During the continuous operation of the nuclear power plant, with the deepening of nuclear fuel consumption in the reactor, the energy generated by nuclear fuel fission can not maintain the power generation of the nuclear power plant. The unburned nuclear fuel taken out is called spent fuel. The newly unloaded spent fuel is highly radioactive, so it needs to be placed in the storage pool for cooling, transported to the spent fuel reprocessing plant at an appropriate time, refined the recyclable elements in the spent fuel, solidified the remaining nuclear waste, and then encapsulated in a metal container and placed in a rock stratum with stable geological structure. At present, there is only one small power reactor spent fuel reprocessing test site in China, and the nuclear power plant has insufficient capacity in the reactor storage pool, and the spent fuel reprocessing capacity is far less than the spent fuel generation rate. When the large commercial reprocessing plant is still put into use for a long time, the off reactor storage of spent fuel becomes very necessary. Therefore, it is urgent to develop the intermediate storage technology of spent fuel.
(1) As a single shell container,container has high integrity, good shielding performance, low overall manufacturing cost and good loading capacity. It is a storage and transportation container material with excellent comprehensive performance.
(2) As a special functional container, the Ferritic Ductile iron storage and transportation container used in nuclear fuel reprocessing has high strength and can pass the test requirements of 9 m drop, 1 m penetration, 30 min (800 ℃) fire and 15 m immersion.
(3) Nodular iron castings used in nuclear fuel reprocessing belong to thick and large section nodular iron castings, which usually have problems such as distorted graphite, regional segregation, uneven microstructure and mechanical properties due to slow cooling speed. These problems can be solved by strictly controlling the chemical composition of molten iron, increasing the solidification rate and high temperature annealing.
(4) As the disposal container of medium and low-level radioactive waste, nodular cast iron tank has good corrosion resistance and radiation resistance. Ideally, it can be placed for long enough to make the radiation disappear.
Dry storage of spent fuel is one of the mature off reactor storage methods in recent years. The method is to store the spent fuel stored in the storage pool for a certain period of time in the spent fuel dry storage facility composed of metal containers or metal concrete containers, and store it for several years before post-treatment or direct storage. For the consideration of long-term storage, dry storage has the advantages of more flexibility, easier management and more economy than wet storage. Early dry storage only has a single function of off pile storage. With the use of storage containers, dry storage has gradually developed into multi-functional storage, transportation and disposal. Compared with the concrete storage container, metal has the inherent characteristics of high density and high thermal conductivity. Under the condition of the same heat dissipation and radiation shielding, it can achieve smaller volume and more compact structure. Metal storage containers are also convenient for operation management and subsequent expansion, and are more conducive to long-distance transportation. Because the nuclear power plants in operation and under construction in China are far away from the reactor storage pool and spent fuel reprocessing plant, the metal storage and transportation container with storage and transportation function has become the preferred means. However, metal storage containers also have the disadvantages of poor economy and high technical requirements.