Solid Radioactive Waste Strategy Report.pdf - UK EPR

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EPR UK N° NESH-G/2008/en/0123 REV. A PAGE 212 / 257 Specific features that have been incorporated into the design to control dose include the following: · Shielding provided by the spent fuel transport container; · Unloading spent fuel from the transport container and loading into the Fuel Storage Pool within a shielded cell and using remote operations to remove the operators from the radiation source; · Shielding provided by the Fuel Storage Pool water. At all times, the water level is well above the top of the fuel. 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. Radioactive Contamination In normal operations the operator shall 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: · Fuel cladding (1 st barrier) and for the 2 nd barrier: o o o The spent fuel transport container during transport; The unloading cell structure and the transport container connected via the docking system during fuel unloading; And during the interim storage period: • The fuel storage pool water; • The fuel storage pool liner; • The storage pool building. Further control of radioactive contamination is provided by the provision of an active ventilation system with HEPA filtration abatement system. Conditioning systems will be provided to remove suspended or dissolved contamination from the Fuel Storage Pool water, and to control water chemistry so as to minimise corrosion of the fuel cladding. Leakage of water from the Fuel Storage Pool could result in spread of contamination within the facility and in extremis in loss of shielding and cooling for the spent fuel. Containment of the water will be ensured by the stainless steel liner and support framework and by the reinforced concrete structure housing it. It should be noted that the liner will undergo a full radiographic examination during manufacture and that any leakage would be collected through a network of leak pipes incorporated in the pool framework and routed to a leak detection cabinet.
EPR UK N° NESH-G/2008/en/0123 REV. A PAGE 213 / 257 Criticality Criticality safety is achieved by ensuring that the geometrical arrangement of spent fuel is safe throughout the handling and storage operations. The fuel assemblies are delivered in a safe configuration within the transport container. They are then individually transferred to and retained in storage baskets, which maintain sufficient separation between the assemblies to ensure there will be no criticality when immersed in water in the Fuel Storage Pool. In addition to this, the use of boron in the storage baskets will contribute to increasing criticality safety margins. Overheating The heat generation of spent fuel stored in the Fuel Storage Pool is not considered to be a fire risk, however the fuel and water temperatures need to be maintained within operating parameters to prevent excessive evaporation of the water, spread of contamination and eventual loss of cooling and shielding functions. The heat exchangers provided in the Fuel Storage Pool and the associated air coolers will ensure that the heat generated by the spent fuel is removed and dissipated into the atmosphere. Redundant cooling circuits will be provided: this redundancy, together with the thermal inertia of the Fuel Storage Pool, will provide protection from overheating. Internal Flooding Internal flooding risks arise from the cooling water in the Fuel Storage Pool, water from the cooling/rinsing enclosure and water in the general building services. These risks are controlled by the following measures: · Limited volume closed circuits for rinsing, cooling and clean up water systems; · High-integrity level control to prevent overfilling the Fuel Storage Pool; · Integrity of the Fuel Storage Pool liner and structure and lack of penetrations at low level - the framework and supporting structure will be designed to withstand earthquake and thermal expansion; · Leak detection systems incorporated in the Fuel Storage Pool framework with alarms linked to the central control room; · Ensuring that any credible failure takes water away from areas where water could present a safety issue; · Safe geometry of arrays of spent fuel assemblies in the process in the event of a flood. External Events: Earthquake The facility will be designed to withstand a design basis earthquake (DBE). All equipment with a nuclear safety function will be designed to maintain the safety of the facility after the DBE. For example, one important feature of the seismic design is the Fuel Storage Pool, which must perform its safety functions following a DBE. It will be considered as a separate structural unit from the remainder of the building, with the uncoupling of the two structures being achieved through the use of neoprene bearing pads. The water supply network would also be designed to withstand the DBE and be able to maintain the appropriate water level above the spent fuel assemblies.
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Solid Radioactive Waste Strategy Report.pdf - UK EPR

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