Sunday, June 1, 2008

Rod Adams comments and I respond on nuclear waste

There are no dumb nuclear bloggers, and in fact I have a very high respect for the brain power of my peers. So when one of them comments on one of my posts, I look at the comment carefully. Rod Adams looked over my "Keys"which I had cross posted on "Energy from Thorium". Rod liked most of what I had said, but he had some disagreements with my comments on nuclear waste. Rod would have to disagree with me, because it is my view that Rod's favorite reactor, the Pebble Bed Reactor, leaves a mess behind it, after it burns nuclear fuel. At reason for the mess is simple, the Uranium-plutonium fuel cycle is wasteful in the use of nuclear fuel and potential nuclear fuel in both the LWR and the PBR. The Thorium-Uranium fuel cycle used in the LFTR, by contrast makes highly efficient use of nuclear fuel.

Adams stated:

"I do not think that anything that we do will "solve the problem of nuclear waste" since it is not really a problem in the first place.

There are plenty of people in the world with an interest in making it an unsolvable problem; those people will never be satisfied no matter how tightly we wind up the technical details.

My solution is to accept the fact that there is opposition and to try to help the rest of the people understand that the opposition is a body of people with financial interests in slowing nuclear power. That way, the opposition does not disappear, but they become far less effective in changing the way that we need to do business

My response:
One major advantages of having an up to 98% burn up rate plus FP recycling is that very little of site construction has to be devoted to post reactor by product storage. The facilities to handle LWR post reactor fuel, are not inconsiderable part of current reactor construction expenses. The fluoride salts FP extraction technology researched and developed at ORNL during the 1950's to 1970's demonstrate that low cost extraction of FPs from nuclear fuel is possible. By separating FPs we change them from "waste" into by products, which have real and/or potential uses in the economy.

I am in complete agreement with the very idea that there is no such a thing as "nuclear waste" in the conventional meaning of the term. Where I differ with Rod is in our evaluation of a once through fuel cycle, which I regard as very inefficient and "wasteful" because it fails to extract more than a small fraction of the potential energy from nuclear fuel. I do see a waste of fuel potential by the once through Uranium fuel cycle.

I discussed the fundamental problem of the uranium fuel cycle in a March post on Nuclear Green. My discussion of the relative merits of the uranium fuel and thorium cycles, rests on the discussion of those cycles in WASH-1097 which makes the issues wonderfully clear.

"The relevant characteristics of the important fissile and fertile isotopes in thermal and fast-spectrum reactors are summarized as follows:

(1) Thermal absorption in U-233 produces more neutrons per neutron absorbed** than does
corresponding absorption in either Pu-239 or U-235.
(2) The neutron production for U-233 is relatively insensitive to change in temperature, but for U-235 and Pu-239 eta decreases as the temperature increases. Thus, the advantage of U-233 over U-235 and Pu-239 is more pronounced in a hard (higher energy) thermal spectrum than in a soft (lower energy) thermal spectrum.
(3) From a nuclear standpoint, the use of U-233 in a thermal reactor makes it possible to achieve
higher fuel conversion ratios and longer fuel burnups than is practical with either U-235 or Pu-239 (Section 2.2).
(4) The higher conversion ratios which can be obtained in thermal-spectrum reactors when using U-233 instead of Pu-239 can result in a significantly better utilization of natural uranium fuel resources with thorium-fueled reactors than with the low-enrichment, light-water cooled uranium-fueled reactors (Section 2.3).
(5) A higher breeding ratio can be obtained with Pu-239 than with U-233 in a very high-energy, fast-neutron spectrum reactor. On the other hand, in a degraded (10 to 100 keV) fast spectrum, U-233 would probably be as good as, or better than, Pu-239. Also, the variation of U-233 and Pu-239 cross sections with energy are such that improved reactivity coefficients would be obtained with the use of U-233 in a large sodium-cooled FBR. This leads to improved nuclear safety characteristics.
(6) The energy dependence of the fast-fission cross sections of Th-232 and U-238 is such that the use of Th-232 would produce an improved reactivity coefficient in a liquid-metal-cooled FBR. The fast fission cross-section of Th-232 is much lower than that of U-238 so that use of the latter leads to much larger conversion ratios in fast-spectrum reactors

The inference is clear, even in fast neutron spectrum reactors, the Thorium fuel cycle is more efficient and thus less wasteful than the Uranium fuel cycle. My disagreement with Rod is not about these facts, but about their implications for reactor and especially PBR construction costs. If i am right, the prize for lowest overall reactor construction should be given to the reactor that uses fuel most efficiently, all other things being equal. There is little doubt that if the price of fuel reprocessing is factored into the price of reactor construction the LFTR would be lss expensive than the PBR.   If you do not pay the price of reprocessing, cost are related to the cost of storing and handling of unprocessed post reactor fuel.  

My other disagreement with Rod has to do with the best approach to dealing with opposition to nuclear power.  I believe that the problems of post reactor nuclear fuel, and the problems of reactor safety are real issues that the nuclear community needs to solve.  The best answer to opponents questions about "nuclear safety," and "nuclear waste," is not simply a public education, being able to say, "our reactors are safe and do no produce nuclear waste," is really what, in my view, is required to answer nuclear critics.  

I must add that I have very high regard for Rod's intelligence, integrity and abilities. Rod isan amazingly talented man, and I am very happy that we have him in our camp.


Ken Talton said...

I am a complete layman in these matters, but it is my understanding that the pebble bed reactor is VERY difficult to use for weapons production and that and its very low maintenance are a large part of its its appeal.

I was under the impression that the PBR reactors and the various types of small reactors referred to as "nuclear batteries" would depend on spent modules (reactors in the case of the "batteries") to be recycled in some sort of breeder anyway.

If this was not part of their plan, then how difficult would it really be to ship off (to a more politically stable area) the disposed of pellets or spent "batteries" for fueling, recycling in a thorium cycle reactor?

The proliferation issue is nontrivial. IIRC thorium reactors using the liquid flouride technology you and Mr. Sorensen advocate are sub-optimum for weapons production, but, they ARE breeders and as such I would think it advisable to keep them out of certain parts of the world for the foreseeable future.

Am I operating under incorrect assumptions?

Charles Barton said...

Actually LFTR can be designed on the to breed on a1 to one ratio. Withdrawing U-233 for weapons purposes would cripple the reactor. The proliferation issue is completely bogus, however. The most likely customers for LFTR would either have nuclear weapons already, or would already posses the ability to build them. Even if nether were the case, it would be significantly more difficult to produce nuclear weapons with U-233 from a LFTR than it would by building a graphite pile reactor and producing Pu-239, as the North Koreans did.

Ken Talton said...

I see. Thanks!

Doesn't this make nations in the developing world the likely candidates for the pebble bed type reactors and the small sealed units like that little Toshiba unit being put in Galena Alaska?

Can the byproducts of these be recycled in a LFTR?

Charles Barton said...

The pebble bed reactor is being developed in South Africa. I assume that the plan includes an intention to sell units to other African countries. Small reactors, including LFTR would probably work better for African countries than big reactors. Africa might also use CSP. I don't know how much future very small reactors have.

Charles Barton said...
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