Abstract
The in-situ characterisation of strontium-90 contamination of groundwater at nuclear decommissioning sites would represent a novel and cost-saving technology for the nuclear industry. However, beta particles are emitted over a continuous spectrum and it is difficult identify radionuclides due to the overlap of their spectra and the lack of characteristic features. This can be resolved by using predictive modelling to perform a maximum-likelihood estimation of the radionuclides present in a beta spectrum obtained with a semiconductor detector. This is achieved using a linear least squares linear regression and relating experimental data with simulated detector response data. In this case, by simulating a groundwater borehole scenario and the deployment of a cadmium telluride detector within it, it is demonstrated that it is possible to identify the presence of Sr, Y, Cs and U decay. It is determined that the optimal thickness of the CdTe detector for this technique is in the range of 0.1 to 1 mm. The influence of suspended solids in the groundwater is also investigated. The average and maximum concentrations of suspended particles found at Sellafield do not significantly deteriorate the results. It is found that applying the linear regression over two energy windows improves the estimate of Sr activity in a mixed groundwater source. These results provide validation for the ability of in-situ detectors to determine the activity of Sr in groundwater in a timely and cost-effective manner.
Highlights
This research aims to develop a methodology for estimating the 90 Sr activity in contaminated groundwater at nuclear decommissioning sites as measured by a cadmium telluride (CdTe) [1,2] detector that is deployed in a groundwater borehole
In order to compete with existing techniques, an in-situ detector should be able to identify the activity of individual radionuclides
The goal of this section is to demonstrate the deconvolution of a gross beta spectrum and evaluate the methodology to establish whether it can identify 90 Sr activity in a contaminated groundwater environment
Summary
Accepted: 19 August 2021This research aims to develop a methodology for estimating the 90 Sr activity in contaminated groundwater at nuclear decommissioning sites as measured by a cadmium telluride (CdTe) [1,2] detector that is deployed in a groundwater borehole. S. Grujic et al [15] report on using the Monte Carlo simulation package MCNP [16] to simulate the response function of a semiconductor Si detector to identify 90 Sr contamination in water samples taken from spent nuclear fuel storage pools. Grujic et al [15] report on using the Monte Carlo simulation package MCNP [16] to simulate the response function of a semiconductor Si detector to identify 90 Sr contamination in water samples taken from spent nuclear fuel storage pools In this case, a PIPS (passivated implanted planar silicon) detector with a surface area of 1.197 cm and a thickness of 502 μm is simulated. The gross radiation spectrum is considered to be the sum of the individual radiation spectra, modified by the response function of the detector—as described in Equation (1)
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