WAM-D - Decontamination and Decommissioning Centennial Ballroom 300D 09:30 - 11:45
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| Chair(s): Phil Rutherford
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WAM-D.1
09:30 Efficiency Comparison of Hybrid Radiation Transport Variance Reduction Methods for Wide Area Environmental Contamination Assay Applications EA Asano*, Georgia Institute of Technology
; SA Dewji, Georgia Institute of Technology
Abstract: In the radiological site remediation process, contaminated media in the field may be analyzed in a laboratory setting to determine whether remediation should take place prior to site release. To reduce the resource burden associated with currently expensive and time-consuming field sampling measurements, Monte Carlo pulse height tallies may be utilized to simulate the spectrum of energy deposition events in a detector model that corresponds to a risk- or dose-based radionuclide concentration in a contaminated medium. Such radiation transport problems can be computationally expensive, especially with simulations of a buried source in a highly attenuating medium reaching a small detector volume, requiring extensive Monte Carlo particle histories to estimate statistically reliable results. The Consistent Adjoint Driven Importance Sampling automated variance reduction method can be used to significantly increase the computationally efficiency of these difficult source-detector problems, such that various contamination scenarios can be simulated in a practical manner to obtain statistically reliable results. Two state-of-the-art tools that implement automated variance reduction, the AutomateD VAriaNce reducTion Generator and Shift codes, developed by at Oak Ridge National Laboratory, were investigated to compare the computational efficiency for generating pulse height simulations involving wide-area, highly attenuating monoenergetic photon sources. Pulse heights were tallied for gamma-ray detector configurations for various contaminated media. The results were analyzed based on the accuracy, convergence, and timing of the simulations, and were compared to Monte Carlo pulse height simulations without the use of automated variance reduction methods. A detector response function methodology employing the Shift code proved to outperform the AutomateD VAriaNce reducTion Generator, and was recommended as the optimized methodology for increasing the computational efficiency of wide area environmental contamination pulse height simulations. Computational benchmarks of the variance reduction methodologies will be presented in the context of utility to complex environmental source term radiation transport problems.
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WAM-D.2
09:45 Visual Sample Plan (VSP) geospatial analysis tools for environmental decision making JC Huckett, Pacific Northwest National Laboratory
; ZD Weller*, Pacific Northwest National Laboratory; LN Newburn, Pacific Northwest National Laboratory; DK Fagan, Pacific Northwest National Laboratory; CD Johnson, Pacific Northwest National Laboratory; BC Simpson, Pacific Northwest National Laboratory; AL Bunn, Pacific Northwest National Laboratory
Abstract: Visual Sample Plan (VSP) is a software tool that aids users in statistical sampling design and data analysis to support characterization, cleanup, and decommissioning decisions. VSP contains several statistical algorithms that can be used to analyze collected geospatial data and provide reliable estimates of contaminant levels over entire regions. Specifically, it includes kriging algorithms to predict contaminant concentrations at unsampled locations. Predicted data are used to test hypotheses about whether contamination at a site exceeds acceptable limits and to identify potential areas within a site that require additional investigation, determined based on statistical confidence and tolerance limits.
As the industry moves toward collecting autonomous and continuous data to support decommissioning decisions, data sets become larger and the computational burden of statistical techniques such as kriging increases. Analyses may require more time or computing resources, or algorithms may fail to reach convergence criteria. Particularly for the purposes of consequence management, when delays could compromise the response, alternative algorithms are required. This presentation presents fixed rank kriging and its implementation in VSP as an alternative to traditional kriging that reduces the computational burden and provides users with a solution quickly.
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WAM-D.3
10:00 Workplace Monitoring and Energy Analysis Of Low Energy Beta Contamination MI Iwatschenko-Borho*, Thermo Fisher Scientific Messtechnik GmbH
Abstract: In the years after the shutdown of a nuclear reactor, the percentage of low energy beta emitters among the inventory of neutron activation products grows steadily. Relying on the correlation measurement of Co-60 therefore becomes less and less applicable. Hard-to-detect long-living isotopes however, such as H-3, Ni-59, Ni-63, Mo-93, Nb-93m, Zr-93, Pd-107, Sm-151, are missed by conventional in-situ frisking or direct measurement of air filters. As an alternative to time consuming laboratory analysis a light-weight manual sample changer for air filters and wipe samples has now been developed. The robust and straightforward field measurement provides fast results regarding the presence of any contamination with neutron activation products. Due to the usage of a windowless scintillation detector, the prevalent isotope Ni-63 (average beta energy 17 keV) on wipes and air filters is measured with better than 30 % of 2 Pi efficiency on-site. In addition to very low detection limits for all beta emitters (including tritium) and electron capture nuclides, the average beta energy of the contamination is calculated and displayed. Consequently, an instantaneous verification or falsification regarding the expected nuclide mix of a detected beta contamination during outage or decommissioning work can be performed. The absence of any heavy gamma shielding allows for easy transport and placement at the workplace. In order to enable the user to locally perform a daily performance check, without the need to return the instrument to the calibration lab or to store and handle radioactive sources, special test adapters were designed using natural beta isotopes. These ultra-low activity discs contain natural potassium chloride, lutetium dioxide or rubidium chloride. These test adapters can be handled without any risk but provide both very reproducible activity values while showing highly different indications of the mean beta energy. Any performance deviation of the instrument is readily detected and the response of the instrument may even be re-adjusted locally using these test adapters.
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WAM-D.4
10:15 Decommissioning in California: 20+ Years of Politics vs. Science PD Rutherford*, Phil Rutherford Consulting
Abstract: Area IV of the Santa Susana Field Laboratory (SSFL) conducted nuclear research for the US Atomic Energy Commission (AEC) and the US Department of Energy (DOE) and was operated by The Boeing Company (Boeing) and its predecessor companies, Rockwell International and North American Aviation from 1954 until 2014. North Wind Portage has been DOE’s prime contractor since 2014. Twenty-five of twenty-seven nuclear and radiological facilities have gone through the decommissioning process including final status surveys by Boeing and its predecessors; confirmation or verification surveys by variously the Oak Ridge Institute of Science and Education, Argonne National Laboratory, Nuclear Regulatory Commission (NRC), California Department of Public Health - Radiologic Health Branch (CDPH/RHB) and/or US Environmental Protection Agency; release for unrestricted use by the appropriate regulatory agency (NRC, CDPH/RHB or DOE); and removal from relevant licenses. Beginning in 2000, a series of activist-led lawsuits against Boeing, DOE, CDPH/RHB and the California Department of Toxic Substances Control (DTSC) succeeded in delaying or blocking decommissioning progress. In addition, numerous Senate and Assembly Bills in the California legislature attempted to usurp the decommissioning process, including removing CDPH/RHB’s authority for regulating radioactive materials at SSFL and assigning that role to DTSC. As of 2022, five Boeing-owned former radiological facilities that have been “released for unrestricted use” have been blocked from demolition, pending ongoing litigation since 2013. In 2020-2021, seven remaining DOE-owned facilities that had either been decommissioned and “released for unrestricted use” or have no history of radiological use, have been demolished. Nevertheless, DTSC mandated that all demolition debris from these facilities be categorized as LLRW and disposed of out of the State of California to the EnergySolutions LLRW disposal site at Clive, Utah, “out of an abundance of caution … and irrespective of having characterization data showing no radioactivity.”
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WAM-D.5
10:45 Business Meeting
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