Applied Study Of A Small Region Monte Carlo Method For Deep Penetration Problem In The Measurement Of Large Volume Radioactive Waste

With the major development of nuclear energy and the extensive application of nuclear materials, plenty of radioactive wastes will be produced in almost every link of the nuclear industrial chain, including uranium mining, smelting, reprocessing, and so on. Before the final disposal of radioactive wastes, accurate measurements of nuclide components and radioactive waste activity are needed to provide scientific evidences to the staging, transportation, and final disposal. During the detection of large volume radioactive wastes, deep penetration problem may occur because of the extensive sized radioactive waste drums.In order to solve the deep penetration problem and get accurate efficiency calibration, the small region Monte Carlo method is developed to simulate those situations. Aiming at solving the deep penetration problem appearing in the process of radioactive waste detection, this paper includes the following research:(1) Studied on laws of particle transport and developed determination method of deep penetration problemAiming at how to judge a deep penetration problem in particle transport, this research established a Monte Carlo simulation model and studied the effects of different thickness, energy, the number of photons, materials. The results showed that there will be a deep penetration problem if the physics thickness is more than 10 mean free path. Therefore, it is necessary to calculate the mean free path in a particle transport and judge whether it is a deep penetration problem before the Monte Carlo simulation.(2) Established an algorithm of the application of Monte Carlo method of deep penetration problemThe small region Monte Carlo method was established by the transformation of particle transport equation. A particle transport problem was converted several particle transport problems in many small regions, in which every transport problem is not a deep penetration problem. On the basis, an algorithm of small region Monte Carlo method was established by recording the information of surface sources. Comparing the results respectively come from general Monte Carlo method and the small region Monte Carlo method, a conclusion that the small region Monte Carlo method could achieve an better outcome rather than that of the general Monte Carlo method when deep penetration may occur is summarized.(3) Established an accurate and efficient efficiency calibration for the measurement of large volume radioactive wasteThere would be possible deep penetration problem during the measurement of large volume radioactive waste drums in nuclear power plant. The research established an integrated efficiency calibration method combined judging whether it was a deep penetration problem and choosing proper efficiency calibration method. If it was a deep penetration problem, the small region Monte Carlo method was chosen. Otherwise, the general Monte Carlo method was chosen.(4) Application of efficiency correction of large volume radioactivity measuring instrumentIn order to measure a large volume of radioactive materials in nuclear power plant accurately, we established a spatial response function to characterize the deviation in measurement which depends on different locations of radioactive materials in the measuring instrument. The small region Monte Carlo method was applied in calculating the spatial response function. Accordingly the corresponding correction factor could be obtained to correct the measurement and to realize the spatial homogenization.