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almost complete recycle is only 0.024 mill/kWhr. The higher cost for the once-through gas cycie is due primarily to the cost of disposing of a relatively large quantity of solid waste and to the purchase of fluorine. The most significant cost for the gas recycle method is amortization of the remote fluorine plant, which has a direct cost of $1.005 million. In making the cost estimate, capital costs were amortized at 13.7%/year. Salt mine storage charges4 were assumed to be $300 per waste container, which is the minimum interment charge. Based on this comparison, the gas recycle method was selected for use in the MSBR fuel reprocessing plant.


M. J. Bell

L. E. McNeese

The thermal power that will be generated in an MSBR processing plant by decay of the noble-metal fission products will depend on the residence time of these elements in the primary reactor system and the fractions of these elements accompanying the fuel salt to the processing plant. We have performed a series of calculations in which the noble metals were assumed to be transferred from the fuel salt, on a 50-sec cycle, into a holdup volume having a residence time ranging from 1 sec to 1 year. The holdup volume was assumed to be in contact with fuel salt so that materials produced by the decay of noble metals could return to the fuel salt if these materials were not noble metals. The model is sufficiently general that the holdup volume could represent noble metals associated with circulating gas bubbles, a stagnant film of noble metals in a pump tank, or noble metals deposited on graphite and metal surfaces. The residual thermal power of the noble metals leaving the holdup volume is shown in Fig. 15.4 as a function of residence time in the holdup volume. The residual thermal power is defined as the integral, over all time, of the instantaneous heat generation rate for all isotopes leaving the holdup volume. The noble metals were divided into two groups: those that form stable volatile fluorides (As, Se, Nb, Mo, Tc, Ru, Sb, and Te) and those that do not (Rh, Pd, and Ag). Elements in the fust group are assumed to be completely removed from the salt in the primary fluorina-

4. Staff of the Oak Ridge National Laboratory,Siting of Fuel Reprocessing Plants and Waste Management Facilities, ORNG 4451 (July 19701, pp. 6-44-6-47.

tor. The elements in the second group will remain in the salt and will be extracted into bismuth in the protactinium isolation system. If the removal of 1% of the noble metals from the holdup volume occurs with a residence time of 1 min, the heat generation in the processing plant will be increased by 200 kW, with the bulk of the heat being generated in the UF6 recovery system. About the same heat generation rate would result if 10% of the noble metals reached the processing plant after a oneday holdup or if 20% reached the plant after a tenday holdup. The heat generated by the halogens (Br and I) in the processing plant will depend upon both the halogen removal time and the noble-metal removal time since halogens are produced by the decay of some noble metals. If the noble metals are removed from the fuel salt on a very short cycle, their daughters are prevented from entering the fuel salt and thus 'will not reach the processing plant. The heat generation rate resulting from the decay of halogen fission products is shown in Fig. 15.5. An effective noble-metal removal time of 0.1 day is believed to be reasonable for the present flowsheet. This would result in a heat generation rate of 210 kW for the halogens for a halogen removal time of ten days or 520 kW for a removal time of three days. For a noble-metal residence time in the holdup volume as long as one year, the halogen thermal power would be increased by only 60% over that for a 0.lday residence time.


M. J. Bell A recent study' has been made of the long-term hazard associated with high-level radioactive wastes produced by nuclear reactors operating on the enriched 2 3 'U, uranium-2 'Pu, and thorium-2 'U fuel cycles. In this investigation, the reference MSBR was assumed to be typical of the thorium-233U fuel cycle. It was found that the ingestion hazards represented by the high-level wastes produced by the three fuel cycles are quite similar after comparable periods of decay. These high-level wastes were assumed to include all fission products produced by the fuel cycle and, in the case of the U and uranium-' 'PU fuel cycles, to include


5. M. J. Bell and R. S. Dillon, The Long Term Hazard of Radioactive Wastes Produced by the Enriched Uranium, Pu230U, and 233U-Thorium Fuel Cycles, ORNLTM-3548 (in press).

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