Clean up Progress on High Hazard Facilities at Sellafield: Magnox Swarf Storage Silos

摘要

British Nuclear Group manages and operates facilities associated with all aspects of the Nuclear Fuel Cyclernincluding the reprocessing of Spent Magnox Fuel at the Sellafield Site in the North West of England. Magnox fuel consists ofrnUranium with a Magnesium Oxide outer casing. The fuel is processed by removing the outer casing to produce swarf wasternwhich was then stored under water in the Magnox Swarf Storage Silos from the mid 1960 's. In addition to Magnox Swarf arnlarge volume of other wastes was stored in these silos such as graphite, fuel debris, various isotopes and contaminatedrnredundant equipment. There is a significant inventory of hazardous and mobile nuclear waste stored in twenty- tworncompartments. Much of the swarf has corroded to form sludge due to its occupancy in a water environment. This sludge and thernother wastes stored in the compartments present the most challenging and hazardous nuclear waste retrieval task facing thernBritish nuclear industry.rnProgress towards retrieval operations is going well with the testing and development of three mobile cave retrieval machines underway. Preparations for the introduction of these machines to the silos are also progressing well with the decommissioning,rnremoval and disposal of 333 tons of redundant machinery from the operations floor. Another significant part of thisrnpreparatory work has been to clean up a contaminated area of the operations floor above compartment seven. The concreternfloor was contaminated to levels in the order of two sieverts per hour. Innovative equipment and techniques have been used tornshave off the contaminated floor surface, resulting in a potentially hazardous mobile dust that was successfully and safelyrnrouted back into a silo compartment.rnOther recent achievements have been to significantly reduce the hazard posed by the facility, such as the first remote welding ofrndiffuser pipeline sections to reinstate direct cooling for specific compartments. Along with presenting the details of these recentrnachievements this paper will serve to provide lessons for facilities undergoing similar treatment and will outline some of thernmajor challenges ahead in the hazardous and technically challenging decommissioning program.