NEUTRON STREAMING INVESTIGATIONS WITH CLASSIC AND HYBRID MONTE CARLO VARIANCE REDUCTION METHODS FOR THE AGN-211-P RESEARCH REACTOR IN BASEL

摘要

The light water pool-type research reactor at the University of Basel was operating for 54 years until 2013. In preparation for its final decommissioning, Nagra has to investigate the activation of the reactor components induced by their exposure to neutron irradiation. In the process of calculating the radiological inventory a very difficult neutron streaming problem was encountered. This paper presents the different variance reduction methods used for effectively capturing the neutron steaming path with the use of MCNP6.1.1 and ADVANTG 3.0.3. Both the engineering and the computational effort required for each method are highlighted and an alternative approach to capture the streaming effect with ADVANTG is presented. The results indicate an increase of FOM through the use of ADVANTG, compared with the classical geometry splitting technique. Finally, the integration of DXTRAN spheres with the aforementioned methods proved to be very successful, further accelerating the simulations.