Fission products hazards from

As to accident 9, here, of course, is the crux of the matter so far as population hazard is concerned. One is left to make up one s own mind as to what parameters to assume—as is the case with what may be thought to be corresponding though different circumstances for gas-cooled reactors (see section II,B). At the present state of the art, this is perhaps inevitable. So far as fission product release from fuel is concerned, we clearly have to consider fuel at temperatures up to the melting point of uranium dioxide, 2800 C some representative values are given in Section III. 

The primary cooling ciicuit in a PWR is a high-integrity, pressure-resistant system that will contain any fission products released from the fuel in an accident until the internal pressure exceeds the values that would actuate the pressure relief devices. A simple, conqiact primary system will be easier to qualify and inspect and to protect from seismic events and external hazards. The RPV penetrations should be as few as possible and of small diameter. All primary system openings would be kept sealed for die duration of autonomous operation. 

The primary issue is to prevent groundwater from becoming radioactively contaminated. Thus, the property of concern of the long-lived radioactive species is their solubility in water. The long-lived actinides such as plutonium are metallic and insoluble even if water were to penetrate into the repository. Certain fission-product isotopes such as iodine-129 and technicium-99 are soluble, however, and therefore represent the principal although very low level hazard. Studies of Yucca Mountain, Nevada, tentatively chosen as the site for the spent fuel and high level waste repository, are underway (44). 

Humans are exposed to radiation from the testing and explosion of nuclear weapons and the wastes of nuclear reactors and power plants. Strontium-90 is a fission product from nuclear reactors. It is of particular concern because it has a long half-life of 38 years and becomes concentrated in the food chain, particularly plants-to-milk. The ban on atmospheric testing of nuclear weapons has reduced this hazard. Strontium-90 does have some industrial uses. Most people in developed countries receive minor exposure to radiation through medical procedures such as X-ray and various treatments for some diseases. 

In an analysis of the hazards of the alpha emitters from reactor operations it has been pointed out (25) that the most significant and hazardous species are plutonium, americium, curium, and neptunium. Plutonium is as hazardous as such fission products as ruthenium-106, cesium-137, cerium-144, and promethium-147, depending on the kind of fuel, the power of the reactor, the storage time of the waste, and whether it is released to the atmosphere or to water. If strontium-90 is removed... 

Spent fuel from a reactor contains unused uranium as well as plutonium-239 which has been created by bombardment of neutrons during the fission process. Mixed with these useful materials are other highly radioactive and hazardous fission products, such as cesium-137 and strontium-90. Since reprocessed fuels contain plutonium, well suited for making nuclear weapons, concern has been expressed over the possible capture of some of this material by agents or terrorists operating on behalf of unfriendly governments that do not have a nuclear weapons capability. 

Fuel reprocessing has three objectives (a) to recover U or Pu from the spent fuel for reuse as a nuclear reactor fuel or to render the waste less hazardous, (b) to remove fission products from the actinides to lessen short-term radioactivity problems and in the case of recycle of the actinides, to remove reactor poisons, and (c) to convert the radioactive waste into a safe form for storage. Fuel reprocessing was/is important in the production of plutonium for weapons use. 

The anthropogenic radionuclides of most concern are those produced as fission products from nuclear weapons and nuclear reactors. The most devastating release from the latter source to date resulted from the April 26, 1986, explosion, partial meltdown of the reactor core, and breach of confinement structures by a power reactor at Chernobyl in the Ukraine. This disaster released 5 x 107 Ci of radionuclides from the site, which contaminated large areas of Soviet Ukraine and Byelorussia, as well as areas of Scandinavia, Italy, France, Poland, Turkey, and Greece. Radioactive fission products that are the same or similar to elements involved in life processes can be particularly hazardous. One of these is radioactive iodine, which tends to accumulate in the thyroid gland, which may develop cancer or otherwise be damaged as a result. Radioactive cesium exists as the Cs+ ion and is similar to sodium and potassium in its physiological behavior. Radioactive strontium forms the Sr2+ ion and substitutes for Ca2+, especially in bone. 

In many ways, the design of a nuclear power plant and that of a fossil fuel burning power plant are very similar. In both cases heat from a reaction is used to generate steam. The steam is then used to drive turbines that produce electricity. In a typical fossil fuel power plant, the chemical combustion of coal, oil, or gas generates the heat, whereas in a nuclear power plant, a nuclear fission reaction generates the heat. Because of the hazardous radioactive fuels and fission products present at nuclear power plants, a dense concrete structure is usually built to enclose... 

A further possible reason for separating plutonium from uranium and the fission products relates to the extreme toxicity of Pu. Plutonium(IV) mimics iron(lll) (the aqueous E° and charge-to-radius ratios of the two ions are very similar), so that cancers are likely to result from the absorption of even microgram amounts of ingested radioactive Pu into organs of the human body (bone marrow, spleen, liver) that store iron(III). It may therefore be considered desirable to remove Pu, a long-lived health hazard, from spent nuclear fuels before disposal of the latter in repositories that may not remain inviolate for thousands of years into the uncertain future (most of the fission products decay away to negligible levels of activity in an acceptable time). 

During its lifetime, a fusion reactor presents little radiation hazard. The internal structure, particularly the vacuum containment vessel and the heat exchanger, will be subject to intense neutron bombardment. The neutrons will convert some of the elements of the structure into long-lived radioactive isotopes. Selecting construction materials that do not easily become activated can minimize radioisotope production. No material is entirely resistant to neutron activation, thus the decommissioning of a fusion reactor will require the handling and disposal of potentially hazardous radioactive isotopes. Because of the lack of uranium, plutonium, and fission products, the total radiation exposure hazard from the decommissioned fusion reactor is 10,000 to 1,000,000 less than from a decommissioned fission reactor. 

In the field of radioactive waste management, the hazardous material consists to a large extent of actinides and fission and activation products from nuclear reactors (such is the case of the fission product Se). The scientific literature on thermodynamic data, mainly on equilibrium constants and redox potentials in aqueous solution, has been contradictory in a number of cases. A critical and comprehensive review of the available literature is necessary in order to establish a reliable thermochemical database that fulfils the requirements of a proper modelling of the behaviour of the actinide and fission and activation products in the environment. 

Radiation. The external radiation hazard from uranium is caused chiefly by beta radiation and is significant only if the uranium surface to which people are exposed is large. The problem presents only minor restraints to the designer, localized shielding normally proving adequate without the extreme measures necessary in fission-product-handling plants. 

Mesler, R, S., and L. C. Widdoes Evaluating Reactor Hazards from Airborne Fission Products, Nucleonics, 12(9) 39 (1954). 

Because of the hazardous radioactive fuels and fission products present at nuclear power plants, a dense concrete structure is usually built to enclose the reactor. The main purpose of the containment structure is to shield personnel and nearby residents from harmful radiation. 

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