ML20052D571

Recommends Comprehensive Review of Reactor by Acrs,Assisted by Appropriate Subcommittees & Ad Hoc Task Force of Experts. Advantages & Disadvantages of LMFBR Presented

ML20052D571
Person / Time
Site:	Clinch River
Issue date:	12/28/1981
From:	Stratton W LOS ALAMOS NATIONAL LABORATORY
To:	Carbon M Advisory Committee on Reactor Safeguards
References
ACRS-CT-1403, NUDOCS 8205060591
Download: ML20052D571 (6)

Text

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c7-Nos JosAlamos LosAlamosNationalLaboratory Los A!arnos.NewMexico 87545 28 December 1981

, A Professor Max Carben

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v Department of Nuclear Engineering University of Wisconsin $

Madison, Wisconsin 53141 "."uo a t M'

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Dear Max,

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N Ni the forthcoming safety review oforthe d'byClinch R and by my belief that the problem of the " Hypothetical Core ent" Disruption Acci "Bethe-Tait Accident," or however n,designated, ca e least and settled safety of thein the sense public. of not offering an undueealth risk to the h or at are much superior to those used for the FFTF (and for earli designs) and that our understanding of the necessary pheno is greatly improved computer programs pe. Certainly, knowledge is not complete nor aremenology also rfect, but both are adequate for the purpose. The present political climate also seems favorable, and ae reactor to examine first is the CRSR.

the appropri t politically, for a comprehensive review andof the matter e proper (and best) forum for this review is the AdvisorynCommittee Reactor o

Safeguards rith the assistance of its appropriate subcomittees suggest that an ad hoc and especial task force of, say,I 8 to 12 .

nationally nuclear recognized engineering, metallury,experts neutron in the appropriate specialties cs, (physi chemistry, or whatever may be necessary)ics, explosives, hydrodynamics, developmental and regulatory agencies be chosen.who are independent of the They should work closely and actively with the ACRS, the NRC, th safety specialists ~in the U.K., France, and German n studying this and related problems for many years,y) that have been probabl A fresh look and an intensive effort of some needed months wou n Alamos,y beginning when the several computational present core proposed for the CRBR.

the ACRS for such a specialized and intensive effortPrecedents exist in the histo

, for example the pressure vessel study completed in 1974.

To put my proposal in perspective .

allow me to set down my perception of the political situation an,d some general n the thoughts o

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(' Prof. Max Carbon 28 December 1981 LMFBR and coment on what I see as its technical advantages and disadvantages. The reasons for this special study at this time are part and parcel of these several factors and discussion.

Political Situation Both the Executive Branch of the govtrnment and the Congress are now in favor of constructing the Clinch River Plant and proceeding with additional developmental plants. I have been told that the Department of Energy has formally requested permission from the NRC to commence construction, but I do not expect that the NRC has yet responded nor should it do so without adequate consideration. However, the NRC has reacted to the President's statement of a few weeks ago by reactivating a review organization within its licensing division and by reviewing its own fast reactor research efforts (a report by L. S. Tong's Special Review Group was posted to you under separate cover). Thus, I believe that this administration is determined to begin construction of the CRBR project; support for efforts to solve its licensing problems, therefore, should be forthcoming.

Advantages of the LMFBR The sodium-cooled reactor is an interesting creation that has a number of safety advantages. A few of the obvious advantages are as follows:

1. The primary system operates at low pressure--only high enough to move the sodium through the system.

2. The coolant is noncorrosive to materials and components designed for its environment. EBR-II experience is showing some remarkable results from components that have been in sodium for nearly a generation.

3. The coolant operates far below its boiling temperature.

4. The large volume of sodium provides an enormous heat sink.

5. The coolant's heat transfer characteristics are excellent. These characteristics--the operating temperature, the heat sink, and the high heat transfer rate--have not been investigated systematically or exploited fully, but it is clear that a significant power transient involving a large temperature rise could be accomodated without damage to the core.

6. The coefficient of expansion of the coolant is large enough that convective cooling can be designed into the system. The advantages of this property of sodium have not been fully exploited in existing designs.

I Prof. Max Carbon 28 December 1981

7. The coolant, sodium, is a marvelous getter for iodine, which is, by far, the most dangerous of the fission products. This property is a safety factor of great significance.

Prima facie, it appears that if the reactivity control and decay heat removal systems operate reasonably effectively, nothing much can go wrong. Indeed, on a second look, this still seems to be the case; even if the latter system works only poorly or not at all, a long time, depending upon design, should be available to take action before the health and safety of the public is threatened.

Some persons regard other factors as good reasons for continuing the development of this reactor concept. These factors include such matters as the following.

1. The fuel is U-238, which is in abundant supply and inexpensive per se. Given a successful design or designs, the price of energy (electricity, hydrogen) frcm this source should be constant except for inflation of the economy for other reasons. For the first time, one can truly speak of a " lid" on the price of power and energy.

2. The limited amount of U-235 in the world would not be consumed in a few generations as will be the case if only U-235 burners are used. U-235 is, after all, the only naturally occurring fissionable isotope, and, like seed corn, we should be niggardly about using it.

3. The supply of uranium already above ground is sufficiently large that mining operations would not be needed for this reactor concept for generations, perhaps a century. This reduction of mining requirements is, of course, a safety matter of significance.

4. Most of the excess plutonium would be in use in reactors and hence inaccessible to terrorists. A chemical processing plant and fuel production plant may well be easier to safeguard than a large number of spent fuel storage pools (sometimes referred to as latent plutonium mines). Additionally, the sodium-cooled reactor can be regarded as a plutonium burner, and hence actually reduces the amount of plutonium in the world and truly lessens the terrorist threat.

5. The breeder reactor is the only sure thing we have for future generations. If we (our generation) are so selfish as to burn all the fossil fuels and U-235, the least we can do for our children and grandchildren is to provide them with the technology to produce an abundant and assured supply of energy. Whether or not they use it is their choice; our task is to create the capability.

Prof. Max Carbon 28 December 1981 Disadvantages of the LMFBR Disadvantages exist, and the last of these get to the crux of my proposal to you and Carson. Some of the difficulties or problems include the following.

1. The optimum design of the sodium-cooled, plutonium-fueled power plant must be at least a couple of decades away, commercialization and accumulation of experience certainly is a matter of decades.

Things take longer now than they did 30 years ago, and introduction of this concept probably will be more time consuming than was the case with the LWR. Its expense is greater than can be afforded by a single corporation, and the first few plants must be funded by the federal government or, perhaps, by a small tax on the entire electric utility industry.

2. The coolant is liquid sodium; large amounts have been handled successfully, but generally, the utility industry is unfamiliar with handling the necessary very large amounts.

3. The coolant is flammable in air and reacts violently with water.

4. The sodium captures neutrons and becomes radioactive with a half-life of about 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br />. Given the fallibility of mankind, one must assume that socner or later serious sodium fires will occur and that some of these will be fires with radioactive sodium.

Fortunately, because of containment or confinement, such a fire need not pose a threat to the health and safety of the public.

5. The sodium-water steam generator is a difficult device to design and construct so that no leaks, even pinhole size, exist. Success has been achieved (e.g! EBR-II), but the task is not easy or inexpensive, and difficulties have been encountered (e.g., PFR in the UK, BN-350 in the Soviet Union). Fortunately, this area of the plant is not radioactive so that additional hazard is not present.

6. The neutronic and reactivity characteristics of the fast neutron core are such that the voiding of sodium coolant from some parts of the core will increase reactivity and thus reactor power. A reactivity control or scram system must work, should a situation develop that involves boiling of sodium in a significant fraction of the core.

7. The core of the fast neutron reactor is not in its most reactive configuration. Should some accident or incident cause the core or some fraction of the core to be driven into a smaller volume by l

even a small amount, its reactivity and the reactor power level l would increase. Again, the reactivity or shut-down controls must i work properly, to avoid damage to the core. j I

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(- Prof. Max Carbon 28 December 1981 Item 7 is the origin of the reactivity accident that is associated with the fast neutron reactor. Indeed, in the early 1950s, during the design of the Dounreay Fast Reactor, some people were willing to postulate spherical implosions of that little core. The resulting calculations naturally predicted explosive energy releases of the order of tons of high explosive equivalent, given such an unrealistic and imaginary situation. In order to resolve this apparent dilemma, in 1957 Bethe and Tait assumed a gravity induced collapse of a voided and molten (but in-place) core and showed that even with these assumptions, the explosive energy could not be more than the equivalent of 160 kg of HE.* The Bethe-Tait result was accepted, even though it was unrealistic, as an upper limit for the Dounreay Reactor and was satisfactory then because it showed that containment of an explosion of this magnitude was quite feasible. Unfortunately, the precedent of assuming a very unlikely or even a near-impossible situation for a worst-case analysis was set and has plagued all subsequent LMFBR proposals and designs and discussions, both technical and popular.

Indeed, the fuel-melting accident ir the Fermi Plant was caused by a hastily installed safeguard to protect against the threat of accumulation of molten fuel and a possible "Bethe-Tait" accident.

Since the time of the Dounreay calculation, the history of analysis of this and related hypothetical accidents (for various reactors) has been to insert more realism and less arbitrariness into the initial assumptions and calculational technique. The result has been a fairly steady reduction of the estimate of the possible magnitude of the

" explosion" or " energetics" as it is sometimes called.

A good many fast reactor designers, analysts, and technical specialists believe that the day of the " explosion" accident concept has come and gone; however, this belief is sometimes based on physical intuition and engineering experience rather than a rigorous investigation and analysis. I place myself in the group of those who think about the problem and have this opinion, but I have worked in this field; hence my proposal in the beginning of this letter is founded on a background of experience and quantitative studies. I believe that a rigorous examination of the facts of the case will show no " energetics" for the Clinch River Plant and, further, will at least be strongly indicative for future, larger LMFBRs.

Conclusions The possible reward is potentially very great as I discussed above; the reactivity accident is about the only conceptual accident characteristic of the LMFBR that would be of significance to the health

• Modern, but still conservative, calculations of the Bethe-Tait model show about the same number of fissions but no explosive energy. Note that the erergy equivalent of 1 kg HE is 4.Tmegajoules.

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,- Prof. Max Carbon 28 December 1981 l

and safety of the public. If this proposed study leads to a positive result, it will certainly suggest that the LMFBR may be unique in regard to its public health and safety characteristics.

In conclusion, I repeat my recommendation for an ad hoc,

, pre-eminent advisory review panel to assist the ACRS in this part of its consideration of the Clinch River Plant. The tools and knowledge are available, and the political climate (and hence funding) is favorable to such a special effort. The ACRS provides the proper forum and commands sufficient respect worldwide to collect the best talent available in the United States and abroad. The task is worthy of our best efforts.

Please be assured that I am available to cooperate with you and the Comittee on this matter at any time.

Sincerely,

'L

<. R William R. Stratton WRS:hmb Distribution:

Dr. Paul G. Shewmon 2477 Lytham Road Columbus, Ohio 43220 Raymond Fraley Advisory Committee on Reactor Safeguards MS-1016-H U. S. Nuclear Regulatory Commission Washington, DC 20555 Carson Mark, T-DO, MS 210 ITO Files CRM0 (2) l l

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