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FFR_chap17.txt
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FFR_chap17.txt
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CHAPTER 17
CONCEPTUAL DESIGN OF A POWER REACTOR*
The design of a homogeneous molten-salt reactor of the type discussed
in the preceding chapters is described below. The choice of the power
level for this design is arbitrary, since the 8-ft-diameter reactor core, chosen
from nuclear considerations, is capable of operating at power levels up to
1900 Mw (thermal) without excessive power densities in the core. An
electrical generator of 275-Mw capacity was chosen, since this is in the
size range that a number of power companies have used in recent years.
It is estimated that about 69 of the power would be used in the station,
and thus the net power to the system would be about 260 M.
Two sodium circuits in series were chosen as the heat-transfer system
between the fuel salt and the steam. Delayed neutrons from the circulating
fuel will activate the primary heat exchangers and the sodium passing
through them. A secondary heat-exchanger system in which the heat will
transfer from the radioactive sodium to nonradioactive sodium will serve
to prevent radioactivity at the steam generators, superheaters, and re-
heaters. The fuel flow from the core 1s distributed among four primary
heat exchangers which serve as the first elements of the four parallel paths
for heat transfer to the steam. A single primary heat exchanger and path
18 provided for the blanket circuit.
Plan and elevation views of the reactor plant are shown in Figs. 17-1
and 17-2, and an isometric drawing showing the piping of the heat-transfer
sy=tems 1s shown in Fig. 17-3. The reactor and the primary heat exchangers
are contained in a large rectangular reactor cell, sealed to contain any
leakage of fission-product gases. All operations in the cell must be earried
out remotely after the reactor has operated at power. The principal char-
acteristics of the plant are listed in Table 17-1.
17-1. FUEL AND BLANKET SYSTEMS
17-1.1 Reactor vessel. The reactor vessel and the fuel and blanket
pumps are 2 closely coupled assembly (I'ig. 17-1) which is suspended
from a flange on the fuel pump barrel. The vessel itself has two regions—
one for the fuel and one for the blanket salt. The fuel region consists of
the reactor core surmounted by an expansion chamber, which contains
the single fuel pump. The blanket region completely surrounds the fuel
region, and the blanket salt cools the walls of the expansion chamber gas
space and shields the pump motor. The floor of the expansion chamber is
*By 1. G. Alexander, B. W, Kinyon, M. E. Lackey, H. G, MacPherson, L. A,
Mann, J. T. Roberts, F. C. VonderLage, GG. D. Whitman, and J. Zasler.
681
682 CONCEPTUAL DESIGN OF A POWER REACTOR [crAP. 17
Primary Sodium
Pump (1 of 5)
Reactor .
Intermediate Heat Primary Sodium To Secondary
Exchanger Cell Sodium Heat Exchanger (1 of 5)
Blanket Pump Primary Secondary
Air Lock Shield Sech?nlcilflfy Sodium Circuits
Fuel Pump Shie Boiler
Hot Maintenance Area / (1 of 5)
\
T A N e -
" N
: ¢!
Maintenance | ; \NCX'.N’"'F ’ 1.'
¥
e .‘:A‘r::a et 'v. .1._- Turbo- {,
Heater | X ‘\ ' J I Ir ] Generator
Removal ) -, g J M _:;' Q= / / |
A
'//‘i—' TITE
B
&
L ,g ,r" b i
y Je 1|1|I o= |t |
Chemical " - ) ‘ o - Reheater
Processing L ud "W Ry {1 of 4)
)
Contral # ""II it . 2
Fuel Drain-
Tank
[
o = Blanket Superheater
Fuel Chemical Enricher Blanket Heat (1 of 5)
Processing ~ Transter Circuit
! FAUEI Expansion Secondary Sodium
Blanket Drain Enricher bump {1 of 5)
Blanket BlanketTo-Sodium
Chemical Heat Exchanger _
Processing Fuel-To-Sodium
Heat Exchanger (1 of 4)
Fic. 17-1. Plan view of molten salt power reactor plant,
a flat disk, 3/8 In. thick, which serves as a diaphragm to absorb differential
thermal expansion between the core and the outer shells.
17-1.2 Fuel pump. The fuel pump is of the type illustrated in Chap-
ter 15 (Fig. 15-3) and is designed to have a capacity of 24,000 gpm. It is
driven by a 1000-hp motor with a shaft speed of 700 rpm. This pump
incorporates three major advanced features that are being developed, but
which are not present in any molten-salt pump operated to date. These
are a hydrostatic lower bearing to be operated in the molten salt, a laby-
rinth type of gas seal to prevent escape of fission-product gases up the
shaft, and a hemispherical gas-cushioned upper bearing to act as a com-
bined thrust and radial bearing. These advanced features are intended
to provide a pump with greater resistance to radiation damage and less
complex auxiliary equipment than necessary for pumps presently used
for molten salts.
17-1.3 System for removal of fission-product gases. About 3.59; of
the fuel passing through the fuel pump is diverted from the main stream,
17-1] FUEL AND BLANKET SYSTEMS 683
Primary Sodium
To Secondary Sodium
Heat Exchanger
(1 of 5)
Fuel To Sodium
Heat Exchanger
{1 of 4) 5 h
. Jet Pump uperheater
p
Fuel Pump S:g}‘:;‘y (1 of 5} {1 of 5]
Manipulator Pump Removable Boiler (1 of 5)
Air Lock (1 of 5) Concrete Slabs
Hot Maintenance Ared
Turbine-Generator
O
Maintenance Area
Steam
Heater Header
Removal
Fuel Drat
Tank
*
i
Reheater
Blanket To Sodium (1 of 5)
Heat Exchanger
Blanket Pump Secondary
Sodium Pump Boiler Feed
(1 of 5) Water Pump
Primary Sodium Secondary Sodium {1 of 5]
Drain Tank Drain Tank
(1 of 5) (1 of 5)
F1a. 17-2. Elevation view of molten salt power reactor plant.
Fia. 17-3. Isometric view of molten salt power reactor plant.
Blanket
| Pump
Fuel Pump Motor
Section A-A Motor
Blanket Expansion
M Tank
Siphon Drain 7
Fuel Lire To 1
-
Heat Exchanger
g L-—-J
Fuel Expansion
Tank
Breeding
Blanket
01 2 3 4 5
. dw o dow dboa ]
Scale—Feet
Fuel Return
3 Rorket
—~- Return
Fi1a. 17-4. Reactor vessel and pump assembly.
17-1] FUEL AND BLANKET SYSTEMS 685
TaBLE 17-1
REACTOR PranT CHARACTERISTICS
Fuel
Fuel carrier
Neutron energy
Moderator
Primary coolant
Power
Electrie (net)
Heat
Regeneration ratio
Clean
Average (20 yr)
Blanket salt
Yefueling eycele at full power
Shielding
Control
Plant efficiency
Exit fuel temperature
Steam
Temperature
Pressure
second loop fluid
Third loop fluid
Structural materials
Fuel circuit
Secondary loop
Tertiary loop
Steam boiler
Steam superheater
Active-core dimensions
I'uel equivalent diameter
Blanket thickness
Temperature coefficient, (Ak/k)/°F
Specific power
Power density
Fuel inventory
Initial (clean)
Average (20 yr)
Clean eritical mass
Burnup
>909, U2y
62 mole 97 LilF, 37 mole 9, BeFs,
1 mole 9, ThF,
Intermediate
LiF Bel';
Circulating fuel solution,
23,800 gpm
260 Mw
640 My
0.63
0.50
71 mole 9 LiF, 16 mole 9, BeF o,
13 mole 9 Thl'y
Semicontinuous
Concrete room walls, 9 ft thick
Temperature and fuel concentration
44 .39,
1210°1" at approximately 83 psia
1000°F, with 1000°F rcheat
1800 psia
Sodium
Sodium
INOR-8
Type-316 stainless steel
50, Cr, 197, i steel
2.59, Cr, 19, Mo steel
507 Cr, 197 Si steel
8 ft
2 ft
—(3.840.04) x 1073
1000 kw /‘kg
80 kw/liter
604 ke of U235
1000 kg of U235
267 kg of U233
Unlimited
686 CONCEPTUAL DESIGN OF A POWER REACTOR [cuAP. 17
A
Y
Fuel 4 ~—Blanket
Pump - Pump A
1.95 SCFM He . 0.65 SCFM
Blanket Expansion 0.1 CFS
Fuel Expansion anl;: Blanket Bypass
1210°F
Tank 1.8 CFS 0.ICFS
1250°F Fuel Bypass Y Yy
- - 4
235 f13 785 Ft3 &1 Ft3 16 Ft3
Cooclant Coolant Coolant Coolant
Fic. 17-5. Schematic flow diagram for continuous removal of fission-product gases.
mixed with helium from the pump-shaft labyrinth seal, and sprayed into
the reactor expansion tank. The mixing and spraying provides a large
fuel-to-purge-gas interface, which promotes the establishment of low
equilibrium fission gas concentrations in the fuel. The expansion tank
provides a liquid surface area of approximately 26 ft* for removal of the
entrained purge and fission gas mixture. The gas removal is effected by
the balance between the difference in the density of the fuel and the gas
bubbles and the drag of the opposing fuel velocity. The downward surface
velocity in the expansion tank is less than 1 in/sec, which should allow all
bubbles larger than 0.008 in. in radius to come to the surface and escape.
In the Aircraft Reactor Experiment at least 979% of the fission-product
gases were continuously purged by similar techniques.
With a fuel purge gas rate of 5 cfm, approximately 350 kw of beta
heating from the decay of the fission-product gases and their daughters
is deposited in the fuel and on metal surfaces of the fuel expansion tank.
This heat is partly removed by the bypass fuel circuits and the balance is
transferred through the expansion tank walls to the blanket salt.
The mixture of fission-product gases, decay products, and purge helium
leaves the expansion tank through the off-gas line, which is located in the
top of the tank, and joins with a similar stream from the blanket expansion
tank (see Fig. 17-5). The combined flow is delayed approximately 50 min
in a cooled volume to allow a large fraction of the shorter-lived fission
products to decay before entering the cooled activated-carbon beds. The
17-2] HEAT-TRANSFER CIRCUITS AND TURBINE GENERATOR 687
capacity of the carbon beds will hold krypton from passing through for
approximately 6 days, and xenon for much longer times.
The purge gases, essentially free from activity, leave the carbon beds to
join the gases from the gas-lubricated bearings of the pumps. The gases
are then compressed and returned to the reactor to repeat the eyele. Ap-
proximutely every four days the gas stream is diverted from one set of
carbon beds to the other. The inactive bed is then regenerated by warming
it to expel the Kr™ and other long-lived fission products. It will probably
be economical to recover some of these gases; others may be expelled to
the stack.
17-2. HEaT-TransrFir CircuiTs AND TurBINE GENERATOR
The primary heat exchangers are designed to have the fuel on the shell
side and sodium inside the tubes. This arrangement makes full use of the
superior properties of sodium as a heat-transfer fluid and appears to yield
the lowest fuel volume.
The heat exchangers, which are of semicircular construction, as shown
in I'ig. 17-3, provide convenient piping to the top and bottom of the
reactor. The thermal characteristics of the primary heat exchanger, to-
gether with the characteristics of other heat exchangers of the reactor
svstem, are listed m Table 17-2.
The sodium in the intermediate heat-transfer system (see Fig. 17-6) is
heated by the fuel in the primary heat exchanger and is pumped out of the
reactor cell and through the reactor cell shield to adjacent cells, which con-
tuin the secondary sodium-to-sodium heat exchangers and the pump. No
control of intermediate sodium flow is required, so there are no valves and
a constant speed centrifugal pump is used. To permit the sodium to be at
u lower pressure than the fuel in the primary heat exchanger, the pump for
the intermedinte sodium is in the higher temperature side of the circuit.
The secondary heat exchangers are of the U-tube in U-shell, counterflow
design, with the intermediate sodium in the tubes and the final sodium on
the <hell side.
The finul sodium circuit, except for the sccondary exchanger, is outside
the shielded area and thus available for adjustment and maintenance at all
times. The principal problems in this circuit are concerned with the ad-
justment of sodium temperature. Iixcessive thermal strains are prevented
in the steam generator by limiting the temperature of the sodium entering
it, und in the intermediate heat exchanger by the regulation of sodium flows
s0 that too cold sodium ig never returned to it. The hot sodium from the
sccondary exchanger is split into three streams with regulating valves for
control of the relative flows. One stream bypasses the steam system and
goes directly to a blender; the flow in it is, of course, greatest at low power
TaBLE 17-2
DaTta For HEaT EXCHANGERS
Primary Secondary
Fuel and sodiwm-to-sodiwm exchangers
Number required 4 4
TFluid TFuel salt Primary sodium Primary sodium Secondary sodium
Fluid location Shell Tubes Tubes shell
Type of exchanger U-tube in U—shell, U-tube in U -shell,
counterflow counterflow
Temperatures
Hot end, °F 1210 1120 1120 1080
Cold end, °F 1075 925 025 25
Tube data
Material INOR-§ Type-316 stainless steel
Outside diameter, in. 1.000 0.750
Wall thickness, in. 0.058 0.049
Length, ft 23 7 21.5
Number 515 1440
Piteh (A), in. 1.144 0.898
Bundle diameter, in. 28 36
Heat transfer capacity, Mw 144 144
Heat transfer area, ft2 2800 5200
Average heat flux, 1000 Btu/(hr)({t?) 175 95
Flow rate, cips 13 .4 461 46 .1 33.6
Fluid velocity, {ps 108 19.7 13.9 13.2
Pressure drop, psi 40} 15.5 10 148
continued
HOLOVIY 4HMOd V 40 NDHISIJA TVALIIINOD RKO
L1 'dVHD]
TaprLe 17 2 (continued)
Sodiwm-to-steam exchanger
Number required
Fluid
Fluid location
Type of exchanger
Temperatures
Hot end, °F
Cold end, °F
Tube data
Material
Outside diameter, in.
Wall thickness, In.
Length, ft
Number
Pitch (A), in.
Bundle diameter, in.
Heat transfer capacity, Mw
Heat transfer area, ft?
Average heat flux, 1000 Btu/(hr)(ft?)
Flow rate, cfps
or 1000 Ib/hr
Fluid velocity, fps
Pressure drop, psi
Steam Generalor Niperheater Reheater
4 4 4
Secondary Water Secondary Steam Secondary Steam
sodium sodium sodium
Shell Tubes Shell Tubes Shell Tubes
Bayonet, U-tube in U-shell, Straight,
counterflow counterflow counterflow
825 621 1080 1000 1080 1000
740 621 930 621 1000 640
2.59, Cr, 19, Mo Alloy
2
0.180
18
362
2.75
55
82.2
2800
100
57.5
410
5.6
5.7 (jet pump)
0.750
0.095
25
480
1.00
23
39.2
1760
76
15.5
406
9.3 61
6.9 10.3
59 Cr, 19, Si Alloy
0.750
0.065
16.5
800
1.00
29.7
22.6
2200
39
16.8
399
7.9 137
3.2 10.4
[z-21
ANTHUOL ANV SIINOUID HHASNVUE-LVIH
HOLVULINHD
689
690 CONCEPTUAL DESIGN OF A POWER REACTOR [cHAP. 17
Low- and
I Intermediate-Pressure
Turbines
Reheat Boiler
-High-Pressure Turbine
~Turbine Stop
-Attemperator
Emergency Relief
Cooling Water
Condenser
De-Superheater
Reducing Station
Condensate Pump
Feedwater
Heaters In Series
Sodium
Superheater
Steamchest Deaerator
Feedwater Pump
Feedwater
Heaters in Series
Sodium
Fig. 17-6. Schematic diagram of heat-transfer system.
levels. The other two streams go to the superheater and the reheater, and
are then combined with the bypass flow in the blender. On leaving the
blender, the sodium stream is split again by a three-way valve into two
streams; one enters a second bypass and goes directly to the main pump
and the other enters a jet pump that keeps a large sodium flow recirculating
through the boiler, which is of the Lewis type. The three-way valve is
adjusted, at design point, so that about two-thirds of the flow goes to the
jet pump and one-third bypasses the boiler. At low power levels the valve
would be adjusted to give very low flows to the boiler.
The centrifugal pump in this circuit has two speeds, full speed and one-
fourth of full speed. The low-speed operation provides for better regulation
of the sodium flow at very low power levels.
The turbine selected uses 1800-psia steam at 1000°F with reheat to
1000°1" and is rated at 275 Mw. It is a 3600-rpm single-shaft machine with
three exhaust ends. The turbine heat rate is estimated to be 7700 Btu/kwh,
or 44.39%, cycle efficiency, while 7860 and 8360 Btu/kwh are the generator
and station heat rates, respectively. With 67, of generator output used
for station auxiliaries, 260 Mw is supplied to the bus bar.
17-3. REMOTE MAINTENANCE PROVISIONS
Remotely controlled mechanized tools and viewing devices are provided
in the reactor cell for making minor repairs and for removing and re-
17-4] MOLTEN-SALT TRANSFER EQUIPMENT 691
placing any component in the cell. The tools will he able to handle any
pump, heat exchanger, pipe, heater for pipe and equipment, instrument, and
even the reactor vessel, and, correspondingly, the components will be de-
signed and located for accessibility and sepuration.
The removal and replacement of components requires a reliable method
of making and breaking joints in the pipe. Cutting and welding of pipe
cections can be used, but in the low-pressure molten-salt system 1t 13 be-
lieved that a flanged-pipe joint (see Section 15-3) may be satisfactory.
All equipment and pipe joints in the reactor cell are luid out so that they
are accessible from above. Directly above the equipment is a traveling
bridge on which can be mounted one or more remotely operated manipu-
lators. At the top of the cell is another traveling bridge for a remotely
operated crane. At one end of the cell is an air lock that connects with the
maintenance area. The erane can move from the bridge in the cell to a
monorail m the air lock.
Closed-circuit television equipment is provided for viewing the mainte-
natce operation in the cell. A number of cameras are mounted to show the
operation from different angles, and a periscope gives a direct view of the
entire cell.
17-4. MoLTEN-SALT TRANSFER lDQUIPMENT
The fuel-transfer systems are shown schematically in Fig. 17-7. Salt
frecze valves (see Section 15-3) are used to isolate the individual eom-
ponents in the fuel-transfer lines and to isolate the chemical plant from
the components in the reactor cell. With the exception of the reactor
draining operation, which is described below, the liquid is transferred from
onie vessel to another by a differential gas pressure. By this means, fuel
mav be added to, or withdrawn from, the reactor during power operation.
The fuel added to the reactor will have a high concentration of UF4 with
respect to the process fuel, so that additions to overcome burnup will re-
quire transfer of only a small volume; similarly, thorium-bearing molten
salt mav be added at any time to the fuel system. The thorium, in addi-
tion to being a design constituent of the fuel salt, may be added in amounts
required to serve as a nuclear polson.
For the main fuel drain circuit, bellows-sealed, mechanically operated,
poppet valves (see Section 15-3) will be placed in series with the freeze
valves to establish a stagnant liquid suitable for freezing. Normally these
mechanical valves will be left open. By melting the plug in the freeze line
and opening gas-equalization valves, the liquid in the reactor will flow by
gravity to the drain tank, and the gas in the drain tank will be transferred
to the reactor system. Thus gas will not have to be added to, or vented
from, the primary system.
Legend:
______ [_ ___Q___TQHS ——Fuel Line
o o g S 1’ v ——-—~Gas Line
| —DDh—Solenoid Valve
— FV FFreeze Valve
S5—Supply
V—Vent
i =——p——Normal Flow
| Direction
Th uy235 Withdrawel ' FP—Fission Products
Reactor
Enricher Enricher Tank
s Heat
Exchanger
e
Processing
Plant
|
|
|
|
1
1
i
\
|
|
|
|
Fia. 17-7. Schematic diagram of fuel salt transfer system.
HOLOVHEY HHMOd V 40 NDISHA TVALIAONOD 69