Study on CsI release rate coefficient from fuel for source term evaluation

Abstract

Fission products released to the environment during severe accidents at nuclear power plants are evaluated using severe accident comprehensive analysis codes such as MELCOR. However, the codes cannot directly evaluate the release of CsI as molecular compound from fuel pellets. This is attributed that the release rate coefficient for molecular compounds such as CsI from fuel is not experimentally obtained yet. In this study, a method to experimentally derive the release rate coefficient of CsI from fuel was pursued. In the experiment, after simulated fuels containing CsI were fabricated using grain size as a parameter, CsI released from the simulated fuels was measured by a quadrupole mass spectrometer. Then the method to derive the release rate coefficients of CsI from fuel in the CORSOR-M model was developed converting experimental data into Arrhenius formula. The results demonstrated that the method can experimentally derive the molecular compounds release rate coefficients from fuel.