A Variational Nodal Expansion Method for the Solution of Multigroup Neutron Diffusion Equations with Heterogeneous Nodes

Journal Article · Mon Jul 15 04:00:00 EDT 2002 · Nuclear Science and Engineering

OSTI ID:20804790

Tsuiki, Makoto; Hval, Sverre

A new nodal diffusion method for the neutronics analysis of light water reactor cores has been developed. The method is based on an expansion of neutron fluxes within a node into a series of functions that are numerically obtained from single-assembly calculations without the process of assembly homogenization. The assembly heterogeneity effect can be taken into account in whole-core calculations in a consistent way with the heterogeneous single-assembly calculations, providing highly accurate results including intranodal pin-power distributions. The expansion coefficients are determined by a classical Ritz procedure in such a way that the solution becomes the most accurate - in the least squares sense - approximation to the exact solution. The present method was implemented in a two-dimensional nodal diffusion code and tested for benchmark cases both for boiling water reactors and pressurized water reactors. The root-mean-square errors of both node average powers and nodal maximum pin powers were observed to be <1%, with computing time of less than a few percent of the reference, fine-mesh calculation. It was also observed that the accuracy of the present method could be improved to almost any desired degree only by increasing the order of expansion polynomials.

• OSTI ID: 20804790
• Journal Information: Nuclear Science and Engineering, Journal Name: Nuclear Science and Engineering Journal Issue: 3 Vol. 141; ISSN NSENAO; ISSN 0029-5639
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
ACCURACY
APPROXIMATIONS
BENCHMARKS
BWR TYPE REACTORS
DIFFUSION
EXACT SOLUTIONS
LEAST SQUARE FIT
NEUTRON DIFFUSION EQUATION
NEUTRON FLUX
NODAL EXPANSION METHOD
POLYNOMIALS
POWER DISTRIBUTION
PWR TYPE REACTORS
TWO-DIMENSIONAL CALCULATIONS
VARIATIONAL METHODS