Operating experience based radiological safety performance improvement in 540/700 MWe PHWR

Tarapur Atomic Power Station Unit - 3 and 4 is first indigenously designed 540 MWe pressurized heavy water reactors. These reactors are operated for 910 effective full power days (EFPD) and 1030 EFPD respectively up to November 2010. Collective dose of the station during operation, refueling, poison shutdown and Long shutdown activities are maintained lowest among all PHWR reactors operated in the world through strong base of radiological monitoring, Good operating practices, development of radiological safety facilities such as radiation Instrument calibration facility, Radiation protection information system, shielding flasks for handling cobalt SPND, review of radiological safety aspects and improvements, operating experience sharing, job observations, trending of low level events, enhancing the sectional and station ALARA meetings, implementation of WANO guidelines and ISO Intergraded management systems. However to enhance the radiological safety performance further, there are radiological safety issues which need to be addressed. The issues identified through the 540 MWe operating experience are replacement cobalt SPND material and MI cable material since presently handling of high active cobalt and vanadium self power neutron detectors are required, high tritium activity buildup in the moderator system, high gamma and neutron radiation fields around the PHT and moderator lines during reactor operation, layout of PHT purification lines in the annular space, moderator heavy water escape through horizontal flux unit during its replacement, heavy water leakages in the feeder cabinet, online PHT system and moderator system monitors for the rate of radiation field buildup, online high sensitive tritium in air and tritium in water monitors. This paper deals with potential radiological safety issues for improvements to achieve best radiological safety performance. (author)