Grand Gulf Nuclear Station Produces Electricity
A nuclear power plant uses steam to generate electricity. Steam, created by heating water through energy produced by a nuclear reaction, drives turbine blades to spin. This rotational energy is then converted to electrical energy by a generator.
A nuclear power plant uses uranium as its fuel. Uranium atoms can be more readily split apart than other types of atoms. This process is called nuclear fission. When the atoms split, energy is released in the form of heat and radiation with fission products left behind. This is the heat source used to create steam in a nuclear power plant. The plant is designed to keep any radiation safely inside.
Once the steam has been used to spin the turbine, it is sent to a condenser. A condenser is a large vessel with thousands of small tubes. Cool water is channeled through these tubes while the exhausted steam from the turbine passes over the outside of the tubes. This process allows the heat of the exhausted steam to be transferred to the cooler water inside the tubes. This allows the steam to condense back into water, which is then recirculated through the system, starting the process over again. The water inside the tubes — now heated up after passing through the condenser tubes — is circulated through a separate cooling system, allowing it to safely release the heat it has absorbed, be cooled back down, and then circulated back through the condenser tubes.
Since the steam passing through the turbine and the water from the cooling tower system are in two separate systems, physically isolated from each other, the cooling tower water contains no radioactive contaminants. This water never intermingles with the water passing through the reactor.
Radiation is Energy
Radiation is a form of energy. It comes from radioactive elements, natural and man-made, whose atoms are unstable. Radiation has been around since the beginning of time.
Radiation is all around us. It is in the air we breathe, the food we eat, and the water we drink. It is in our homes and even in our bodies. This is called natural or background radiation.
In addition to background radiation, there is also man-made radiation. It comes from such things as medical and dental x-rays, color televisions, smoke detectors and some watches with dials that glow in the dark. Very small amounts of radiation come from nuclear power plants.
Radiation is measured in units called millirems. A millirem is a unit used to measure radiation dose to humans. The drawing below shows how much radiation we get from different things.
For radiation to cause any measurable biological effect in human beings, most scientists agree that the exposure must reach about 25,000 millirems – in a single, short-time exposure.
Federal standards drawn up and enforced by the Nuclear Regulatory Commission (NRC) require that workers at nuclear power plants receive no more than 5,000 millirems of radiation a year.
Average Radiation Exposure Levels in Millirem (mrem)
Terms You Need To Know (Emergency Classification Levels)
Emergencies at nuclear power plants are classified in four ways.
1) A Notification of Unusual Event is the least serious of the four emergency classifications. It means there is a problem that is being handled by plant workers. Strict federal rules require that a number of problems are reported as Unusual Events even though they pose no danger to the public. They are reported to the Nuclear Regulatory Commission and to the local and state officials.
2) An Alert is an event that could affect plant safety. Even though there is still no danger to the public, local and state officials may set up emergency operation centers in case the situation at the plant gets worse.
3) A Site Area Emergency is an event that could possibly affect the public. The sirens may be sounded to alert the public to listen to their radios for information and instructions.
4) A General Emergency is the most serious of the four emergency classifications. Local, state and federal authorities would take action to protect the public. Designated radio stations and the Emergency Alert System would continue to give information and instructions. If necessary, some areas would be sheltered or evacuated.
Protective Action Guidelines (PAGs) are guides used in planning for protective actions to safeguard public health. The actions are taken to limit the radiation dose from ingestion by avoiding or reducing the contamination in or on human food and animal feeds following the release of radionuclides. In order to ensure public safety, Derived Intervention Levels (DILs) have been recommended by the US Food and Drug Administration (FDA) to protect food, milk, and water from radioactive contamination. Each DIL is a set point where protective measures should be considered. For example, if levels of radioactive cesium in milk approach the preventive “response level,” surveillance and protective actions for dairy animals may be recommended (e.g., placing dairy animals on uncontaminated feed and water).
Emergency Protective Actions
The following are examples of protective actions that may be recommended if a release of radioactive materials occurs and contamination of agricultural products is verified or suspected.
• When you go outside, wear clothing that covers all portions of the body. Remove outer clothing before going indoors.
• Wash hands thoroughly before preparing or consuming food.
• Do not engage in any dust producing activities such as cultivating, disking, baling, or harvesting. Wear a dust mask or a folded, dampened cloth over your nose and mouth to reduce the quantity of radioactive materials inhaled when such activities can not be avoided.
• Do not process or distribute agricultural products until they have been sampled and found to be free of contamination.
• Do not destroy, slaughter or market animals.
Several of the response actions, which may be taken to protect agriculture products, animals, and other agriculture commodities, include:
• Temporary holding of food crops from market.
• Quarantine of food, animals, and other agriculture commodities.
• Placing animals on stored feed in place of grazing or forage.
Giving Animals Protected Feed
You may be advised to place animals on protected feed and water. This will help prevent contamination from harming your animals, and from entering the human food supply. Types of protected feed include:
• Grain stored in covered bins;
• Hay stored in a barn or covered shed.
One way of protecting your animals is to provide them with shelter. Dairy cows and other milk-producing animals should be given priority as these animals can pass contamination on to humans through their milk. Secondary consideration should be given to egg-producing fowl, breeding stock, other livestock and poultry. Barns, milking parlors, machine sheds, garages, corn cribs, and swine or poultry buildings are all possible livestock shelters. Generally, masonry or concrete buildings offer the best protection. Although a ventilation system is needed to keep sheltered livestock healthy, it allows radioactive material to enter the building. Therefore, it is important to limit outside air entering the building to the minimum amount necessary for the animals’ safety. Do not use fans for ventilation unless absolutely necessary. If you must use fans, set them on low speed to reduce air intake.
Protection From Packaged Food Products
Food in packaging prepared before the release of radioactive material will not be harmful to eat as long as the outer wrappings are carefully removed and discarded.
Food, Milk Processors, Warehouses, and Commodity Terminals
Windows and vents to the outdoors should be closed. Any system that draws air from the outdoors to the inside should be shut down, such as vacuum systems, air conditioners and compressed air systems.
Preventative Protective Actions
Preventative Protective Actions are measures taken to prevent or minimize contamination of food products.
Milk: Remove all dairy animals from pasture, shelter them if possible, and provide them with protected feed and water.
Fruit and Vegetables: Wash, scrub, peel or shell fruits and vegetables, including roots and tubers to remove surface contamination.
Meat and Meat Products: Place animals on uncontaminated feed and water.
Poultry and Poultry Products: Monitor poultry if they are raised outdoors, especially if they are used for egg production. Poultry raised indoors and given protected feed and water are not likely to be contaminated.
Soils: If officials find that the soil is contaminated, proper soil management procedures can be implemented to reduce contamination to safe levels.
1) Idling, the nonuse of the land for a specific period of time may be necessary in some cases. However, in a worst case situation, removal and proper disposal of soil may be more appropriate.
2) Alternating types of crops may be beneficial.
3) Deep-plowing the soil may keep radioactive substances below the plant root zone, preventing plants from taking up contaminated nutrients, and allow the level of radioactivity to decrease with the passage of time.
Grains: Permit grains to grow to maturity. Additional milling and polishing will remove most of the radioactive contamination.
Water: Cover open wells, rain barrels, and tanks to prevent contamination. Filler pipes should be disconnected from storage containers that are supplied by runoff from roofs or other surface drain fields.
Food Processors and Distributors: Radioactive contamination of milk or food products in an affected area can occur during processing or transportation. These products should not be released for consumption until they are deemed safe or a decision is made to dispose of them.
Effects Of Contamination Of Human Food And Water Supplies
The amount of radioactive material released into the atmosphere, the duration of the release, and weather conditions, all can affect the accident's impact on people, animals, crops, land, and water near the site of the emergency. An initial concern would be the condition of fresh milk from dairy animals grazing on pasture and drinking open sources of water. Testing may be performed at the farm, the transfer station, or the processing plant. If fresh milk and processed milk products are shown to be contaminated, state officials will decide whether to dispose of them or hold them until safe for consumption.
Another concern would be the possible contamination of vegetables, grains, fruits, and nuts. The severity would depend on the time of year the emergency occurred. The time just before or during harvest is the most critical period. Crops may be sampled and analyzed by state officials to determine if they are safe to eat.
An additional concern would be the possible impact of the contamination on livestock and poultry. Pasture, feed, and water sources, as well as meat and poultry products, may be sampled and analyzed to determine if the meat and poultry products are safe to eat. Contamination of drinking water supplies is not likely to be a problem. If it occurs, it probably will affect only surface water supplies and not ground wells or underground water sources.
If land becomes contaminated, proper soil management techniques can reduce contamination of crops grown on the land. The procedures to be used would depend on the severity of contamination and specific crops to be grown.