7 is needed to fill gaps in our basic knowledge. The Council's secon report develops radiation protection guidance for the intake o specific radionuclides (Ra226, I131, Sr39, and Sroo). 1-3.5 Maximum Permissible Concentration (MPC) Values The ICRP and NCRP have recommended maximum body burdens in various organs calculated from the maximum permissible exposure levels to given body tissues. From these body burdens MPC's for radionuclides in air and water for occupational exposure have been calculated. The MPC's for occupational exposure to some 200 radionuclides have been recommended for each of several possible critical organs.4.5 In the development of permissible concentrations applicable to the general public, various reduction factors have been applied to these recommended occupational values. Originally the recommendation was that the maximum permissible occupational concentration be reduced by a factor of 1⁄4 to provide limits applicable to members of the public living in the neighborhood of controlled areas. Recently the ICRP recommended that average permissible concentrations for large populations be set at one-thirtieth of the concentrations for continuous occupational exposure. Details concerning these factors will be found in the ICRP recommendations 4.8 and in a report of an Ad Hoc Committee of NCRP.11 The recommendations published by the ICRP and the NCRP have no direct legal connotation in themselves. Only those specific items therefrom which are incorporated in the regulations of the Atomic Energy Commission or of other federal agencies are applicable on a national basis. Several points must be considered in using the recommended,4,5 or legal, values included in the maximum permissible body burden and concentration tabulations. The values are calculated for a fictitious person known as "standard man" with standardized body organs. As a result, these values cannot be applied directly to children because their organ weights vary with age. Furthermore, the values reported apply only to the radionuclide for which they are given, and it is assumed that all the radiation exposure is due to that individual nuclide. If more than one nuclide is present in the waste, the permissible public exposure due to each must be evaluated in terms of the total resulting exposure. Similarly, if radioactive materials are already present in the environment in which disposal is planned, the permissible concentrations or calculated rates of release will have to be modified to take into account the overall exposure situation. This problem has been examined in a general way, and equations have been developed to fit different conditions below the point of were calculated on the basis that no noticeable damage from radiation will occur to the critical organ over an exposure period of 50 years At best, the recommendations of the ICRP and the NCRP, and any regulations based on them, can serve only as guides. 1-3.6 Guidance on Intake Levels Guidance on intake levels has been provided by the Federal Radiation Council for four radionuclides. The Council has divided these levels into three ranges; the values for the top of Range II correspond to the respective Radiation Protection Guides (RPG).6.7 Intakes for the three ranges are summarized in Table 1.2. TABLE 1.2-RADIATION PROTECTION STANDARDS RECOMMENDED BY THE FEDERAL RADIATION COUNCIL' A LOC *Range I: Calculations based on source information. Surveillance adequate to confirm calculations. Range II: Surveillance adequate to demonstrate levels. Control at source to avoid excess exposure as levels increase to top of Range II. Intakes do not exceed the recommended RPG. Range III: Surveillance to check effect of control actions. Control designed to reduce levels to Range II or lower. Intakes in Range III will result in exposures exceeding the RPG if continued for a sufficient period. 1-3.7 Drinking-water Standards The Public Health Service Drinking Water Standards 13 list concentrations for Ra226, Sr90, and gross beta activity for interstate-carrier water supplies. These are given in Table 1.3. TABLE 1.3-RADIONUCLIDE LEVELS RECOMMENDED IN THE PUBLIC HEALTH SERVICE DRINKING WATER STANDARDS 13 1-4 TREATMENT REQUIREMENTS Before significant quantities of radioactive-waste material a released to the environment, measurements should be made to de termine existing environmental exposure levels. As a result of thes measurements, it may be necessary to apply release-rate limits for given facility which are lower than criteria recommended by th ICRP, NCRP, and other agencies. If the level of radioactivity in the waste to be discharged exceed the permissible levels determined above, the waste will have to b treated to reduce its activity to a level that will permit release to th environment. The required degree of treatment should be provide at the least cost. Indigenous materials can be used in the treatmen of wastes if they prove to be economical. Detailed information o treatment processes for the removal of specific and gross radioactiv materials is given in subsequent chapters. It must be remembere that treatment does not result in the removal of radioactivity, bu only in the transfer of radioactivity from one phase to another or i its concentration. For example, filtration of radioactive airborn particulates transfers the activity from the air to a filter. The filte must be carefully handled, treated, and disposed of to avoid huma exposure. 1-5 BROAD ENVIRONMENTAL EFFECTS The use of the environment controls the degree to which it may b contaminated. In the case of a stream, the amount of radioactiv material released to it will depend upon its use for: (1) domestic wate supply, (2) industrial water supply, (3) irrigation, (4) food supply, (5 waste disposal, (6) recreation, and (7) navigation. The chemical com position of the medium into which release takes place must also b considered. Information on exposure pathways, i.e., the routes by which radio active materials will cause exposure to man, must be obtained Parker 14 has outlined these pathways as follows: 1. Exposure pathways from radioactive wastes in rivers, streams or lakes Use as drinking water Immersion in the water Close approach to the water Biological chains in the river Industrial processes Sewage disposal Direct radiation from ambient air Direct deposition and ingestion 3. Exposure pathways from general disposal of liquid wastes At the disposal site From underground travel This outline shows that considerable information is needed to evalua radiation exposure from environmental sources. All sources must evaluated if radiation exposure is to be kept within acceptable limi The permissible concentrations in effluent air and water are d rived values, based upon standard inhalation and ingestion rates. more significance in terms of human exposure is the determination total daily intake, which is set at a level that will not exceed t average permissible body burden for the general population over specified period of exposure. The values of the maximum permissib occupational air and water concentration are determined on the bas of inhalation of 20 million ml of air per day and a standardized wat intake from all sources including food materials of 2200 ml per da If these two quantities are multiplied by the MPC values indicat for a given radionuclide in that medium, a maximum permissib daily intake can be obtained for the given period of intake (50 yea recommended by the ICRP) during which the recommended bo burden will not be exceeded. In turn, the maximum daily intal would have to be multiplied by appropriate constants to give t average population intake level. A possible way of calculating the permissible intake of Sr.90 illustrated below: Water intake=2200 ml/day Air intake=2 × 107 ml/day Sr0=10-10 μc/cm3 Occupational intake Srwater=2.2 × 103 ml/day × 10-6 μc/ml =2.2 × 10-3μc/day or 2200 μμc/day Occupational intake Sr=2 X 10' ml/day X 10-10 μc/cm3 =2 X 10-3 μc/day or 2000 μμc/day 3 From the above, assume that the occupational intake level regar less of source is 2000 μuc/day; then 90 Thus the average permissible population intake of Sr0 not to exce permissible average body burden in 50 years is 67μμc/day. Similar calculations can be made for other radionuclides present and the total intake can be adjusted in such a way that the overal dosage does not exceed the permissible average population dose. From measurements of a given radionuclide in air, water, and food the total intake of that radionuclide can be calculated; this level can then be integrated over the period of intake to give the dose resulting from such intake. For this dose to be adjusted to a permis sible level, account must be taken of the doses contributed from all other radionuclides ingested or inhaled, as well as the dose from external radiation sources. If the total dose is less than the permis sible dose, the difference will represent the possible leeway or margin available for waste-disposal activities. From this margin can be calculated the concentration of specific radionuclides that might be permitted in waste discharges to the environment. Either the entire amount or some fraction of the total amount of leeway may be assigned to waste-disposal activities. This approach meets the recommendations cited earlier by Wolman. 1-6 REGULATIONS 9 Regulations have been established by the AEC for the protection of licensees, their employees, and the public against radiation hazards arising out of the possession or use of special nuclear, source, or byproduct material under licenses issued by the AEC. These regulations apply primarily to the users of radioisotopes. State and federal regulations are not applicable to laboratories and facilities operated by, or on behalf of, the AEC. However, whenever possible, the AEC has required that such installations operate within the recommendations of the ICRP and the NCRP. In the commercial power-reactor field, facilities must first meet AEC requirements and then must meet certain state regulations pertaining to the release of waste products, including radioactive materials, into the environment. When the AEC approves state inspection of isotope users, this area of regulation will come under the direct control of state agencies. Some states have proposed regulations patterned after the model law or enabling act recommended by NCRP in NBS Handbook 61.15 Others, like Pennsylvania, have provided for discharge of radioactive-waste materials under criteria developed through consultation with the industry and with the federal agencies concerned. The license granted the Duquesne Light Company by the Commonwealth of Pennsylvania permits release of radioactive materials under the following conditions: 16 (1) that the average radioactivity, exclusive of tritium activity, of these wastes over any consecutive 365-day period shall not exceed 1590 microcuries per day, |