Radiation Protection Measures During the Decommissioning of DR 2

摘要

DR 2 (Danish Reactor 2), one of the research reactors at the Ris? site, has been in the process of beingdecommissioned during the last two years. The decommissioning will be completed in 2008.The reactor went critical for the first time in late 1958 and was shut down in 1975. The construction was a 5 MWlight-water moderated and cooled tank type reactor.Although the process of decommissioning was formally initiated in 2005, it was preceded by a characterizationproject with the purpose of determining activity contents in key materials and dose rates at relevant spots in the reactor.The paper describes the removal of neutron beam plugs, grid plate and a thermal column with focus on radiationprotection issues. The primary objective is, however, to describe the measures taken to control radiation doses duringthe removal of the reactor block concrete and the reactor tank.The demolition and removal of concrete was done by an external contractor. The contractor had to comply with acomprehensive set of requirements. This included splitting activated concrete from concrete containing activitiesbelow clearance levels with no use of fluids of any kind, as the risk of not being able to control diffusion of contaminatedfluids was an important issue.The experience from the decommissioning of the DR 1 reactor in 2005 showed that water-cooled cutting made itvery difficult to monitor the levels of air contamination as the filters of the air monitors were blocked frequently.Certainly, dry cutting turned out to be a great technical challenge to the external contractor.Another demand was that the work should take place inside a de-pressurized containment in order to control aircontamination and thereby minimize internal doses.The experience gathered from the practical implementation of dose reducing measures will be discussed.Problems involving the use of external contractors will be discussed, including training of personnel with no priorknowledge of radioactivity and radiation.Possible conflicts between project management interests and radiation protection issues will be addressed.