MCNP force collision variance reduction technique in case study of neutron multiplication factor calculation of AP-1000 reactor type

Force collision is a variance reduction technique in the MCNP program. The purpose of using force collision variance reduction technique is to obtain smaller standard deviation with shorter calculation time. In this study the force collision variance reduction technique was used to calculate the multiplication factor in the AP-1000 reactor core MCNP model in cold state at start-up operation. The study starts from designing the AP-1000 reactor core MCNP model with the amount of particle is 200,000 particles and the iteration cycles are 600; 800; 1,000 and 1,500 times. The result of calculation cycle at 1,500 iteration is chosen as reference of analysis. After that, the multiplication factor without using the force collision variance reduction technique is calculated, with amount of particle is 200,000 particles and calculation cycle is 1,500 times. The calculation start with force collision 1 then 0.9 for every enriched U-235 IFBA fuel and not IFBA. The force collision 0.8 is calculated for IFBA fuel with 2.35% enrichment and not IFBA fuel with 1.58% enrichment. The next is calculation for force collision 0.78, 0.7, 0.6 and 0.5 at IFBA fuel with 2.35% enrichment. From the result of calculation with 200,000 particles and 1,500 iterations, the application of force collision variance reduction technique for multiplication factor calculation of AP-1000 reactor at cold state doesn’t produce smaller standard deviation. While the calculation time using the force collision variance reduction technique is longer than without force collision variance reduction technique.