Abstract
The decontamination and decommissioning (D&D) of nuclear facilities and post-accident areas require the characterization and sorting of all materials based on their radioactive content prior to removal, reuse, or storage. Performing direct or in-situ measurements of large, bulky objects is a cost-effective strategy. It eliminates the need to disassemble, cut, crush, pre-treat, or re-package them into smaller items. These costly activities are also potential sources of additional exposure to workers through excessive contact and handling.
Calibrations based upon radioactive standards and sources are often time-consuming or difficult if the objects are large, have irregular shapes, or if the distribution of contamination is not homogeneous. This problem gets worse if the items are numerous or if these parameters change from item to item. Mirion Technologies’ In Situ Object Counting System (ISOCS) is a suite of software tools that can be used to generate efficiency calibrations based upon mathematical representations of the measurement geometry. These representations are created from models generated and benchmarked at the detector factory using Monte Carlo methods (MCNP) and NIST-traceable sources. ISOCS provides a large range of templates for most nuclear waste components in nuclear facilities, and it has an extensive history of benchmarking, validation, and regulatory acceptance in several countries.
Regardless of the calibration method, any deviation or mismatch in the distribution of the contamination compared to the calibration can introduce biases in the reported results. Recently, Mirion has developed an advanced type of general ISOCS template called SuperISOCS. With SuperISOCS, it has been demonstrated that complex scenarios and objects can be accurately represented and validated by adding up primitive template shapes. These have included entire glove boxes and its contents, stratified waste tanks, and thousands of truckloads containing sacks of soil of various sizes and fill heights.
This work presents the latest studies using SuperISOCS in D&D applications as a fast and effective tool to perform efficiency calibrations and uncertainty estimations of complicated geometries. The benefits of the ability to set whether any surface or sub-item has contamination will be demonstrated. Examples of comparisons between SuperISOCS and MCNP of conduit and pipes with arbitrary bends, and complex machinery, such as turbine assemblies, will be highlighted. Cost-benefit evaluations of these scenarios will provide some guidance to stakeholders and end-users on when approximations can be made using general templates and when SuperISOCS calibrations are recommended.
