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SP3 (simplified P3) theory is widely used in LWR (light water reactor) analyses to partly capture the transport effect, especially for pin-by-pin core analysis with pin size homogenization. In this paper, a SP3 code named STELLA is developed and verified at SNERDI (Shanghai Nuclear Engineering Research and Design Institute). For SP3 method, neutron transport equation can be transformed into two coupled equations in the same mathematical form as diffusion equation. In this work, SANM (semi-analytic nodal method) is used to solve diffusion-like equation, due to its easy to handle multi-group problem. Whole core nodal boundary net current coupling is used to improve convergence stability in SANM, instead of solving two-node problem. CMFD (coarse-mesh finite difference) acceleration method is employed for 0-th SP3 equation, which represents the neutron balance relationship. Three benchmarks are used to verify the SP3 code, STELLA. The first one is a self-defined one dimensional problem, which demonstrates SP3 method is extremely accurate, due to no academic approximation in one dimensional for SP3. The second one is a two dimensional one-group problem cited from Larsen’s paper, which is usually used to verify and prove the SP3 code correct and accurate. And the third one is modified from 2D C5G7-MOX benchmark, whose numerical results indicate that STELLA is accurate and efficient in pin size level, compared to diffusion model.

Development and Verification of an SP3 Code Using Semi-Analytic Nodal Method for Pin-by-Pin Calculation