- 244 - Consequently, according to the ILL's analyses, the margins for the SSCs lie between values of less than 1 (protection framework, cask maintenance station, reactor coolant pump bunkers, cask reflooding system) and values above 3 (containment isolation source penetrations). The margin for the polar crane is 1.2. The following are noted with regard to the control of reactivity, cooling and containment. For the control of reactivity the ILL considers that only a rupture of the heavy water inlet manifold - if it occurs in the light water pool - could cause a BORAX-type reactivity accident. It considers that the heavy water inlet manifold should remain intact up to an earthquake of intensity SSE + σ. It does however identify elements situated in water inlet manifold environment (such as the cask handling gantry crane) that could constitute threats and jeopardise the integrity of the water manifold at earthquake intensities below the reference earthquake. Furthermore, the "instrumentation & control" part of the emergency shutdown system is not designed to be operational in the event of an earthquake. Regarding the control of cooling, three cases can be identified: management of the water inventory in the pile block, management of the water inventory in the transfer cask when changing the water, and management of the water inventory in canal 2. Given the scenarios and key SSCs identified by the ILL in its CSA report, the licensee considers that: the integrity of the pipes in pools is guaranteed up to an earthquake intensity corresponding to the SSE + σ; the integrity of the pipes outside pools is guaranteed up to 1.5 times the SSE; the integrity of the siphon breaker valve situated near the main pipe should be ensured up to an earthquake intensity of SSE + σ ; the integrity of the natural convection valves would be guaranteed up to an earthquake intensity of SSE + σ ; the integrity of the thimbles and their clamping should be guaranteed up to an earthquake intensity of SSE + σ ; the safety valves should be operable during an earthquake of the SSE intensity, but they are not seismic qualified; up to an earthquake intensity corresponding to SSE + σ, the potential threats to the key SSCs should not threaten these key SSCs, except as regards the structural steelwork of the cold neutron source, the experimental equipment, the handling gantry and the handling cask maintenance station; the venting and drainage lines, and the safety valves situated at level C could be threatened should the primary coolant pump bunkers collapse; the emergency water make-up system (CES), which enables water to be introduced into the pile block, the pool and canal 2, should be operable up to an earthquake intensity of SSE + σ. Nevertheless, as the CES does not start automatically, it would enter service too late to prevent the meltdown risk in the event of a primary cooling system breach. The licensee therefore proposed in 2008 installing an ultimate reflooding system that can automatically inject water from the reactor cavity into the pile block via three injection lines; as regards the transfer cask, the "light water reflooding" and "emergency letdown" functions would be lost in an earthquake of the reference earthquake intensity; the leak-tightness of canal 2, with its gates, is ensured up to an earthquake intensity approaching the SSE + σ. Lastly, concerning the control of containment with respect to the seismic risk, it must be emphasized that the containment is automatically isolated if an earthquake is detected. This being said, the requirements defined in 2008 for the seismic safeguard gaseous effluents system, which has two filtration lines (THE and PAI) from which discharges could be made to limit the pressure increase in the internal concrete containment (deflation and maintaining negative pressure in the reactor building), should be modified so that this system can withstand the SSE+ σ earthquake . Moreover, the licensee has noted that the truck door is the only containment penetration that does not have a margin of more than 2 with respect to the SSE, and also identified potential threats to the containment (the fresh air inlet, the cask maintenance station and the level C crane). Lastly, the metal containment will undergo a specific study to substantiate the expert judgement that concludes that its buckling would not cause any significant damage to the concrete containment.
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