Manual Dose Control at Nuclear Power Plants

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by Winfried Koelzer

In its review of available data, the committee noted that, as was the case for airborne effluent releases, the availability and completeness of the data varied significantly from plant to plant, particularly during the early years of operation. Also, the quality of the reported data was likely much poorer in the early years of operation prior to implementation of improved QA procedures. The committee evaluated the quality and availability of liquid effluent release data for a few selected plants and years see the discussion in Section 2.

The committee judges that if release data are available, they are likely to be sufficiently accurate to develop credible dose estimates.

Nuclear reactor

The most important uncertainties in terms of data sufficiency involve liquid effluent releases, particularly the determination of the dispersion of liquid effluents in receiving waters, the evaluation of the contamination of sediments, and the use of the contaminated water for human purposes e. Although there are no specific regulatory requirements for licensees to conduct routine onsite environmental surveys and monitoring for potential abnormal spills and leaks of radioactive liquids, regulations do require that licensees keep records of information important to the safe and effective decommissioning of their plants.

Because the decommissioning of a nuclear plant requires licensees to clean up radioactive spills and leaks at the site, facility records include information on known spills or other unusual occurrences involving the spread of contamination that might require action as part of any decommissioning activities. These records can be limited to instances where significant contamination remains after procedures to remediate an uncontrolled liquid release, or when there is reasonable likelihood that contamination may have spread to inaccessible areas.

They also include routine liquid releases initially prepared and monitored in accordance with regulatory guidance, but which were discharged to an unanalyzed environmental pathway as a result of degraded radioactive waste equipment or piping. Many of the uncontrolled liquid release events documented in Table 2. In the offsite environment, groundwater monitoring is required only if groundwater sources are likely to be impacted by the operation of the nuclear plant. Consequently, there are no regulatory requirements for the regular monitoring of groundwater for the purpose of detecting inadvertent radioactive contamination and its fate and transport either on- or offsite.

As a result of lack of historical groundwater monitoring data, estimation of public dose impacts arising from uncontrolled liquid releases at many sites has required licensees to retroactively undertake the following activities:. Conduct additional radionuclide analyses to define the actual source-term radionuclides and their quantities. Perform supplemental bounding dose calculations to back-calculate potential public health impacts associated with releases. The Task Force did not find any instances where the available data indicated that the near-term health of the public was impacted by uncontrolled liquid releases to the environment USNRC, , p.

For many of the identified sites, the lack of a public dose impact resulted from the radioactive contamination remaining within owner controlled areas. However, several of the reviewed abnormal release event scenarios did, or potentially could, impact ground-water sources relative to established EPA drinking water standards. However, if this finding is correct, there is no obvious scientific advantage 16 to including these data as part of any Phase 2 dosimetry study.

A complete understanding of the dose impacts to the public arising from uncontrolled liquid release events would require detailed knowledge of the liquid source terms at the time of release as well as the distribution of released radionuclide concentrations in the environment through time; the latter would require a comprehensive spatial and temporal understanding of the environmental parameters influencing the fate and transport of the released liquid s.

There is considerable uncertainty associated with source terms, subsurface environmental conditions, and subsurface fate and transport behavior at most nuclear plant sites where uncontrolled liquid releases have occurred. The same is true at industrial sites where hazardous chemicals have inadvertently been released to groundwater. Indeed, it is notoriously difficult to recreate distributions of released subsurface contaminants over time and, hence, difficult to estimate the risks such contaminants have posed, or continue to pose, to public health.

The quality and completeness of available data on uncontrolled liquid releases at nuclear plants differs from site to site but, in all cases, uncertainty exists in how these liquids have migrated over time and, thus, the exposure pathways and possible historic doses associated with these releases.

As a result of groundwater contamination associated with uncontrolled liquid releases, the nuclear industry took action in to implement a voluntary Groundwater Protection Initiative GPI Yhip et al. In January , the NEI also issued guidelines for the management of buried pipe integrity NEI, ; these guidelines are intended to provide proactive assessment and management of buried piping systems at plants to reduce possibilities of future inadvertent radioactive liquid releases.

Both steps have potential to provide future data that might better inform dose impacts to the public living in the vicinity of a nuclear power plant, depending on the quantity and quality of the data being gathered. Unlike nuclear plants, it is difficult to make general statements about airborne effluent releases from front-end nuclear fuel-cycle facilities, beyond the fact that the majority of releases involve uranium and uranium progeny with lesser amounts of other radionuclides see Appendix E.

Four examples of recent effluent release data for front-end nuclear fuel-cycle facilities are shown in Tables 2. A key take-away message from an examination of Tables 2.

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The reported releases shown in the table are for normal operations only; they do not include unplanned releases. As for any operating industrial facility, significant unplanned releases from fuel-cycle facilities as well from nuclear plants could have large impacts on doses to populations. Moreover, the toxicological risks of uranium releases in addition to the radiation risks also need to be taken into account in any epidemiologic study.

With one exception, fuel-cycle facility licensees are required to report their effluent releases to the USNRC or to agreement-state regulators 20 on a semiannual basis. The exception is for licensees of gaseous diffusion plants e. Prior to , gaseous diffusion plant licensees were required to report their effluent releases on a quarterly basis.

From onward, licensees are only required to report their effluent releases when they renew their facility operating licenses. Consequently, it will be necessary to obtain this information for each facility, either through ADAMS or from plant licensees directly, for use in an epidemiologic study. Given the range of facility types, the fact that some facilities were operating as far back as the s as part of the U.

Department of Energy , and the fact that reporting requirements have varied over the years, the availability of effluent release data prior to the mid s when the USNRC assumed regulatory responsibility for many of these plants is unclear. The committee contacted the licensee for the Nuclear Fuel Services NFS facility in Erwin, Tennessee, to determine whether records of effluent releases could be made available.

The NFS plant was selected because it has a long operating history it initiated operations in and has nearby residents who are concerned about effluent releases from the plant. Crowley, February 15, :. The committee judges that if release data are available, they are likely to be adequate for estimating doses for a Phase 2 epidemiologic study see Chapter 3. The licensee reports provide effluent data for individual radionuclides for both air emissions and liquid effluents at each point of release.

The committee was not able to assess the availability and quality of data for early years of plant operations when releases were highest. However, as was the case for nuclear power plants, the quality of effluent release data in recent years is likely much better than for the early years of operation due to more stringent QA requirements as well as stricter requirements to ensure releases and doses meet regulatory requirements. Nuclear plants and fuel-cycle facilities are required to have Radiological Environmental Monitoring Programs REMPs to monitor radioactivity in the environment around their sites.

This program is described in Appendix H.

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The potential usefulness of environmental monitoring data for this purpose is discussed in this section. It is important to note that REMPs at nuclear facilities are not intended to provide a comprehensive assessment of radionuclide distributions and concentrations in the environment surrounding the facilities.

Instead, their purpose is to demonstrate that facility operations are in compliance with regulations.


Epidemiological studies of nuclear power plants

Monitoring therefore focuses on sampling of environmental media that might serve as pathways for radiation exposure to humans, based on effluent release pathways and the local site characteristics. The media of interest are air, water, and foodstuffs.

Pathways for exposure are internal and external radiation. The following sections provide examples of environmental monitoring data for nuclear plants. Similar kinds of data are generated for monitoring around fuel-cycle facilities but are not presented in this chapter for the sake of brevity. For environmental pathways associated with airborne releases, monitoring usually involves air sampling and TLD 22 measurements at various locations in the vicinity of the plant, in addition to the monitoring of foodstuffs see Section 2. Typically, air sampling measurements are made at a minimum of five stations: three stations near the plant boundary in the direction of prevailing winds i.

Several types of analyses are carried out on the air samples: Radioio-dine is measured weekly, and gross beta activity of particulates captured on filters is also measured weekly.

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  4. Analyses to identify alpha- and beta-emitting radionuclides are made quarterly on composite samples. Typically, radionuclide concentrations measured in air samples at downwind stations are comparable with those at the control station. That is, normal operations of a plant do not result in measurable radionuclide concentrations in air, even though the measurement techniques are quite sensitive and can identify occurrences of releases at distance e.

    Measurements of gross beta and iodine activity in air samples at the Fermi plant located in Michigan from to The measurements are sensitive enough to detect air emissions from Chinese nuclear weapons testing in the early s and the Chernobyl more Measurements of direct radiation exposure using TLDs are discussed in detail in Section 2. These measurements are generally not sensitive enough to detect increases above background levels except at locations close to plant boundaries.

    Examples of environmental monitoring data collected at the North Anna located in Virginia and Dresden plants are shown in Tables 2.

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    The data in these tables further illustrate that, for the s as well as in recent years, environmental monitoring programs did not detect radioactive materials above control or background levels at these plants. Results of Environmental Monitoring at the Dresden Plant for For environmental pathways associated with liquid effluent releases, monitoring usually involves sampling of surface water, groundwater, and drinking water in locations near the plant, as well as shoreline sediments from existing or potential recreational facilities see Appendix G.

    Surface and groundwater samples are analyzed for gamma-emitting isotopes and tritium; drinking water samples are analyzed for gross beta, gammaemitting isotopes, tritium, and in some cases iodine; and sediments are analyzed for gamma-emitting isotopes. View in own window. Reports were selected from a recent monitoring period, namely , and an earlier monitoring period, namely The committee observed that the spatial distribution of monitoring stations for surface water, groundwater, well water, and sediments at these plants were not sufficient to provide a spatial map of environmental radioactivity resulting from liquid effluent releases.

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    This is not surprising given that the goal of the REMP is to obtain measurements to demonstrate regulatory compliance, not to obtain measurements for making radiation dose estimates. The most frequently detected radiological contaminant in water samples is tritium; see, for example, the measurements around the North Anna plant in Figure 2.

    Variations in tritium concentrations at a surface water monitoring station in the vicinity of the North Anna plant from to Many of the radiological concentration measurements collected under REMP yield values below detection levels. All sampling locations are located within 3 km of the site. Radionuclide concentrations were below detection limits in the vast majority of cases. Tritium was detected in surface and groundwater samples but at levels well below those established by USEPA for drinking water.

    Monthly composites of surface water samples revealed gross beta concentrations that are similar at indicator and control locations. Cesium was detected in sediment samples and is likely due to fallout from above-ground nuclear weapons testing. Environmental Monitoring Data for the Dresden Plant for Dresden has experienced a number of leaks over its year-plus operating history from underground lines and spills from above-ground systems containing radioactive water. The program includes 39 groundwater monitoring wells within the protected area, 26 wells outside the protected area, and 6 surface water sampling points at five different canals and one cooling pond within the controlled area.