Regulatory Guide 1.21 recommends that licensees monitor all locations at the plant at which image1 percent of activity is discharged as:

  • liquid effluent,
  • noble gases into the atmosphere, or
  • anything else into the atmosphere.

Title 10, Part 50 of the Code of Federal Regulations (10 CFR 50.36(a)(2)) requires licensees to report the principal radionuclides in effluent releases.

These locations are referred to as significant release points and include vents and stacks for airborne effluents and liquid waste discharge points for liquid effluents. Releases are assessed using a combination of sample analyses, radiation monitoring, and flow, tank level, and system pressure indications, as appropriate, to ensure that the amount of radioactive material is not underestimated.

Licensees are also required to monitor unplanned leaks and spills. If such leaks and spills result in offsite releases, then the magnitude of the releases must be estimated and reported to the USNRC along with the releases from routine operations. If the leak or spill occurs onsite, then a bounding analysis can be used to assess the potential offsite hazard.

Continuous effluent releases are typically monitored by measuring gross radioactivity with a continuously indicating radiation monitoring system such as a sodium iodide detector. These gross measurements can be used to activate alarms and terminate effluent releases if radioactivity levels exceed allowable limits. These continuous measurements are combined with analyses of physical samples (e.g., particulate materials trapped on filters or air samples) from the effluent stream to obtain quantitative estimates of the radionuclide concentrations in the effluent stream. Such samples are usually taken at specified frequencies, the value of which depends on the expected variability of radioactivity in the effluent stream.

Batch effluent releases are sampled prior to purging or venting. Certain radionuclides, referred to as “hard-to-detect” radionuclides (e.g., iron-55, strontium-89, and strontium-90), may be analyzed after the release takes place. “Continuously indicating” radiation monitoring equipment may be used during the release to verify the representativeness of the grab sample or to more fully characterize the release.

Table G.1 summarizes the guidance on sampling and analyzing airborne and liquid waste. The guidance specifies analyses type, minimum sampling frequencies, and lower limits of detection for each type of release. The guidance for pressurized-water reactors in NUREG-1301 are similar, but some of the specified sampling points are different owing to the different design of these plants. Table G.1 footnotes list the principal radionuclides that should be measured by the monitoring program.



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