ALGORITHM FOR PLUTONIUM(PU)HOLDUP MEASUREMENTS BY LOW-RESOLUTION GAMMA-RAY SPECTROMETRY

摘要

One of the important tasks of NMC&A at radiochemical sites is the control of Pu in holdup. Implementation of this task is restricted by limited access to equipment to clean out the accumulated Pu.Non-destructive assay(NDA)measurements are the main approach for determining Pu mass in holdup.Existing methods for determining the quantity of Pu in holdup do not correctly interpret the results of gamma-ray spectra measurements sometimes and require modification to increase accuracy. The gamma-ray spectrometry technique to determine Pu quantities in holdup that was developed at the Russian Methodological Training Center(RMTC)is presented here.This technique is based on using low-resolution gamma-spectrometer and processing measured spectra with a special algorithm. The algorithm includes a correction for self-absorption in the holdup,attenuation from the walls of the equipment,and attenuation by an unknown thickness of lead shielding applied to the equipment. The procedure has the following features:background correction,iterative correction for self- absorption by“thick”holdup layers,correction for shielding material and calculation of its thickness, correction of ~241 Am influence,calculation of ~241 Am content in Pu of holdup,calculation of the effective area for surface type holdup in pipe depending on the radius of the pipe and distance between detector and pipe,and calculation of detector efficiency.The results are then presented in the form of a report. The collected spectra and results are also stored in a database. The computerized algorithm is named GADEM(Gamma Deposit Measurements).GADEM was tested using equipment at a radiochemical plant.A summary of the algorithm and the computer software is presented below.Screenshots of the main windows in the program and the results of its testing with reference materials are also presented.