Other fuel locations than SFP Depending on the plant design, apart from the SFP there may be other locations where fuel is present e.g. cleaning loops, fuel handling systems, dry storage, and transport casks. It is plant specific whether events in these locations can lead to fuel damage in the related system, or whether an event in these systems can trigger other failures and fuel damage in other locations, however this guidance is focused on fuel damage only in SFP. Shared SFPs Not each reactor is assigned to one dedicated SFP. For example, two reactors may a single pool. Also, a single reactor may store fuel in more than one pool, or two reactors at the same site may move fuel between both pools located in common or separated buildings that may or may not be connected. Thus, guidance is needed to address the differences and potential interactions between shared SFPs in an integrated way. Density of spent fuel racks Some pools contain high-density spent fuel racks which allow multiplying the number of stored assemblies. In such a case the consequences of fuel damage may propagate too much larger populations of fuel assemblies. These racks also have much higher overall decay heat and larger fission product inventory. Therefore, the density of the fuel racks should be considered. Spent fuel building ventilation The spent fuel building ventilation flow rate is important in determining the overall building energy balance. Airflow through the building is an important heat removal mechanism. On the other hand it also provides a source of oxygen for zirconium oxidation. Particular heat transfer mechanisms for fuel pools There are several heat transfer mechanisms that can influence the cooling of spent fuel during various postulated severe accident scenarios. These include: convective cooling to the surrounding steam cooling from surrounding steam generated by boiling coolant, conduction through the ends of the fuel rods, radiation cooling. The degree of success associated with different heat transfer mechanisms depends on the configuration of the SFP, rack/canister design (e.g., closed or open lattice), density of the fuel assemblies, arrangement of the hottest bundles within the SFP lattice and the SFP level. Structural integrity of fuel racks For recently discharged fuel or for severely restricted air flow (e.g. high density spent fuel racks) the exothermic oxidation reaction is predicted to be very vigorous and failure of both the fuel rods and the fuel racks is expected. The steel racks may not be able to maintain structural integrity because of the sustained
Other fuel locations than SFP Depending on the plant design, apart from the SFP there may be other locations where fuel is present e.g. cleaning loops, fuel handling systems, dry storage, and transport casks. It is plant specific whether events in these locations can lead to fuel damage in the related system, or whether an event in these systems can trigger other failures and fuel damage in other locations, however this guidance is focused on fuel damage only in SFP. Shared SFPs Not each reactor is assigned to one dedicated SFP. For example, two reactors may a single pool. Also, a single reactor may store fuel in more than one pool, or two reactors at the same site may move fuel between both pools located in common or separated buildings that may or may not be connected. Thus, guidance is needed to address the differences and potential interactions between shared SFPs in an integrated way. Density of spent fuel racks Some pools contain high-density spent fuel racks which allow multiplying the number of stored assemblies. In such a case the consequences of fuel damage may propagate too much larger populations of fuel assemblies. These racks also have much higher overall decay heat and larger fission product inventory. Therefore, the density of the fuel racks should be considered. Spent fuel building ventilation The spent fuel building ventilation flow rate is important in determining the overall building energy balance. Airflow through the building is an important heat removal mechanism. On the other hand it also provides a source of oxygen for zirconium oxidation. Particular heat transfer mechanisms for fuel pools There are several heat transfer mechanisms that can influence the cooling of spent fuel during various postulated severe accident scenarios. These include: convective cooling to the surrounding steam cooling from surrounding steam generated by boiling coolant, conduction through the ends of the fuel rods, radiation cooling. The degree of success associated with different heat transfer mechanisms depends on the configuration of the SFP, rack/canister design (e.g., closed or open lattice), density of the fuel assemblies, arrangement of the hottest bundles within the SFP lattice and the SFP level. Structural integrity of fuel racks For recently discharged fuel or for severely restricted air flow (e.g. high density spent fuel racks) the exothermic oxidation reaction is predicted to be very vigorous and failure of both the fuel rods and the fuel racks is expected. The steel racks may not be able to maintain structural integrity because of the sustained
ASAMPSA_E-WP40-D40-7-vol4-L2PSA-RD-and-SFP-1.docx