Department of EnergyOffice of Worker Protection Programs and Hazards ManagementRadiological Control Technical PositionRCTP 95-05Technology Shortfalls and Dose Determinations for Radioactive Material IntakesIssue:The detection capability of bioassay techniques for certain isotopes approaches, and may in some cases, be greater than the derived investigation level. In situations where the derived investigation level is less than the bioassay detection capabilities, a technology shortfall occurs. Internal dose determinations in these situations can be difficult.Introduction:Title 10, Code of Federal Regulations, Part 835 (10 CFR 835), "Occupational Radiation Protection," contains requirements for internal dose evaluation programs. 10 CFR 835.402(d) requires that internal dose evaluation programs be adequate to demonstrate compliance with the dose limits in 10 CFR 835.202.The "Department of Energy (DOE) Radiological Control Manual" (RadCon Manual), DOE/EH-0256T, contains additional requirements for internal dose evaluation programs. Article 522.3 requires that routine bioassay monitoring methods and frequencies be established for personnel who are likely to receive intakes resulting in a committed effective dose equivalent (CEDE) greater than 100 millirem (mrem). Discussion:Bioassay10 CFR 835.202, "Occupational Exposure Limits for General Employees," and RadCon Manual Article 213, "Radiological Worker Dose Limits," provide the annual occupational exposure limits for general employees. Section 835.202 and table 2-1 of the RadCon Manual contain two annual occupational exposure limits that are pertinent to intakes of radioactive material: total effective dose equivalent (TEDE) of 5 rems (10 CFR 835.202(a)(1)) and total organ dose equivalent of 50 rems (10 CFR 835.202(a)(2)). TEDE is the sum of the CEDE from internal intakes and the effective dose equivalent from external exposures. Total organ dose equivalent is the sum of the deep dose equivalent from external exposures and the committed dose equivalent to any organ or tissue other than the lens of the eye from internal intakes.In the "Internal Dosimetry Program Implementation Guide," G-10 CFR 835/C1, an investigation level of 0.1 rem (0.001 Sv) CEDE from intakes occurring in a year is recommended for general employees. Investigation levels for declared pregnant workers, minors, and members of the public visiting a DOE site or facility should be evaluated on a facility specific basis. The implementation guide (IG) further recommends that internal dosimetry programs should establish derived investigation levels (DILs) for each bioassay method applied for the analysis of all radionuclides to which workers are likely to be exposed and document the derivation of such DILs in the internal dosimetry technical basis document. The Department recognizes the DILs for reasonable and practical routine bioassay programs may be significantly less than the detection capability for certain radionuclides such as plutonium. By definition, a technology shortfall exists when the bioassay program's DIL is less than the detection capability of the routine monitoring method. A technology shortfall occurs when a performance objective (expressed as a DIL) cannot be achieved with the best available technology or equipment. 10 CFR 835.209(c) and the RadCon Manual article 521.2 require the use of bioassay measurements in preference to air concentration values for the estimation of internal dose unless the bioassay data are unavailable, inadequate, or internal dose estimates based on representative air concentration values are demonstrated to be as or more accurate. These provisions allow the determination of internal dose through calculations using air concentration values when bioassay measurements meet the above conditions. Bioassay data may meet these conditions as a result of instrumentation limitations, sampling discrepancies, etc. In the case of a technology shortfall, the IG recommends the site/facility should:
Air Monitoring and Sampling10 CFR 835.403, "Area Monitoring," and the RadCon Manual Article 555, "Airborne Radioactivity Monitoring," require measurements of radioactivity concentrations in the ambient air of the workplace under specific circumstances. 10 CFR 835.403(a)(1) and the RadCon Manual article 555.2 require air sampling be performed in occupied areas where, under typical conditions, an individual is likely to receive an annual intake of 2 percent or more of the specified Annual Limit on Intake (ALI) values. Two percent of an ALI is equivalent to a 40 Derived Air Concentration - hour (DAC-h) exposure or a CEDE of 100 mrems or a committed dose equivalent to the limiting organ of 1 rem.Air sampling is performed to detect and evaluate the level or concentration of airborne radioactive material at an individual's work location. Air sampling results must be representative of the air breathed to be used for dose determinations, as required by 10 CFR 835.209(c)(3) and the RadCon Manual article 521.2.c. 10 CFR 835.403(a)(2) and the RadCon Manual article 555.3 require that real-time air monitoring using continuous air monitors be performed in normally occupied areas where an individual is likely to be exposed to a concentration greater than 1 DAC as specified in appendix A of 10 CFR 835. These provisions also require the use of continuous air monitors in areas where there is a need to alert potentially exposed individuals to unexpected increases in airborne radioactivity levels. This situation is independent of initial airborne radioactivity concentration. The "Workplace Air Monitoring Implementation Guide," G-10 CFR 835/E2, contains additional guidance for air sampling and monitoring programs. By performing the air sampling discussed above and documenting the results, in combination with an effective access control program, worker exposure measured in DAC-h can be tracked. Internal dosimetry programs typically base bioassay frequency and type on levels of actual or anticipated exposures to individuals. By tracking DAC-h for individuals, the type and frequency of required bioassay measurements can be determined. For example, if a radiological worker receives less than 40 DAC-h (2 percent of an ALI) in a year with no respiratory protection, the individual would not be required to participate in the bioassay monitoring program for that year. Additionally, participation of the individual in the bioassay monitoring program for the next year should be considered. In the case where bioassay measurements may not be available or their validity is questionable, internal dose estimates can be determined from the number of DAC-h tracked for that individual. When DAC-h are used for this purpose, any adjustments, such as protection factors for respiratory protection, must be documented. Additional guidance can be found in the "Internal Dosimetry Program Implementation Guide," G-10 CFR 835/C1. Technical Position:Based upon the information cited above and the requirements of 10 CFR 835 and the RadCon Manual, dose determinations for internal intakes of radioactive materials can be determined through an effective internal dosimetry program. An effective internal dosimetry program includes routine and special bioassay as well as workplace air sampling and monitoring. When technology shortfalls occur, the enhancements recommended in the "Internal Dosimetry Program Implementation Guide" provide an acceptable method for complying with 10 CFR 835.Air sampling and monitoring play an integral role in dose assessment for all isotopes, including those where the DIL is less than the detection capability. By tracking DAC-h, the expected magnitude of the exposure can be determined. As mentioned above, DAC-h can be used to determine an individual's dose when necessary. Air monitoring provides early warning of an immediate and significant exposure hazard and provides indications of the need for special bioassay monitoring. References:
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