Shielding analysis in the design phase of the new emergency operation facility for Tihange nuclear power plant

In this document, several methodologies are proposed for sizing the internal and external walls, floor, roof and doors of an Emergency Operation Facility (EOF) dedicated to manage a severe accident in a nuclear power plant. The particularity of such facilities is that the radioactive sources are expected both around and inside the building (considering the ventilation system). All the proposed methodologies use the MicroShield code which is, usually, less adapted for complex geometries. The source term definitions and the models used for the shielding calculations with this code were developed and are illustrated, in this document, by calculations performed for the basic design of a new EOF for the Tihange nuclear power plant. In that framework, it was considered that effective dose rate inside the habitable zone of the EOF had to be kept below 1 mSv/h after a severe accident, taking into account radioactive sources from inside and outside the building. Such a dose rate is achievable if a minimum thickness of about 50 cm for external walls and roof is considered. In addition, results have shown that internal shielding was not necessary, except for the floor where the HVAC filters are localised