Sources during shutdown accidents

It should also be noted that releases of radioactivity from spent fuel pools can also occur during shutdown conditions if decay heat removal is not maintained. 

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This report examines the severe accident sequences and radionuclide source terms at the Sizewell pressurised water reactor with a piestressed concrete containment, the Konvoi pressurized water reactor with a steel primary contaimnent, the European Pressurised water Reactor (EPR) and a boiling water reactor with a Mark 2 containment. The report concludes that the key accident sequences for European plant designs are transient events and small loss-of-coolant accidents, loss of cooling during shutdown, and containment bypass sequences. The most important chemical and transport phenomena are found to be revaporisation of volatile radionuclides from the reactor coolant system, iodine chemistry, and release paths through the plant. Additional research is recommended on release of fission products from the fuel, release of fission products from the reactor coolant system, ehemistry of iodine, and transport of radionuclide through plants. 

The IDS is eapable of providing reliable power for the safe shutdown of the plant without the support of battery ehargers during a loss of all ac power sources coincident with a design basis accident. The system is designed so that no single failure will result in a condition that will... 

Provisions should be made for shielding the radiation sources, in addition to those provisions required during operation, to ensure that personnel can have access to and can occupy the plant control room or the supplementary control points (e.g. the location of the remote shutdown panel) so as to operate and maintain essential equipment without exceeding established dose limits as specified in paras V.27-V.32 of the BSS [2] and paras 4.57-4.65 of Ref. [20]. This includes access to equipment in cases where maintenance or repair may be necessary after an accident. In general, provision should be made to render direct intervention by operators superfluous by instaUing automatic or remote controlled equipment (e.g. remote controlled valves). 

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