Plan for the safe decommissioning of the BAEC 3MW TRIGA MARK-II researchreactor

摘要

The 3 MW TRIGA Mark-II research reactor of Bangladesh Atomic Energy Commission (BAEC) has been operating since September 14, 1986. The reactor is used for radioisotope production (131I, 99mTc, 46Sc), various R&D activities, and manpower training. The reactor has been operated successfully since it's commissioning with the exception of a few reportable incidents. Of these, the decay tank leakage incident of 1997 is considered to be the most significant one. As a result of this incident, reactor operation at full power remained suspended for about 4 years. However, the reactor operation was continued during this period at a power level of 250 kW to cater the needs of various R&D groups, which required lower neutron flux for their experiments. This was made possible by establishing a temporary by pass connection across the decay tank using local technology. The reactor was made operational again at full power after successful replacement of the damaged decay tank in August 2001. At present the reactor is operated 5 days a week at a full power level of 3 MW for production of 1-131 and R&D purposes.Up to December 2005 total burn-up of the core stands at about 358 Megawatt Days (MWDs). BAEC has planned to increase the production of 131I and as such, the core burn-up is expected to be increased very significantly in the years to come. There is a declaration from the US DOE that all US origin research reactor spent fuel generated within 2006 will be taken away to the USA at their own cost within 2009. But the fuel burn up of the BAEC research reactor is about 6%. So the reactor can operate for about 10-20 years more. An initial decommissioning plan for the BAEC TRIGA reactor and relevant facilities should be established as early as possible as recommended in the IAEA Safety Standards Series No.WS-G-2.1 (Decommissioning of Nuclear Power Plants and Research Reactors - Safety Standards Series No.WS-G-2.1, IAEA, Vienna, 1999).During the design and construction phases of the BAEC TRF, aspects to facilitate the decommissioning process and reduce occupational exposures such as selection of material to reduce activation products, use of modular form of items for easy dismantling, designing to avoid contamination or to allow easy decontamination were considered. To reduce contamination and to allow easy decontamination, the floors of the reactor top areas were coated by plastic paint. The primary pumps and demineralization system pump were selected such that all their parts that come in contact with primary coolant were made of high quality stainless steel (ss type 304 and 316). The reactor facility is not susceptible to produce liquid waste in bulk quantity. However, any liquid waste produced in the facility will be processed and, if required, stored in the Central Waste Radioactive Waste Processing and Storage Facility (CWPSF) constructed at the AERE campus and located very close to the reactor facility. CWPSF has been constructed under the project "Establishment of Central Radioactive Waste Processing and Storage Facility" and it is financed by the Government of Bangladesh.During the operational phase of the reactor facility, certain measures are taken into consideration so as to facilitate decommissioning and reduce resource requirements and radiological hazards associated with decommissioning. The measures taken include;the operating history of the facility, including changes of the core components;radiological surveys (radiation and contamination level);modifications to the facility;operation and maintenance records of systems/equipment and design and location of experimental deices used during the operational lifetime of the facility. The paper summarizes the decommissioning plan of the TRIGA Mark-II research reactor of Bangladesh.