- 140 - when the primary system is closed, the core will become exposed more than 24 hours after the start of the accident; when the primary system is just open, if the primary system vents fail to close, the fuel will become exposed after about ten hours; this situation is similar to loss of the off-site electrical power supplies and all the backup supplies of a reactor; when the primary system is sufficiently open: o for the 900 MWe series, the chemical and volume control system (CVCS) charging pumps are no longer available; if no complementary measures are taken, the fuel will become exposed a few hours after the start of the accident; o for the 1300 MWe and N4 series, the technical specifications (TS) limits this situation to just one reactor on a site, always leaving the possibility of using the mobile motor-driven cooling pump; the fuel will become exposed several days after the start of the accident; for the spent fuel pools, as all the pumps of the fire-fighting water production or distribution system (JPP or JPD) are out of service, the fuel will become uncovered within a day and a half. For the EPR reactor, EDF specifies in its CSA reports that the extension of the loss of off-site electrical power supply to the entire site does not change its analysis of the reactor section, but it does not give any details on the spent fuel pool section; in this situation, reactor management does not require any equipment that is specific or common to the site. ASN considers that EDF must adopt a position regarding the missing assessment. Regarding the external measures planned to prevent the fuel being damaged, EDF has specified in its CSA reports that the means for managing loss of the off-site electrical power supplies and the conventional backup supplies would be implemented by competent and qualified personnel, assisted and advised by the crisis management teams. The planned external actions for managing loss of the off-site electrical power supplies and the conventional backup supplies over the entire site, examined by EDF in its complementary safety assessments, correspond to the requirements of ASN decision No. 2011-DC-0213. Regarding the measures that can be envisaged to prevent the cliff-edge effects or to reinforce the robustness of the facility, EDF has proposed in its CSA reports, for the reactors in service; to study and verify the resistance of the EFWS system turbine-driven pumps and the backup turbine generator (LLS) to the temperature rise in the buildings beyond twenty-four hours; to install on each reactor an "ultimate backup diesel generator set": o its role will be to energise one motor-driven pump of the EFWS system, and to take over the functions of the LLS if this is not available; o it will be able to ensure in total autonomy for 48 hours, the partial electrical supply of one backed-up electrical panel within about one hour after losing the external and internal electrical power supplies; o it will be powerful enough supply electricity for one primary system injection means and one motordriven pump of the EFWS system; o it will also be capable of supplying electricity for the auxiliaries that isolate the reactor containment, for the ventilation systems of the control room, the nuclear auxiliary building and the fuel building, and the backup of the system for placing the inter-containment space under vacuum; o it shall be designed for hazard robustness; pending installation of this "ultimate backup diesel generator set", to provide one or more small emergency generator sets that will guarantee the electrical supply for the minimum necessary instrumentation & control and control room emergency lighting; to install on the 900 MWe series reactors a motor-driven cooling pump for injecting water into the core from the PTR system tank; to put in place lasting ultimate backup means (wells, ponds, etc.) for replenishing the EFWS and PTR systems and the spent fuel pool with water, along with the associated material and human resources;
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