Scheme of the DIVA Facility, ASNR

Fire is a significant contributor to overall core damage frequency for both new and old nuclear reactor designs. Furthermore, it may severely affect plant safety in nuclear fuel cycle facilities. Some of the technical issues that need to be addressed in fire probabilistic safety analysis are the propagation of heat and smoke between rooms, including the effects of openings and ventilation systems, resulting stresses to sensitive safety equipment, fire spreading in real complex fire sources such as cable trays and electrical cabinets, and studies of the performance of various fire detection and extinction systems.

The Fire Risk Assessment through Innovative Research Project is a follow-up of the PRISME project series and addresses new fire scenarios and new topics of interest for an improved fire risk assessment in nuclear power plants (NPPs) and other nuclear facilities. It covers three major topics:

• fire propagation along cable trays with a focus on the effects of long-length cables and cable ageing,
• fires in confined and mechanically ventilated compartments, with a focus on the effects of hot and vitiated environments on the combustion and re-inflammation of unburned gases,
• multi-source and multi-compartment scenarios, with a focus on fire propagation between discrete sources and smoke propagation in complex multi-compartment configurations.

The experimental campaigns of the FAIR Project includes tests carried out in the GALAXIE platform facilities (operated by the French Autorité de Sûreté Nucléaire et de Radioprotection (ASNR), formerly IRSN, at Cadarache), either on a large scale in the DIVA, SATURNE and PLUTON facilities, or with more analytical devices on a medium scale, such as the CISCCO and NYX devices, or still to be designed devices (as for unburned combustion).

An in-depth analysis of the results of all the test campaigns will be carried out  (physical phenomena, data processing, uncertainties). This work will be supported by a dedicated analytical working group. Additionally, support tests (for instance, regarding the characterisation of material properties in open atmosphere) will be performed all along the experimental programme.

The project was launched in June 2023. In 2024, test campaigns related to fire propagation along cable trays and fires in confined and mechanically ventilated compartments progressed well. Candidate cables to study cable ageing effect were selected.