The consequences of a light water ingress accident scenario have been analyzed for the French High Flux Reactor, an heavy-water cooled, moderated and reflected reactor. It is found that the use of safety analysis code such as RELAP or CATHARE are required and neutronic tool alone cannot provide an accurate description of all phenomena involved. It is also found that even a loose coupling between neutronic and safety analysis code can be implemented and used to analyze the accident scenario

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... dered. As a result, despite the substantial reactivity increase induced by the ingress of light water in the core, it is concluded that the RHF reactor would remain safe (peak cladding temperature well below melting temperature) in any conditions considered and at any time.