Assessment of the operational characteristics of the filtration function used during the recirculation phase of safety injection system (ECCS) and containment spray system (CSS) in the event of a break of the primary system in the containment has been performed by the "Institut de Radioprotection et de Sûreté Nucléaire" (reference 1) for the French pressurized reactors (58 reactors) in particular the CPY series, 900 MWe pressurized water reactors (30 reactors) designed according Regulatory Guide 1.82 (revision 1).
To estimate the risk involved, the following points were studied:
_ Inventory of debris generated of the following types:
_ Glass wool thermal insulation fibers,
_ Dusts present in the containment, in suspension or on the walls,
_ Vertical transfer of different debris,
_ Structural modification of debris in the containment,
_ Horizontal transfer of debris at the bottom of the containment,
_ Filtration efficiency under realistic conditions (temperature, ph, quality of the water, effects of different particulates),
_ Modification of sump hydraulics / air and debris ingestion,
_ Operation of SI and SS circuit equipment with mud and air present.
The subjects giving rise to important questions have been collected.
For some of them, assumptions have been taken. They concern the insulation debris generation for which a spherical model of degradation has been adopted for double-ended break (NUREG 6762) with a ratio of L/D=12 and the insulation debris repartition established on the basis of KASHIRA test results.
For the other ones, an experimental approach was chosen due in one hand to some lack of knowledge, in the other hand, to the difficulty to use generic results to assess the French units and their specificities.
The corresponding full-scale experimental program concern:
_ IVANA loop (VUEZ / SLOVAKIA): transfer of generated debris to the bottom of the containment under mechanical action of falling water, as it crosses the grating system and also under the action of chemical and thermal breakdown (reference 2),
_ VITRA loop (EREC / RUSSIA): settling and transport of generated debris at the bottom of the reactor building (reference 3),
_ MANON loop (VUEZ / SLOVAKIA): pressure drop value and ingestion of air at the 4 filters of each suction inlet (references 4 and 5),
_ ELISA loop (VUEZ / SLOVAKIA): behavior of the fiber bed under realistic conditions (temperature, ph, quality of the water, effects of particulates) (references 6 and 7).