 per g of U pro- j
duced 0. 67 0.65 0.77 (.72 0.41
Estimated cost, mills/kwh
Uranium inventory 0.27 0.20 0.15 0.11 0.38
D20 inventory and losses (.27 0.25 (.25 0.29 0.45
Thorium inventory and feed 0.01 0.01 0.01 0.01 0.01
Fixed chemical processing 0.76 0.76 0.76 0.76 0.76
Core processing 0.13 0.13 0.07 0.08 0.19
Blanket processing 0.09 0.12 0.18 0.18
TUranium sale, credit 0.33 0.26 0.29 0.15 0.04
Net fuel cost 1.22 1.22 1.16 1.29 1.76

 

 

 

 

 

 

 

 

used in the core can be seen by comparing results for the two 6-ft-core-
diameter reactors.

(4) Reactor power. The above results are based on the concept of a three-
reactor station of 1440-thermal-Mw capacity, each reactor producing
125 Mw of electricity. The effect of varying power alone is shown in
Table 10-4; the fuel cost is found to be a strong function of power capa-
bility. The greater part of the change is due to variation in the fixed
chemical-processing charge. Since the total fixed processing cost
($5500/day) is assumed to be independent of throughput, this charge on
a mills/kwh basis is inversely proportional to the reactor power.
10-3] FUEL COSTS IN THOo—UO3—D20 SYSTEMS 527

TavLr 104

Errect oF Power LeveL ox I'uen Costs

 

 

 

Ileetric power per Net fuel cost, lj]"fe(‘i .('hen;u':?l.-
reactor, Mw mills ‘kwh pl()(,es'smg Charse,
’ mills/kwh
80 1.75 1.19
125 1.22 0.76
200 0.88 0.48

 

 

 

 

 

(5) Nuclear parameters. The values of n(U?%) and the resonance escape
probability of thorium-oxide slurries are not known with certainty. There-
fore the etfects of changes in these parameters on the results were com-
puted in order to examine the reliability of the nuclear caleulations. The
fuel cost increases by about 0.2 mill/kwh if %% is changed from 2.25 to
2.18, and 1s reduced by about the same amount if the 23 value is taken to
be 2.32 rather than 2.25.

The importance of resonance escape probability for thoria-D»O slurries
(p") upon fuel cost was studied by using values for (1 — p®) which are
209, higher or lower than a standard value. With a core thorium concen-
tration of about 200 g/liter, the changes in p®? have a negligible effect upon
fuel cost. At lower core thorium concentrations, the changes in p°2 result
in fuel-cost changes of about (.05 mill /kwh.

(6} Xenon removal. For most of the cases studied, the contribution of
xenon to the poison fraction is assumed to be 0.01. To achieve this condi-
tion, about 80% of the xenon must be removed before neutron capture
occurs. Since xenon-removal systems for slurries have not been demon-
strated to date, the effect of operating without xenon removal was studied
by increasing the xenon poison fraction to 0.05 (the samarium contribution
was held at 0.008). In the systems examined, when the xenon poison frae-
tion was increased by 0.04, the total poison fraction yielding the lowest fuel
cost also increased by approximately the same amount. The values in
Table 10-5 illustrate this etfect by comparing two cases at optimum total
poison fraction, but at different xenon poison levels. Thus the variable
part of the core poison fraction (and the core processing rate) remains about
the same. The higher fuel cost at the higher xenon level appears to be al-
most entirely a result of the reduction in breeding ratio.

10-3.3 One-region spherical reactors [8]. (1) Poison fraction. The
poison fraction producing the minimum fuel cost for a given system is in
the range from 0.06 to 0.10, the exact value depending on the specific di-
528 HOMOGENEOUS REACTOR COST STUDIES [cHAP. 10

 

   
    

 

 

 

2.4
\ |
Core Diameter (ft) 18
2.2 1—
&=
3
-
%
E 20| 1
E 10
o
2 14
% 18— 1
z
1.6 | | | l | \
50 100 150 200 250 300 350 400

Thorium Concentration, g/|i1er

Fra. 10-4. Fuel cost as function of thorium concentration in one-region reac-
tors. Power per reactor = 480 Mw (heat), poison fraction = 0.08, %3 = 2.25.

ameter and thorium concentration. However, a value of 0.08 gives costs
which are close to the minimum for all cases.

(2) Diameter and thorium concentration. The fuel costs for some of the
single-region reactors studied are shown in Fig. 10-4. Detailed information

TaBLE 10-5

ErrFect oF XENON PoisoN FractioNn oN FuerL Costs

 

 

Xenon poison fraction 0.01 0.05
Optimum total poison fraction 0.08 0.12
Core cycle time, days 637 718
Breeding ratio 1.102 1.070
Fuel inventory charge, mill/kwh 0.27 0.29
Core processing charge, mill/kwh 0.13 0.14
Fuel product (credit), mill/kwh 0.33 0.22
Net fuel cost, mills/kwh 1.22 1.35

 

 

 

 

for a typical one-region reactor is given in the last column in Table 10-3.
In general, for thorium concentrations less than 400 g/liter the reactor
diameter must be greater than 10 ft in order to have a breeding ratio greater
than unity; the 12-ft-diameter reactor is a breeder (breeding ratio = 1.0)
at a thorium concentration of 350 g/liter, while at 250 g Th/liter the
14-ft-diameter reactor is a breeder. For reactors between 10 and 16 ft in
diameter, the thorium concentration yielding the lowest fuel costs is be-
10-3] FUEL COSTS IN THO2-UO03-D20 SYSTEMS 529

tween 200 and 275 g/liter. The lowest fuel cost is about 1.76 mills/kwh
(for a 14-ft-diameter reactor containing 270 g Th/liter). In the curve for
the 14-ft reactor, the inflection in the neighborhood of 225 ¢ Th/liter is a
result of the reactor changing from a breeder to a nonbreeder. This in-
flection is associated with a marked increase in U236 concentration (concen-
trations are based on equilibrium conditions), which produces an increase
in fuel processing charges (in all cases it is assumed that U233 is fed to
the system).

(3) Power and nuclear parameters. The effect of reactor power on the
fuel costs of one-region reactors is similar to that mentioned earlier for
two-region systems. For example, if the total fuel cost for a three-reactor
station is 1.76 mills/kwh at 125 Mw of electric capability per reactor, it
would be only 1.38 mills/kwh if the output per reactor were increased to
200 Mw,

The importance of changes in nuclear parameter is generally the same
for the one-region reactors as for the two-region systems, although the
effect upon fuel costs of a reduction in n(U?33) is somewhat greater for the
one-region cases.

10-3.4 Cylindrical reactors [9]. The effects of geometry on fuel cost
are due to the associated changes in inventory requirements and breeding
ratio. Accompanying these effects are changes in the average power den-
sities and the wall power densities within the reactor. Because of corrosion
difficulties associated with high power densities, it is desirable to operate
with reasonahly large reactor volumes. Cylindrical geometry permits re-
actors to have large volumes without necessitating large reactor diameters.

One-region spherical reactors would have to be large in order to prevent
excessive neutron leakage, and so power densities would not be high
(average power densities of about 30 kw/liter). Also, closure problems
with respect to maintenance of an inside vessel would not exist. Therefore
there is little incentive to increase reactor volume by using cylindrical
geometry for one-region homogeneous reactors.

For two-region reactors, cylindrical geometry may prove advantageous
with respect to feasibility and relative ease of reactor maintenance. How-
ever, the associated larger fuel inventories (in comparison to inventories
for spherical geometry) will increase fuel costs. Comparison of results for
two-region cylindrical reactors with those for spherical two-region reactors
shows that cylindrical geometry gives minimum fuel costs about
0.2 mili/kwh greater than does spherical geometry, if in either case there
were no restrictions on core-wall power density. The difference is even
greater if the core-wall power density influences the reactor size. However,
cylindrical geometry does permit low wall power densities in combination
with relatively small reactor diameters.
530 HOMOGENEOUS REACTOR COST STUDIES [cHAP. 10

]

Conversion of | Enriched U
Feed Preparation UF g to UO5
30-Day Reserve

U, Pu Feed

    
    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Partial Decontaminatio Separation of Pu
of All Fuel Sent to o and Complete Natural U
U Pu FP Chemical Plant Decontamination of Fuel afura
o 20-Day Cooling to Diffusion Plant
FP. F.P.
r‘ Waste
Waste

 

Fi1c. 10-5. Fuel cycle for one-region, U-Pu reactor.

10-4. EFFecT oF DESIGN VARIABLES oN Furn Costs
IN URANIUM-PLUTONIUM SYSTEMS

Fuel costs in uranium-plutonium systems will depend on whether the
plutonium is removed continually or allowed to remain in the reactor. In
the latter case, there is little difference in fuel costs between a
U0:804-Pu02-D20 system and a UO3-PuQOs-D20 system. Fuel-cost
studies have been made on the basis of either maintaining plutonium
uniformly within the reactor or removing the plutonium immediately after
its formation by means of hydroclones. In addition, the effect upon fuel
costs of LijSO4 addition to UO2S04 solutions is shown. The additive
serves to suppress two-phase separation of the UO2S04 solution, and per-
mits reactor operation at temperatures higher than would otherwise be
feasible.

10—4.1 One-region PuOy-UQO3-D;0 power reactors [11,12]. Fuel costs
of one-region homogeneous power reactors fueled with PuO.-UQO3-D20
slurries are given as functions of operating conditions, based on steady-
state concentrations of U235 U236 Pu?39 Pu240 and Pu?¢!. All other
higher isotopes are assumed to be removed in the fuel processing step or to
have zero absorption cross section. Although large reactors require feed
enrichments equal to or less than that of natural uranium, minimum fuel
costs are obtained when the reactor wastes are re-enriched in a diffusion
plant. In the reactor system considered, the plutonium produced is fed
back as reactor fuel after recovery in a Purex plant. The separated uranium
is recycled to a diffusion plant for enrichment. Since in all cases the breed-
ing ratio is less than unity, the additional fuel requirement is met by
uranium feed of an enrichment dictated by the operating conditions. Asa
result of the feedback of plutonium, the concentration of plutonium in the
reactor is high enough for resonance absorptions and fissions to have an
appreciable effect upon fuel concentrations.
10-4] FUEL COSTS IN URANIUM-PLUTONIUM SYSTEMS 531

The fuel eycle is shown in Fig. 10-5. Slurry is removed from the reactor
at the rate required to maintain a specified poison level. The fuel is sepa-
rated from the D20, cooled for 20 days while the neptunium decays, and
partially decontaminated in a Purex plant. Part of the fuel is then sent
directly to the reactor feed-preparation equipment. Plutonium is sepa-
rated from the remainder of the uranium and added to the reactor feed.
The uranium is completely decontaminated, stored for 100 days until the
U237 decays, and sent to the diffusion plant. A 30-day reserve of reactor
feed is kept on hand.

TaBLE 10-6

Cost BrEAKDOWNS FOR ONE-REGION PUu0s-TUQ0;-D-0
REacrors* HaviNg A DIAMETER oF 12 ¥T

 

 

Process characteristies:
U238 concentration, g/liter 175 200 225
nil 1.9 2.2 2.4
Reactor poisons, 9 6.0 6.0 6.0
Total system volume, liters 50,000 50,000
Chemical process cycle time, days 151 138
Initial enrichment (no Pu), U235/7 0.011 0.011 0.011
U235 feed, g/day 579 430
Feed enrichment, 9, U235 0.99 0.70 0.52
U235 concentration, g/liter 1.12 0.82
Pu?3? concentration, g/liter 0.86 1.17
Pu?4? concentration, g/liter 0.49 0.62
Pu?#! concentration, g/liter 0.36 0.49
Np239 concentration, g/liter 0.03 0.03
U236 concentration, g/liter 0.10 0.06
Conversion ratio 0.74 0.84
Fuel costs:
Fuel inventory, mills/kwh (at 497) 0.08 0.07
D20 inventory, mills/kwh (at 497) 0.15 0.15
D20 losses, mills/kwh (at 59) 019 0.19
Net uranium feed eost, mills/kwh 1.15 0.48
Variable chemical processing cost,
mills/kwh 0.27 0.32
Fixed costs for chemical processing T,
mills/kwh 0.76 0.76
Total fuel cost, mills/kwh 2.60 2.20 1.97

 

 

 

 

 

 

*Operating at 280°C; 480 thermal Mw, 125 elec. Mw; 809, load factor; optimum
poisons, 5-75.

tEssentially assumes a chemical processing plant servicing three reactors pro-
ducing 1440 thermal Mw.
532 HOMOGENEOQUS REACTOR COST STUDIES [cHAP. 10

2.3

 

[ 1T

221

21—

  
   

20—

Reactor Dia.
’7 12 ft

Variable Fuel Cost, mills/kwh

 

 

 

150 200 250 300 350 400

Uranium Concentration, g/liter

Fic. 10-6. Effect of uranium concentration and reactor diameter on fuel cost in
one-region reactors. 300 Mw of electricity, 1000 Mw of heat, Avg. reactor tem-
perature = 330°C, U02804-LiaS04-D20 solution with dissolved Pu, molar ratio
of Lig804 to U080, =1, optimum poisons = ~ 5%,

Some typical results are given in Table 10-6 for a 12-ft-diameter reactor,
in which different values were assumed for n*! (the “best value” for n*! is
2.2; therefore, based on these results, natural uranium is adequate feed
material to ensure criticality). Where required, the cost of slightly en-
riched feed is based on the established schedule of charges by the AEC.
Plutonium in the reactor is assumed to have a value of $16/g. Fuel costs
were somewhat lower at larger reactor diameters, but a 12-ft diameter
corresponds to a more feasible reactor size.

10—4.2 One-region UO3S0;4~Li;S04-D30 power reactors [13]. For mini-
mum fuel costs, one-region reactors require fertile-material concentrations
of several hundred grams per liter. The addition of Li2SO4 in molar con-
centration equal to that of the uranium increases the temperature at which
phase separation appears and also acts as a corrosion inhibitor for stainless
steel. Because of the high neutron-capture cross section of natural lithium,
high isotopic purity in Li7 is necessary. Fuel costs for power-only reactor
systems fueled by U050 4-Li2S04-D20 solutions are given here in which
10-4] FUEL COSTS IN URANIUM-PLUTONIUM SYSTEMS 533

TaLe 10-7

REstrrs ror SeveERAL ONE-REGroN REAcTORS®
NEAR OpTiIMUM CONDITIONS

(Minimum fuel costs)

 

Process characteristics:
Reactor diameter, ft 12 16 20
U238 coneentration, g/liter 200 200 200
Feed enrichment, w/o U235 2.11 1.48 1.22
Feed rate, g/day of U232 1078 923 838
Chemical processing cycle, days 359 408 543
Poisons, 95 H 5 5
Reactor volume, liters 23,600 0,700 119,000
Total system volume, liters 88,000 127,000 181,000
Power density, kw/liter 39.0 16.5 8.4
Isotope concentration, g/liter:
235 2.11 1.47 1.21
236 (.37 0.26 0.21
P29 0.97 0.88 0.84
Pu240 0.51 0.50 0.49
Np23o 0.03 0.02 0.02
Pu?#! 0.52 (.45 0.43
(C'onversion ratio 0.67 0.72 0.74
Variable fuel cost, mills/kwh:
Net feed cost 1.42 1.12 0.96
Variable chemical processing 0.11 0.11 0.10
Fuel inventory 0.10 0.09 0.10
D50 inventory 0.11 0.16 0.23
D20 losses 0. 14 0.20 0.29
Lithium losses and inventory (. 006 0.008 0.011
Hydroclones 0.04 0.04 .04
Total variable fuel cost 1.93 1.73 1.75

 

 

 

 

 

 

#1000 Mw (heat); 300 Mw (electrical); 330°C reactor temperature.

all plutonium 1s assumed to remain either in solution or uniformly sus-
pended throughout the reactor. The plutonium is returned to the reactor
following fuel processing, and steady-state conditions are assumed. The
same type of fuel cycle as shown in Fig. 10-5 is considered. The results
shown in Fig. 10-6 are for spherical reactors operated at an average tem-
perature of 330°C, producing 1000 Mw of thermal energy, and delivering
300 Mw of electricity to a power grid. The variable fuel costs given do
not include fixed charges for fuel processing; these fixed charges would add
about 0.76 mill/kwh to the fuel costs given. Results are based on a 4%
 

 

 

 

 

 

 

TaBLE 10-8
FurL Costs For Barcu-Operatep HomogENEOUs U02804~D20 Powrr ReacTors®
Initial uranium Fuel costs,® mills/kwh
concentration
Hydroclone . ’ .
s . Ve I 2 -Vea ¢
Crzjse eycle time Additive® g/liter 0-vear operation
(days) 238 {285 U and Pu No U and Pu
recovered recovered
1 © None 100 2.72
2 o None 200 4. 18 2.61 2.67
3 w None 300 5.99 2 42 2.48
4 o0 None 400 8.32 2. .34 2.44
5 0 L1250, 100 299 2.96 3.03
6 o0 LiaSOy 200 4 82 2 .62 2.69
7 © 112504 300 7.21 2 44 2 .53
8 1 None 300 5.99 2,24 216
9 16 None 400 8.32 2.16 2.07

 

 

 

 

 

 

 

 

(a) Average temperature, 280°C; power, 480 thermal Mw, 125 electrical Mw; diameter, 6 ft;
system volume, 27,200 liters; fuel solution, UO2804-D20.

(b) Molar concentration of additive was assumed to be equal to the molar concentration of
uranium,

(¢) Based on the assumption that the fuel processing plants are servicing enough reactors to
make the fixed charges for chemical processing negligible.

(d) Details in these cases are shown in Table 10-9.

() Plutonium was assumed to be completely soluble and not removed by hydroclones.

(254

SUIANLS IS0D HOIDVHY SNOUNIDONWOH

0T 'dVHO]
10—4] FUEL COSTS IN URANIUM-PLUTONIUM SYSTEMS H35

inventory charge and $28/1b D20, Table 10-7 gives a breakdown of costs
for =everal reactors near optimum conditions., The Li7 cost is assumed to be
X100 lb; at this value the effect of lithium cost upon fuel cost 1s negligible.
However, the added LijSO4 acts as a neutron poison and diluent which
lowers the conversion ratio; these effects increase fuel costs by 0.2 to 0.3
mill kwh over those which would exist if no LiZSO4 were required.

The above results are for equilibrium conditions, with continuous fuel
processing. These reactors can also be operated with no fuel processing,
in which case nonequilibrium conditions apply. Under such conditions the
variable fuel cost would be greater than for the case of continuous fuel
processing; therefore any economic advantage associated with batch opera-
tion can exist only if fixed charges for fuel processing (or storage) at the
end of batch operation are effectively lower than fixed charges associated
with continuous processing. Fuel costs are given below for spherical one-
region reactors operating on a batch basis, utilizing an initial loading of
slightly enriched uranium. In all cases, fuel feed is highly enriched U235
The total reactor power is 480 thermal Mw (125 electrical Mw), and an
0.8 load factor is considered. Inventory charges are 49 /yr, cost of 120
is %28 Ib, and the cost of uranium as a function of enrichment 1s based
on official prices. A summary of the fuel costs is given in Table 10-8 for
b-ft-diameter reactors. More details for two reactors are given in Table
10~ Credit for plutonium is based on a fuel value of $16/g; it is assumed
that plutonium will remain within the reactor. The shipping costs do not
include tixed charges on shipping containers.

For these reactors (6-ft diameter), the addition of Li2SO4 (99.98% Li7)
(cases 5, 6, and 7) to the fuel solution raises the fuel cost slightly, the max-
imum increase being about 0.1 mill 'kwh. The use of hydroclones (cases 8
and U for partial poison removal (assuming no plutonium removal) for
these reactors shows an economic advantage, particularly in the “throw-
away’’ fuel costs (no uranium or plutonium recovery). For these latter
costs, the removal of fission-product poisons reduces the fuel costs by 0.3
to 0.4 mill kwh for 20-year operation. In view of its low solubility, how-
ever, plutonium would be extracted along with the fission-product poisons.
The economic feasibility of hydroclones in these circumstances, in a power-
only economy, is dependent upon the savings effected by posion removal
relative to the costs associated with recovery of the plutonium for fuel
use. Fuel costs for 10-year operation were 0.1 to 0.2 mill /kwh higher than
those for 20-year operation.

10-4.3 Two-region UO3~-PuOy,-D;0 power reactors [11]. The major
advantage associated with two-region reactors is that good neutron econ-
omy can be combined with relatively low inventory requirements. None
of the uranium-plutonium fueled agueous homogeneous reactors appear
536 HOMOGENEOQUS REACTOR COST STUDIES [cHAP. 10

TasLeE 10-9

IsororE CONCENTRATIONS AND COST BREAKDOWN FOR
Barco-OpERATED HoMOGENEOUS REACTORS*
(20-year operation, no hydroclones, 300 g U238 /liter)

 

Initial U235 concentration, g/liter 5.99 7.21
Additive 0 LigS04
Average U235 feed rate, kg/yr 136 136
Initial U235 inventory, kg 163 196
Final polson fraction 0.27 0.25
Final isotope concentration, g/liter:
U234 1.22 1.28
U235 12 2 13.2
[J236 13.9 14.0
U238 223 223
Np?23° 0.03 0.03
Puz3? 3.54 3.95
Pu240 3.62 4.04
Py2# 1.24 1.38

Estimated fuel costs, mills/kwh:

 

Uranium inventory 0.08 0.11
D20 inventory and losses 0.19 0.19
Uranium feed 2.12 2.12
Chemical processing 0.18 0.18
Hydroclones 0.04 0.04
Shipping 0.04 0.04
Plutonium sale (credit) 0.07 0.08
Diffusion plant (credit) 0.12 0.12
Total (fuel cost) 2.42 2.44

 

 

 

 

*Same conditions as listed in Table 10-8.

capable of producing more fuel than is burned; however, it is possible to
operate a two-region reactor with such a low steady-state concentration
of U235 in the blanket that natural uranium can be fed to the reactor and
the waste discarded.

In a power-converter the plutonium is extracted from the blanket and
fed to the core as fuel material. Natural uranium is fed to the blanket,
and the plutonium formed is extracted by Purex processing. By adjusting
the concentrations of fissionable materials in the blanket, the net rate of
production of plutonium in the blanket is made equal to the consumption
in the core. The fuel cycle considered for a two-region reactor is shown in
Fig. 10-7. Plutonium from the core is processed continuously through a
10-5] FUEL COSTS IN PLUTONIUM POWER REACTORS 537

Conversion of |
U Feed - Feed" ] UFg te UO3
reparatio 30-Day Reserve

 

  
 

 

 
 
  

DR
. W
) g Matural U

|Partial Decontamination Complete 100-Day Cooling
5 and Pu Separation Decontamination of U and
Feed

20-Day Cooling i to Diffusion Plant UFg Preparation

Pu Decontamination
20-Day Cooling

 

 

   
  
  

 

Waste

Pu

 

Pu Feed Core Feed
Preparation \
Waste

 

 

Fi1ac. 10-7. Fuel cycle for two-region U-Pu reactor.

Purex plant to maintain a constant poison fraction. Uranium from the
blanket is also processed through the Purex plant, the rate of processing
being governed by the required plutonium feed to the core. Although it
is possible to operate the reactors without an enriching plant by using
natural-uranium feed to the blanket and discarding the waste, there ap-
pears to be a slight cost advantage in operating the reactors in conjunction
with an enriching plant.

Table 10-10 gives fuel costs and associated information for a two-region
reactor having a core diameter of 6 ft and a 10-ft over-all diameter. The
value of 7! is assumed to be 1.9. (A more recent value of 7*! = 2.2 is be-
lieved to be more accurate.) Comparison of these costs with those for
one-region reactors of 12 to 14 ft diameter indicate that two-region U-Pu
reactors have fuel costs about 0.2 to 0.3 mill/kwh lower than do one-region
reactors.

10=5. FuerL Costs IN Duar-PurposE PrutonNium Power REACTORS

Since plutonium is quite insoluble in U02S04—D20 solutions and can
be removed by hydroclones, it is possible to produce high-quality plu-
tonium (Pu24® content less than 29%). Based on the AEC price schedule,
this high-quality plutonium has a net value of at least $40/g after allow-
ing $1.50/g for conversion to metal). At this value it is more economical
to recover plutonium than to burn it as fuel. Fuel costs based on recovery
of the plutonium are given here for one- and two-region U-Pu reactors.
538

HOMOGENEQOUS REACTOR COST STUDIES

TasLe 10-10

Furn Costs ror A Two-Reaiox,

U-Pu Power ReacTor*

[cuap. 10

 

 

Core diameter, ft

Core power, thermal Mw

Core Pu concentration, g/liter
N40/N49 in core

N41/N4% 1n core

Blanket thickness, ft

Blanket power, thermal Mw
Blanket U concentration, g/liter
N?Z5/N?8 in hlanket

N49/N28 in blanket

N10/N28 in blanket

N41/N?8 in blanket

Blanket feed enrichment, N25/NU
Fraction fissions in U232
Fraction of U consumed

Fuel costs, mulls/kwh

Core processing (variable)
Blanket processing (variable)
D20 recovery

U + Pu losses

Pu mventory

U inventory

D20 inventory plus losses at 9%,/yr
Feed cost minus credit for returned U
Fixed charges for chemical processingt

Total fuel costs, mills/kwh

 

500

oo Do o oD

N oo o oo oo O o

003

001
0003
00005
004

16
31
07
005
04

005

30
62

76
27

 

 

*Average temp., 250°C; total power, 500 thermal Mw;
thermal efficiency, 259,; load factor, 809,; #* = 1.9,
TAssumes chemical-processing plant servicing three reactors.

net

10-5.1 One-region reactors [14]. Fuel costs are given for UO:304-D 20
and U02804-LiZ804-D>0 fuel systems operating at 280°C, in which the
plutonium is assumed to be removed by means of hydroclones on about a

one-day cycle.

Table 10-11.

Characteristics of the assumed systems are presented in
10-6] FUEL COSTS IN U BURNER REACTORS 539

TasLE 10-11

CHARACTERISTICS OF REACTOR SyYSTEM

 

 

Itlectrical power, Mw 125
Heat generation, Mw 480
Reactor diameter, ft 12
Power density in system external to core, kw/liter 20
Average reactor temperature, °C 280
Reactor poisons, %, 5
Chemical processing rate, g U233 /day 1000
Plutonium removal Instantaneous
Isotopic purity of lithium, % 99.98
Processing method Purex
Li7 cost, $/1b 40
Inventory charges, 9 4
D20 losses, 9, of inventory/yr 5

Ii losses, ¥ of inventory/yr 1

 

 

 

Because of the high credit for plutonium, the fuel costs are negative even
if the fixed charges for chemical processing (0.76 mill/kwh) are included.
The total fuel costs obtained are shown in IFig. 10-8. The effect of the
Lis=(), addition is to decrease the conversion ratio; because of the rela-
tively high value assigned to plutonium, this causes the LisSO4 addition
(added in the same molal concentration as the U02S04) to increase fuel
costs by 0.8 mill/kwh over those if no LioSO 4 were required.

Caleulations indicate that batch-type operation of a plutonium pro-
ducer i= undesirable if plutonium has a value of $40/g; any savings i fuel-
processing costs using batch-type operation is more than compensated by
a loss in product value associated with the decrease in plutonium pro-
duction.

10-5.2 Two-region reactors {15]. Since the conversion ratio is greater
in a two-region reactor, it is expected that a high plutonium value will
cause this reactor type to have lower fuel costs (greater fuel credits) than
a one-region reactor. Caleulations for a reactor having a 6-ft-diameter core
and an over-all diameter of 12 ft, in which the plutonium is recovered with
a fuel cycle similar to that given in Tig. 10-7, indicated fuel costs from
0.5 to 0.6 mill /kwh lower than in one-region reactors.

10-6. FueL Costs 1IN U235 BUurRNER REACTORS

A homogeneous reactor fueled with a dilute, highly enriched UO2S04
solution is potentially capable of operating without removing fission
540 HOMOGENEOUS REACTOR COST STUDIES [cHAP. 10

 

0.2+ —

—0.4 + |

—0.6

UOESO4 — Li2504 — DQO Fuel Solution

—0.8

|
=
o

 

Net Fuel Cost, mills/kwhr

 

 

 

UO 4804 — D2O Fuel Solution
i | ] i i

—2.2

 

200 300 400 500 600 700 800

238
U Concentration, g /liter

Fia. 10-8. Effect of Li2SO4 and U238 concentration on fuel cost of a one-region
spherical plutonium-producer power reactor. Diameter = 12 ft, avg. reactor tem-
perature = 280°C, electrical power = 125 Mw, heat generation =480 Mw, avg.
lithium cross section = (0.2 barn, plutonium credit = $40/g, inventory charge = 497,
molar ratio of Li2aSO4 to UOQ2S04 = 1, processing rate = 1000 g U235 /day.

products if additional U23% is continually added to offset the buildup of
poisons.

The results of fuel-cost studies [16,17] for spherical one-region reactors
containing dilute, highly enriched UQ2S04 in either D20 or H20 are given
in Table 10-12. The noble gases are assumed to be removed continuously.
The removal of poisons and corrosion products by hydroclones is con-
sidered, but the fuel cost is about the same whether hydroclones are used
or not. (assuming corrosion rates of about 1 mil/year). The results are for
nonsteady-state conditions.
10-6] FUEL COSTS IN U23° BURNER REACTORS 51l

TasLE 10-12

IsotorE CoNCENTRATIONS AND FUEL CosT BREAKDOWN
For SomEe U235 BURNERS
(Average temperature-280°C; 125 Mw cleet.; 6-ft-diameter core)

 

 

Moderator H:0 H;0 D20 D20
Haydroclone eycle time, days 1 o0 1 w0
Operating time, days 2000 3400 4200 4400
Initial U235 inventory, kg 353 353 34.3 34.3
Total system volume, liters | 27,000 27,000 27,000 27,000
Average U235 feed rate,
kg /vr 239 233 237
U concentration, g/liter* 24.7 36 18.6 22.8
Fraction poisons,™®
| 20 Z(25) 0.05 0.17 0.23 0.53
- Estinated costs, malls/kwh
- Uranium inventory at 49, 0.29 03 0.03
- DO inventory and losses at
oo 0 0.19 0.19
. Uranium feed cost 3.71 3.64 3.70

|
! Chemieal processing cost
(varinble cost at end of

‘ operating period) 0.08 0.03 0.03
- Hydroclone cost 0.02 0.02 0
Shipping cost 0.02 0.02 0.02
} Plutonium sale (credit,
- S16 gm) 0.0005 0.01 0.0003
. Diffusion plant (credit) 0.002 0.02 0.08
Total (fuel cost) T 4.13 4 .06 3.91 3.90

|
i

 

 

 

 

 

 

*At indicated operating time.
+Includes no fixed charges for fuel processing.

With D20 reactors, it appears that fuel processing can be economically
eliminated if the reactor operating cycle is about 10 years and if the spent
fuel is disposed of cheaply at the reactor site. Such a procedure with the
Hs0-moderated reactor is more expensive because of higher uranium
inventory. For low fuel-shipping and -processing charges, the fuel costs
are nearly independent of the reactor size and moderator, and are about
4 mills/kwh. If fixed charges associated with fuel processing are greater
than ~0.5 mill/kwh, it may be more economical to store the fuel than to
have it processed.
542 HOMOGENEOUS REACTOR COST STUDIES [cHAP. 10

Tarre 10-13

SUMMARY oF FUuiL CosTs oF DIFFERENT SYSTEMS

 

 

 

 

mills/kwh

(1) One-region burner; power only; UQ:804-D20 solution

(for 14-year operation) 3.93
(2) One-region burner; power only; U0:80,—H,0 solution

(for 7-year operation) 4.12
(3) One-region converter; power only; UO3~PuQ,-D20 slurry 2.20
(4) One-region converter; power-plutonium; UQ3S0,-D,0

solution —2.00
(5) Two-region converter; power only; core, PuO2-D20 slurry;

blanket, UO3-Pu02-D 50 slurry 1.90
(6) Two-region converter; power-plutonium; UQ,80,-D;0

solution . —2.66
(7) One-region breeder; power only; U03-ThOs-D»0 slurry 1.76
(8) Two-region breeder; power only; UO3-ThO2-D20 slurry 1.22
(9) Two-region breeder; power only; core, TOs80,-D20 solu-

tion; blanket, UO3-ThO2-D20 slurry 1.29

 

 

 

10-7. SumMmary oF HomoceENEoUs Reacror FurL-Cost CALCULATIONS

10-7.1 Equilibrium operating conditions. Fuel costs in different homo-
geneous systems are summarized in Table 10-13. Appropriate nuclear data
and general reactor characteristics have been given previously.

10-7.2 Nonsteady-state operating conditions [18]. A comparison of fuel
costs 1s given here for several one-region reactor systems, operating under
nonsteady-state conditions. The reactors are moderated with either H.O or
D>0 and fueled with enriched UOy plus ThO3, or U0.S04 of varying en-
richments. The effect of adding LisSO4 to the TV0.S0) is also considered.
In the UO3 4 ThOs system, it is assumed that the initial fuel is U233 and
that sufficient U233 is available as feed material.

Cost factors which make only a small contribution to the total fuel cost
are fuel processing losses (0.297 of fuel processed), D20 losses (357 of 120
inventory/year), hydroclone costs ($70/day), 30-day inventory supplies,
and shipping charges (it is assumed that the amortization charges for
shipping costs are negligible). In all cases the inventory charges are hased
on the volume of the reactor vessel plus the volume of the external system.
This latter volume is calculated on the basis of an average heat-removal
10-7] HOMOGENEOUS REACTOR FUEL-COST CALCULATIONS 543

 

 

 

 

 

4
{4, 800)
¢ UO3504 —H0O (6,0 800)
"; 3 r(o,m,zooi N
-\: UQG950 4 —D20
ol (10,500,300)
g [ 4300300
a p
S UO3 —ThO5 —D70
2l 12,500,300} ]
&
0 | i | i i ] | |
100 200 500 1000

Reactor Power, Thermal Mw

F1a. 10-9. Fuel costs in single-region reactors as a function of power level. Values
in parentheses refer to core diameter (ft), fuel processing cycle time (days), and
fertile material concentration (g/liter) at near-optimum conditions. Inventory
charge = 49, relative chemieal processing = 1, relative poisons == 3, 9?5 = 2.08,
749 = 1.93, n*3 = 2.25.

capability of 20 kw/liter of external volume. The enrichment of the heavy
water is assumed to be 99.759; D20, and the D20 cost is taken as $28/1b.

Only the optimum or near-optimum reactor conditions are given In
Fig. 10-9. The optimum conditions refer to the diameter, fuel-processing
cycle time, and fertile-material concentration which give the minimum fuel
cost of all the diameters, cycle times, and fertile-material concentrations
studied for the particular case.

A value of unity for relative fuel processing implies a charge of $0.54/g
of U233, U3 U235 and U?36 processed; $1/g Pu processed; and $3.50/kg
fertile material processed. A value of two implies processing charges twice
the above values. Fixed charges for chemical processing are not included
in the calculation of fuel cost. A relative poisoning of unity implies repre-
sentation of the fission-product poisons by two effective nuclei having
vields of 0.11 and 1.81 atoms/fission, and thermal absorption cross sections
of 132 and 13.9 barns, respectively (based on values of Robb et al. [19]).
A value of 1/2 implies cross sections 1/2 the above values, corresponding
closely to the values of Walker [20].

Fuel costs were calculated for both 10 and 25 years of reactor operation;
these costs are usually slightly lower after 25 than after 10 years, but the
differences are small, usually between 0 and 0.1 mill/kwh. Therefore, only
results for 10-year operation are given here.

The reactor system and power level influence the fuel cost as indicated
in Fig. 10-9. Changing the power level affects optimum reactor conditions
significantly. The variations in relative poisons and relative chemiecal
processing considered here did not change fuel costs to a large degree, the
individual effects usually being about 0.1 mill/kwh. The influence of re-
actor composition on fuel cost is due to the values of 5 for the various
544 HOMOGENEOUS REACTOR COST STUDIES [cHAP. 10

 

2.5 1 N ! [

i
I |

 

Relative Poisons=1
— =— — =Relgtive Poisons = %3, Relative Chemical Processing=1

(12,200}

20

.,
12% Inventory Charge

® (10,300)
-

    
 

Y
4% Inventory Charge

‘—
\__.__—"

(12.200) {12,200)

Fuel Cost, mills/kw-hr
wn

 

“(10,500) {12,200
y
1.0 T ./

{12,300}

 

I ] \ j I

0.002 0.604 0.006 0.008 0.010 0012
Fuel Processing Rate, Fraction of Reactor Inventory Processed/Day

 

 

0.5

o

Fic. 10-10. Effects of fuel-processing rate, fuel-processing charge, and poisoning
by fission products upon fuel cost in UQ3-ThO2-D20 reactors. Values in paren-
theses refer to core diameter (ft) and thorium concentration (g/liter) at near-
optimum conditions (independent of relative poisons and relative chemical process-
ing values shown). Reactor power = 500 Mw, %3 = 2.25; UZ3? feed.

fissionable materials and fraction poisons associated with the different
systems. Increasing the inventory charge from 4 to 12% increases fuel
cost by about 0.5 mill/kwh for the DO systems. Although not shown,
the effect of LiaSQ4 addition to the UO2504-H20 system has negligible
effect upon fuel cost, owing to the high poison fraction associated with the
H,0. The addition in equimolar proportions of Li2SO4 to the UO2S04-D»0
system increases fuel costs by about 0.1 mill/kwh.

The influences of fuel-processing rate, fuel-processing charge, and
fission-product, poisoning upon fuel eost are shown in Fig. 10-10 for the
UQO3-ThO2-D20 system. The fuel-processing rate corresponds to the
fraction of the reactor inventory processed per day. It is seen that doubling
the fission-product poisoning increases the fuel cost about 0.1 mill/kwh for
10-8] CAPITAL €COSTS FOR LARGE-SCALE PLANTS 545

the fuel-processing rates considered, and that doubling the processing
charge increases the fuel cost about 0.1 mill/kwh at optimum conditions.

The fuel costs given in Figs. 10-9 and 10-10 include no fixed charges
for fuel processing; the magnitude of these charges would be dependent
upon the number of reactors processed by the processing plant. Increasing
the fuel-processing charges decrcases the optimum fuel-processing rate.
Although fuel would undoubtedly be processed at the end of reactor
operation (and this was always assumed in obtaining the results), the per-
missible unit cost for processing at that time is high compared with the
permissible unit cost associated with a high processing rate. If the fixed
charges for processing correspond only to that period required to process
the fuel (for a given processing-plant capacity), then the optimum process-
ing rate is less than the rate obtained on the basis of fixed charges being
independent of fuel processing rate.

10-8. CaritaL CosTts FOR LARGE-ScALE PLANTS

The homogeneous reactors that have been built are small and have in-
vestment costs of over $1000/electrical kw. The capital costs of large
nuclear plants, based largely on paper studies, have been estimated to be
1.2 to 2 times that of conventional power-cost investments. If capital costs
are $100/kw, corresponding fixed charges are 9 mills/kw at 80% load
factor and 12 mills/kw at 60% load factor, considering a 15% annual fixed
charge. It follows that one of the conditions necessary for low-cost power
is a high load factor. The essential problems are to achieve low fuel costs
and to obtain reliability and long plant lifetime. To date, little experience
has been obtained in operating power reactors; therefore it is difficult to
estimate accurately the lifetime and also the reactor reliability over that
lifetime. Although most economic studies are used to measure the relative
economic advantage of different types of reactors, this cannot be firmly
established so long as the investment and maintenance costs remain un-
certain. Consequently, no hard and fast conclusions concerning power
costs can be obtained other than what the ultimate power cost might be.

The initial cost of the reactor building and other buildings associated
with the plant, as well as the site development costs, are strongly influ-
enced by the philosophy behind the design with regard to such factors as
safety and security. Estimates for these costs are usually based on cor-
responding costs for a large conventional steam power plant. Land costs
for nuclear plants are extravagantly high if containment is not assured.
The cost of containment vessels has been estimated to be in the range of
$10 to $40/electrical kw [21]. Equipment costs usually assume that the
desired equipment has been developed and all development costs paid for.
Even so, the depreciation charges on reactor equipment may be considerably
546 HOMOGENEOUS REACTOR COST STUDIES {crAP. 10

TasLE 10-14

PrESENT EsTIMATES OF REACTOR PLANT CosTs FOR A THREE-REACTOR
StaTiON OPERATING AT A Torar Power oF 1350 THErRMAL Mw

(315 Electrical Mw) [23]

 

 

 

Min. Cost Max. Cost
High-pressure system for one reactor
Reactor vessel (and core tank) 530,000 970,000
Gas separators (3) 120,000 240,000
Heat exchangers (3) 2,030,000 2,680,000
Fuel and blanket eirculating
pumps (3) 670,000 720,000
High-pressure storage tank and
catalytic recombiner, core system 110,000 220,000
High-pressure storage tank and
catalytic recombiner, blanket
svstem 40,000 90,000
20-Mw gas condenser 40,000 70,000
6.5-Mw gas condenser 20,000 30,000
Condensate storage tanks (2) 10,000 20,000
Gas blower for core system 30,000 60,000
Gas blower for blanket system 20,000 40,000
High-pressure process piping and
valves 3,250,000 6,430,000
Steam piping, valves and expansion
joints in cells © ©
Instrumentation 330,000 700,000
Sampling equipment (b o)
Installation of high-pressure equip-
ment (foundations, supports,
erection, ete.) 1,430,000 2,210,000
Subtotal for one reactor 8,630,000 14,500,000
Subtotal for three reactors 25,900,000 43,500,000

 

 

 

 

 

(a) Includes installation, insulation, inspection.
(b) In low-pressure estimate.

(¢) In steam-system estimate.

(d) With no contingency.
 

 

 

 

10-8] CAPITAL COSTS FOR LARGE-SCALE PLANTS 547
TaBLE 10-14 (continued)
Min. Cost Max. Cost
Low-pressure system for one reactor
Dump tanks (6) and associated
equipment, [Condensers (2},
condensate tanks (2), recombiners
(2), evaporators (2), feed and
circulating pumps, D20 recovery
and fisston-product adsorption
system] 1,260,000 1,800,000
Piping and valves, instrumentation,
sampling equipment 1,080,000 2,270,000
Installation of low-pressure equip-
ment 540,000 770,000
Subtotal for one reactor 2,880,000 4,840,000
Subtotal for three reactors 8,640,000 14,500,000
Reactor structure
Reactor and low-pressure equipment
cells 3,000,000 4,000,000
Equipment transport shield, crane,
maintenance handling equipment 430,000 950,000
Control room, laboratory, and proc-
ess area 2,000,000 4,000,000
Cell ventilation system {cooling
water, waste disposal) 890,000 1,750,000
Subtotal $6,320,000 $10,700,000
Summary Cost
Direct cost $40,900,000 $68,700,000
Contractor’'s overhead and fees
(279%) 11,000,000 18,500,000
Engineering and inspection (109;) 4,100,000 6,900,000
Total® 56,000,000 94,100,000
Reactor plant cost, $/thermal kw 56,000,000 __ 4l 94,100,000 — 0
1,350,000 1,350,000
Reactor plant cost, $/elec. kw 56,000,000 _ 178 94,100,000 _
315,000 315,000

 

 

 

 

 
548 HOMOGENEOUS REACTOR COST STUDIES [cHAP. 10

 

44 T 140

Net Station Efficiency, %

 

 

 

 

2 1 | | | | 80

300 500 700 200 1100
Steam Temperature, °F

F1a. 10-11. Turbine plant cost and net station efficiency vs. steam temperature.

 

DT TTTT | T TTT]

  

Present Technelogy

  

Unit Cost, $/elec.kw

 

 

| [ I L il

 

100
10 30 60 100 300 600 101
Net Electrical Capacity, MW

Fia. 10-12. Capital costs of aqueous homogeneous reactors.
10-9] OPERATING COSTS IN LARGE-SCALE PLANTS 549

higher than those for conventional power plants. Also, the insurance costs
for a nuclear plant may be much higher.

Conceptual designs for one- and two-region homogeneous reactors con-
sider stainless steel and stainless-steel-clad carbon steel as materials of con-
struction. Either type reactor will require pressure vessels, gas separators,
stcam generators, recombiners, sealed motors, pumps, storage vessels,
valves, and piping. Preliminary estimates [11] of capital investments show
no significant difference in costs between one- and two-region reactor plants.

Engineering considerations place limits upon the operating pressure and
the size of the pressure shell. A spherical reactor shape is desirable, inas-
much as the neutron leakage and the required shell thickness for a given
reactor diameter are thus minimized for a given reactor volume. Fabri-
cators of pressure vessels agree that even though very large shells
can be made, the smaller diameter vessels are more feasible. Because of
the temperature limitation associated with the pressure limitation, satu-
rated steam at relatively low pressures is generated in the heat exchangers
(see Chapter 9).

Although analyses of the turbine plant indicate that thermal efficiency
improves as throttle pressure increases, the reactor system mvestment
costs rise sharply with increased operating pressure. The effect of saturated-
steam temperature upon turbine plant cost and net station efficiencies is
given [22] in Fig. 10-11.

In estimating reactor plant costs, it is necessary to determine the cost of
the various items of equipment. Present estimates [23] of reactor plant
costs for a large reactor station are given in Table 10-14. The equipment
costs are based on per-pound costs of HRE-2 equipment, cost estimates
obtained from industry, and the assumption that costs are directly propor-
tional to (reactor power) 6. The effect of station size upon reactor station
costs are estimated [23]in Table 10-15, while the possible effect of technical
advances upon capital investment costs is indicated [22] in Fig. 10-12.
In all these estimates, a developed and operable system is postulated.

10-9. OPERATING AND MAINTENANCE CosTs IN LARGE-SCALE PLANTS

Because of the high level of radioactivity associated with nuclear plants,
maintenance and repair of nuclear systems will have to be done remotely.
This type of operation is, in general, more time-consuming and expensive
than methods used in maintaining conventional coal-fired power plants.
To minimize operating and maintenance (O and M) costs, it will be
necessary to design reactor plants so as to simplify maintenance problems;
however, construction costs associated with such design will be higher than
the costs of huilding a reactor plant in which O and M costs are not so
economically significant. These higher costs are associated with the ability
950 HOMOGENEQUS REACTOR COST STUDIES {cHAP. 10

TABLE 10-15

PrEsENT EsTiMATES oF HoMoGENEOUS REACTOR POWER STATION
CosTs as A FuNcTioN oF STATION Size [23]

 

Plant size:

Thermal Mw
Electrical Mw

1350
315

240
60

60
15

 

Min.

Max.

Min,

Max.

Min.

Max.

 

 

Direct cost of reactor
plant,
millions of dollars

Engineering and design
(at 159),

millions of dollars

Contractor overhead and
fees (at 239),
millions of dollars

Total cost reactor plant,
millions of dollars,
$/elec. kw

Turbine-generator plant,
millions of dollars,
$/elec. kw

Reactor station total cost,
millions of dollars,
3/elec. kw

41

56
180

90
280

69

10

16

95
300

33.4
100

128
400

16

2.4

3.6

22
370

29
480

27

37
620

7.0
120

44
730

7.6

1.1

1.8

10.5
700

13.5

2.0

3.1

18.6
1240

2.0

130

12.5
830

20.6
1370

 

 

 

 

 

 

to be able to inspect, repair, or replace components in a high radiation
field; this requires component compartmentalization and accessibility.
Operating and maintenance costs cannot be predicted accurately be-
cause of the lack of knowledge and experience; however, the information
available [24] indicates that O and M costs may run as high as 4 mills/kwh
in the first plants constructed. Difficulties associated with predicting O and
M costs concern predicting component lifetimes, component repair/discard
ratio, maintenance procedures, and downtime required for maintenance.
Also, detailed design studies of various maintenance schemes are required
before these various schemes can be fully evaluated. Based on present
|

10-#t dio—

F———r &-ft core dio—‘-l

49 U233/|i?er -
| e \ |
‘ ldg U233/liter + Zr !
0.2 g U235 liter J
\

 

as U0,50,, D,O

1000 g Th/liter, D,0

T

Total System Yolume = 40,000 liters

Two-Region Breeder,
Solution Core

 

e 14-ft dia

 

6.8 g U233/ lirer +
0.7 g U*35/liter +
250 g Th/liter
in D,0

 

Total System Volume = 66,000 liters

One-Region Thorium Slurry

Fic. 10-13. Equilibrium fuel concentrations and reactor dimensions for homogeneous systems operating at 280°C and producing

125 Mw electrical power.

 

‘.,—___ 10-ft dio
6-f core dia ‘—-1

074 U235/ iter as UO3 +
200 g Th/liter, D,0

   
  

1000 g Th/liter; 4 g U?3%/liter, D,Q
- o

Total System Volume = 40,000 liters

Two-Region Breeder,
Slurry Core

 

12-ft dia

 

1g U35/ liter +
200 g U?38/liter as U0, +
2 g Pu/liter as PuO,
in D,0O

 

N

Total System Volume = 50,000 liters

One-Region Uranium-Plutonium Slurry

/ 9.4 g U233/ iter + Zr\

 

14 g U235/iter as UO2SO‘
in H,0
or
4q U235/liter as U02504
in D,0

 

Total System Volume = 27,000 liters

One-Region U?3% Burner
{Conc. are for 10-yr opr., no fuel processing)

— ]

 

heet——— - ——— 12-ft dia

/ 7.5 g U235 /liter +

400 g U238 /liter as U02504
in Dzo
(Pu removed as Pqu)

 

 

 

Li,SO,

Molar ratio ———— = 1
uo,so,

Total System Yolume = 50,000 liters

One-Region U0,50, Plutonivm Producer

SINVId HTVOS-HDYVI NI 81800 DNILVIELO (601

169
TaBLE 10-16

Power CosTs 1N LARGE-ScALE AQUEoUs HoMoGENEOUS REACTORS

(125 electrical Mw; 500 thermal Mw; 809, load factor; 280°C) [22]

 

 

 

 

 

 

Fixed charges at 159, O and M,7 Total power costs,
ills/kwh Fuel costs ills/k i
Fuel system mills/kw ue costs, mills/kwh mills/kwh
mills/kwh
Present*® Future Present Future Present Future
Two-region
solution core 7.5-11.0 4.4-5.0 1.4 2-4 1-2 10.9-16.4 6.8-8.4
Two-region
slurry core 7.5-11.0 4.4-5.0 1.3 2-4 1-2 10.8-16.3 6.7-8.3
One-region
U235 4 D0 6.5-9.5 4.0-4.6 3.9 2-4 1-2 12.4-17 .4 8.9-10.5
One-region
U235 + H,0 6.5-9.5 4.0-4.6 4.1 2-4 1-2 12.6-17.6 9. 1-10.7
One-region
ThO2 slurry 7.0-10.3 4 3-4.8 2.0 2-4 1-2 11.0-16.3 7.3-8.8
One-region
UO3 siurry 7.0-10.3 4. 3-4.8 2.1 2-4 1-2 11.1-16.4 7.4-8.9

 

 

 

 

 

 

 

 

 

*Present: Based on present technology, assuming the fuel systems are feasible.
TOperating and maintenance costs.

ces

SHIANLS LS00 YOLOVHA SNOANUTHONWOH

01 dvHD]
10-10] SUMMARY OF ESTIMATED POWER COSTS 553

technology and a feasible reactor system, it is estimated that these costs
will be 2 to 4 mills/kwh.

As more experience is gained in maintaining plants and in designing for
O and M, it is expected that these costs will decrease; even so, because of
the nature of the problems, O and M costs in future plants will prob-
ably be 1 to 2 mills/kwh, or about two or three times those associated with
a conventional coal-fired plant.

10-10. SumMARY oF EsTiMATED PowEgER CosTs

The power cost is the sum of the fixed charges on capital investment,
fuel costs, and operating and muaintenance costs. Iigure 10-13 specifies the
reactor systems considered, along with typical fuel concentrations and re-
actor dimensions. Estimates of the power cost for these systems are given
in Table 10-16, and are based on operation at 280°C and a power level of
125 electrical Mw (500 thermal Mw). Although operating and maintenance
costs are undoubtedly different for the various systems, it is assumed that
the range considered covers the differences involved.

The design power of a reactor plant will markedly influence power costs,
primarily because the investment cost per unit power is a function of power
level. Table 10-17 indicates the influence of power level on power costs,
by comparing costs for U235 burner-type reactors having power outputs of
125 and 10 electrical Mw, respectively.

TaBLE 10-17

InFLUENCE oF PoweER LEVEL UpoN “"PrESENT’ Powgr CosTts IN
U235 BurNers (259, THERMAL ErF.; 809, 10oAD FACTOR; 280°C)

 

 

 

 

 

 

Electrical power level, Mw
10 125
Fixed charges at 159, /yr, mills/kwh 16 8
Operating and maintenance, mills/kwh 5 3
Fuel costs, mills/kwh 5 4
Total power costs, mills/kwh 26 15

 

 

 

 
554 HOMOGENEOUS REACTOR COST STUDIES [cHAP. 10

REFERENCES

1. White House press releasc and AEC press release, Nov. 18, 1956; AEC
press release No. 1060, May 18, 1957; AEC press release No. 1245, Dec. 27,
1957; AEC press release A-47, Mar. 12, 1958.

2. U. 8. Federal Register, Mar. 12, 1957, Vol. 22, p. 1591.

3. K. Courn, The Theory of Isotope Separation as Applied to the Large-Scale
Production of U?35, National Nuclear Encrgy Series, Division III, Volume 1B.
New York: McGraw-Hill Book Co., Inc., 1951.

4. J. A. LLANE, The Economics of Nuclear Power, in Proceedings of the Inter-
natronal Conference on the Peaceful Uses of Atomic Energy, Vol. 1. New York:
United Nations, 1956. (P 476, p. 309)

5. M. Benepicr and T. H. Pigrorp, Nuclear Chemical Engineering. New
York: McGraw-Hill Book Co., Ine., 1957. (p. 403)

6. E. D. ArnoLp et al., Preliminary Cost Estimation: Chemical Processing
and Fuel Costs for a Thermal Breeder Reactor Station, USAEC Report ORNL-
1761, Oak Ridge National Laboratory, Jan. 27, 1955.

7. 8. GrasstoNe and M. C. Evvunp, The Elements of Nuclear Reactor Theory,
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