Underwater Determination of Radionuclide Levels in 105-KE Basin Floor and Walls Using a Gamma-Ray Detector System

Abstract

The 105 K East Basin was originally built to store spent nuclear fuel from the Hanford K East Reactor before processing the fuel in the Plutonium-Uranium Extraction facility. In the 1970s and later years, the basin was used for longer-term storage of N Reactor fuel, which is still the primary content of the basin today. The basin is divided into three bays by two concrete partition walls and contains various pits as well as a discharge-chute area adjacent to the K East Reactor. Each basin contains water nearly 17 feet in depth and has a wetted area of concrete floor and walls of approximately 26,500 ft 2 (i.e., floor 9,900 ft 2 and walls 16,600 ft 2). Currently, sand filter and ion exchange modules provide pathways to remove particulate and contaminants from the water. The K East Basin concrete floor and walls are primarily uncoated. Exceptions are 1) an approximately 1.5-ft band of concrete running around the current basin waterline, which has been wire brushed and coated with epoxy (Huang and Moore 1997) as part of the dose-reduction activities in 1995 (with the water level of the basin subsequently raised approximately 1 foot to its current level) and 2) the Discharge Chute area and portions of the Tech View Pit, which reportedly have been painted (Vargo et al. 1994). Activities to remove spent fuel, sludge, and debris from K East Basin have begun. Once all the radioactive hazards (i.e., fuel, sludge, and debris) are removed from the basin, the basin water will be removed, and the basin will be turned over to a deactivation and decommission contractor. However, the specific approach to achieving this end state is dependent on knowledge of contamination levels in the concrete walls and floor once the water is removed. The Spent Nuclear Fuel Project contracted (a) with the Pacific Northwest National Laboratory (PNNL) to perform nondestructive evaluation of the K East Basin for the purpose of determining concrete contamination levels, including depth of penetration, from selected wall and floor locations below the basin waterline. The definition of the initial requirements and specific approach were controlled through a Data Quality Objectives (DQO) and Sample Analysis Plan (SAP) methodology managed by the Spent Nuclear Fuel Project (Makenas 2002, Baker et al. 2002). This initial approach sought to maximize the useful data from these analyses to make decisions related to final disposition of the K Basins. The K East Basin presents the greatest challenge from the perspective of decontamination for the Spent Nuclear Fuel Project. This is because K East Basin has been in service, storing N reactor fuel, longer than K West Basin (i.e., 1975 versus 1981) and, unlike K West Basin, K East Basin walls and floors were not cleaned and coated with epoxy before entering this type of service. K East Basin also has the greater amount of fuel-bearing sludge in contact with the floor and walls (Baker 1995; Baker 2001). The fact that canisters of fuel in K East Basin do not have lids and often have perforated bottoms (again, unli...