11.23. The radioactivity concentrations in the 10 CFR Part 20 regula­tions are intended to provide guidance as to the maximum permissible discharges of radioactive effluents to the environment. Licensees of nuclear power plants are required, however, to control the effluents in such a manner that radioactivity levels be kept “as low as is reasonably achiev­able.” This requirement is interpreted as meaning that the levels should be kept “as low as is reasonably achievable taking into account the state of technology and the economics of improvements in relation to the benefits to the public health and safety. …”

11.24. In principle it should be possible, by increasing the complexity and hence the cost of constructing and operating the equipment of the “radwaste” system for the treatment of radioactive waste liquids and gases (§11.93 et seq.), to decrease the level of the radioactivity in effluents almost without limit. However, any such decrease means an increase in the ra­dioactive material that must be stored, at least temporarily, in the plant, thereby increasing the potential risk to people working there. Furthermore, the greater the complexity of the radwaste system, the greater the chances of failures which might interfere with plant operation. The extent of the treatment of radioactive wastes in a given plant is thus based on an analysis of the benefits that would be expected to accrue, balanced against all the costs (including risks).

11.25. In expressing the numerical guides, the effluents from a plant are considered in three categories: liquid effluents, gaseous effluents, and radioiodines and radioactive material in particulate form. The liquid ef­fluent generally contains some tritium (as tritiated water) and dissolved and suspended fission products and corrosion and erosion products that have become radioactive (§11.91). The gaseous activity consists mainly of radioisotopes of the noble gases krypton and xenon, most of which emit both gamma rays and beta particles. Because the gaseous effluent from PWRs is held up for a longer time before discharge than from BWRs, the shorter-lived isotopes have largely decayed leaving mainly krypton-85, which is almost exclusively a beta emitter, and xenon-133. The radioiodines and particulate matter are present, together with the noble gases, in the air­borne effluents from the LWR installation. Some of the solid particles are formed by radioactive decay of the noble gases.

11.26. It should be understood that the purpose of the guidelines is to assess the adequacy of a proposed nuclear plant design, especially the design of the radwaste treatment system, before construction. When the plant is operating, the radioactivity concentrations in the effluent at the plant boundary must satisfy the requirements of 10 CFR Part 20. Fur­thermore the actual radiation doses to the public must comply with the EPA standards for the fuel cycle (40 CFR 190) [5].