Solid Radioactive Waste Strategy Report.pdf - UK EPR

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EPR UK N° NESH-G/2008/en/0123 REV. A PAGE 244 / 257 13.3.4.2.4Safety Features for a Vault-Type Dry Interim Storage Facility Generic safety aspects of spent fuel storage facilities are provided in previous section. Only specific safety aspects related to vault storage are described hereafter. Direct Radiation Specific features that have been incorporated into the design to control dose include the following: · Shielding provided by: o o o o o the spent fuel transport container; the remotely-operated unloading cell; the transfer tunnel; the remotely-operated canister handling machine; the storage vault structure. · Fully shielded, interlocked features for interfacing: o o o the spent fuel transport container with the unloading cell; the canister handling machine with the transfer tunnel; the canister handling machine with the storage well in the vault. Operator doses will be monitored and operations in the facility optimised to ensure compliance with the IRRs. Areas in the facility will be designated in accordance with the IRRs based on the radiological hazard present in that area. Some areas of the facility (for example welfare areas) will not require designation in accordance with the IRRs. Radioactive Contamination The spent fuel storage facility must provide an environment which protects the long term integrity of the fuel assemblies. This is important as the spent fuel will need to be transported and repackaged prior to disposal. In normal operations the operator and environment will be isolated from contamination by at least two containment barriers during each stage of the process of fuel unloading and storage. These barriers are as follows: · Spent fuel transport container during transport; · Unloading cell structure and the transport container connected via the docking system during fuel unloading; · Seal-welded spent fuel storage canister, filled with inert gas; · Tight storage wells in the vault; · Facility buildings. Assurance of containment integrity after closure is provided by scheduled checking and monitoring. All equipment, including the spent fuel transport container, will be manufactured with surface finishes that aid decontamination. Further control of radioactive contamination within buildings is provided by an active ventilation system with HEPA filtration abatement system.
EPR UK N° NESH-G/2008/en/0123 REV. A PAGE 245 / 257 Criticality Criticality safety is achieved by ensuring that the geometrical arrangement of spent fuel is safe throughout the handling and storage operations. Fuel assemblies are individually located in the transport container and in the storage canister by fixed partitions, which maintain sufficient separation between the assemblies to ensure there will be no criticality under any conceivable conditions,. Fuel assemblies in the unloading cell are handled in an adapted canister, with a similar arrangement of partitions. Procedural controls will be put in place to prevent fuel assembly handling errors such as loading extra assemblies into the unloading cell. Overheating The facilities will be designed to maintain the temperature of spent fuel assemblies within the identified safe limits under all expected combinations of radioactive decay heating and ambient temperature. During storage and transport, spent fuel cooling is achieved entirely by passive processes, aided by features such as: · heat conducting design of canister partitions; · selection of a gas with good heat transfer properties for backfilling canisters; · vault design with air channels to provide good convection in all conditions. Long term temperature control in the fuel storage vaults is important for preventing the progressive oxidation of UO 2 in the fuel to U 3 O 8 which has a much lower density. Conversion of the uranium dioxide in such a manner could lead to failure of fuel cladding due to internal expansion of the fuel. Loss of electrical power supply With the spent fuel cooling system being passive by design, the continued cooling of spent fuel will not be affected by a power failure. External events Flooding The dry storage vault is such designed that it will remain sub-critical even if flooded. Earthquake The facility will be designed to withstand the design basis earthquake (DBE). All equipment with a nuclear safety function will be designed to maintain the safety of the facility after the DBE. The process building, in particular the unloading cell, and its associated vessels and pipework will be designed to withstand the DBE without failure of containment.
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Solid Radioactive Waste Strategy Report.pdf - UK EPR

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