PIUS core performance analysis

Abstract

A detailed evaluation of the fuel-burnup dependent power distribution and the scram reactivity for the PIUS reactor design has been performed. The analyses were carried out using the CPM lattice physics and NODE-P2 core neutronics/thermal-hydraufics codes, and are based on the information provided in the PIUS Preliminary Safety Information Document.Cycle depletion calculations were performed for a set of nine representative initial core loadings and the threedimensional core power distributions were determined. These calculations indicate that the PIUS radial FAh and total Fa power peaking is stronger than that indicated by the PIUS reference-design values.The scram reactivity resulting from the injection of highly borated pool water was calculated for a series of timedependent linear ramp and square-wave pool flows. The three-dimensional distribution of the borated pool water throughout the core was modeled and the spatial reactivity effects of the distributed boron were determined. For pool flows that increase as a linear ramp, the spatial reactivity effects of the distributed boron were very small. In this case, a constant core-average boron reactivity coefficient can be used to model the PIUS scram reactivity.

Validation of the Serpent 2 Monte Carlo code for reactor dosimetry applications

“…MCNP input files of the STD and PLS numerical benchmark problems were facilitated by one of the authors of NUREG/CR-6115 [3]. Corresponding Serpent inputs were created from scratch.…”

“…In addition to identical geometry, material, and fixed source definitions, the Serpent 2 models also feature the same Variance Reduction (VR) techniques used in Ref. [3], namely cell importances and energy cut-off. The adoption of cell importances increases the complexity of the geometry definition because it necessitates individual cells where the cell importances are set.…”

“…(2) Additional STD and PLS cases not present in Ref. [3] were calculated with Serpent. In these, the VR was switched from cell importances to one-group weight windows (WWs) generated by Serpent.…”

“…Two PWR verification cases were selected: a specification with Standard Core Loading Pattern (STD); and a Partial Length Shield Assembly (PLS) core [3]. Fast fluxes were calculated with MCNP [4] version 6.1 and Serpent 2, based on identical geometry and material definitions.…”