Open Access

Table 1

Comparison between the cold and the warm roof slab

Cold roof slab Warm roof slab
Advantages – Reduction of thermal expansions of the bottom plate
– Reduction of uncertainty of horizontal locations of ACS
– Reduction of temperatures of seals, concretes and electrical devices
– NPP availability (shorter shutdown)
– No restricted access to the roof slab due to temperature during normal operation
– Reduction of thermosiphons effects along components penetrations
– Reduction of risk of Na deposit in components penetrations
– Reduction of thermal power to evacuate through cooling system: allow to replace complex thermal insulation (Na compatible) by a simple baffle
– Reduction of thermal stress within structures
Drawbacks – Cost
– Increment of thermal insulation and of roof slab total height
– Impact of the active gas cooling system on the reactor building
– Increment of the risk of thermosiphons effects along components penetrations
– Risk of Na deposit in component penetrations and impossible removal of components for maintenance/ renewal
– Increment of thermal gradients within structures (including the main vessel and components)
– Reduction of seals lifetime
– Limitation of tightness performances of seals on the roof slab during accident (due to higher temperatures)
– Height of the cylindrical skirt that supports the roof slab and the main vessel
– Reduction of NPP availability due to cooldown transients before shutdown and heating transients before start
– Needs of thermal insulation on top of the roof slab
– Higher temperature of electrical devices
– Increment of uncertainty of horizontal locations of ACS
– Resistance of concrete to higher temperatures

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