Development of combined filter units for ventilation systems of new generation NPPs

The air cleaning systems at NPPs are an important safety element, as regards the attending personnel, normal operation of equipment or the environmental control. The selection of an effective cleaning technology and the structure of cleaning system depends on a specific character of the ecological NPP safety assurance under normal and accident operation conditions. The main requirements imposed for such systems lie in achieving a high-efficient cleaning (99.0-99.95 %) and the safety. In this regard, of importance for the new generation WWER-based NPPs under design is the development of combined filter units (CFU) capable of providing in one assembly the integrated cleaning of air from moisture, radioactive aerosols, molar (I2) and organic (CH3I) iodine. The CFU incorporates the following filtering sections installed in series: a drop-mist separator; an electric heater. a filter of coarse cleaning from radioactive aerosols; a filter of fine cleaning from radioactive aerosols; iodine cleaning filter. By now, the all-up testing of the mock-up for the rated consumption of 3500 m3/h (CFU-3500) has been conducted for the purpose of determining the functional efficiency of the separate filtering sections by the condensed moisture, radioactive aerosols, radioiodine and its organic compounds as well as the efficiency of the unit as a whole. The efficiency of cleaning from ra aerosols provided by the CFU-3500 mock-up amounts respectively to Eβ 99.98 %, Eα = 99.98 %, the cleaning efficiency in terms of molar iodine is 99.99 %, methyl iodide 99.9 %. The CFU sizes have been developed, which are designed for the following output capacity of air to be purified: 3500 m3/h, 7000 m3/h, 10500 m3/h, 14000 m3/h, and 21000 m3/h. The CFU was tested for seismic stability. According to the test results, the filtering unit meets the requirements GOST 17516.1-90, GOST 16962.2-90, PNAEhG-55-006-87, Mu 7.4-01 in terms of seismic stability at the SSE intensity of seismic impacts equal to 7 and 8 deg (MSK-64 scale), the elevation up to 70 m. The aerodynamic tests of the CFU and the tests for purification efficiency as to atmospheric aerosols performed after the seismic stability tests showed no degradation of the unit performances. In December 2003, the production prototype of the CFU-3500 was set at the Kalininskaya NPP for performance testing. (author)