Storage and capsulation system of spent fuel in the Egyptian research reactor

Full text: In Egypt, the first research reactor (ET-RR-1) has been used for a long time in conducting research work in the fields of reactor physics, heat transfer and thermohydraulics. Also, it is used in the production of radioisotopes for medical purposes and chemical researches. Due to the operation of the reactor for about 40 years, the need for larger and modern spent fuel storage arises. The defects appearing in the fuel elements imply an investigation of the reactor fuel and the design of a new system of capsulation of the defective fuel elements for long-term storage. The new spent fuel storage facility is a structure containing the storage and a so-called receiving and fuel handling area arranged in a separate building. The fuel storage is a stainless steel tank filled with water and located in a concrete pit under the ground level. The tank is covered by slabs made of steel and concrete. Aluminium storage tubes are fixed in the tank for vertical storage of the fuel assemblies in a rectangular matrix arrangement. The capacity of the storage tank is up to 176 fuel assemblies. In the design of the storage, both of the thermal and physical aspects are taken into consideration. The temperature, conductivity and the pH value of the water are measured. The water supply and air-ventilation of the reactor are used also for the storage. The storage ventilation depression as well as the water level is always maintained at the design values for the safety of the personnel and the facility. Also, the water is filtered regularly using two mechanical filters, one of them is operating and the other is spare. The capsulation system is so designed to prevent the leakage of fission fragments from the defective assemblies to the water of the storage. The defective fuel assembly is capsulated in a tightly closed aluminium tube filled with nitrogen containing 5% of helium as an innert gas to prevent the corrosion of fuel rods. The capsulation tube is provided with a non-return valve to avoid escape of nitrogen. The capsulation system includes two casks, one for the fuel transport and the other for capsulation process. The system contains a drying unit, nitrogen charging unit and a welding mechanism to weld a special cap containing the non-return valve. The leakage of nitrogen gas is tested by an apparatus, which is very sensitive to the helium gas molecules. The capsulated assembly is located again in the storage for long time storage. (author)