NEW OUTCOMES FROM COMBUSTION OF WOOD INSIDE PACKAGE SHOCK ABSORBERS AFTER FIRE TEST

According to the IAEA transport regulation, a fire test (800°C for 30 minutes) is required following the mechanical tests in accident conditions of transport. Some package designs are equipped with wood shock absorbers in a steel casing. After the mechanical tests, the casing may be damaged in some places, in particular due to the penetration of the 15 cm diameter steel bar used for the regulatory 1 m drop test. After the 30 minutes fire test, the heated wood, combined with air accessibility inside casing due to the damages, may provide the necessary conditions to maintain combustion of wood. Then, the heat generated by the combustion of the wood could increase the temperatures of the package components located near the shock absorber, as for example the elastomer O-rings of the closure system. In order to investigate this phenomenon, and thus appraising its consequences on safety analysis, IRSN has performed recently a fire test. A full-scale model, representative of shock absorbers which equip packages used to transport fuel assemblies, has been manufactured with simulated damages on the casing resulting from the 1 m and 9 m regulatory drop tests. A dedicated heat exchanger has been developed to simulate the thermal power of the radioactive content. This exchanger maintains the inner surface of the shock absorber at constant temperature. Moreover, a specific instrumentation was implemented to locate and characterize the heat flux between the shock absorber and the package (during the fire test and the cooling time). After the end of the hydrocarbon fire, wood combustion continued for four days inside the steel casing inducing important heat fluxes towards the lid (up to 8 kW/m²) and high temperatures (up to 460°C locally) on the rear side of the shock absorber. Finally, we evaluated by numerical calculations the temperature increases of the gaskets, which equipped the package components, taking into account the fire configuration and measurements performed on the specimen.