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- Burning of wood (1) (entfernen)
The safety of packages for the transport of spent nuclear fuel or radioactive waste has to be proven by consecutive testing and/or numeric analysis.
For damage protection these casks are equipped with impact limiters. German package designs usually include wood filled impact limiters encapsulated by steel sheets. Because the steel sheets suppress the oxygen supply into the wood, the scenario of impact limiter burning as a safety disturbance was not yet considered.
The safety of these packages is proven in compliance with IAEA regulations by accomplished cumulative mechanical and fire tests. Mechanical reliability is proven by different drop tests. Drop testing might cause significant damage of the impact limiter steel sheets and might enable sufficient oxygen supply to the impact limiter during the following fire test. During the fire test the package is exposed to an engulfing 800 °C fire with a heat flux of about 75 kWm-2 for 30 minutes.
After these both tests the degradation of the package has to be within defined prescriptive limits. Leak tightness of the cask is of particular importance.
The aim of this project is to consider the case of impact limiter burning as a safety disturbance and to investigate the behaviour of a real size impact limiter during and after a fire test.
The objective is to find out whether a self-sustaining smouldering fire is initiated. A smouldering fire is expected because of previously conducted promising small scale tests at BAM. The amount of energy, transferred from the impact limiter into the cask is of importance and will be quantified with a therefore designed test bench. The impact limiter specimen has got a volume of about 3 m³ wood.
The impact limiter is mounted onto a water tank which simulates the cask and its heat generating radioactive inventory. The water tank is mounted on a frame. By pipes a closed water circuit through the water tank is realized. To answer the question of how much heat is transferred from the smouldering fire into the cask, the mass flow and the temperature at the tank inlet and outlet is measured. With that the time dependent heat transfer rate can be calculated.
The second objective was to determine the fire spread inside the impact limiter. Therefore, the impact limiter is equipped with about 50 thermocouples to determine the global fire spread on the one hand and the local spread of particular spots on the other hand.