Need for Advanced Radiation Detection Simulations for Nuclear Decomissioning Applications*

The Institute for Clean Energy Technology (ICET) at Mississippi State University has a history of developing semi-autonomous radiological surveying systems for assisting government agencies clean sites contaminated with radioactive materials. Data from radiation detectors are synced with GPS-registered data as the robotic platforms systematically scan areas of concern for radiological materials. These data are used to construct heat maps of residual contamination after the radiation data is converted to residual activity concentration (Bq/g) in soil. Current governmental guidance on calculating minimum detectable concentration (MDC) of residual contamination relies on using exposure-rate data from point-kernel simulations (Microshield^®) of the detector-source geometry, detector response measurements within calibrated radiation fields, background radiation measurements, and known physical properties of the detector. These data are combined to calculate the theoretical lower limit of detectable residual contamination. Current simulation tools are off-the-shelf software packages that are geared for site personnel to operate without an extensive background in software development. These simulations are rooted in International Commission on Radiological Protection (ICRP) published methods. ICRP methods are geared toward the safety and protection of radiation workers and are not necessarily intended to be used for simulating detector-source geometries. Currently, the United States Nuclear Regulatory Commission technical reports site using these simulations, but more advanced Monte Carlo methods can be more appropriate. Due to the advanced nature of the surveying technology being developed at ICET, advanced Monte Carlo simulations are required to address deficiencies in simulation detector-source geometries. There is also a need to develop methods for conducting experiments in simulation to reduce the risk of exposing staff unnecessarily to ionizing radiation. This work describes the current state of simulation and characterization methods in the nuclear decommissioning industry, associated limitations, and most importantly, the need for a more robust simulation package.