RRFM 2009 Transactions - European Nuclear Society

VALIDATION OF PLTEMP/ANL V3.6 CODE FOR EVALUATION OF
SAFETY MARGINS AT THE BR2 REACTOR
S.KALCHEVA 1 , A.P.OLSON 2 ,
E.KOONEN 1 AND J.E.MATOS 2
1 SCK•CEN, BR2 Reactor Department
Boeretang, 2400 Mol – Belgium
2 RERTR Program, Nuclear Engineering Division, Argonne National Laboratory,
Cass Avenue, IL 60439 Argonne – USA
ABSTRACT
The aim in this paper is to validate the PLTEMP/ANL V3.6 code for thermal
hydraulics analysis of the BR2 reactor at steady-state operation under forced flow
cooling conditions. Hot channel factors and operation limiting conditions based on
selected safety system settings (SSS) with uncertainties were reviewed and
included into PLTEMP. Safety margins to ONB (Onset-of-Nucleate-Boiling) and to
FI (Flow Instability) are calculated for the BR2 HEU fuelled core and compared
with the existing safety limits for the heat fluxes in SAR-BR2. A preliminary
thermal-hydraulics analysis is performed for the LEU (UMo) fuel preserving the
geometrical parameters of the standard BR2 fuel assembly. Power peaking factors
evaluated by MCNP for both HEU and LEU fuel assemblies are included in
PLTEMP. Thermal-hydraulics studies are extended to include conditions of natural
circulation cooling. The margins to ONB and to FI are estimated for both HEU and
LEU cores.
1. Introduction
This paper presents a thermal hydraulics analysis at steady state operational conditions,
which is a mandatory part of the safety studies needed for the conversion of the reactor BR2
from HEU to LEU. The safety margins at the BR2 reactor have been determined in 70’s
using the code of S. Fabrega [1]. The purpose in this paper is to review and to repeat the
major part of the studies in order to validate PLTEMP/ANL code [2] for the thermal hydraulics
calculations of the BR2 reactor. The geometrical BR2 standard, six-tube fuel assembly model
has been developed at Argonne National Laboratory. As a first step, hot channel factors and
operating limiting conditions (power, inlet mass flow, inlet pressure and temperature) based
on selected safety system settings with uncertainties were reviewed and included into
PLTEMP. The safety margins to ONB (Onset-of-Nucleate-Boiling) and to FI (Flow Instability)
are calculated for the BR2 HEU fuelled core under forced flow conditions. A preliminary
feasibility study with U-Mo dispersion fuels has shown that the current fuel assembly design
would not change in the conversion of the BR2 reactor from HEU to LEU fuel. Therefore, a
preliminary thermal-hydraulics analysis has been performed by PLTEMP for the LEU fuel
preserving the geometrical parameters of the standard BR2 fuel assembly. Power peaking
factors evaluated by MCNP for both HEU and LEU fuel assemblies are included in PLTEMP.
Thermal-hydraulics studies are extended to include conditions of natural circulation cooling.
2. Review of thermal-hydraulics studies for the BR2 reactor [3-4]
2.1 Determination of maximum heat flux at nominal operating conditions
The maximum heat flux at nominal operating conditions is calculated from the power
generated in the hottest fuel channel with the implementation of Hot Spot Factors (HSF)
according with the following formulae:
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