Determination of the Gas Plenum Temperature of the P2M Instrumented Fuel Rodlets on the Basis of a Thermal-Hydraulic Study of the Belgian Reactor 2 Pressurized Water Capsule

Abstract

To refine knowledge about pressurized water reactor fuel melting, the Power to Melt and Maneuverability (P2M) project in the Framework for Irradiation Experiments II (FIDES-II) managed by the Nuclear Energy Agency of the Organisation for Economic Co-operation and Development aims to perform two irradiation tests to reach fuel centerline partial melting using instrumented experimental fuel rodlets irradiated in a pressurized water capsule (PWC) of the Belgian Reactor 2 (BR2) [Studiecentrum voor Kernenergie (SCK CEN), Belgium]. Prior to these experiments, two preliminary tests will be performed in the PWC for qualification purpose toward safety. The experimental rodlets will be instrumented with a fuel centerline thermocouple in the lower part of the fuel and a pressure sensor (PS) in the upper part. An objective of the P2M experiments is to determine the amount of fission gas released from the fuel thanks to the PS measurement. The plenum pressure evolution is known from the measurement, and knowledge of the gas plenum temperature is required to determine the amount of fission gas released from the fuel to the plenum. The gas plenum temperature will depend on natural convection of the PWC coolant, and no temperature measurement will be possible within this gap during the test. This paper describes the setting up of a model of the BR2 PWC equipped with the P2M rodlets based on the coupled NEPTUNE_CFD (multiphase fluid calculation code) and SYRTHES (solid thermal module) simulation tools. Simulations performed thanks to this model allow assessment of the thermal-hydraulic (TH) behavior of the pressurized water in the capsule and the thermal behavior of the rodlet, in particular, regarding the temperature of the gas located in the plenum. For consistency of the results, computations presented in this paper were performed using a single and consistent set of TH models. A mesh sensitivity analysis was carried out for all the studied cases. Simulation results related to the water capsule behavior were found to be in good agreement with the available experimental data. The gas plenum temperature results obtained from this study will be used to assess the fission gas release during the test from the plenum pressure measurements. Overall experimental validation of fission gas release during the test will be possible after the transient test in BR2 based on the postirradiation examination program foreseen on the rodlets at the LECA-STAR facility [Commissariat à l’énergie atomique et aux énergies alternatives (CEA) Cadarache, France].

Keywords:

• FIDES-II
• P2M
• BR2
• pressurized water capsule
• Neptune_CFD
• fission gas release

View correction statement:

Correction

Acronyms

ALCYONE:	=	fuel performance code of the CEA PLEIADES simulation platform
BR2:	=	Belgian Reactor 2
CEA:	=	Commissariat à l’énergie atomique et aux énergies alternatives
CCRT:	=	Center de Calcul Recherche et Technologie
CD:	=	calorimetric device
CFD:	=	computational fluid dynamics
CHF:	=	critical heat flux
EDF:	=	Electricité de France
FIDES-II:	=	Framework for Irradiation Experiments II
Hf:	=	hafnium
IRSN:	=	Institut de Radioprotection et sûreté nucléaire
LHR:	=	linear heat rate
LVDT:	=	linear variable differential transformer
MTR:	=	Material test reactor
NEA:	=	Nuclear Energy Agency
ONB:	=	onset of nucleate boiling
PS:	=	pressure sensor
PWC:	=	pressurized water capsule
PWR:	=	pressurized water reactor
P2M:	=	Power to Melt and Maneuverability
SCK CEN:	=	Studiecentrum voor Kernenergie
TC:	=	thermocouple
TH:	=	thermal-hydraulic
3D:	=	three-dimensional

Nomenclature

$\mathit{a}$	=	= interfacial area concentration $\left({\mathrm{m}}^2/{\mathrm{m}}^3\right)$
$C_p$	=	= specific heat capacity (J/kg/K)
$D_b$	=	= bubble departure diameter ($\mathrm{m}$)
$f_b$	=	= bubble departure frequency $\left(\mathrm{Hz}\right)$
$\mathit{g}$	=	= gravity acceleration constant (kg∙m/s2)
$\mathit{h}$	=	= heat exchange coefficient (W/m2/K)
$h_{\mathit{fg}}$	=	= latent heat of vaporization $\left(\mathrm{J}/\mathrm{kg}\right)$
$L_c$	=	= characteristic length $\left(\mathrm{m}\right)$
$N_a$	=	= nucleation site density $\left(\mathrm{\#}/{\mathrm{m}}^2\right)$
$R_a$	=	= Rayleigh number
$\mathit{T}$	=	= temperature $\left(\mathrm{K}\right)$
$T^{+}$	=	= nondimensional temperature
$u^{\ast }$	=	= wall friction velocity $\left(\mathrm{m}/\mathrm{s}\right)$

Greek

$\mathit{\beta }$	=	= thermal expansion coefficient (K–1)
$\mathrm{\Gamma }$	=	= mass transfer term (kg/m3/s)
$\mathrm{\Delta }$	=	= difference
$\mathit{\lambda }$	=	= thermal conductivity (W/m/K)
$\mathit{\mu }$	=	= dynamic viscosity (Pa∙s)
$\mathit{\nu }$	=	= kinematic viscosity $\left({\mathrm{m}}^2/\mathrm{s}\right)$
$\mathit{\rho }$	=	= density $\left(\mathrm{kg}/{\mathrm{m}}^3\right)$
$\mathit{\varphi }$	=	= heat flux density $\left(\mathrm{W}/{\mathrm{m}}^2\right)$

Subscripts

c	=	= convection
e	=	= evaporation
g	=	= gas
i	=	= interfacial
l	=	= liquid
q	=	= quenching
sat	=	= saturation
wall	=	= wall

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Correction Statement

This article was originally published with errors, which have now been corrected in the online version. Please see Correction (https://doi.org/10.1080/00295450.2024.2343641).