Exposure limits radionuclides

Deterministic responses from exposure to hazardous chemicals generally are of concern in health protection of the public because many of the exposure limits derived from the assumed thresholds and the applied safety and uncertainty factors fall within the range of potential routine exposures. However, the possibility that the large safety and uncertainty factors normally used in setting exposure limits are quite conservative (pessimistic) could be taken into account in developing a risk-based waste classification system. Deterministic responses from exposure to radionuclides should not be of concern in health protection of the public or in classifying waste, because the dose limits intended to prevent deterministic responses are substantially higher than the dose limit intended to limit the occurrence of stochastic responses. 

For the purpose of developing a risk-based hazardous waste classification system, prevention of deterministic responses should be of concern only for hazardous chemicals, but not for radionuclides. Deterministic responses from exposure to radionuclides can be ignored because radiation dose limits for the public intended to limit the occurrence of stochastic responses are sufficiently low that the doses in any organ or tissue would be well below the thresholds for deterministic responses (see Section 3.2.2.1). 

Risk Index for Multiple Substances That Cause Deterministic Responses. The risk index for mixtures of substances that cause deterministic responses should be expressed in terms of dose, rather than risk, because risk is not proportional to dose and the goal of risk management is to limit doses to less than the threshold in the dose-response relationship (see discussion of Equation 6.2 in Section 6.3). As noted previously, deterministic responses from exposure to radionuclides should not be of concern in classifying waste, in which case only the risk index for chemicals that induce deterministic responses needs to be considered. 

Safety and uncertainty factors used in establishing exposure limits that are intended to prevent deterministic responses normally much larger for hazardous chemicals that induce deterministic effects than for radionuclides ... 

Radionuclide Exposure of the Embryo/Fetus (1998) Recommended Screening Limits for Contaminated Surface Soil and Review of Factors Relevant to Site-Specific Studies (1999) Biological Effects and Exposure Limits for Hot Particles (1999) Scientific Basis for Evaluating the Risks to Populations from Space Applications of Plutonium (2001)... 

Some aspects of conventional quality assurance discussed in Chapter 11 cannot be applied to screening processes that require data reporting soon after sample receipt. Nevertheless, statements based on measuring radionuclides—notably their concentrations relative to exposure limits or their absence—must be carefully checked in emergencies because of their impact on efforts for protecting humans and area control and remediation. 

The RS shall limit radionuclide release from the core so that exposure to personnel shall be <10 percent of limits specified in 10CFR20 (Applies to normal operation and AOOs only). 

Exposure limit the concentration of a snbstance under which it is believed that nearly all workers may be repeatedly exposed day after day without adverse effects Exposure pathway a route by which a radionuclide or other toxic material can enter the body Exposure rate a measure of the ionization produced in air by x-rays or gamma rays per unit of time... 

Based on the negligible annual dose to individuals of 10 pSv and assumed scenarios for unrestricted disposal of waste, IAEA has developed recommendations on exemption levels for radionuclides in solid waste (IAEA, 1995) the recommended exempt concentrations have values in the range of about 0.1 to 104 Bq g 1 depending on the radionuclide. IAEA also has issued recommendations on total activities and activity concentrations of radionuclides that could be exempted from any requirements for notification, registration, or licensing of sources or practices, based on the same exemption principles and assumed scenarios for exposure of the public (IAEA, 1996). The recommended exemption levels for naturally occurring radionuclides are limited to their incorporation in consumer products, use as a radioactive source, or use for their elemental properties. 

Application of NCRP Recommendations to Waste Classification. NCRP s recommendations on dose limits and a negligible dose for individual members of the public, and their associated cancer risks, could be used in developing a risk-based waste classification system. Specifically, the dose limits applicable to all man-made sources of exposure combined could be used in establishing concentration limits of radionuclides or hazardous chemicals in dedicated hazardous waste disposal facilities based on assumed scenarios for exposure of the public. Similarly, the negligible individual dose could be used in establishing concentration limits of radionuclides in disposal facilities for nonhazardous waste. These applications are discussed in Sections 6.2 and 6.3 where NCRP s recommendations on risk-based waste classification are presented. 

In developing a risk-based waste classification system, the primary emphasis would be on risk management, rather than estimation of risk for actual exposure situations. However, differences in the state of knowledge of the carcinogenicity of ionizing radiation and chemicals could be taken into account in establishing limits on allowable doses (hypothetical risks) for radionuclides and chemicals to be used in classifying waste. 

Classification Using Pre-Established Limiting Concentrations and Enhanced Access. The same process as in the previous calculation was used to screen this example waste under conditions where intruder access to the waste would be enhanced. For example, if the cover for the waste is less than 2 m, it would be appropriate to consider that an intruder would remove sufficient cover material to expose the waste. The maximum allowable concentrations of selected radionuclides for this scenario calculated using the RESRAD code are listed in Table 7.3. The analysis assumes that the intruder is exposed via external exposure, ingestion, and inhalation for a period of 1,000 h. Using the sum of the ratios of the radionuclide concentrations in the waste to the maximum allowable concentrations as a... 

The purpose of the MCLs for radioactivity (radionuclides) is to limit human exposure. Some waters in contact with radioactive geologic strata (e.g., certain shales) are known to possess radioactivity. Since radioactivity in organisms is cumulative, monitoring should be carried out. 

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