Application of MCNP Perturbation Technique and Difference Method in AP1000

The Monte Carlo N-Particle (MCNP) code is the internationally recognized code for calculating the keff for AP1000 system with specific nuclear material compositions, geometric structures and core size by the Monte Carlo method. For a PWR system, we calculated keff which arise from system nuclear material compositions, geometric structures and core size changes, by two different approaches, the MCNP perturbation technique and the MCNP difference method. When we simulate the core of AP1000 through the MCNP code, we find that as material compositions, geometric structures and core size changes in AP1000 system are small compared to the whole system, the keff results obtained from the MCNP perturbation technique are much more efficient and reliable than the results from the MCNP difference method. When material compositions, geometric structures and core size changes in AP1000 system are significant compared to the whole system, both the MCNP perturbation technique and the MCNP difference method can give satisfactory results.