Development of accelerated exponential method for burnup calculation in nuclear material balance code

Okamura, Tomohiro*; Nishihara, Kenji  ; Oizumi, Akito   ; Nakase, Masahiko*; Takeshita, Kenji*

Tokyo Institute of Technology and Japan Atomic Energy Agency are jointly developing a nuclear material balance code (NMB code), which is a mass balance analysis code for nuclear fuel cycle. The burnup calculation of this code is performed for each reactor or fuel batch using the matrix exponential method. Since the number of burnup calculations is very large depending on the analysis conditions, reducing the calculation cost has been an issue. In particular, to solve the short half-life nuclides by the matrix exponential method, the time step must be sufficiently shorter than the half-life and the calculation must be performed to a high order, which requires computational cost. Therefore, the accelerated exponential method was devised as a method to calculate the short half-life nuclides with enough accuracy for nuclear fuel cycle simulation without incurring computational cost.