Nuclear accidents yield

An accident involving the detonation with partial nuclear yield of a nuclear weapon is also considered a nuclear accident. 

In nuclear reactors water used as a coolant or moderator should be as pure as possible to minimize dissociation during the time in the reactor. The formation of an explosive gas mixture of H2 and O2 must be carefully avoided in all reactors in order to prevent accidents. Moreover the deconq)osition products of water can increase the corrosion of fuel elements, structural material, etc. Many reactors use N2 as a protective gas. In this case the radiolysis can lead to the formation of HNO3 unless suppressed by an excess of H2 which preferentially yields NH3. The pH of the water may be regulated by the H2(g) pressure. 

Weapons involved in accident or incidents, or jettisoned weapons, produce a nuclear yield. 

Hopefully, answers to some of these questions may become apparent by examining a profile of the competent criticality specialist. Opportunities for enriching the nuclear physics curricula for the Student who desires the information may also be revealed. Unfortunately, the experimental data available to the criticality specialist, by which computational techniques may be verified, are not as complete as those available in other dlscfolines. Accordingly, calculational models are designed to yield conservative results and frequently incorporate the two contingency criteria aiul Murphys Law to meet the objective of zero-criticality accidents. 

From these two main groups of the Periodic System of Elements, only the elements bromine, iodine, rubidium and cesium are produced by nuclear fission to an extent worth mentioning. Iodine and cesium are of particular interest during plant normal operation as well as in accident situations, because of their comparatively high fission yields, their enhanced mobility in the fuel at higher temperatures and the radiotoxicity of some of their isotopes. Both elements are often summarized under the term volatile fission products their similar properties justify their treatment in the same context, despite pronounced differences in their basic chemical behavior. 

Any industrial activity both yields benefits and incurs risks. For the purpose of this publication, risk is taken to be the probability that a specified harmful effect will occur within a specified period. Complex industrial activities, such as the operation of nuclear installations, usually have associated risks of various types. The risks may be borne by the site personnel, by people living near the installation and by the whole of society. The environment may also suffer harm if radioactive materials are released, particularly under accident conditions. Consequently, it is necessary to limit the risks to which people and the environment are subject for all reasonably foreseeable circumstances. A further discussion of the concept of risk and of various methods for risk evaluation and limitation is found in the Annex. 

Radiological assessment is the process of evaluation of radiological hazards. An initial assessment should be carried out as part of a safety analysis to identify possible events that could warrant urgent protective actions. Specific assessments should be made when a nuclear or radiological emergency occurs and develops. The assessment should be made on the basis of the available information, and should be promptly updated in the light of any information that would yield more accurate results. Post-accident impact assessments should also be carried out. 

An ET is a graphical model of an accident scenario that yields multiple outcomes and outcome probabilities. An ET is constructed during ETA and is frequently used as one of the tools in a probabilistic risk assessment (PRA). ETs first made their appearance in risk assessment in the WASH-1400 nuclear power safety study, where they were used to generate, define, and classify scenarios specified at the PE level. 

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