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.
Based on forensic evidence, a smouldering fire was observed to have occurred at a murder scene. Identification of a reasonable timeline – specifically the fire dynamics of the ignition and fire growth that occurred coincident with the death that took place – became an important focus of the criminal investigation that followed. The fire service was called when a neighbour saw a grey smoke escaping through the ventilation system of the bathrooms on the roof of the house. One flat door with elevated temperatures was found. The fire fighter who entered the flat first reported later that the flat was completely filled with smoke and all windows were closed. When the fire fighter opened the balcony door, he saw flames on the sofa that he extinguished. Then he found a body on the floor. The autopsy showed later that the victim was dead before the fire started. The police suspected that the murderer probably had deliberately set the fire to destroy evidence. One suspect had been witnessed to be in the flat approximately 2 h before the fire was detected by the neighbour. The aim of this project was to investigate how the fire most likely started and developed.
Chemical-analytical investigation of fire products in intermediate storages of recycling materials
(2012)
Organic materials like paper, cardboard, textiles or plastics are mostly flammable. In intermediate storages for recycling products, these materials are stored in large amounts. If fire occurs in these stores, large emissions of smoke and other potentially harmful products are likely. In the present study, the gaseous products released from fires of such materials—for example, because of self-ignition—were investigated. Different fractions (paper/cardboard, textiles and plastics) were crushed at low temperatures (about 80 K) and subsequently allowed to smoulder at different temperatures using the German standard Deutsches Institut für Normung 53436. The gases produced were sampled and analysed using Fourier transform infrared spectroscopy. The chemical composition of these gases differed considerably depending on fuel type. For flammable materials without heteroatom, the gases consisted predominantly of toxic compounds like carbon monoxide and carbon dioxide. Smouldering of materials containing heteroatoms showed, in addition to carbon monoxide, carbon dioxide and water vapour, further toxic components containing the heteroatom. Materials containing chlorine produced hydrogen chloride, and materials containing nitrogen produced ammonia and hydrogen cyanide.