Study on characteristics of void reactivity coefficients for high-conversion-type core of FLWR for MA recycling

Fukaya, Yuji   ; Nakano, Yoshihiro ; Okubo, Tsutomu

The investigation on the characteristics of void reactivity coefficients for the high-conversion-type core of the FLWR (HC-FLWR) concept for MA recycling has been performed. They are the major restrictions for the core design of HC-FLWR for MA recycling, because the loaded MA makes them worse. Thus, the investigation of void reactivity coefficients has been performed using the exact perturbation calculations. In the exact perturbation theory, the reactivity is divided into scattering, leakage, absorption, and fission terms. Then, the worsening of the void reactivity coefficient caused by the MA loading mainly via the scattering term is found. Moreover, the void reactivity coefficient becomes better via the scattering term for the smaller fuel rod diameter, and via the leakage term for the lower core height. In addition, it is found that the 100% void reactivity coefficient cannot be negative only with the scattering effect, but can be negative with the leakage effect.