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OAK RIDGE NATIONAL LABORATORY COPY ’
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UNION CARBIDE NUCLEAR COMPANY
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= CENTRAL FILES NUMBER
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External Transmittel Authorized

October 8, 1958 " COPY No. ¢}/¢7
U233 Breeders - Comentary and General Remerks

 

 

 

 

Listed Distribution
W. K. Ergen

ABSTRACT

Breeding 1s expected to became & necessity in about 40 years
and in view of the 20 years development time end %0 years service
life of breeder reactors, develomment of such reactors at present
is timely. In plutonium breeders, the specific pover is inherently
low and the doubling time long. This seems to prevent such breeders
from furnishing a large fraction of the energy demends of the
exganding economy from urenium recoverable at- or about present cost.
US33 breeders can be designed to the requirements of low inventory
and short doubling time, but the aqueous homogeneous reactor seems
to be the only type vhich can adequately meet these requirements.

NOTICE PROPERTY OF
natars Soument contains information of o preliminary WASTE MANAGEMENT

at the Qok Ridge National Laborotory, It is subject
to revision or correction and therefore does not

represent a final report, DOCUMENT
The information 15 not to be abetracted,
_ reprinted or otherwise given pubiic digremination
. without the approval of the URNL patent oranglh, “BRAHY
- Togad and lnfarmation Coatrol Departmant, UCN-15212

@3 2-84) 8"'“"C’,5

 
 

 

 

 

 

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-Du
I. HISTORY AND SCOPE OF THE STUDY

The Osk Ridge Natlonal Laboratory has conducted a study regarding breeding
on the 2‘11252«-U25 > cycle. Object of the study was, on one hand, the importance
of breeding on this cycle and, on the other, a camparison of the various reactor
types with respect to thelr sultability as U2 breeders.

The study was prompted, in part, by temporary difficulties in the Aqueous
Homogeneous Reactor Program. These difficulties made 1t advisable to re-
Investigate the velidity of the old reasons which originally made the aqueous
homogeneous reactor appear as one of the desirable reactor types, in order to
see vhether these reasons still hold. Breeding on the T.112.52--U233 was one of

these reasons.

During the course of the study, the homogeneous reactor experiment;
operated in a far more satisfactory manner than snticipated at the time when
the study was originated, and this inereased expectation that the aqueous :
homogeneous reactc_)r will be a desirasble reactor t'ype even without U23'3 breeding.
This made 1t less important to carry the study to its final form at the present
time. On the other hand, enough unexpected phenomenn bre eppearing in the
homogeneous reactor experiment to let it seem posatble. that: Inmporbent. past:.
rameters for breeding, for instance potsamizng by, corrvsion products, .may. turnk
out differently than anticipated. These uncertainties plus the recently de-
veloped large uncertainty in the o?.of U233 will be resolved in the nesr future.
The final form of the study should be postponed until these uncertainties are
resolved. This memo serves the purpose of an interim report. '

The importance of breeding on the Th252-U233 cycle depends primerily on
the importance of breeding in géneral, and secondly on the camparison of the
U258-Pu239 breeding cycle with the '.11}1252--U25 5 cycle. As to the necessity
of breeding in genersl, E. D. Arnold and J. W. Ullmenn have reached conclusions
which are reported in ORNL CF-—58--8—.‘L6.l As to the comparison between Pu?

 

1. E. D. Arnold and J. W. Ullmann, Use of Raw Materials in an Expanding
Nuclear Power Economy, ORNL CF-58-8-16, Aug. L4, 1958,
=B

and 0255 breeding a few remarks are contained in theé present memo.

The desire to compare various reactor types as to their sultability
as 0233 breeders resulted in an investigation by A. M. Pexrry, C. A. Preskitt,
and E. C. Halbert on the use of gas-cooled, graphlite-moderated reactors for
this purpose. This investigation is now being extended to ges- cooled, heavy-
water-moderated reactors.

E. Guth, 8. Jaye and A. Ssuer spent comsiderable time on the optimizstion
of the aqueous homogeneous reactor for U233-breeding purposes (as contrasted
to the much dlscussed optimization as to cost per kwh). This part of the
| study is not finished and 1s most strongly affected by the above-mentioned
uncertainties. |

II. THE NECESSITY FOR BREEDING

The fuel burmup cost in a straight burner, with present prices, is
about 3.mills/k#h. Thus a difference of 10% in breeding ratio amounts to
about 0.3 mills/kwh, since & reactor of breeding ratio p could buy fuel
smounting to 10% of its burnup for 0.3 mills/kvh and end up with the seme
amount of fissionablé material as & reactor of breeding ratio B + 0.l A
breeder and a’convertef of reesonably high conversion ratio will not differ
in conversion ratlo by more than a small multiple of 10%, and the difference
in fuel-burnup cost will thus be smeller then the uncertainty in the esti-
meted power cost of a nuclear reactor. Fuel burnup cost on the basis of
present prices will thus not offer a strong reason in favor of breeding.

Any justification for breeding thus involves an element of planning
for the future, a consideration of the time when the fissionable material
recoverable alt reasonable cost willl be exhausted and the nuclear-power
econamy depends on tapping the energy content of fertile material.

The Justificatlion for breeding is then analogous to the Justification
- of nuclear-power production in general - muclear-power production is justi-
fled with a view to fubure depletion of fossile fuel, rather than with a

view to present prices. The long-range planning is needed in the ruclear-
pover fileld because of the long development and design time - estimated st
4

20 years - and long life of power plants, estimated at 20 years. Thus,
1f breeding will be necessary 20 + 30 = 50 years hence, it is not too
early to proceed with the development now. Otherwise, we will have,

50 years hence, a large installed capacity which still could be used
except for the fact that it burns fissionable material which we can no
longer afford to burn. If it is the intention to scrap these reactors
before they are worn out, they would have to be burdened by larger
depreciation costs during ‘their use.

Any estimate of future supply and demand of fissionsble material is
very uncertain. Estimate of how much fissionable materisl will be svail-
abie, and at what price, depends on guesses as to future discoveries of
deposits and also on how much fissionable material the U, S. will be able
to import from abroad, or will export to other countries. Demand depends
not only on the extremely uncertain requirements of the power economy it-
self, but to a large extent on the demand for nuclear-powered naval vessels,
alreraft, rockets and weapons. Conceivably the latter could even become &
source rather than a sink of fissionsble material,as within the time periods
considered muclear disarmement and release of stock-piled material could
becone g reality On the other hand, scme of ‘the uses of nuclear energy
could be extremely wasteful of fissionable material. An exnnmflfi for this
1s the "bomb rocket" intended to propel a large weight into outer space by
a large number of "small" nuclear-bomb explosion behind the weight to be
1ifted.

The lmpact of fusion on fission reactors is likewise very uncertain.
Conceivably, fusion could produce power cheaper than fission and put fission
power reacfors out of business, or fusion based on the D-D reaction could be
a source of neutrons and hence of flssionable material. On the other hand,
large-scale power generation by fusion msy be uneconamical, or unfessible,
or dependent on outside supply of tritium end hence on fission reactors with
good neutron economy.

An accurate prediction of the supply and demand situation with respect
To fissionable material is obviously impossible, but 1t is also unnecessary
-5~

for the purpose of deciding on the develomment of a breeder reactor. If
there is a reasonable probabllity of breeding being attractive during the
next 50 years, such develomment would be indicated. In fact, 1t 1s quite
likely that applications of muclear energy will be proposed which consume
large emounts of fissiomsble materdal. The bomb rocket is an example. If
there 1s a prospect of fissicmable materinl beeaming scarce, the decision
regarding such proposals may very well depend on the feaslbility of a sult-
able breeder. In that case, any effort spent on development of a breeder
would pay off in terms of hard information regarding the feasibility of the
breeder, and in a firmer basis for the above decision.

Even if breeding were of 1little interest for the nesr future in the
United States, it may well be important in foreign eountries with less
netive supply of fisslonable material. The potentdal need of foreign
countries for power is one of the main Justifications for development of
miclear-power resctors. An analogous srgument could Justify the development
of breeders.

It appears that, for a breeder, the doubling time is the more important
concept than the breeding ratio. In part this is due to0 the scmewhat
philosophical point that breeding ratio is not alweys easy to define. Breed-
ing ratio 1s the ratio of the amount of fissionable materdsl avallable at the
end of a fuel cycle to the amount of fissionable material at the 'béginning
of the cycle. If different parts of the fissiomable materisl have different
histories, the "cyele" is a semewhat controversial concepte On the othex
hand, the doubling time, thet is the time at which the amount of fissionable
materlal has doubled, is clearly defined.

More important than the above philosophical point is the fact that
the doubling time of the reactor can be compared directly with the doubling
time of the demand of the fission-power economy. If the reactor doubling
time 1s longer than the doubling time of the demand, then the reactors ecsnnot
keep up with demand. A future shortage of the supply of fisgionable material
will be reflected back to earlier dates. '
“ba

Doubling time has to defined as the time in which the whole fission-
able inventory of a resctor is doubled. This inventory'includes fissioneble
material contained in the reactor core, the blanket, the reprocessing plant,
etc. Reprocessing losses have to be taken into account.

In considering the reactor doubling time one should really consider
the average over the whole econamy. Since there will be a large number of
reactors which will not breed(mobile reactors, for instance),the incentive
for short doubling time will be high in those reactors which can be made %o

breed.,

As to the actual mumbers, Arnold and Ullmenn sssume & U. S. nuclesr-
power production which at filrst increases very rapidly as the nuclear-power
production increases its share of the total power production which, in turn,
is increasing. Finelly, the nuclear-power production is assumed to increase
with the same doubling time as the total power production, this doubling
time being between 5 and 10 years. Assuming that the United States power
rroduction can draw on the ores of the U, S. and Canada, the raw material
whlch could be recovered at up to twice the present cdst would last until
1590-2000. From this, Arnold and Ullmsnn concluded that breeding will not
be necessary for about 30 to 40 years.

As has been discussed above, a case can be made for the development of .
breeder reactors up to 50 years ashesd of the time when breeding is necessary.
Thus the figures of Arnold and Ullmann seem to show that develomment of
breeders is quite timely at present. This conclusion is made even stronger
1if considerstion is given to the possibility that the non-power use of
flssionable materisl, export of Canadiasn ore to other parts of the world,
etes, could advance the date at which breeding will be & nécessity.

Since the power economy is expected to have & doubling time of 5 to
10 years, the doubling time of the breeders should be the same, or preferably
shorter to make up for non-breeding uses of fissionable materisl.

Arnold and Ullmann point out, however, thet other factors are more
important than breeding. Among these factors is high thermal efficlency,
which means high operating temperature of the reasctor. This deserves
-~

underlining. A reactor with high thermal efficilency, which does not breed,
uses a relatively small amount of figslonable material, and, though it does
not convert sufficient fertile into fissionsble material, it leaves the
energy comtent of same fertile material untouched, to be available for fubure
users who are ingenious enough to extract it. A low-thermsl-efficiency
breeder replaces the fissionable material 1t uses, but it uses a relatively
large amount of fissionsble, and hence fertile atoms, and whatever is washed
is gone forever. In this respect, high temperature reactors, like the
liquid-metal fuel reactor and the molten-salt reactor are more desirable even
1f they are no breeders.

Another parsmeter of great importance in an expanding nuclear-power -
econamy is, as Arnold and Ullmann point out, a low inventory. ILow inventory
is closely comnected with short doubling time, the Importance of which has
bemmentioned above. A further drastic example of this will be mentioned
below.

Arnold and Ullmenn emphasize that there is an enormous supply of
urandum, estimated at 100,000,000 tons for the U. S. and Cenada, which could
be recovered at up to $100/1b U308' This supply will not be exhausted within
a foreseeable future, and even if a breeding program fails to produce enough
fisslonable material for the energy requirements s only an increase in power
cost,but no catastrophic‘ power shortage,will result.

III.. GCOMPARISON OF PLUTONIUM AND U-22 RREEDTNG

From a practical viewpoint, the main difference betieen plutonim and
yeod breeding lies in the inventory of fisslonsble material. This inventory
is much larger for plutonium breeders than for Uo7 breeders. lLarge
inventory is connected with low specific power (kw/kg of fissionsble material)
and long doubling times. The large inventory is meinly & consequence of
basic physical facts: because of the energy dependence of the 7] of Pu239,
plutonium breeders have to operate at high neutron energies where the cross
sectlons are small and where it takes many plutonium stoms to catch a
neutron with sufficient probability before i't escapes or slows down. A
-8-

contributing cause of the large inventory is the intricate core structure
of fast breeders and the resulting large hold-up of flsslonable material
external to the reactor.

The specific power of the Enrico Fermi Fast Breeder Reactor is 149 kw/kg
of total inventory of fisssionsble materi&l,e or approximately 1 kw/kg of
natural uraniun (assuming that essentially all U7 contained in natural
uranium could be used in the reactor). The U. S. and Canadian uraniium re-
sources recoverable at present prices are, according to Arnold and Ullmann,
020,000 tons, which would allow the production of 550,000 Mw (thermal), or
1.6 x 1016 Btu/year. The time when this would have covered the total energy ¥
input of the United States alone-has, according to Putnam,a passed around
1910,

At a given specific power, the energy production can increase only at
a rate determined by the doubling time. At 149 kw/kg, the time of 1009 burnup
would be 1k years. Hence, with any reasonsble breeding gain, the doubling
time of the reactor, and hence of its power production, would be around
100 years. 1In practice the non-breeding uses of fissionable msterial would
more than use up the small yearly production of plutoniwm in the:breedefs.

- With the above figures, the plutoniwm breeders could supply only s smsall
part of the energy requirements of the U. S., and because of thelr long
doubling time, they would fall further and further behind the rapidly increasing
demand,,

The U253 breeders, on the other hand, operate Best in the thermal region
where the cross sections are large, and fewer atoms suffice to prevent an
adequate mmber of neutrons from esceping. More lmportant, atoms other than
fisslonable ones can be used to do a large part of the neutron scattering and

 

2. Technical Progress Review, Power Reactor Technology 1,No. 3, 57{1958),quoting
Enrico Fermi Fast Breeder Reactor Plant, APDA 115, Nov. 1956.

3. P. C. Putnam, Energy in the Future, p. 75, Fig. 4-3%, D. Van Nostrand Co.,
Toronto, New York, London (1953%).

*Thus when other power sources were used up and we had to rely on the above
uranium resources and the sbove specific pover, we would have to revert to
the 1910 standard of totsl energy consumption. Total energy means gll the
energy, including the part now derived from fossile fuel for space heating,
vehicle propulsion, ete,
..9_

escape prevenbting. Neutron-energy degradation by these "other atoms" does
not have to be prevented and is in fact desired. '.fhus, the critical mass
and inventory in a 0235 bi'eeder can be made very low, and the specific power
very high. (The design parameters of a 300 Mwe aqueous-homogenecus reactor
station call for about 4500 thermal kw/kg of fissionable meterisl.’ With
this specific power a breeding gain of 8.2% would correspond to 5 years

doubling time.)

Unless these design data are upset by low Y/ velues resulting from new
measurements, or by unexpected changes necessitated by new experdlences with
‘the homogeneous reactor experiment, the power genersted from the available
U255 resources could be conslderably higher than with the fast plutonivm
breeder, and after conversion to U->° the doubling time would be in line with
the doubling time of the muclear-power economy. |

The above is not meant to imply that the specific power of ‘the Enrico
Fermi Fast Breeder Reactor 1s the maximm thet can be achleved in a fast
plutonium breeder. However, in view of the somewhat fundsmentsal consider-
~ atlions which lead to low specific power in this type of reactor, it is un-
1ikely that the specif:!.é power can be raised by a large enough factor to
setisfy the expanding power economy, and to compete in this respect with
thexmal U=~7 breeders. At the very least, it seems considerably simpler to
achieve the required specific power with thermal U‘q?’3 breeders.

Another important point of comperison for the breeding cycles is the
availability of the fertile materials, US2° for the plutoniwm cycle end
‘I'h232 for the 0255 cycle. For the world as a whole, the amount of high
grade ore are about the same for uraniuwm and tho:'.h,mz.3 The largest deposits
of thorium are, however, in Brazil and Indie, and both countries have at
present embargoes against the export of thorium. Whether this is gerious for
the time period under considerstion in this Study is debatable. The

 

L, Computed from "Fluid FueX Reactors" (J. A. Iane, H., G. MacPherson and
F. Maslan, Editors), Addison-Wesley Publishing Co., Inc., Reading, Mass.,
(1958), Table 9-9, p. 508. To the fissionable inventory quoted in the
table, 16 kg have been added to allow for holdup in the "Chem Plant", etec.
This was done on the basis of orsl commnication from R. B. Korsmeyer.
-10-

North American continent, Us S. and Camada, have about 200,000°tons of High
grade thorium ore, which is a fraction of the high grade uranium-ore supply
but still of the same order of magnitude and very substantisl. If all
converted into energy this supply would correspond to 17 x.lQl8 Btu which is
quite comparable to the whole fossile fuel supply of the U. S. and Canads.

It would cover, according to Arnold and Ullmann's figures, the snticipated

Ue S. requirement of electrical energy well beyond the year 2000. Congidering
the U. S. alone, the known thoriim supply 1ls relatively small, but this is
probably largely dve to the lack of interest in finding thoriwum.

In sumary of the supply situation there are considerably less thoriim
deposits in the U. S. than uranium depositss but 1f thorium were needed, it
could be found in sufficlent quantities either by - further exploration or by
import from Canada, if not from India or Brazil.

As far as price goes the U238 1s obviously cheaper than thorium because
it is obtainable from the tailings of U235 production which is needed.fiy.
users other than commercial power plants. However, the price of the fertille
material makes an insignificant contribution to ‘the cost of power derived
from s breeder. | . | |

Both recycled thorium end plutoniwm are radiation hazards.. However,
there seems to be no significant difference in the handling of the two
substances.,

A strong case can be made for parallel development of the plutonium and
U235 breeding cycles. Nelther cycle has been demonstreted +o glve breeder
reactors of sufficlently low inventory and doubling time. Gambling on one
cycle - with the possibllity that the other cycle would have been the only
successful one - would be dangerous to the extent that breeding ls necessary.
More important, the optimm development might very well involve & start with
a low-inventory, short-doubling-time U235 breeder which would allow, with s
limited supply of fissionable material, to produce & substantisl asmount of
power and a substantisl yearly inerease in the power production. With the
fisslonable material supply increased by these breeders, high inventory
plutonium breeders could be put into operation in orxder to tap the U258 supply .

 

5+ "J. C. Johnson, Resources of Nuclear Fuel for Atomic Power, Second United
States International Conference on Peaceful Uses of Atomic Energy, Geneva
Paper A/Conf. 15/P/192.
1l

IV. COMPARISON OF DIFFERENT REACTOR TYPES FOR U->° BREEDING

As mentioned in Section I, Perry, Preskitt and Halbert investigated the
use of gas-cooled, graphite-moderated reactors for U235 breeding. The
breeding gain fiurned out to be small, if not negativé,‘mainxy because of the
dilemms between, on one hand, large C:U ratio and large absorption in graphite,
and, on the other hand, & smaller C:U ratio with insufficient moderation and
lower 72~values corresponding to higher neutron energies. The inventory was
of course large. With respect to breeding, the gas=-cooled, graphite-moderated
reactors are not competitive with the aqueous homogeneous reactors.

The seme authors are now investigating gas-cooled, Deo-moderated reactors,
with some misgivings about the absorptions in the zirconlum-pressure tubes..
Liquid-metal fuel reactors and molten-salt reactors are bound to have large
inventories anfi, at best, low breeding galns, and are no good as breeders for
this reason. Thelr high-thermnl efficiencies speek, however, in thelr favor,
even if conservation of fissionsble and fertile material is made the primary
consideration (see Section I). |

In view of the uncertainty in the'n -values, 1t is not plamned to extend
in the immedlate future the calculations regarding U235 breeders, other than
the aqueous homogeneous reactors, beyond the already scheduled computations
of the gas-cooled, 320~moderated reactors.
12- 21.
02,
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T +

Albrecht
Alexander
Arnold
Blanco
Bresee
Briggs
Brown
Bruce
Charpie
Culler
Eister
Ergen
Ferguson
Goeller
Gresky

Guth

~12-

DISTRIBUTION

26,
27 .
28.
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30,
31
32-0
53
355
36
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3839
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hh_sa *

Ce. BE. Guthrie

J+ P. Hammond

S‘o Ja-ye

P. R. Kasten

J. A. Iane

R. B. Lindaver

A, M. Perry

C. A, Preskitt

M. J. Skinner

J. W. Ullmann

A, M, Weinberg

C. E. Winters

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