Development of Estimation Method for Radioactivity Concentration Distribution of Radioactive Wastes in a Box-shaped Container - 17034

We are developing a new estimation method suitable for determining radioactivity concentration distribution of radioactive wastes stored in a square box-shaped container. This method uses the Maximum A Posteriori (MAP) method which is a way to solve the inverse problem, and it estimates the radioactivity concentration distribution by comparing simulated data with measured data. In the measurement, gamma rays emitted from the radioactive wastes are measured by several gamma ray spectrometers which are set at different positions in relation to each other. On the other hand, the gamma ray spectrum data of each spectrometer are simulated by a Monte Carlo simulation code. The method uses an iterative calculation to solve the concentration distribution with measured spectrum data and simulated spectrum data. We conducted a simulation test to check the algorithm of our estimation method. And we also conducted an experiment using activated objects. We found that the concentration of the wastes in a box-shaped container could be estimated within a 20 % error for the simulation, and within a 40 % error for the experiment and we confirmed that feasibility of our method was favorable. (authors)