Modeling the consequences of fuel assembly bowing on PWR core neutronics using a Monte-Carlo code

Abstract

The effect of assemblies bowing in PWR nuclear reactors onto core neutronics is an observed phenomenon still poorly understood which can lead to Power Ratio Tilt. Studies of the consequences of rod/assembly bowing involve many different fields addressed by nuclear power plant, such as neutronics, thermohydraulics, mechanics.. . in a complex combination of multi-physical interactions. For the neutronic part, the modeling of bowed assemblies in Monte Carlo codes must allow to correctly describe the shape of fuel rods. In this article, two discrete ways to model bowed geometries are tested: the first one consists in a stacking of vertical small cylinders following the shape of the fuel rod by small shifts between neighboring cylinders; the second one, newly introduced in the present research, consists in a sequence of rotated cylindrical segments arranged to as to follow the shape of the fuel rod more closely. Both models are used to reproduce two specific bowing patterns, namely C-shape and S-shape, for which a reference modeling involving an analytical toroidal volume cut by planes is available for use with CEA's Monte Carlo code Tripoli-4 Ò. Results of comparisons between both models and analytical reference show that, even if the segment modeling requires a specific effort to handle implementation constraints, it appears preferable compared to stacking modeling. It provides accuracy with fewer discrete entities and is therefore computationally affordable and it is far more robust when increasing bowing deflection. This approach is thus only considered ready for its application to any kind of bowing patterns.

An illumination-robust edge detection method for nuclear fuel assembly deformation measurement

“…If excessive deformation in FAs is not promptly addressed, it may result in incomplete insertion of fuel rods or prevent accurate alignment with the lower core plate. This can lead to interference with adjacent components and, in extreme cases, make the rod insertion impossible, posing a serious threat to the safe operation of the nuclear reactor [3]. Therefore, regular deformation inspection for all FAs in the nuclear reactor is essential.…”

Numerical investigation on effects of fuel rod with different shapes of bow deformation on the subcooled boiling of coolant in a fuel assembly

“…At present, a large number of works have conducted in-depth analysis on the mechanism of fuel rod bow deformation through the finite element, subchannel code, and CFD methods. [5,7,15] They studied the influence of various factors on the shape, direction, and bowing rate of fuel rod bow deformation, [16][17][18] and put forward many methods to prevent or slow down the bow deformation accordingly. [3] On the one hand, the bow deformation of fuel rod could cause the redistributions of neutronic flux and core power.…”

A panoramic image stitching method for nuclear fuel assemblies

“…Fuel assembly (FA) is the core component and is used to store nuclear reaction raw materials in a nuclear reactor [1], as shown in figure 1. Working in an environment of high temperature, radiation, pressure, and vibration, FA is prone to bending and deformation [2,3]. The FAs with significant deformation can hinder the precise alignment of the FAs with the lower core plate.…”