Dr. Ditmann has some interesting observations on LMFBRs. He claims that
the IAEA data base for fast reactors does not present any evidence that a positive breeding gain has been obtained with past and present FBR reactors. On the contrary, the presented data indicate at best that a more efficient nuclear fuel use than in standard PWR reactors can be achieved during normal running conditions. However, once the short and inefficient running times of FBR's, in comparison with large scale PWR's, are taken into account, even this better fuel use has not been demonstrated. In fact, the required initial fuel load in FBR's contains at least twice as much natural uranium equivalent and with a fissile material enrichment that is roughly 5 times larger than that in a comparable PWR. A fair comparison of the fuel efficiency should include the efficiency to recycle fissile material from used nuclear fuel in both reactor types.In addition Dittmar notes that there are three areas of further concern about LMFBRs"
Fast reactors are known for their worrying safety record. For example, it might be true that serious incidents, like the one that happened with the Chernobyl graphite moderated reactor, cannot happen with modern PWR's. However, only very few nuclear experts would agree to such a statement for sodium cooled FBR's.Indeed Dittmar's view seems to be that
FBR’s are known for their huge construction costs relative to PWR's, and it might be tempting to compare some of the past FBR's to a monetary "black hole." An equivalent of 3.5 billion Euros has been invested in the construction of the SNR-300 in Germany. Because of safety concerns related to sodium leaks and other problems, this small FBR has never started operation. This amount of money corresponds to the price tag for a five times more powerful modern PWR reactor.
A third problem is related to the FBR requirements to have a large inventory of high purity fissile material. The amount of fissile material listed in Table 3 should be compared to the few tenths of kgs required for a Pu239 bomb. This problem makes even small experimental FBR reactors highly sensitive to the proliferation problem.
* The breeding of Pu239 with fast neutrons has huge problems, and it would be great if another nuclear fuel could be found.
* Thorium breeding shows interesting potential if the remaining large number of problems can be mastered in the long term, . . .Dittmar nots evidence for thorium breeding in the Shippingport LWBR experiment. Dittmar also noted some advantages for thorium breeding:
- The possibility of utilizing an abundantly available resource that has hitherto been of so little interest that it has never even been properly quantified.
- The production of power with few long-lived transuranic elements in the waste.
- A reduction of radioactive waste, in general.
- The high cost of fuel fabrication due partly to the high radioactivity of U233 chemically sepa rated from the irradiated thorium fuel.
- Separated U233 is always contaminated with traces of U232 (69 year half-life but whose daugh ter products such as thallium-208 are strong gamma emitters with very short half-lives). Although this confers proliferation resistance to the fuel cycle, it results in increased costs.
- The similar problems in recycling thorium itself due to highly radioactive Th-228 (an alpha emitter with two-year half life) present.
- Some concern over weapons proliferation risk of U233 (if it could be separated on its own), although many designs such as the Radkowsky Thorium Reactor address this concern. The tech nical problems in reprocessing solid fuels are not yet satisfactorily solved. However with some designs, in particular the molten salt reactor (MSR), these problems are likely to largely disap pear.
- Much development work is still required, before the thorium fuel cycle can be commercialized, and the effort required seems unlikely while (or where) abundant uranium is available. In this respect, recent international moves to bring India into the ambit of international trade might result in the country ceasing to persist with the thorium cycle, as it now has ready access to traded uranium and conventional reactor designs.
The well known use of nuclear fission energy in PWR's is unsustainable. The problems related to long-lived transuranic elements, e.g. plutonium and heavier elements, as well as nuclear waste in general, are unsolved. The concern with nuclear weapon proliferation cannot be dismissed either.
"Much development work is still required, before the thorium fuel cycle can be commercialized, and the effort required seems unlikely while (or where) abundant uranium is available. In this respect, recent international moves to bring India into the ambit of international trade might result in the country ceasing to persist with the thorium cycle, as it now has ready access to traded uranium and conventional reactor designs."
This statement requires multiple answers:
1. The expression "much development" work is extremely ambiguous. ORNL researchers in the 1974 analyzed the developmental tasks required to for the development of a Molten Salt Thorium Breeder (ORNL-5018, Program Plan for the Development of Molten-Salt Breeder Reactors). The cost would have been somewhere around 2.5 billion 2009 dollars, to prototype stage. To date the United States has spent about $25 billion on the development of the Liquid Metal Fast Breeder Reactor without a product. Even if the development cost were several times higher that $2.5 billion, it would still be cheap, even in terms of what the United States spends researching renewables. A mini-Manhatten Project approach would vastly shorten the development time frame. With an investment of $15 billion, less than the United States spends on its space program every year, the United States could have a viable commercial LFRTR prototype in 5 years.
2. There is a strong motive for LFTR/TMSR development. Namely low cost rapid substitution of nuclear energy for fossil fuels. The LFTR is significantly simpler than the LWR, and it can be built with less materials, fewer parts and less labor. LFTRs that produce between 100 MWe and 400 MWe will be small and light enough to transport by truck, rail or barge. Factory ass production of LFTRs would greatly increase labor productivity. Because of its small size, and high level of safety, LFTR site construction would be less expensive. Thus dramatic savings in nuclear construction costs could be realized by switching from LWR to LFTR technology. Finally factory production would dramatically increase the scaleability of nuclear power, making the replacement of 80% of fossil fuel energy sources by 2050
3 Indian efforts to develop the thorium cycle are likely to presist for some time for several reasons:
A.The international imbargo on uranium sals to India, will not be forgotten quickly, and a determination to make India independent of international uranium sources will remain fixed for some time to come.
B. India has at least a low cost thousand year fuel supply in surface thorium deposits, that beg to be used.
Dr. Dittmar thus has suggested views that are supportive of the case for thorium generally, and offers indirectly for the Liquid Fluoride Thorium Reactor. The major problems for thorium breeding molten salt reactors, which Dittmar notes have more to do with the current scale of development, than development difficulties. A much larger development effort, could vastly shorten development time.