The assessment of the operational characteristics of the filtration function used during the recirculation phase of safety injection system (SI) and containment spray system (SS), in the event of a primary system break in the containment, has been performed by the "Institut de Radioprotection et de Sûreté Nucléaire" (IRSN) for the French pressurized reactors (58 reactors). Those one have been designed according with the RG 1.82 (rev. 1). The IRSN has focused in particular on the CPY series, 900 MWe 3 loops pressurized water reactors (28 reactors).
A general overview of the literature has been conducted between October 1999 and November 2000, which resulting in defining of an approach methodology and the writing of technical specifications. In this purpose, the "Institut de Radioprotection et de Sûreté Nucléaire" has decided to perform an experimental program of studies on the sump plugging risk. Those studies have been carried out for the different sizes of primary breaks: large, intermediate and small LOCA. For each size of breaks, located on the welding between SG and hot leg, the different characteristics of generated debris, flows of SI and SS systems have been defined.
Methodology of event trees has been used to define the characteristics of the debris and their arrival point at the bottom of the containment using the results of the performed tests.
To estimate the risk involved in each case, the following points were studied:
_ an inventory of debris generated. This consists of the following types:
_ glass wool thermal insulation fibers (spherical model: L = 12.D),
_ paints and particulates,
_ dusts present in the containment, in suspension or on the walls,
_ vertical transfer of debris,
_ structural modification of debris in the containment,
_ horizontal transfer of debris at the bottom of the containment,
_ filtration efficiency and modification of sump hydraulics / air and debris ingestion,
_ operation of RIS and EAS circuit equipment with mud and air present.
The subjects giving rise to important questions have been collected and a corresponding full-scale experimental program concern:
_ transfer of generated debris to the bottom of the containment, as it crosses the grating system and also under the action of chemical and thermal breakdown,
_ settling and transport of generated debris at the bottom of the reactor building,
_ the pressure drop value and the ingestion of air at the 4 filters of each suction inlet,
_ the behavior of the fiber bed under realistic conditions (temperature, ph, quality of the water, effects of different particulates).