Evaluation of Guidelines for Exposures to Technologically Enhanced Naturally Occurring Radioactive Materials (1999) / Chapter Skim
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11 Issues in Developing Guidances for TENORM
11 Issues in Developing Guidances for TENORM
Pages 218-242
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From page 218... ...
· Specific areas in which the technical approaches to risk assessment of radionuclides developed by EPA differ from the approaches normally used by other organizations and the question of whether the differences have been important in developing guidances for TENORM. · Specific areas in which the differences between EPA guidances for TENORM and those developed by other organizations are based on differences in policies related to risk management, rather than scientific and technical issues.
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From page 219... ...
That conclusion is based on the observations that all organizations that have developed guidance on indoor radon have assumed essentially the same risk related to exposure to radon and its short-lived decay products on the basis of data obtained from studies of underground miners, and that all organizations that have developed guidances for TENORM other than indoor radon have assumed essentially the same risk related to uniform Radiation of the whole body on the basis of data obtained primarily from studies of the Japanese atomic-bomb survivors. Thus, for purposes of health protection of the public, including establishing guidances for acceptable levels of indoor radon and acceptable levels of exposure to TENORM other than indoor radon, all organizations have assumed essentially the same risks related to radiation exposure.
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From page 220... ...
By the time the proposed revision of the federal guidance was issued (EPA 1994d) , the genetic risk was reduced in importance, cancer risks had been estimated from the atomic-bomb survivor data, and the estimated risks were used in conjunction with an assumption about the maximum tolerable risk posed by radiation exposure as a justification for lowering the annual dose limit for individuals to 1 mSv (see chapter 7~.
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From page 221... ...
The white paper includes discussions on similarities and differences in the methods of risk assessment of radionuclides used by EPA and the Nuclear Regulatory Commission. The pr~rnary purpose of this section is to discuss and comment on the differences between the EPA and Nuclear Regulatory Commission approaches to risk assessment of radionuclides, and to discuss the importance of these differences with regard to the development of guidances for TENORM.
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From page 222... ...
EPA's approach described above gives different estimates of risk from the approach used by the Nuclear Regulatory Commission, which is based on the effective dose equivalent (ICRP 1977) , and the current approach of ICRP (1991)
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From page 223... ...
Third, in estimating doses and risks related to exposure to alpha particles, the Nuclear Regulatory Commission uses a radiation quality factor of 20 to convert absorbed dose to dose equivalent for all irradiated organs, on the basis of the ICRP recommendation (ICRP 1991, 1977) of a single radiation quality factor for alpha particles that would apply to any tissue and stochastic biologic end point of concern.
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From page 224... ...
However, for internal exposure, EPA estimates risks posed by chronic lifetime exposure of the public on the basis of age-specific dose rates and agespecif~c cancer risks rather than committed effective dose equivalents for adults and a nominal risk factor, as in the Nuclear Regulatory Commission approach (Eckerman and others 1998; Dunning and others 1984, Sullivan and others 1981; Dunning and others 1980~. Particularly for internal exposure to long-lived radionuclides with long retention times in the body, EPA's approach more properly accounts for the dose received as a function of age at intake and time after intake.
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From page 225... ...
All the factors described in the previous section-the use of organ-specific risks for many organs instead of risks based on the effective dose equivalent and a nominal risk from uniform whole-body irradiation, the use of updated biokinetic models in estimating dose from ingrowth of decay products in the body, the use of organspecific RBEs for alpha particles, and the use of age-specific dose rates from internal exposure in conjunction with age-specific cancer risks-should result in more realistic estimates of risks associated with chronic lifetime exposure. Second, the differences between EPA and Nuclear Regulatory Commission approaches to estimating radiation risks do not always result in substantial differences in estimated risks.
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From page 226... ...
, EPA uses essentially the same nominal risk per unit effective dose for any radionuclide as does ICRP (1991~; but EPA does not take into account the results given by the more sophisticated models that continuous intakes of different radionuclides corresponding to a given annual committed effective dose equivalent for reference adults can correspond to substantially different lifetime risks. Finally, given the differences between EPA and Nuclear Regulatory Commission approaches to risk assessment and the fact that EPA and the Nuclear Regulatory Commission use the same approaches in demonstrating compliance with radiation standards expressed in terms of dose, it is important to appreciate that the simplified approaches to risk assessment developed by ICRP (1991; 1977)
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From page 227... ...
in estimating risk even for purposes of radiation protection. Many of the differences between EPA and Nuclear Regulatory Commission approaches to risk assessment described in this section result from the use by the Nuclear Regulatory Commission, and other federal and state agencies, of the now outdated effective dose equivalent.
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From page 228... ...
Therefore, on the basis of the discussions in the previous two sections, the more rigorous approach to risk assessment would be used by EPA only for investigating the feasibility of any particular guidance for TENORM. However, TENORM other than indoor radon has some unique characteristics among the various controlled sources of public exposure that could encourage a reexamination of the conventional approach to developing an annual dose criterion based on an assumed acceptable risk and ICRP's nominal risk factor.
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From page 229... ...
The extent to which rigorous approaches to estimating risk posed by chronic lifetime exposure are used in developing standards for radionuclides in the environment expressed in terms of dose or some other quantity, such as concentrations in environmental media, partly involves a judgment about the extent to which a standard should correspond to a particular risk related to exposure to any radionuclide of concern. Radiation protection of the public has not been unduly concerned with actual risks corresponding to a particular limit on annual dose as long as compliance with the dose limit and the ALARA objective is achieved.
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From page 230... ...
Two justifications have been given for truncating risk assessments in time (Nuclear Regulatory Commission/EPA 1995~. For some situations, available alternatives for managing future risks might not yield substantial differences in risks beyond some time.
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From page 231... ...
The need for caution is exemplified by the standards for 226Ra noted above. Transfer of the cleanup standards for 226Ra in contaminated soil at uranium mill tailings sites to other exposure situations involving 226Ra might be inappropriate in several respects.
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From page 232... ...
Second, the cleanup standards for 226Ra in contaminated soil at uranium mill tailings sites correspond to an annual dose that is an appreciable fraction of the annual dose limit of 1 mSv (100 mrem) for all controlled sources combined in EPA's proposed federal guidance on radiation protection of the public (EPA 1994d)
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From page 233... ...
indicates that EPA and the Nuclear Regulatory Commission have fundamentally different views about a limit on acceptable risk related to radiation exposure and, therefore, about a limit on acceptable dose that might be included in guidances for TENORM other than indoor radon and for any other controlled sources of exposure. In particular, the white paper indicates that the annual dose limit of 1 mSv (100 mrem)
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From page 234... ...
The effect of vigorous application of the ALARA objective has been that doses to the public achieved by nearly all licensees are only a few percent or less of the dose limit. Therefore, the practical effect of Nuclear Regulatory Cornrnission requirements is that doses from nuclear facilities currently operating under Nuclear Regulatory Commission or Agreement State licenses are limited to levels that EPA would judge acceptable according to its preferred annual dose constraint of 0.15 mSv (15 mrem)
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From page 235... ...
In this case, however, the important difference is that EPA's criterion can be relaxed, whereas the doses allowed by applying the ALARA objective to Nuclear Regulatory Commission licensees are always lower than the Nuclear Regulatory Commission's dose limit. This committee also notes that it is somewhat misleading to label annual doses approaching 1 mSv (100 mrem)
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From page 236... ...
Conditions for restricted release also are specified, and the standards allow for alternative criteria for license termination, provided that the annual effective dose equivalent from all sources combined does not exceed 1 mSv (100 mrem)
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From page 237... ...
First, the Nuclear Regulatory Commission's annual dose constraint of 0.25 mSv (25 mrem) for unrestricted release of contaminated sites does not comply with EPA's lifetime risk objective of 104, which is applied in establishing preliminary remediation goals under CERCLA.
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From page 238... ...
Difference Between Environmental Protection Agency and National Council on Radiation Protection and Measurements Guidances for TENORM Other Than Indoor Radon As discussed in chapter 10, EPA has issued proposed federal guidance on radiation protection of the public that includes an annual dose limit of 1 mSv (100 mrem) for all controlled sources combined, including human-made radionuclides and TENORM other than indoor radon (EPA 1994d)
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From page 239... ...
However, the annual dose limit of 1 mSv (100 mrem) for all controlled sources combined, including human-made radionuclides and TENORM other than indoor radon, in EPA's proposed federal guidance on radiation protection of the public (EPA 1994d)
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From page 240... ...
The issue of the most appropriate way of taking natural background into account in establishing guidances for radiation exposure is particularly important for TENORM other than indoor radon. As indicated by the discussions in the previous section, two approaches could be taken.
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From page 241... ...
This committee assumes that a guidance for TENORM other than indoor radon could be expressed in one of three ways: a limit on acceptable risk, a limit on acceptable dose, or limits on acceptable concentrations of radionuclides in various environmental media. Each has different implications for risk assessment.
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From page 242... ...
However, it could be a considerable challenge to develop a standard expressed in terms of measurable quantities that reasonably could be applied to the variety of exposure situations of potential concern. Such complexity makes a standard expressed in terms of concentrations of radionuclides in the environment less attractive than a dose standard, which is the usual approach.
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