Overview

Lead-cooled Fast Reactors (LFR) are rather new concepts which have gathered increasing international attention after the Generation-IV International Forum (GIF) selected them as promising candidates for a new generation of nuclear energy systems. However, very limited operating experience exists to support the design, verification and licensing of LFRs and especially of the LFR core design. 

Under the guidance of the OECD NEA Working Party on Scientific Issues and Uncertainty Analysis of Reactor Systems (WPRS), the OECD NEA Expert Group on Physics of Reactor Systems (EGPRS ) and the OECD NEA Expert Group on Expert Group on Reactor Core Thermal-Hydraulics and Mechanics (EGTHM) are mandated to provide expert advice to the WPRS and the nuclear community on the development needs in the domain of neutronics, radiation transport, reactor physics and nuclear fuel feedback along with uncertainty analysis, and on multi-scale core thermal-hydraulics modelling and simulation of existing and proposed nuclear reactor systems. 

EGPRS and EGTHM endorsed together a two-staged benchmark to assess simulation capabilities for LFR systems:

• Stage 1 - Neutronics 
• Stage 2 - Thermal-Hydraulics 

The Advanced LFR European Demonstrator (ALFRED) is assumed as reference system for the LFR physics benchmark exercise. The ALFRED design is being carried out by the Fostering ALFRED Construction (FALCON) International Consortium, signed by Ansaldo Nucleare (IT), ENEA (IT) and RATEN-ICN (RO). Links with ENEA – the organisation responsible within FALCON for the core design of ALFRED – secure access to all the required information for the participants to the benchmark exercise.

Benchmark Description

Stage 1: Neutronics

The neutronics stage of the benchmark comprises three phases:

• PHASE 1: Pin cell
  • Heterogeneous modelling of the cell of a fuel pin and criticality analysis of the cell in an infinite lattice. 
•  PHASE 2: Sub assembly/super-cell simulations
  • Simulation model is extended to the level of a whole Sub Assembly (S/A), or of a super-cell comprising several S/As.
• PHASE 3: Whole core simulations
  • Modelling of the whole core, including control, shutdown and reflector/shield elements.

Stage 2: Thermal-Hydraulics 

The thermal-hydraulics stage of the benchmark also consists of three phases:

• PHASE 1: Grid-spacers effect
  • Separate effect validation of grid-spacers dynamic modelling based on Texas A&M University experiments on 127-rod grid-spaced bundles.
  • Modelling will be based on the realistic grid spacer geometry provided by Westinghouse Electric Company.
• PHASE 2: Fuel assembly
  • Parametric study of the ALFRED fuel assembly.
• PHASE 3: Integral validation
  • Integral validation against experimental data in the lead bismuth-cooled CIRCE facility.

NEA expresses its gratitude to the ENEA for the co-ordination effort, to the FALCON (Fostering ALfred CONstruction) consortium for its support of the benchmark, to Texas A&M University’s Thermal Hydraulic Research Laboratory for providing data obtained at their 127-rod grid-spaced bundle test facility, to Westinghouse Electric Company for providing the realistic grid spacer model, to the H2020 MYRTE project and to the SESAME project, which were funded by the European Commission under grant agreements No. 662186 and No. 101017258, for providing experimental data.