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Report No.

Development of simple method to incorporate out-of-core cooling effect on thorium conversion in multi-pass fueled reactor and investigation on characteristics of the effect

Fukaya, Yuji   

Development of a simple method to incorporate the out-of-core cooling effect on the thorium conversion in multi-pass fueled reactors and investigation on characteristics of the effect have been performed. For multi-pass fueled reactors, such as Molten Salt Breeder Reactor (MSBR) and Pebble-Bed Modular Reactor (PBMR), fuel moves in the core and exits from the core. The nuclides decay also out of the core, and it should be also considered if it is important for core characteristics. In the present study, $$^{233}$$Pa is considered to evaluate the thorium conversion accurately. To take the effect into account, in the present study, an effective decay constant is proposed to make equilibrium concentration of $$^{233}$$Pa without out-of-core cooling equal to that of out-of-core cooling. With the effective decay constant, the out-of-core cooling effect can be incorporated even with the code system using macroscopic cross sections generated by cell burn-up calculations without any code modification. In addition, the characteristic of out-of-core cooling effect for the thorium conversion is evaluated for thorium fueled reactors of MSBR and PBMR. It is concluded that the out-of-core cooling effect is suitable for MSBR to enhance thorium conversion because of the fast flow rate of fuel salt. On the other hand, the effect is not important and not realistic to employ for PBMR because the in-core residence time of approximately 100 days is longer than the half-life of $$^{233}$$Pa of 27.0 days, and the effect cannot improve the conversion ratio drastically.



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Category:Nuclear Science & Technology



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