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3 Radiation Dose Assessment
Pages 97-142

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From page 97...
... 3.1 BACKGROUND ON DOSE ASSESSMENT AND DOSE RECONSTRUCTION When ionizing radiation interacts with the human body it transfers part or all of its energy to the molecules and cells of body tissues. The response of these tissues to the deposition of energy in terms of physical, chemical, and biological changes is dependent on the amount of energy deposited per unit mass of tissue, or absorbed dose (see Table 3.1)
From page 98...
... , whereas effective dose is the weighted sum of the equivalent doses over all organs and tissues of the body. An additional difference is that different wT values are used in the calculation of effective dose equivalent and effective dose.
From page 99...
... Thus, effective dose and equivalent dose have been used for regulatory 1 As noted in Chapter 2, direct radiation exposure refers to external whole-body radiation exposure from ionizing radiation emitted by radionuclides in the air, soil, sediments, or water bodies as well as radiation from sources within the site boundary. The latter includes radioactive wastes buried or stored onsite as well as N-16 produced in the turbines of boiling water reactors.
From page 100...
... For such studies, absorbed dose is usually estimated for specific organs on an annual basis, expressed as rad/yr. In the context of this discussion, the term dose assessment refers to the estimation of absorbed doses received by individuals as a result of exposure to ionizing radiation.
From page 101...
... . This radiation can be received directly FIGURE 3.1 Pathways for exposure to radiation from effluent releases from nuclear plants and fuel-cycle facilities.
From page 102...
... For radiation protection and epidemiologic studies, the level of averaging of radiation doses has consistently been at the tissue or organ level. Retrospective dose assessments related to effluent releases of radioactive materials into the environment can be classified in two categories: 1.
From page 103...
... 2. Dose assessments made for research purposes, for example, in epidemiologic studies.
From page 104...
... , estimated external radiation doses to even the most exposed individual as a result of plant airborne effluent releases was likely only a fraction of the dose received from ambient natural background radiation. TLD measurements at various locations at some nuclear plants suggest that the direct radiation dose from stored waste onsite and nitrogen-16 gamma rays (see Chapter 2)
From page 105...
... However, doses in the 1970s and 1980s at some nuclear plants were higher, but even these doses were still much lower than doses from natural background radiation. Table 3.2 compares estimates of MEI doses for the early years of reactor operations at selected nuclear plants with estimates for more recent years.
From page 106...
... As indicated in Chapter 2, the releases of carbon-14 are, as of 2010, included in the effluent release reports that are submitted by facility licensees. Table 3.4 provides the estimated carbon-14 releases and corresponding equivalent doses for a sample of reactors that supplied that information in TABLE 3.3 Measured and Calculated Airborne Exposures at Seven Locations near the Millstone Plant Measured Calculated Location Length of Monitoring Period Absorbed Absorbed Distance (km)
From page 107...
... Even though different assumptions were used by the facility operators to estimate both the releases and the equivalent doses, it is clear that carbon-14 is currently a major contributor to the equivalent dose to the MEI from atmospheric effluent releases. Not included in these estimates is the equivalent dose to the MEI from nitrogen-16 and stored wastes, which is, for some reactors, the most important contributor to the total equivalent dose to the MEI.
From page 108...
... . Figure 3.2 shows PNL's collective dose estimates for persons living between 2 and 80 km from selected nuclear plants that have a range of effluent releases.10 As can be seen from the figure, the total collective doses for some plants (e.g., Millstone and Dresden plants)
From page 109...
... Pilgrim LaCross Arkansas Dresden McGuire Trojan Hatch Oconee Big Rock Cooper Arnold Zion Cook N Anna FIGURE 3.2 Collective doses to populations living between 2 and 80 km from selected nuclear plants.
From page 110...
... aFor individuals living between 2 and 80 km of the plant boundary. SOURCE: Population information from Table 1.3 in Chapter 1; other information from NUREG/CR-2850 (PNL-4221)
From page 111...
... Collective Dose Dose (Percent) Tritium 39 28 18 35 Carbon-14a 1 0.4 0 0.1 Manganese-54 0 1 2.8 <0.1 Iron-55 0 0 4 0.5 Iron-59 0 0 1 0.2 Cobalt-58 0 1 1.1 <0.1 Cobalt-60 2 1.0 3 2.3 Zinc-65m 0 4 1.6 <0.1 Krypton-88 8 7 0 0 Strontium-90 1 1 1.4 <0.1 Iodine-131 0 1 0 <0.1 Xenon-133 17 31 0 0 Xenon-135 3 13 0 0 Cesium-134 0 11 28 <0.1 Cesium-137 0 0.3 18 24 No release 0 8 Total number of plants 71 71 Total collective dose 9.6 65 (person-rem)
From page 112...
... Figure 3.4 shows the reported annual collective doses from airborne and waterborne radioactive effluent releases from all operating nuclear plants from 1975 to 1992. In the early years of operations when doses were highest, most of the collective dose was from exposure to airborne effluents.
From page 113...
... If so, the use of annual effluent releases and annual average meteorology to estimate doses would not reflect these spatial variations. This would be particularly true for plants that do not release effluents randomly in time such as PWRs, which release effluents in batches.
From page 114...
... . bitmap 3.3 REPORTED DOSE ESTIMATES AROUND NUCLEAR FUEL-CYCLE FACILITIES As is the case for nuclear plants (Section 3.2)
From page 115...
... . Because of the small populations, the collective doses to populations living within 80 km of these facilities have probably been small relative to collective doses to populations near nuclear plants.
From page 116...
... 3.3.3 Uranium Enrichment Facilities The maximum dose that a member of the public was estimated to have received from reported effluent releases from the Portsmouth enrichment facility in 2009 was 0.94 mrem: 0.024 mrem from airborne radionuclides, 0.037 mrem from radionuclides released to the Scioto River, 0.72 mrem from direct radiation from the depleted uranium cylinder storage yards, and 11 Total effective dose equivalent. This is the sum of the effective dose equivalents from internal and external exposures.
From page 117...
... . Based on estimated 2002 census data, the total committed effective dose equivalent (CEDE)
From page 118...
... This guidance can also be used to estimate equivalent doses to representative individuals in the vicinity of the nuclear plant. For example, a computer program was developed by PNL to estimate doses received via airborne and waterborne pathways by representative individuals living in the vicinity of operating nuclear plants from 1975 through 1988 (Baker, 1996)
From page 119...
... As noted in Chapter 2, these data represent summed quantities typically over periods of weeks to months. The PNL model was used to estimate equivalent doses for representative individuals of population groups living in 160 segments around nuclear plants defined by 22.5-degree radial slices of the 16 compass points (i.e., N, NNE, NE, ENE, E, ESE, SE, SSE, S, SSW, SW, WSW, W, WNW, NW, NNW)
From page 120...
... Consequently, the model would need to be modified to make it useable in a modern epidemiologic study. Needed modifications are discussed below, using as a framework a general form of the calculation of the radiation dose, D, resulting from releases of radioactive materials into the environment (Till and Grogan, 2008)
From page 121...
... However, the underlying computer code would need to be modified to include doses received from direct radiation from onsite sources, from external irradiation from the shoreline of a contaminated water body, and from internal irradiation due to the consumption of irrigated food products where these doses comprise greater than 1 percent of the total dose. 3.4.1.3 Location of Representative Individuals As noted previously, the PNL model estimates doses to representative individuals in each of 160 segments surrounding a nuclear plant.
From page 122...
... However, special consideration would be warranted for red bone marrow or bone surfaces in case they are tissues of interest in an epidemiologic study. 3.1.4.6 Type of Dose The PNL model estimates the committed equivalent dose per year of effluent release for representative individuals resulting from internal radiation.
From page 123...
... As noted in Chapter 2, nuclear plants and fuel-cycle facilities release different types of radionuclides and have different effluent release reporting requirements. 3.4.2.1 Nuclear Plants As indicated in Chapter 2, the effluent releases of specific radionuclides are available on a monthly, quarterly, semiannual, or annual basis for any year since 1975.
From page 124...
... . In the PNL model, atmospheric dilution factors are calculated as averages over 160 segments and also for specific locations near the plant site (site boundary, closest residence, closest garden, and closest pasture)
From page 125...
... Airborne Effluent Releases Air submersion Atmospheric Indoor shielding Dose coefficient (FGR dilution factor and occupancy 12) factors Ground irradiation Atmospheric Indoor shielding Dose coefficient (FGR dilution factor; dry and occupancy 12)
From page 126...
... that differed from one plant to another to obtain annual joint frequency distributions. For the purposes of the epidemiologic study, it seems sufficient for recent years of effluent release to use the annual average atmospheric dilution factors calculated for the appropriate release height(s)
From page 127...
... In the PNL model, the annual average values of the aquatic dilution factors are, whenever possible, taken from the environmental information provided by the licensees; when no information is available, the PNL model provides default values. For the purposes of the epidemiologic study, it also seems sufficient to use annual averages of the aquatic dilution factors.
From page 128...
... are discussed in Appendix I Generally speaking, the factors related to external irradiation appear to be adequate for use in an epidemiologic study, but those related to internal irradiation will have to be updated with data included in the publications of the ICRP-56 series (ICRP, 1990, 1992, 1995a,b)
From page 129...
... . Thus, direct external radiation doses to persons living near nuclear plants due to facility effluents were much less than the doses they received from ambient natural
From page 130...
... Variations over shorter intervals were likely even greater. Because the ambient background doses are so much higher than expected doses from facility effluent releases and vary both with direction and distance, the epidemiologic study will need to consider variations in background radiation not only from facility to facility, but also around each facility.
From page 131...
... 131 RADIATION DOSE ASSESSMENT FIGURE 3.7 Daily variations in background radiation for a site in New Jersey. SOURCE: Beck and Miller (1982)
From page 132...
... bitmap FIGURE 3.9 Variations in background radiation around the Millstone plant for 2009 based on TLD data. Note the relatively higher values near the fence line and variations with distance and direction.
From page 133...
... as well as the large variation in radiation doses that an individual receives from a given medical procedure depending, for example, on that individual's age and what body part is being irradiated. Medical radiation could be a potential confounding factor in an epidemiologic study if individuals who live closer to nuclear facilities are exposed to radiation from medical diagnostic procedures at different rates compared to those who live farther away.
From page 134...
... This could be especially problematic if the epidemiologic study focuses on cancers that have both radiation and chemical etiologies such as bladder cancer and leukemia. It will be important to identify major industrial facilities in the vicinity of nuclear facilities that are examined in the epidemiologic study.
From page 135...
... 3.6 CHARACTERIZING AND COMMUNICATING UNCERTAINTIES The uncertainties in dose estimates for an epidemiologic study are likely to be substantial. These uncertainties arise from uncertainties in source terms (i.e., reported effluent releases; see Chapter 2)
From page 136...
... that require individual dosimetry data, this uncertainty will depend on the ability to determine individual lifestyle behaviors. Considering the complexity and range of uncertainties discussed above, a detailed quantitative analysis of uncertainty in an epidemiologic study is not practical, particularly for an ecologic study.
From page 137...
... This would at least place upper bounds on effluent releases. 3.7 FINDINGS AND RECOMMENDATIONS This chapter provides the committee's assessment of methodological approaches for assessing offsite radiation doses to populations living near nuclear plants and fuel-cycle facilities to support an epidemiologic study.
From page 138...
... to obtain estimates of absorbed doses to the whole body and individual organs result ing from airborne and waterborne effluent releases. This model should be similar in scope and complexity24 to that used by the 24 The committee uses the phase "similar in scope and complexity" to mean that the model should use the same general approach as the PNL model to estimate annual absorbed doses as a function of direction and distance from a facility based on effluent release and meteorological data averaged over daily to quarterly periods.
From page 139...
... 2. Demonstrate the utility of this model for dose reconstruction to support the epidemiologic study designs recommended in Chapter 4 (See Section 4.4 in Chapter 4)
From page 140...
... . Method for obtaining radiation exposure due to a boiling water reactor plume from continuously monitoring ionization chambers.
From page 141...
... . Models and Computer Codes for Evaluating Environmental Radiation Doses.
From page 142...
... . Westinghouse Electric Company LlC Nuclear Fuel, Columbia Plant ALARA Report, Calendar Year 2002.


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