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which ROD-HISTRY averages fuel compositions over much shorter intervals. It is evident, however, that measures to maintain a well-thermalized flux spectrum will probably be required to use recycled plutonium effectively for the startup of high-performance thorium23 U converter reactors. We are continuing to study plutonium startup, with the object of reducing the initial fissile loading. One method would be to increase the moderator ratio by simply lowering the thorium concentration in the reactor that we have been studying. In addition, we plan to study reactors designed specifically as plutck nium-fed converters (in contrast to the reactor studied thus far, whose core characteristics were optimized for breeding with continuous processing). We would expect

Table 2.7. Performance of a lOOO-MW(e) fied-moderator molten-salt reactor operated as a converteP with enriched uranium as feed material Case identification Feed material purchased Initial loading, kg fissile Lifetime purchases, kg fissile Recovery at end of life, kg 233


235u Net lifetime requirements: kg fissile Lifetime averaged conversion ratiod Fuel costs? mills/kWhr Inventory Fissile salt Salt replacement Fissile burnup Total

the optimum converter reactor designs to have a well-thermalized core flux spectrum. The results of the enriched-uranium feed case shown in Table 2.7 indicate that very good performance can be obtained from the breeder reactor operated as a converter with batch processing. The changing fuel composition over the reactor lifetime is shown in Fig. 2.3. The conversion ratio of over 90% is good for a reactor processed only every six years. The fuel cost of about 0.76 mill/kWhr excluding processing is attractive. The cost of processing and disposal of the spent fuel has been roughly estimated'to add about 0.1 mill/kWhr to this cost. The high fissile inventory cost relative to the burnup cost suggests that a lower thorium concentration would give a lower overall fuel cost for a reactor designed specifically as a converter. This would result in a lower fissile inventory at some sacrifice in conversion ratio. 2000

A21-1 235ub


2430 3599 1950 381 1268 0.946

1600 1400

-2 -



0.566 0.051 0.092 0.054 0.763










aReactor described in Table 2.4. Salt and plutonium discarded and uranium recovered at end of four six-EFPYcycles. Recovered uranium used for startup and feed in next cycle. b93% enrichment. CLifetime purchases less fissile uranium recovered at end of last cycle. dlrlet, taking into account discard of plutonium and neglecting any loss of uranium in each processing cycle. eExcluding processing costs. Obtained from present-worth calculation of fissile, fertile, and carrier salt purchases and ffisile sales over life of reactor, with discount rate = 0.07 year-', compounded quarterly, and inventory charge rate = 0.132 yea-'. Values of 11.9 $/g 235U,13.8 $/g233U, and 9.9 $/gfissile plutonium were assumed.

400 200 0







TIME (equivgient full-power years)

Fig. 2.3. Fuel nuclide inventories for enriched uranium feed case A21-1.