THAM-D - Risk Assessment North 226ABC 08:00 - 11:15
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THAM-D.1
08:00 Continuing Efforts for NORM Regulatory Development and Risk-Informed Decision Making: Results of a Stakeholder Workshop RE McBurney*, Conference of Radiation Control Program Directors, Inc.
Abstract: Since the management of technologically-enhanced naturally occurring radioactive material (TENORM) is not regulated at the federal level as are source, special nuclear, and byproduct materials, the Conference of Radiation Control Program Directors has been involved in developing model state regulations for the material since the mid-1980's. During the 9th International Symposium on Naturally Occurring Radioactive material in September 2019, CRCPD held a workshop entitled "Continuing Efforts for NORM Regulatory Development and Risk-Informed Decision Making." The workshop brought together a panel of speakers that included professionals with experience and involvement in both past and present NORM issues, as well as national and international participants. The workshop goals were to identify priority issues in the regulation of NORM and barriers to the regulatory framework. The results of the workshop were documented and have been useful in establishing a path forward for providing consistent, risk-informed regulatory guidance in the management of NORM.
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THAM-D.2
08:15 ICRP TG114: The “Rs” of Reasonable in Radiation Protection JS Wieder, U.S. Environmental Protection Agency
; NE Martinez*, Clemson University
Abstract: Determining what is “reasonable” is an abstract, somewhat intuitive, concept with many potential answers depending on both the situation and the players. ALARA (as low as reasonably achievable) is embedded within radiation protection practice, but is often misconstrued as “as low as possible.”
ICRP Task Group 114, Reasonableness and Tolerability in the System of Radiological Protection, is taking on the challenge of providing practical advice on how decisions can be undertaken in light of these concepts. As this group continues to review how reasonableness, optimization and tolerability are addressed in existing, planned and emergency radiation exposure situations (along with other hazards), we continue to see optimization as a process of active evaluation, which may be numeric, but is more likely procedural.
This presentation, by members of ICRP TG114, proposes a simple, broadly applicable tool to help radiation protection practitioners reflect on all of the factors that make up “reasonable” before making a decision. The proposed “Rs” of Reasonable represent Relationships (stakeholders, transparency, empathy), Rationale (technical and ethical justifications), and Resources (technology/technique, time, cost).
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THAM-D.3
08:30 AN INVESTIGATION OF MEDICAL COUNTERMEASURE REQUIREMENTS NEEDED TO MEET LIFETIME ASTRONUAT CAREER RADIATION EXPOSURE LIMITS FOR CANCER DEATH CM Werneth*, NASA Langley Research Center
; TC Slaba, NASA Langley Research Center; LC Simonsen, NASA Langley Research Center
Abstract: The space radiation environment consists of ionizing radiation that poses health risks to crew members who embark on a mission to Mars. NASA requires that astronaut career radiation limits for the Risk of Exposure Induced Death (REID) should not exceed 3% at the upper 95% confidence level for cancer mortality. For most missions, this is achieved by passive shielding design concepts and limiting permissible exposure days in space. However, the lifetime career limit is likely to be exceeded for even the shortest round-trip mission scenario to Mars. As such, an alternate approach to risk reduction is sought. A recent study showed that medical countermeasures (MCM) which reduced background cancer mortality rates may be effective in mitigating the REID, where the data employed in the sensitivity analysis were limited to cohort studies of aspirin and warfarin. The present work addresses the general MCM requirements that are needed to meet the lifetime career exposure limits by examining modifications to the background cancer mortality rates, radiation quality factor, and low LET radiation risk models for a plausible Mars mission scenario. These results may be used to help inform decision-makers about potential experimental measurements that facilitate the greatest propensity for MCM risk reduction.
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THAM-D.4
08:45 The Potential Facility-level Risk Index (PFRI) – an assessment tool for radiological security SV Rane*, Purdue University
; JT Harris, Purdue University
Abstract: The 2020 coronavirus (COVID-19) has shown how devastating ill-preparation can be. Similarly, the consequences of a radiological dispersal device (RDD) detonation or nuclear power plant attack would have world-wide implications. Some of the lessons that COVID-19 has taught us about the radiological threat is the urgency of being prepared now, the need to be proactive in planning, and understanding risk. Rather than waiting to respond to a calamity, our research intends to prevent it. The research develops a risk-based methodology to evaluate facility-level radiological security. The methodology is applied to an RDD incident from three radionuclides of concern: Cesium-137, Cobalt-60, and Iridium-192. The results of the research have led to the creation of a potential facility risk index (PFRI) for radiological security. The PFRI is mathematically represented as the exponential product of the maximum expected utility among the threat groups, the sum of geographic vulnerability and cultural vulnerability, and net consequences. The theoretical framework is followed by a (C++) MATLAB based graphical user interface (GUI) to provide the facility licensee decision makers with a fast, facility-based risk assessment apparatus for evaluating potential RDD incidents. The PFRI may be implemented by radiological facility (i.e., healthcare facility) staff to conduct self-assessments and evaluate their PFRI value on the heat map to determine whether an urgent security problem exists and where the greatest weaknesses lie. Lastly, the PFRI methodology is a useful starting point for any healthcare facility risk assessment, and it is a valuable input to facility decision makers considering potential investments in security upgrades.
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THAM-D.6
09:30 Research Reactor Nuclear Safety and Security Risk Analysis with Vulnerability and Consequence Values EM Bragers, Purdue University
; EK Rekeweg, Purdue University; DB White, Purdue University; JT Harris*, Purdue University
Abstract: Nuclear facilities face risks from both safety and security events. While safety concerns may be less for research reactors compared to larger nuclear facilities, they may become more desirable targets to malicious actors due to reduced security measures. Moreover, security scenarios, like sabotage, can cause safety scenarios, thus necessitating the final impact determination of both concurrently. By analyzing two safety and two security scenarios for the PUR-1 research reactor at Purdue University, we identified the probability of effectiveness for the security scenarios and estimated economic and personal consequences for each event. Parameters such as population demographics, local economic measures, meteorological conditions, reactor properties, and radioactive material characteristics were included in the consequence calculation. Parameters contributing to the facility risk were analyzed along with existing vulnerabilities. This work attempts to demonstrate a means of objectively measuring consequence values in order to generate a Probabilistic Facility Risk Index (PFRI) score that can be compared to other facilities.
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THAM-D.7
09:45 Air Exchange Rate Impact on Actinon, Thoron, and Radon Activity Equilibrium Factor and Inhalation Fractional Equilibrium Factor Determination in Vapor Intrusion Risk and Dose Models EA Asano*, Texas A&M University
; F Dolislager, Oak Ridge National Laboratory; S Walker, U.S. Environmental Protection Agency
Abstract: Exposure to the radioactive isotopes of radon are of high concern and, when present in vapor form, may pose a significant risk to humans in an indoor air environment. Screening levels based on an annual target risk and dose limit were determined for the actinon, thoron, and radon decay series for inhalation and submersion in a cloud exposure in a residential and commercial setting. The screening levels are analogous to preliminary remediation goals, where the values are isotope specific. If the concentration of a parent isotope of radon or its progeny is found to exceed the screening level, then further action to ensure cleanup of the contaminant may be necessary. In an indoor air residential and commercial setting, the screening levels will vary based on the air exchange rate present. A computational method in MATLAB was developed to determine the impact of the air exchange rate on the activity equilibrium factor and inhalation fractional equilibrium factor. Both factors are values that reflect equilibrium concentrations of progeny to parent in the air. These factors have direct impact on the preliminary remediation goals and have applications in risk and dose models. The activity equilibrium factors for the actinon, thoron, and radon decay series were ultimately calculated using an ordinary differential equation solver in MATLAB at air exchange rates ranging from zero to nine hundred per hour over a period of two hundred hours at each air exchange rate. The activity equilibrium factors were then used to calculate the inhalation fractional equilibrium factors at each air exchange rate using a deterministic method. As the air exchange rate increases, the inhalation fractional equilibrium factor decreases. This decrease results in less carcinogenic risk, dose, and Working Levels. This work is being incorporated into the Environmental Protection Agency Superfund Program’s Radon Vapor Intrusion Screening Level calculator scheduled for release in 2021.
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THAM-D.8
10:00 Comparison of Cancer Risk Estimates from Internalized Uptake of Environmental Radionuclides A Kalinowski*, Department of Nuclear Engineering, Texas A&M University
; D Pawel, United States Environmental Protection Agency; K Eckerman, Oak Ridge National Laboratory; M Bellamy, Memorial Sloan Kettering Cancer Institute; D Jokisch, Francis Marion University; S Dewji, Department of Nuclear Engineering, Texas A&M University
Abstract: The US Environmental Protection Agency’s (EPA) Radiation Protection Division has utilized modeling of age- and sex-specific dosimetric models to derive concentration limits for radionuclides in the environment. This methodology was described in detail in Federal Guidance Report 13 (FGR 13). The overarching goal is to ensure that doses from the exposure to and intake of these radionuclides result in an acceptable lifetime cancer risk. The FGR 13 methodology assumes a constant environmental concentration to which a reference individual lives out their life. The dose rate to tissues of the body depends on the age-dependent uptake rate and the retention within the body. Risk coefficients for acute and chronic age-specific uptakes using the dose coefficients and BEIR VII risk models in FGR 13 were compared with approaches in computing effective dose in the methodology applied in International Commission on Radiological Protection (ICRP) Publication 103 to discern sensitivity of cancer risk as a function of age of uptake. A comparison of the two methods will be discussed, in addition to a comparison of the magnitude of variation using updated dose coefficients for selected radionuclides.
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THAM-D.9
10:15 Clarifying Some Misconceptions about EPA’s Superfund Approach St Walker*, U.S. Environmental Protection Agency
Abstract: The U.S. Environmental Protection Agency (EPA) Superfund program when selecting cleanup levels for radioactively contamination at sites are generally expressed in terms of risk levels (e.g., 10-4), rather than millirem or millisieverts, as a unit of measure. Although EPA and other US agencies have issued millirem based regulations under other statutory authorities, under CERCLA EPA promulgated a risk rang of 10-4 to 10-6 as a standard of protectiveness for all carcinogens including radionuclides. CERCLA guidance recommends the use of slope factors when estimating cancer risk from radioactive contaminants, rather than converting from millirem. Current slope factors are based on risk coefficients in Federal Guidance Report 13. The Superfund remedial program uses 10-6 as a point of departure and establishes Preliminary Remediation Goals (PRGs) at 1 x 10-6. PRGs not based on other environmental standards known as Applicable or Relevant and Appropriate Requirements (ARARs) are risk-based concentrations, derived from standardized equations combining exposure information assumptions with EPA toxicity data. The policy rationale and technical underpinnings for this risk management approach, is often misunderstood by radiation professionals. This presentation will help clarify some of these misunderstandings by focusing on misstatements about the Superfund approach that the author has encountered from radiation professionals. Often they are citing the wrong EPA documents or portions of documents incorrectly, or not reading sections of the correct Superfund guidance.
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THAM-D.10
10:30 Quantitative evaluation of the conservativeness in the committed dose concept for radiation workers M Sasaki*, Central Research Institute of Electric Power Industry
; T Hattori, Central Research Institute of Electric Power Industry
Abstract: We have developed an approach to quantitative evaluation of the conservativeness in the concept of committed dose from internal exposures for radiation workers from the viewpoint of radiological risk. Committed dose coefficients (Sv/Bq) of selected radionuclides from ICRP Publications were reproduced to obtain annual effective doses rate (Sv/Bq/y) that would be actually delivered each year. Then, by assuming that a worker at the age of 18 years would continuously take in the same amount of radionuclides each year until the age of 64 years (i.e., 47 years), unconditional death probability rate (1/y) was calculated and compared with those indicated in the ICRP Publication 60 where setting the annual dose limit was developed. In addition to the previous results for Sr-90, Cs-137, and Pu-239, conservativeness for important radionuclides for radioactive waste management, such as Fe-59, Tc-99, and I-129, were also estimated quantitatively.
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THAM-D.11
10:45 RELATIONSHIP BETWEEN TERRESTRIAL BACKGROUND AND REMEDIAL CRITERIA FOR NATURALLY OCCURRING RADIOACTIVE MATERIAL IN THE UNITED STATES SH Brown*, SHB Inc
Abstract: In the United States (US), Federal and State agencies have established radiological public exposure limits and remedial action (“clean up”) criteria for naturally occurring radionuclides (NORM - primarily for uranium and thorium series radionuclides). Often, these criteria are intended to control human exposure to what is referred to in the US as “Technologically Enhanced Naturally Occurring Radioactive Material (TENORM). This can be any naturally occurring radioactive material for which the potential for human exposure has been enhanced due to anthropogenic (human activities), e.g., removal from its “place in nature”, and/or processed in some way resulting in concentration.
In some cases, the values of these regulatory criteria can be similar to, or even less than those levels of exposure and those concentrations of NORM that exists in nature independent of any previous human activity. The potential variability of NORM radionuclides in the soil and rocks can be significant, even over relatively short distances or depths due to factors such as geology, hydrology and geochemistry. Given this, it is important to recognize that defining “the radiation background” for purposes of establishing and/or comparing remedial action criteria and/or exposure limits requires recognition of the specificity at the location(s) of interest, not in other geological and/or mineralogical regimes several miles away.
The purpose of this paper is to demonstrate this variability for comparison to exposure levels and concentrations being defined in the US as levels above which require regulatory control and / or above which are being defined as an “unacceptable risk”. The primary background exposure component of specific interest here is the annual dose contribution from terrestrial radiation exposure, i.e., from uranium and thorium series radionuclides in the ground, excluding radon inhalation.
The exposure sources being controlled by some US regulatory limits are primarily associated with the primordial radionuclides in soil. The average annual terrestrial component of background can vary by upwards of a few tenths of a mSv across the US that can be several times higher than the applicable exposure limits. This can result in “unacceptable risk” or “remedial action” concentration criteria statistically equivalent to or less than the background concentrations of these same primordial nuclides. The statistical and analytical uncertainties of distinguishing naturally occurring radionuclides (i.e., NORM) from those resulting from anthropogenic (human caused) activities (i.e., TENORM) can be quite challenging and in some cases may be technically impossible. Consideration must be given to the relationship of the amount of actual total risk avoidance achieved if any, relative to the traditional health and safety risks of construction and associated construction and waste management costs for remedial activities, so that a practical and scientifically based approach for development of these criteria can be achieved.
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