Chapter 5 Nuclear Power Plant Steam Generators Flashcards
How is radioactivity detected?
The instruments commonly used are Geiger Muller counters, scintillation counters, gamma survey meters, and proportional counters. The instrument to be used depends on the type and density of radiation to be measured. Geiger-Muller counters are used to detect beta and gamma radiation and are not effective for measuring alpha radiation.
What is radiation as applied to nuclear plants?
Unstable isotopes of certain chemical elements undergo spontaneous change in the atomic structures of the element. This change is called radioactive decay. While this phenomenon is going on, rays of energy are emitted; thus the term radiation of particles describes the radiation that that is experienced in a nuclear power plant, primarily under controlled conditions in the reactor pressure vessel.
How is an isotope defined?
Isotopes are elements that have the same number of protons but differ in the number of neutrons in their nucleus. Isotopes of an element have the same chemical properties and somewhat the same physical properties, but have different atomic weights as a result of the difference of the neutrons in the nucleus.
What is half life of a radioactive substance?
Half life is defined as the time required for a radioactive substance to reach one half of its radioactive emitting strength.
What units are used to measure radioactivity?
The Roentgen ( R ) is the unit most frequently used to measure the quantity of radiation emanating from a body. It is primarily used to measure x-rays and gamma rays. Exposure tolerances are usually expressed in milliroentgen ( mR ), or one thousandth of a roentgen. The Radioactivity of material undergoing radioactive decay is expressed in curies (Ci), which is equal to 3.7 x 10 to the 10th power atomic disintegration per second.
How are alpha, beta, and gamma rays detected?
Alpha radiation particles consist of two protons and two neutrons. This makes them identical to the positively charged nucleus of the helium atom. They cannot penetrate the human skin, but are dangerous to human health if inhaled or ingested into the body. This could occur from inhaling alpha bearing dust or eating alpha contaminated food or water.
Beta particles are high speed electrons with penetrating power sufficient to go through aluminum up to 1 inch thick. Thus they are a health hazard to the entire human body.
Gamma radiation is an electromagnetic type ray similar to light, radio waves, and x rays with a speed approaching that of light. Its penetrating power can reach up to 3 feet of concrete. This radiations is most dangerous to human health in the operation of nuclear power plants
7-Name some typical methods employed to protect workers from excessive radiation doses
1-Control the length of an exposure
2-control the distance between the human body and the radiation source
3-provide shielding between the body and the source of radiation
4-establish a strict and precise radiation monitoring program in the work area
5-have medical facilities available at all times to handle any accidental exposure above normal stipulated levels.
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8-What procedure are generally followed in decontaminating radioactive material?
Radioactive material cannot be destroyed. Therefore the process of decontamination involves one of the following methods of lessening the hazard of radioactivity:
1-Isolate the area of radioactive contamination until such time as the radioactivity is decreased to a safe level as a result of radioactive decay. The half life of the contaminant will influence the procedure.
2-treat the surface so that the radioactive material is absorbed , cleaned off, swept, ect. And taken to a site where the radioactive substance will not harm people. The most difficult decontamination is where the containment is absorbed into porous material such as concrete. Complete removal of walls, floors, and similar contaminated areas may be necessary under this type of contamination.
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9-What is a thermal shield in a nuclear reactor?
It consists of iron or steel plates surrounding the core inside the reactor vessel, so as to conserve heat and reduce the temperature and thermal stresses in the wall of the reactor vessel. The inner layer of the shield next to the core is subject to intense neutron and gamma radiation, which is converted to heat. The thermal shield often is cooled by circulating water.
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10-What is a biological shield?
Consists of high density concrete or lead plates around the reactor. It prevents the excape of neutrons and radiation out of the vessel wall so as to protect personnel. Radiation is present in operation and shutdown periods because of the radioactivity of the fuel elements.
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11-What is a containment vessel?
To prevent the release of fission products in case of a fuel meltdown or explosion of the primary reactor, most power reactors are housed in steel airtight containers. Not pressurized, designed to withstand the max pressure or shock waves that could develop as a result of an accident.
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