In order to consider the appropriate reduction of radioactive release from nuclear power plants in light of existing government regulations and natural levels of radiation, a brief review of the natural level of radiation is appropriate.

Airborne Radiation Considerations. Every day every one of us is receiving radiation from the sky, the ground, the air, even the food we eat. The magnitude of this radiation level is strongly influenced by where we live, what we do, and even what kind of house we live in. For most towns in the United States, this natural radiation level averages about 140 mrem/yr. This magnitude of exposure is composed of contributions from outer space and the sun of between 50 and 150 mrem/yr, depending on where one lives and how frequently he travels by jet. There are also con­tributions from radioactive material in the ground of about 15 mrem/yr, from radioactive material in the air of about 5 mrem/yr, and finally from buildings and structures man has built from stone and other materials found under the ground of about 45 mrem/yr. How these exposures com­bine for any one person is different depending on where he goes and what he does. If we then consider the added man-made contribution from such things as medical or dental X rays, the total exposure for the average resi­dent of the continental United States is about 200 mrem/yr. The accom­panying tabulation summarizes this information. It must be recognized that this is the background level and has been for years.

Radioactivity in Water and Liquids. As in the case of the atmosphere, potable liquids also have a natural radiation level which should be meas­ured before an effective design basis for reactor radioactive release can be established. The accompanying tabulation shows some of the radiation levels. With respect to sea water and many other commonly known liquids, nuclear waste is truly a minor contributor; nuclear power plants produce far less (.001) than allowable radioactivity levels: 5—10 p/1 of nuclear waste, when the mpc> 10,000 p/1.

From this simple review, two conclusions should be obvious. In the first place, nuclear reactors are not bringing to us a new kind of exposure, as does the automobile with high-speed collisions. We had radiation of 50 to 100 times the new level all the time. All we are doing now is measur­ing it with sensitive instruments and talking about it. In this perspective, the addition of less than 5 mrem/yr through the atmosphere and 0.05 mrem/yr through the liquid from a nuclear power plant should be insig­nificant.

Liquid

Domestic tap water

River water…………

Beer (4 per cent).

Sea water……………

Whiskey……………..

Milk…………………..

Salad oil……………..

Design Basis for Gaseous and Liquid Waste

In order to arrive at a design basis to minimize the potential release of any radioactive wastes to the environment, several things must be studied and placed in their proper perspective. It is worthwhile to mention these briefly before discussing typical radiation protection designs.

First of all, one objective is to make certain that regulatory limits are not exceeded. Second, information on natural background radiation and its significance in terms of radiation exposure is gathered and studied. Since the Federal Radiation Council (frc), the National Council on Radiation Protection (ncrp), and the International Commission on Ra­diological Protection (icrp) throughout the years have recognized that man has always lived in an environment which has nonzero radiation, a design decision had to be made as to what level of radiation the nuclear plant waste emissions would not exceed.

Airborne Release Path. The basic question is what level of incre­mental radiation exposure traceable to a power plant would be considered insignificant by most people compared with either the natural radiation exposure of 200 mrem/yr or the permissible exposure of 500 mrem/yr. A judgment was made at the General Electric Company that sufficient design features should be added to its nuclear power plants to bring this radiation level to about 1 per cent of the permissible exposures. This was the “Good Neighbor” design objective. It was felt that most people would consider an incremental exposure of 5 mrem/yr insignificant compared with either natural radiation or the permissible federal radiation exposure limit. Certainly, the variation in background levels from place to place across the United States is much more than the 5 mrem/yr design ob­jective.

Waterborne Release Path. The permissible radioactivity limits for liquid waste discharge in General Electric-designed plants are based on aec regulation 10CFR20, with the general assumption that water released by the discharge canal can be used directly for drinking water. This regu­lation lists about 230 radioisotopes along with the appropriate maximum permissible concentrations (mpc) that must not be exceeded on an annual
average basis. Since this list is quite general and must apply to many uses of radioactive material, only a small fraction of these mpc’s apply to the liquid releases from a power reactor waste system.

A conservative method to demonstrate compliance with these regu­lations is to assume that all of the activity results from the presence of a relatively hazardous radioisotope, strontium 90. This original assumption results in a limit of 100 picocuries per liter (pCi/1) in the discharge canal entering a public waterway. This limit was adopted for the design of our plants because it incorporates many assumptions about discharge that are set forth in the accompanying tabulation as doses from drinking water downstream from a bwr plant.

"Calculated"

Reduction Dose to Drinker

Factor Comment (mrem/yr)

First of all, from analysis work it is known that of all of the curies in the liquid waste, only a small amount is actually strontium. The great bulk of the total curies represents a mixture of corrosion products and fission products, for which the mpc would be about 10,000 pCi/1 if calculated in detail, or about 100 times the 90Sr limit of 100 pCi/1. Therefore, someone taking all his drinking water from the discharge canal for a year would get 5 mrcm, not 500 mrem.

Second, to give this maximum possible dose of 5 mrem/yr to the drinker of canal water, the plant must generate a certain quantity of activity. Actual experience in bwr plants indicates that about 10 Ci/yr is a reasonable expectation for yearly output of liquid wastes, which, for a typical flow of 500,000 gal/min in the discharge canal, results in an an­nual average concentration of 10 pCi/1, not 100 pCi/1. Therefore, this drinker of canal water would receive 0.5, not 5 mrem after one year.

Finally, nobody should drink the water in the discharge canal itself; that water usually is less than desirable from a cleanliness standpoint, since it has not had the usual drinking water purification treatment. How­ever, people do drink water from rivers downstream from plants. In the case of a city ten miles down the river, where the water is used for drink­ing, the effluent water will have been diluted by the river by a factor of perhaps 5 and would have been filtered and chlorinated. On filtering the water, the radioactive content will drop by a factor of about 2. Thus, there is another reduction factor of 10. Those who drink their annual water supply from rivers containing the reactor discharge would receive only about 0.05 mrem/yr, not the regulatory annual average dose of 500 mrem/yr, a factor 10,000 times greater.

When one recalls that the inescapable minimum yearly dose of radiation for all individuals is near 200 mrem/yr — or about four thou­sand times as much as that from drinking water downstream from a bwr plant — the magnitude of this liquid waste disposal can be put in proper perspective, as we have seen in the tabulation above.