Triangular Polynomial Expansion Nodal Method for VVER Core Analysis

Abstract

Due to the low computational cost, nodal diffusion methods are still commonly used to simulate full-core reactor problems. This work represents the developmental effort to build an accurate nodal kernel to treat hexagonal geometry in the core simulator code PARCS. An innovative method called TriPEN-9 has been developed by splitting a hexagonal assembly into six triangular nodes and solved using cubic polynomial expansion for the scalar flux with nine-term expansion coefficients. The nodal diffusion calculation is further accelerated with the multilevel coarse-mesh finite difference method. The verification of the TriPEN-9 method on the VVER full-core problem is provided with the model based on the NURESIM (Nuclear Reactor Simulator)-SP1 V1000-2D-C1-tr benchmark problem. The Serpent Monte Carlo code is used as a reference solution for verification and to generate homogenized group-constants data for PARCS. Exact discontinuity factors were generated in GenPMAXS, a cross-section processing code, using a similar expansion method as the TriPEN-9 core solver method with the utilization of heterogeneous solutions from Serpent. Implementing the TriPEN-9 method in PARCS, this approach can exactly reproduce the solutions from the high-fidelity Serpent calculations.

Keywords:

• Triangular node
• PARCS
• Serpent
• discontinuity factors
• VVER

Disclosure Statement

No potential conflict of interest was reported by the authors.

Acknowledgments

This work was conducted as part of NRC PARCS maintenance and user support with contract no. NRC-HQ-60-15-C-0012. The authors would also like to thank Mathieu Hursin and his team at the Paul Scherrer Institute for providing the Serpent inputs of the benchmark problem.