Study on A-FNS shielding analysis with variance reduction parameter generation code

Abstract

Design activities of advanced fusion neutron source A-FNS have been conducted to perform the irradiation tests for fusion reactor materials. It is necessary to evaluate the effective dose rate of the lateral access cell in the A-FNS facility by shielding calculations. In the calculation, a variance reduction method using an effective bias data is necessary to reduce statistical errors. The weight window generation (WWG) function had been used in the analyses with MCNP code and McDeLicious source subroutine. There were some difficulties in the usage of WWG such as many iterative calculations, experiences, and skills required to obtain appropriate bias data. Therefore, the automatic variance reduction parameter generator code ADVANTG has been introduced to the calculation, creating a source description in the general source definition (SDEF) of MCNP for the A-FNS by approximating the neutron and photon generations of the McDeLicious source subroutine. The ADVANTG code was successfully applied to the calculation, and the dose rate of the lateral access cell in the A-FNS was obtained with small statistical errors by a once-through calculation.