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Federal Register / Vol. 86, No. 156 / Tuesday, August 17, 2021 / Proposed Rules protection requirements relate to stochastic and nonstochastic effects.
Stochastic risks or effects from exposure to radiation are primarily the long-term potential for cancer induction and adverse hereditary effects, while deterministic or nonstochastic risks or effects are those that can be directly correlated with exposure to high or relatively high doses of radiation, such as the formation of cataracts.12 The NRCs second assumption was that the severity of a stochastic effect is independent of, or not related to, the amount of radiation dose received.13
The NRCs third assumption was that there is an apparent threshold; i.e., a dose level below which the nonstochastic effect is unlikely to occur. 14 Therefore, the LNT model only applies to stochastic effects.
In the 1991 final rule, the NRC stated that these assumptions are necessary because it is generally impossible to determine whether or not there are any increases in the incidence of disease at very low doses and low dose rates, particularly in the range of doses to members of the general public resulting from NRC-licensed activities. 15 The NRC further noted that there is considerable uncertainty in the magnitude of the risk at low doses and low dose rates. 16 The NRC concluded:
In the absence of convincing evidence that there is a dose threshold or that low levels of radiation are beneficial, the Commission believes that the assumptions regarding a linear nonthreshold dose-effect model for cancers and genetic effects and the existence of thresholds only for certain nonstochastic effects remain appropriate for formulating radiation protection standards and planning radiation protection programs.17

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Thus, the NRC, as a regulator statutorily charged under the AEA 18
with protecting the public from radiological harm, determined in 1991
that it was prudent to assume the validity of the LNT model because of the considerable uncertainty with respect to the effect of low doses of 12 The NRC defines the term stochastic effects as meaning health effects that occur randomly and for which the probability of the effect occurring, rather than its severity, is assumed to be a linear function of dose without threshold. Hereditary effects and cancer incidence are examples of stochastic effects. 20.1003. The NRC defines the term nonstochastic effects as meaning health effects, the severity of which varies with the dose and for which a threshold is believed to exist.
Radiation-induced cataract formation is an example of a nonstochastic effect also called a deterministic effect. Id.
13 56 FR 23360.
14 Id.
15 Id.
16 Id.
17 Id., at 2336061.
18 42 U.S.C. 2011 et seq.

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radiation. The NRCs 1991 final rule was premised, to a large extent, upon the recommendations of ICRP Publication 26, Recommendations of the International Commission on Radiological Protection 1977, several of which, in turn, were premised upon the LNT model.19 The 1991 final rule also referenced the government-wide Federal Radiation Protection Guidance for Occupational Exposure, signed by President Reagan in 1987, which was similarly premised upon the ICRP
Publication 26 recommendations.20
The NRCs position remains unchanged from 1991. Convincing evidence has not yet demonstrated the existence of a threshold below which there would be no stochastic effects from exposure to low radiation doses.
As such, the NRCs view is that the LNT
model continues to provide a sound basis for a conservative radiation protection regulatory framework that protects both the public and occupational workers.
Despite the various studies cited by the petitioners, uncertainty and lack of consensus persists in the scientific community about the health effects of low doses of radiation. For example, the Health Physics Society HPS has stated that health risks of radiation exposure can only be estimated with a reasonable degree of scientific certainty at radiation levels that are orders of magnitude greater than limits established by regulation for protection of the public. 21 The HPS has further stated that radiation protection literature is filled with differing views as to the 19 56 FR at 23360. In its Publication 26, the ICRP
states for radiation protection purposes it is necessary to make certain simplifying assumptions.
One such basic assumption underlying the Commissions recommendations is that, regarding stochastic effects, there is, within the range of exposure conditions usually encountered in radiation work, a linear relationship without threshold between dose and the probability of an effect. ICRP Pub. No. 26.
20 56 FR at 23360. The Federal Radiation Protection Guidance for Occupational Exposure concerned the protection of workers from ionizing radiation and was published in the Federal Register on January 27, 1987 52 FR 2822. The guidance was prepared by the Environmental Protection Agency, the NRC, and several other Federal agencies having an agency program or function that involved the use of radioactive material. The guidance stated we have considered these ICRP
recommendations, among others, and believe that it is appropriate to adopt the general features of the ICRP approach in radiation protection guidance to Federal agencies for occupational exposure; and based on extensive but incomplete scientific evidence, it is prudent to assume that at low levels of exposure the risk of incurring either cancer or hereditary effects is linearly related to the dose received in the relevant tissue. 52 FR at 2824.
21 Position Statement of the Health Physics Society HPS, PS0082, Uncertainty in Risk Assessment, Adopted July 1993, Revised April 1995, February 2013.

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shape of the radiation dose-response curve at low doses and dose rates. 22
According to HPS, some data support a linear no-threshold model, whereas other data support models that predict lower estimates of risk and perhaps even a threshold below which no detectable radiation health risk exists. 23
Although there are studies and other scholarly papers that support the petitioners assertions, there are also studies and findings that support the continued use of the LNT model, including those by national and international authoritative scientific advisory bodies. Those authoritative scientific advisory bodies that have a specialty in the subject matter area of radiation protection include, domestically, the federally chartered National Academy of Sciences NAS 24
and NCRP,25 and, internationally, the ICRP and the International Atomic Energy Agency IAEA. All four of these bodies support the continued use of the LNT model. It has been the longstanding practice of the NRC to generally place significant weight on the recommendations of these authoritative scientific advisory bodies.26
National Authoritative Scientific Advisory Bodies Favoring Continued Use of LNT
In 2006, the NAS published its Biological Effects of Ionizing Radiation BEIR VII report, Health Risks from Exposure to Low Levels of Ionizing Radiation, the seventh in a series of reports that concern the health effects from low doses of radiation, and by extension, the appropriateness of the LNT model.27 The report was prepared by the Committee to Assess Health Risks from Exposure to Low Levels of Ionizing 22 HPS

PS0082 at 2.

23 Id.
24 The NAS is a private, non-profit society of distinguished scholars. Established by an Act of Congress . . . the NAS is charged with providing independent, objective advice to the nation on matters related to science and technology. Scientists are elected by their peers to membership in the NAS for outstanding contributions to research.
http www.nasonline.org/about-nas/mission/.
25 The NCRP is a private, non-profit corporation whose mission is to formulate and widely disseminate information, guidance and recommendations on radiation protection and measurements which represent the consensus of leading scientific thinking. http ncrponline.org/
about/mission/.
26 E.g., 56 FR at 23360.
27 NAS, Health Risks from Exposure to Low Levels of Ionizing Radiation, BEIR VIIPhase 2
2006 NAS BEIR VII. The BEIR VII report may be viewed online at https www.nap.edu/catalog/
11340/health-risks-from-exposure-to-low-levels-ofionizing-radiation. The NRC was one of several Federal agencies that provided funding to NAS for the BEIR VII study.

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