Gaseous radioactive waste

Gaseous RAW is mainly generated from degassing of the primary system and ventilation systems in the radiation controlled area of NPPs. Gaseous waste from the primary system is treated by gas decay tank or charcoal decay bed to reduce radioactivity, and released into the atmosphere through a radiation monitor. Gaseous waste from the building ventilation system is also exhausted under continuous monitoring through high-efficiency par­ticulate (HEPA) and charcoal filters into the environment.

The MEST addresses the maximum radioactivity concentration, ECL, for gaseous effluent being released into the atmosphere at the restricted area boundary (MEST Notice No. 2008-31). The licensee must conduct a peri­odic evaluation of the anticipated off-site dose due to gaseous effluent released into the environment, and routinely report results to the KINS. The Enforcement Decree of the AEA and the MEST Notice No. 2008-31 (Standards on Radiation Protection, etc.) prescribe discharge limits of gaseous and liquid radioactive effluents to be released from nuclear facili­ties into the environment, along with annual dose constraints of the popula­tion living around nuclear facilities.

In practice, nuclear facilities are operated with targets which are more restrictive than the discharge limits. In addition, some facilities also apply the derived release limits based on a small fraction of the dose limits for convenience for a field application. Whether related limits are met is veri­fied by periodic inspection or the examination of regular reports submitted to the regulatory body.

The radiation dose and its effect on individuals around nuclear facilities are assessed monthly by using the Off-site Dose Calculation Manual (ODCM, Reg. Guide 1.109) [US-NRC, 1977]. The assessments are based on the radioactivity of released liquid and gaseous effluents, atmospheric con­ditions, metabolism, and social data including agricultural and marine prod­ucts of the local community within a radius of 80 km.

The Korea Atomic Energy Research Institute (KAERI) in Daejeon and KHNP carry out R&D on RAW management. Treatment and disposal of HLW/SF is studied by KAERI. KHNP studies the treatment and disposal of LILW and interim storage of spent fuel. Technological developments are currently focused on the following topics: [34]

• LILW disposal and safety assessment technology

• improvement of existing technology for spent fuel storage and transpor­tation, and development of advanced spent fuel storage technology.

In addition to current use of conventional treatment methods such as evap­oration, compaction, drying and cementation, advanced technology for LILW treatment is being developed. Vitrification has been identified as the most promising innovative technology from the point of view of being environmentally sound and of being able to substantially reduce the volume of LILW, to improve the waste stability and to enhance the public accept­ance of its disposal. Vitrification immobilizes the radionuclides in a stable solid glass form and the associated volume reduction should result in effi­cient and prolonged use of a repository, which is most important for a small, densely populated country.

A feasibility study of the vitrification process was initiated in 1994 and a pilot-scale vitrification facility was installed in July 1999. This facility con­sists of an induction heater, cold crucible melter (CCM) for combustible waste, a plasma torch melter (PTM) for non-combustible waste, and an off-gas treatment system. KHNP’s research center (CRI) located in Daejeon has developed the technology with a target for commercialization of the process from 2005. The Ulchin Vitrification Facility (UVF) is the world ’s first commercial facility for the vitrification of LILW generated from NPPs using CCM technology. The construction of the facility began in 2005 and was completed in 2007. From December 2007 to September 2009, all key performance tests, such as the system functional test, the cold test, the hot test, and actual waste testing, were performed successfully. The UVF started commercial operation in October 2009 for the vitrification of LILW waste (Jo et al, 2010).

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