GENERATION OF NODAL CORE SIMULATOR UTILIZING VERA

Paul Turinsky,Aaron Graham,Benjamin Collins,Hisham Sarsour,M Margulis,P Blaise

doi:10.1051/epjconf/202124702018

Abstract

Nuclear core simulators based upon few-group nodal diffusion method currently are widely used to predict light water reactor core behavior. Nodal parameters’ input, e.g. cross-sections, discontinuity factors, and pin form factors, are typically generated utilizing lattice physics codes. In doing so, a number of approximations are introduced related to using zero current boundary conditions, 2-D radial geometry, and uniform thermal conditions in coolant and fuel. Usage of full core models with prediction fidelity typical of lattice physics to predict nodal parameters would eliminate these approximations. The VERA code can serve as such a full core model and was so utilized in this work. Via subsequent processing of VERA predictions, for a range of state points, nodal parameters and their functionalization in terms of coolant density, fuel temperature, and soluble poison concentration, were obtained and input to the NESTLE nodal code. By processing VERA predictions using consistent nodal methodologies as used in NESTLE, when using nodal parameters after functionalization based upon All-Rods-Out (ARO) VERA state points, the maximum reactivity and pin power differences between VERA and NESTLE were 2 pcm and 0.003 for ARO core simulations. For rodded core simulations, these maximum differences grew to 58 pcm and 0.04. Increases in differences were determined to be attributed to usage of unrodded nodal parameters generated using the VERA ARO state points whether the core is partially rodded or not, consistent with lattice physics practice. Obtaining unrodded nodal parameters using the VERA rodded state points reduced maximum differences to 2 pcm and 0.003 in pin powers.

Highlights

INTRODUCTION~1 hour wall clock time using ~1K cores for a single state point of a 3-D quarter core PWR model), which would noticeably impact how engineers function to complete nuclear core design and safety analysis, and prohibit usage in training simulators and core monitoring systems
The difference when contrasted to a lattice physics code approach to obtaining the pin form factors (PFF) is that since VERA predicted pin powers will mostly capture the within node flux variation due to history, control rod insertion, boundary conditions and local thermal-hydraulics feedback effects, any correction imposed by the intra-nodal flux would be expected to be small
The capability to utilize a high fidelity core simulator (VERA) in support of determining nodal parameters has been demonstrated with regard to producing accurate predictions of core reactivity and pin power distribution from a nodal code (NESTLE)

Summary

INTRODUCTION

~1 hour wall clock time using ~1K cores for a single state point of a 3-D quarter core PWR model), which would noticeably impact how engineers function to complete nuclear core design and safety analysis, and prohibit usage in training simulators and core monitoring systems. These points would delay potential adoption of usage, thereby delaying the associated benefits. If a highfidelity core simulator’s usage was limited to mainly replacing a lattice physic code, the required amount of usage could be minimized with the bulk of required simulations done by a nodal core simulator This would minimize the impact of reason (1) and completely address reason (2). We provide furthers details as related to how the nodal parameters have been determined, followed by a section contrasting VERA with NESTLE predictions, concluding with a section presenting conclusions

Generation of Nodal Parameters

Functionalization of Nodal Parameters

CONCLUSIONS