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Federal Register / Vol. 86, No. 156 / Tuesday, August 17, 2021 / Proposed Rules
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the establishment of a public education system to dispel fears of low-level radiation is not a mission or responsibility of the NRC and is beyond the NRCs statutory authority. The NRC
supports communication efforts to accurately convey the radiological risks associated with any given regulated activity. The NRC, through its communication efforts, engages stakeholders in order to foster transparency and communication between the NRC and the public e.g., through public meetings, public comment on NRC rulemakings and guidance development, the NRCs public website, and the NRCs use of social media.
Comment: The NRC received several comments requesting that the NRC
conduct research on topics raised by the petition.
Response: The NRC disagrees with these comments. The comments requesting that the NRC engage in additional research is outside the scope of the subject petitions. Other Federal agencies are charged with conducting basic radiation research, such as the Department of Energy and the National Institutes of Health.
Comments Supporting the Petitions Assertions That the LNT Model Lacks an Adequate Scientific Basis Comment: Several commenters questioned the scientific basis of the LNT model and asserted that it should no longer be the premise of the NRCs radiological protection regulations.
Response: The NRC disagrees with these comments. The NRCs goal as a regulatory agency is to protect both the public and occupational workers from the radiological hazards associated with NRC-licensed material, activities, and facilities. The NRC uses the LNT model to establish radiation protection measures that quantify radiation exposure and set regulatory limits. The premise of the LNT model is that the long-term biological damage caused by ionizing radiation i.e., risk of cancer induction or adverse hereditary effects is directly proportional to the dose received by the human receptor. The LNT model provides for a conservative, comprehensive radiation protection scheme that protects individuals in all population categories male, female, adult, child, and infant and exposure ranges by reducing the risk from lowdose radiation exposure.
As described earlier in this document, the consensus among various domestic and international authoritative scientific advisory bodies and the three Federal agencies that submitted comments NCI, NIOSH, and EPA is that the LNT model
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should remain the basis for the NRCs radiological protection regulations.
Similarly, the ACMUI recommends that the NRC continue to use the LNT model.
Based upon the external organizations recommendations, the ACMUIs recommendation, and its own professional and technical judgment, the NRC has determined that the LNT
model continues to provide a sound basis for minimizing the risk of unnecessary radiation exposure to both members of the public and occupational workers.
Comment: One commenter noted that multiplying the LNT-based risk coefficient by a population dose to derive a hypothetical number of cancer deaths in no way shows, proves, or demonstrates that anyone is getting cancer.
Response: The NRC disagrees with this comment. The petitions for rulemaking request that the NRC amend 10 CFR part 20 to discontinue use of the LNT model as the primary scientific basis for the agencys radiation protection standards. The NRC does not use the LNT model for deterministic mortality projections.
Comment: One commenter noted that the LNT model is flawed, because it lacks timescale modeling to account for the differences between getting a large dose over a long period of time as opposed to a large dose in a short period of time.
Response: The NRC disagrees with this comment. The LNT model, as applied by the NRC in its licensing and regulatory decisions, effectively addresses the potential health impacts of any given dose received either acutely or chronically.
Human epidemiologic studies have established that there is an increased incidence of certain cancers associated with radiation exposure at high doses and high dose rates acute exposure.
The principal source of information for risk estimation is the Japanese survivors of the atomic bombing of Hiroshima and Nagasaki in 1945, who were exposed to a range of doses at a high dose rate.100
The NCRP defines high dose rate as a dose rate above which recovery and repair processes are unable to ameliorate the radiation damage.101
Both the ICRP and NCRP estimate that the risk of death from radiation-induced cancer resulting from an acute exposure is 10 102 per Sv for a population of all ages.102 However, experimental 100 NAS

BEIR VII, at 6.
Report No. 116, at 60.
102 ICRP, 1990 Recommendation of the International Commission on Radiological Protection, Pub. No. 60 1991, at 22; NCRP Report No. 116, at 29.
101 NCRP

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results in animals and other biological systems suggest that cancer induction from acute exposures at low doses and involving low dose rates should be less than that observed after high doses involving high dose rates.103
If the radiation dose is received chronically i.e., over a long period of time, the biologic response differs because much of the radiation damage is effectively and efficiently repaired.104
To account for this difference in response to chronic low dose and low dose rate radiation exposure as compared to high dose and high dose rate radiation exposure, the ICRP and NCRP recommend, and the NRC has adopted, adjusting the risk of death from radiation exposure using a DDREF of two.105 The DDREF is assumed to apply whenever the absorbed dose is less than 200 mSv 20 rem and the dose rate is less than 100 mSv 10 rad per hour.106
Consequently, the risk coefficient for members of the public pertaining to low dose and low dose rate radiation exposure is 5 102 per Sv. This risk coefficient is further reduced to 4 102
per Sv for occupational workers because this population excludes both the very young and elderly who may be slightly more sensitive to radiation-induced carcinogenesis.107 The risks of radiation exposure to occupational workers are described further in Regulatory Guide RG 8.29, Instruction Concerning Risks from Occupational Radiation Exposure, Revision 1 1996.
Although the appropriate value of the DDREF may depend on the specific low or very low dose scenario,108 the use of a DDREF, particularly one with a high value, does not mean that there are no harmful health effects from low and very low doses of radiation. The use of a DDREF also does not demonstrate the presence of a threshold below which no permanent harmful effects will occur.
The NRC staff concludes that the use of 103 ICRP

Pub. No. 60, at 111.
Non-stochastic effects of irradiation, Report to the General Assembly, ANNEX J 1982 at 575.
105 ICRP Pub. No. 103, at 53; ICRP Pub. No. 60, at 18; NCRP Report No. 116, at 29. Although the NRC has not formally adopted a DDREF in regulation, it has relied upon a DDREF in computer modeling. E.g., NUREG2161, Consequence Study of a Beyond-Design-Basis Earthquake Affecting the Spent Fuel Pool for a U.S. Mark I Boiling Water Reactor, September 2014 at 195 incorporating DDREF into computer modeling for offsite consequences of a postulated spent fuel pool accident.
106 ICRP Pub. No. 60, at 19; NCRP Report No. 116, at 60.
107 ICRP Pub. No. 60, at 22; NCRP Report No. 116, at 29.
108 For example, a DDREF value of 1 no dose and dose rate effect is used for certain tissues such as the thyroid and a higher value e.g., a 2 or a 3 is used for other, less radio-sensitive tissues.
104 UNSCEAR,
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