Uncertainty analysis of minor actinides transmutation in fast reactor cores

- A method for calculating sensitivity coefficients of minor actinides (MAs) transmutation has been developed.
- The method has been applied to two MA transmutation fast reactors with MA contents of 6 and 11%.
- The uncertainties of total MA transmutation amounts are about 3%.
- The transmutation uncertainties of Np-239, Am-233, Cm-243 and Cm-245 are large.
- The transmutation of Cm-244 has large uncertainties of 10∼13%.
- This large uncertainties have to be considered in fuel fabrication and fuel reprocessing.

The uncertainty of minor actinides transmutation in fast reactors has been estimated for individual nuclides of minor actinides (MA). The burn-up dependent sensitivities of MA number densities are calculated using the generalized perturbation theory, and a method is derived to transform the sensitivities to the sensitivities of minor actinides transmutation. The sensitivities are used to obtain the uncertainties of minor actinides transmutation together with the cross-section covariance data of JENDL-4. The method is applied to the two MA transmutation fast reactor cores with MA content of 6% and 11%. It is seen that the uncertainties of the total MA transmutation amounts are about 3% and 4% for the two cores because the uncertainties of Np-237 and Am-241 transmutations which mainly contribute the total transmutation are small (about 3%).The contribution to the uncertainties is mainly caused by the Np-237 and Am-241 capture cross-sections.The transmutation uncertainties for Np-239, Am-233, Cm-243, and Cm-245 are rather large. However the transmutation amounts of these nuclides are very small, and the large uncertainties are not the problem in practice. However, it is found that the transmutation amount of Cm-244 has large uncertainties of 10% and 13% for the cores with MA content of 6% and 11%, and this large uncertainties have to be considered when MA fuels are fabricated and reprocessed because Cm-244 produces large decay heat and neutron emission.