Study of energy deposition in the coolant of LFR

TL;DR

This paper quantifies energy deposition in the coolant of Lead-cooled Fast Reactors using coupled neutron-photon transport simulations, highlighting the dominant photonic processes and the influence of core design parameters.

Contribution

It provides a detailed assessment of energy deposition fractions in LFR coolant and introduces a correlation for predicting coolant heating based on simple pin cell calculations.

Findings

Energy deposition in LFR coolant is approximately 5.6%.

Photon interactions are the main contributors to energy deposition.

Coolant temperature has minimal impact, while core pitch affects energy deposition.

Abstract

The determination of the fraction of energy deposited in the coolant is required for the setup of accurate thermal-hydraulic calculations in reactor core analysis. This study focuses on assessing this fraction and analysing the neutronic and photonic processes contributing to energy deposition in Lead-cooled Fast Reactors (LFRs). Using OpenMC, coupled neutron-photon transport calculations were performed within a fuel pin cell geometry, representative of the one under development at \textsl{new}cleo. Additionally, the implementation of lattice geometry was tested to gauge the impact of reflective boundary conditions on computational efficiency. In the context of a surface-based algorithm, the pin geometry has proven to be computationally more cost-effective. The fraction of energy deposited in the LFR coolant was evaluated at $\sim5.6$\%, surpassing that of pressurised water Reactors ($\lessapprox 3\%$), with photon interactions emerging as the principal contributor. The influence of bremsstrahlung radiation was also considered, revealing minor impact compared to other photonic processes. Given the continuous exploration of various core designs and the expectation of diverse operational conditions, a parametric analysis was undertaken by varying the coolant temperature and pitch values. Temperature changes did not significantly affect the results, while modifying the pitch induced a rise in the fraction of deposited energy in lead, highlighting its dependence on the coolant mass. This mass effect was explored in various fuel assembly designs based on the ALFRED benchmark and on the typical assembly model proposed by \textsl{new}cleo, leading to a correlation function for the prediction of coolant heating in realistic assemblies from simple pin cell calculations.