Implementation and Full Scale Tests of Sand Bed Filter

Abstract

All French PWA's operating plants are now equiped with a containment postaccident decompress ion filtration system using a sand bed filter. The system also possesses a real time gamma spectrometry radioactivity monitor. Firstly the paper covers: the design and sizing requirements of the system resulting from a R&D program (PITEAS) carried out at the Cadarache Nuclear Studies Center jointly by Electricite de France and the French Atomic Energy Commission, . the detailed description of the radioactivity monitor which would display the activity concentration for the main radioactive elements (iodine, caesium, etc) with a large range, the principles and the results of full scale tests carried out on a test loop (FUCHIA) with a representative geometry of the French plants. The aim was to know the operating limits of the system in two different kinds of tests; filtration efficiency tests with aerosols generated by means of plasma torches, thermohydraulic and thermic behaviour tests with residual power simulation by means of electrical heaters. The FUCHIA tests have definitively qualified the system showing global efficiencies of about 200 for the aerosols. In its present state the system is able to mitigate most cases of severe accidents scenarios. Nevertheless, Electricite de France has decided to improve the ability of the system and to reduce the dose rate on site in still severer postaccident conditions. Therefore, the paper also covers: the design of the complementary radiological shieldings; for the 900 MW series and the first 1300 MW series these consist of glass fiber thermosetting resin containers filled with water at the right time for all other series they consist of a concrete slab, the principle of the sand bed filter heat removal; after use the filter tank can be water sprinkled or cooled by a sufficient fresh air flow, the design of the hydrogen risk protection by preheating; this consists of heated air flow blown with a fixed fan and an electric heater which can be supplied by an independent electric generator. The paper ends with the present program for the implementation of these complementary systems.