Methods to Account for CAP-88 PC-Omitted Nuclides in Radioactive Air Emissions From DOE Facilities

ABSTRACT

Routine research and development activities at US Department of Energy facilities can result in the release of radioactive emissions, potentially exposing the public and the environment. Such emissions are subject to certain Clean Air Act regulations, specifically those outlined in 40 CFR Part 61, Subpart H, which are enforced by the US Environmental Protection Agency. Compliance is determined in part with a dose standard. Doses to members of the public from most US Department of Energy facility airborne emissions are modeled using CAP-88 PC software, the latest version of which contains more than 1,200 radionuclides. Radioactive effluents from US Department of Energy facilities may contain radioisotopes that are not available in CAP-88 PC, and those radioisotopes must still be evaluated to determine whether doses to members of the public are below established limits. CAP-88 PC-omitted radionuclides can be accounted for using alternate methods, including the use of surrogate radionuclides. This paper elucidates the process of accounting for CAP-88 PC-omitted radionuclides by providing criteria and rationale for surrogate selection, a compilation of surrogate radionuclides used in the past by US Department of Energy facilities, a discussion of alternate methods used to account for CAP-88 PC-omitted radionuclides and a comparison of methods and impacts on receptor doses. Ultimately, this paper aims to aid in the process of surrogate selection and consequently to simplify and expedite compliance with Clean Air Act regulations.

Radiocesium accumulation and germline mutations in chronically exposed wild boar from Fukushima, with radiation doses to human consumers of contaminated meat

Genetic effects and radioactive contamination of large mammals, including wild boar (Sus scrofa), have been studied in Japan because of dispersal of radionuclides from the Fukushima Dai-ichi Nuclear Power Plant in 2011. Such studies have generally demonstrated a declining trend in measured radiocesium body burdens in wildlife. Estimating radiation exposure to wildlife is important to understand possible long-term impacts. Here, radiation exposure was evaluated in 307 wild boar inhabiting radioactively contaminated areas (50-8000 kBq m^-2) in Fukushima Prefecture from 2016 to 2019, and genetic markers were examined to assess possible germline mutations caused by chronic radiation exposures to several generations of wild boar. Internal Cs activity concentrations in boar remained high in areas near the power plant with the highest concentration of 54 kBq kg^-1 measured in 2019. Total dose rates to wild boar ranged from 0.02 to 36 μGy h^-1, which was primarily attributed to external radiation exposure, and dose rates to the maximally exposed animals were above the generic no-effects benchmark of 10 μGy h^-1. Using the estimated age of each animal, lifetime radiation doses ranged from <0.1 mGy to 700 mGy. Despite chronic exposures, the genetic analyses showed no significant accumulation of mutation events. Because wild boar is an occasional human dietary item in Japan, effective dose to humans from ingesting contaminated wild boar meat was calculated. Hypothetical consumption of contaminated wild boar meat from radioactively contaminated areas in Fukushima, at the per capita pork consumption rate (12.9 kg y^-1), would result in an average effective annual dose of 0.9 mSv y^-1, which is below the annual ingestion limit of 1 mSv y^-1. Additionally, a consumption rate of about 1.4 kg y^-1 of the most contaminated meat in this study would not exceed annual ingestion limits.

Dose Reconstruction Using Electron Paramagnetic Resonance Dosimetry on Tooth Enamel From Wild Boar Living in the Fukushima Exclusion Zone

The goal of the study was to establish characteristics of Japanese wild boar tooth enamel in the dose region of 0.25-2.0 Gy and to reconstruct external absorbed doses to wild boar native to the Fukushima exclusion zone using electron paramagnetic resonance dosimetry. The significance of Japanese wild boar in their ecosystem and their position within the trophic hierarchy make the wild boar a species of particular importance and therefore, the focus of this study. Dose response linearity and variability of enamel originating from various wild boar were investigated. Radiation dose response of Japanese wild boar tooth enamel in the range of 0.25-2.0 Gy was found to be linear, and the average variation in dose response between teeth originating from the same boar specimen was nearly 30%. No statistically significant difference in dose response was found based on sex of the boar or in permanent molar teeth of boar of differing ages. Electron paramagnetic resonance absorbed doses to boar tooth enamel were successfully reconstructed using the calibration curve method and converted into estimates of absorbed dose to soft tissue with large associated confidence intervals. The critical level dose value for the calibration curve was 1.0 Gy and the detection limit dose was 1.8 Gy, suggesting that this method would be more beneficial for boar with lifetime absorbed doses greater than 1.0 Gy. The method of reconstructing external absorbed doses using electron paramagnetic resonance dosimetry with tooth enamel from Japanese wild boar as dosimeters has proven to be a viable method which can be used to reconstruct absorbed doses to wildlife in accident-stricken areas in the absence of alternative dosimetry.

A Brief Review-EPR Dosimetry and the Use of Animal Teeth as Dosimeters

The technique of electron paramagnetic resonance dosimetry using tooth enamel was established in the late 1960s, and considerable research has been conducted to learn more about the benefits of using human teeth as dosimeters for the purpose of retrospective dose reconstruction. Comparatively few studies have been done which have investigated animal teeth for the same purpose. The potential exists for utilizing animal teeth as dosimeters to reconstruct doses received by a species, as well as by humans. Animals investigated in electron paramagnetic resonance studies included cows, rats, mice, dogs, pigs, rhesus monkeys, goats, reindeer, walruses, bison, polar foxes, moose, and polar bears. Much has been determined regarding the characteristics of animal teeth, and overall the use of animal teeth for electron paramagnetic resonance dosimetry appears to be a viable means of estimating external dose. Although much has been learned from animal studies, there remain unanswered questions related to electron paramagnetic resonance dosimetry and the use of animal teeth as electron paramagnetic resonance dosimeters. This article summarizes the findings of animal electron paramagnetic resonance studies and outlines what is still unknown.