Verification and validation of the ALEPH3 fuel depletion code for Spent Fuel Characterization

Introduction

On December 13th, 2023, an agreement – PHOENIX – was signed between the Belgian State and ENGIE for the lifetime extension of two nuclear power plants. Additionally, responsibilities regarding spent nuclear fuel management, including storage and geological disposal, were transferred to NIRAS/ONDRAF, the National Agency for Radioactive Waste and Enriched Fissile Materials, which has been responsible for the safe management of radioactive waste in Belgium since 1980. Thus, an accurate characterization of all spent nuclear fuel assemblies available in Belgium will be needed to ensure a safe, secure, ecological and economical transport, storage and disposal of this fuel by NIRAS/ONDRAF.

In the framework of the PHOENIX project, WP4 is dedicated to the Characterisation of the whole spent fuel inventory, and the development of a validated calculation route for the Belgian spent nuclear fuel is the keystone of this WP.

SCK CEN has experience in modelling the nuclide inventory change in nuclear fuel ranging from pin cell models to full core depletion models, including effects of nuclear data quality, modelling assumptions and their impact on uncertainty quantification. It has built up this experience using a Monte Carlo reactor physics-based approach (where models can be easily built at different granularities from single fuel pin cell to full core models) coupled to its in-house developed depletion solver, ALEPH, which has been in development at SCK CEN since 2004.

Currently a new version, ALEPH3, based on the use of SERPENT2 code for Monte Carlo transport calculations to obtain particle spectra, coupled with a depletion module based on the RADAU5 solver, is underway. ALEPH3 will be used by SCK CEN within PHOENIX to perform core calculations.

However, to ensure the accuracy and validity of the calculations, and since it is a new development, ALEPH3 needs to be validated. Validation means the development of confidence that the code can be trusted in a predictive manner. For this, code calculations need to be compared to experimental measurements. These experimental data have been generated for code validation in spent fuel programmes in which SCK CEN has contributed such as ARIANE, MALIBU and REGAL but also in international programmes, some of which are open access through the SFCOMPO database or the EPRI Decay Heat report.

The objective of this work is to model spent nuclear fuel samples from SFCOMPO database and EPRI Decay Heat report with ALEPH3 code in order to validate its prediction capabilities.

Objectives

This project envisages a 6-9 month workload where the following tasks must be achieved:

• theory and modelling of the burnup problem;
• familiarization with the ALEPH3 fuel depletion code;
• modelling of cases from SFCOMPO database;
• modelling of cases from EPRI Decay Heat report;
• analysis of results and comparison against experimental data;
• and, production of scientific outputs.