MUC-LAO-40.txt

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Subject  NOTES -
ON MEETING OF WEDNESDAY Copy 6 Wei
JULY 14, 1944 it 5w
By Ohlinger I
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Date =
ame
Date

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CENTRAL RESEARCH LIBRARY
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Those present:
‘Hogness Creut

AIlzson, Vernon, Hilberry, Cooper, Ferm. ; Wigne:
- Young,. Seitz, and'ohlinger

At sn earlier meeting, Mr. Wigner mentioned his "pulsating"

plle, Today, he <'bexi.>la'£ned‘its o;':ération in more detail and inclfideé : ;.

some estmated. Operatmg data.'

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Faiay WIGNER PULSATING

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If one thinks of a power producing pile, one is naturally faced -
with the general problem of a liquid medium which can stand high tempera-
tures, This problem was discussed before and a solution of some enriched
material in a liquid metal, or a solution or slurry of a compound in a

~solvent with high beiling point but low neutron absorption was suggested.

However, since this problem is not solved, the following considerations
will assume that we have to deal with heavy water. as solvent. The heavy
water is used only as a typical liquid, in reality it is not very suitable
for the purpose because of its low bolling point,

The pile proper would then be a tank containing a slurry or solu-
tion of enriched material in heavy water.,

Surrounding the pile tank would be a series of heat exchangers.
The tubes through these exchangers would connect directly to the pile tank
at the lower end of the tubes and to a series of large, flat tanks at the
upper end. These tanks would serve for brief storage of the slurry during
the surging cycle with as large a liquid surface as possible to permit_a
maximum release of the gases of decomposition during the brief sojourn of
the liquid in the tanks. Connecting to each of the surge tanks would be
a deep liquid seal to prevent the escape of the gases, The operating’
cycle would be as follows: The slurry in the pile tank would be under
pressure while one or more of the surge tanks would have their pressure
reduced so that a portion of the slurry from the pile would flow up through

. the exchangers into the surge tanks. Simultaneously pressure in.other surge

tanks would be increased above the pile pressure so as to force partially
cooled slurry from those tanks back through the heat exchangers into the
pile. Pressures in the first tanks would then be built up to force the
partially cooled slurry back through the exchangers into the pile while
the latter tanks would be evacuated, and so on. The purpose of this
arrangement is many-fold. It provides a back and forth motion of the

hot slurry through the heat exchangers simply by adjustment of pressures
without the use of pumps. It provides an arrangement for cycling the

_.slurry through heat exchangers with a minimum of P-9 hold-up volume out-

side the pile proper. It does both these things in a manner that exposes

a maximum of the liquid for release of the gases of decomposition,

Some of the data calculated by Mr. Wigner for a pile for the
production of power follow, There will probably be as many as 1,000
tubes of 4 cm diameter emanating from the pile. The pile would probably
operate at somewhat high temperatures, about 150° C if a P-9 solution is
used, to get a better yield. The pressure in the pile proper would be
about 10 atmospheres. The variation in pressure in the large, flat
surge tanks would be about 2 atmospheres. The time of pulsation would

be about 1 second.

!

L
——— e et e e mmas e

Two different sizes were calculated by Mr. Wigner, one the critical
size and the other a size somewhat larger than the optimum,

-3

size would. undoubtedly lie somewhere between these two units.

Jtem

TABLE I

Concentration of 49 in P-9

L9 required

P-9 inside pile

P=9 outside pile (hold-up)

The quantity of liquid outside of the pile or the holdup.in Table II

Critical Size

0.001 gms/cc
1 kg.
1000 liters

300 liters

The optimum

QOver Size

0.0003 gms/cc

11 kg.

L200 liters

800 liters

is a function of the time of pulsation (t) and is based on the assumption

that the total cross section area of the exchanger tubes is 1/60 of the pile

area (pile face = 1/3 of the area and 1/20 of that is tube area).

The
amount of slurry being moved is proportional to the tube area and the veloc-

ity while the amount outside of the pile at any time is 1/2 that streaming

out in the period of one pulsation.
the cooling water keeps the tubes 200 C below the temperature of the

liquid. .

TABLE II

Length of pipe through exchanger (L) _ 100

Diameter of pipe through exchanger (D)

Hold=up in liters for critical size- pile ¢ 320t

Hold-up in liters for over size pile 860 t
Velocity (based on 1 atmosphere dif-

ferential pressure between pile and

surge tank) 8 m/sec
Temperature drop in one pulsation (as-

suming tube 20° less than the liquid

temperature LOo° C
Power in megawatts for critical size pile Sk
Power in megawatts for over size pile 140

200

250 ¢
660 t

7 m/sec

80° C
8l

It was assumed, for Table II, that

300

210 ¢
560 t

- 6 m/sec

120° C

105

-

The temperature of the tooling water through the shells of the ex-
changer would not be much above 70 - 809 C, At this low temperature the
pile would be practically valueless as a power producing unit. Accordingly,
the temperatures must be increased to get higher cooling water temperatures.

Mr, Fermi pointed out that a unit of this type would use up the
149 which it contains-in a few days if it is run at the high power indicated.
Mr, Wigner suggested cutting the 20° temperature drop across the
tubes 10° which would cut the power in half. For the critical size with
an L/D of 100 and a power production of 5S4 megawatts, the calculated ex-
ternal power required would be 6L kw., '

Mr, Cooper questioned the advantage of the "pulsating" method of
moving the liquid in contrast to its circulation by mechanical means and
Mr, Wigner indicated that the purpose of his "pulsating" method of handling
the liquid was to get rid of the moving mechanisms or pumps which would be
completely unapproachable after once being put into operation and to pro-
vide a better means of removing the gases of decomposition. Mr. Hogness
asked whether the object of this pile was to remove the power as useful
power or as heat. Mr. Wigner said that it would become the former as soon
as a suitable liquid is found in which to dissolve the L9 and which can be
used at high temperatures.

Mr. Seitz pointed out that the efficiency of such a pile would be
quite low unless other materials were used for the moderator, Mr. Wigner
agreed that this was correct and suggested the use of some other liquid
or internally cooled tubealloy rods to obtain. a higher temperature.

Mr. Wigner then turned to the application of the pulsation method
for a L9 producing pile and presented data for a large homogeneous pile
containing probably a slurry of uranium oxide in P-9. In this case the
pile volume would be about 30 cu.m. and the pile would probably operate
at around 150° C. The assumed temperature difference between the average
tube temperature and that of the liquid in the pile is 50°. This has
been chosen rather high because no power is wanted from this particular
pile. The tube diameter would be around 2 cm,

. TABLE III
Length of exchanger tube (L) 200 cm 300 cm 500 cm
Velocity : | 1l m/sec 12 m/sec 10 m/sec
Time of pulsation 2 sec 2 sec 2=3 sec
Power in megawatts 2750 3000 3250 - 3300
Hold-up of P-9 in tons 22 19 . 15% - 23%
Power
foTd=p in watts per cu cm (or 125 160 210 - 1LO

kw per liter)

A8 no further discussion on the "pulsating".pile was forthcoming,
Mr. Wigner said a few words about the possibility of piles employing an
endothermic chemical reaction for the direct removal of heat. He did not
favor the arrangement because he foresaw considerable difficulty in ob-
taining suitable materials for such a pile, In this ‘case cooling is not
by a liquid which cools by its heat capacity but by a gas which cools by -

decomposition, for example (¢s ) #Hiafigcan be broken down to CO and 0o which— ..

can be burned outside the pile for the production of power. Carbon dioxide
is suggested because it has a higher heat capccity and gives off chemical
as well as mechanical energy. However, a chemical reaction would probably
take place with many materials including the tubealloy so it would be :
necessary to coat the tubealloy, %
In addition, the advantage to be gained-from the use of a chemical’
reaction is not very large. The advantage of using a gas coolant in~whi§h
chemical reaction goes on can be described, phenomenologically, as an :
increased specific heat which is, of course, favorable. In order to have
maximum specific heat, one must operate around the-teqperatfire at which ;|
the chemical equilibrium is about half complete. In the preceding example: «
this would mean that about half of the CO, is decomposed. The specific |
heat per mole then is ‘ _ A

ST ———

c(R(ln..‘I%..)v.

i
In this, « is a rather small numerical constant, of the order of 1/10, Rl
is the gas constant, ¥ is a small integer, degending on the order of the!
reaction, N is the number of molecules per cm’?, A is a combination of
the chemical constants of the compounds of the reaction. 1In practice, ‘it
is difficult to bring the above expression above 10R to 20R. This, of;
course, is much more than an ordinary specific heat, However, in order
‘to obtain it, one must stay at relatively low pressures--which entails
high pumping speeds in order to attain a large power output. Furthermore,
most substances which undergo chemical reactions at reasonable temperatures
have a rather high atomic weight ¥%hich increases the ratio of the power
needed for pumping to the heat absorbed by the gas. One is led to the
conclusion that He or Hy at high pressures is as good a cooling gas as
any, even if one disregards problems of chemical stability, f

Mr. Cooper reported that methane and steam react to give carbon
monoxide and hydrogen. This reaction is highly endothermic but occurs
at relatively low temperatures (in the range of 600 - 800° C), This

'reaction is used for starting many chemical processes such as the manu-
facture of methanol, etc,

Mr., Creutz questioned whether the hydrogen gas given off in the
reaction might not attack the tubealloy to give the hydride which breaks
down readily, but Mr. Hogness said that the temperature (2500°) was too
high,
5=

Another advantage of the methane-steam reaction is that it is
non-reversible and so the products remain decomposed away from the pile
and can serve useful purposes of greater importance than their heat
values. Unfortunately the methane~steam reaction requires the presence
of a catalyst which is unfavorable because of the probable breakdown of
the catalyst under radiation. An advantage of the methane-steam reaction
is that it occurs at low pressures (around 1 atmosphere) and leaves very
little residue.

The attached sheet gives pertinent information on various types
of naval equipment.

e s .
e Ar -
- L4
‘
: Type Dignlacement {tons) Knots X¥
. Battleships - 33,000 30. 75,00
g Heavy Cruisers 10,300 38 75,000
' Light Cruisers 8,000 55
Aircr‘aft. Carriers ‘25,-363 30
llinelayers 3,0C0 20 £
Destroyers 1,800 23 35,300
Submarines : 1,800 7 4,800
Torpedo Beats 1,000 45 2,000
Patrol Vessels 2,000 7 T.2E0