Fission product release accident

Rodgers, S. J., Udaveak, R. J. and Mausteller, J. W. In International Symposium of Fission Product Release and Transport under Accident Conditions, Oak Ridge National Laboratory, TN, USA, 1965, pp. 1204 1215. 

Code of Federal Regulations (lOCFR) part 100 provides reactor siting criteria. It specifies that the fission product release calculated for major hypothetical accidents shall produce a w hole... 

An accident sequence source term requires calculating temperatures, pressures, and fluid flow rates in the reactor coolant system and the containment to determine the chemical environment to which fission products are exposed to determine the rates of fission product release and deposition and to assess the performance of the containment. All of these features are addressed in the... 

Of these phenomena, the first three in particular, involve thermal hydraulics beginning with the pre-accident conditions. Items 4 through 7 address the meltdown of the core and its influence on (1) hydrogen production, which affects containment loads, (2) fuel temperatures, which affect in-vessel fission product releases, (3) thermal-... 

Table 2.6. Release of fission products in accident at Three Mile Island...

Osborne, M.F., Collins, T.L., Lorenz, R.A. Strain, R.V. (1986) Fission product release and fuel behaviour in tests of LWR fuel under accident conditions. In Source Term Evaluation for Accident Conditions, IAEA, Vienna, pp. 89-104. 

Public interest in radioactive aerosols began in the mid-1950s, when world-wide fallout of fission products from bomb tests was first observed. The H-bomb test at Bikini Atoll in 1954 had tragic consequences for the Japanese fisherman, and the inhabitants of the Ronge-lap Atoll, who were in the path of the fallout. In 1957, radio-iodine and other fission products, released in the accident to the Windscale reactor, were tracked over much of Europe, and these events were repeated on a much larger scale after the Chernobyl accident. 

Reactor accidents and fission product release (after Vinjamuri et al., 1982)... 

The sorption of the fission products Cs and Sr by the graphitic materials, from which the core and the fuel elements of High-Temperature Gas-Cooled Reactors (HTGRs) are made, is important for the prediction of fission product release in the case of an accident. Hilpert et al. [564, 565] determined, therefore, Cs and Sr partial pressures over such graphitic materials with different Cs and Sr concentrations. The vaporization enthalpies obtained showed a strong chemisorption of Cs and Sr by these materials. The vaporization enthalpy of Sr exceeds that of the pure Sr metal by about 210kJmol at 1500 K, if fuel element matrix graphite with a Sr concentration of 4.0 mmol kg is considered [564]. This value for Cs amounts to about 230 kJmol" at 1250 K for a similar concentration of 4.2 mmol kg[565]. In addition, sorption isotherms were evaluated. 

The principal barriers against fission product release into the environment are the high quality TRISO fuel, the reactor pressure vessel, and the reactor building. The calculation of the fission product release during normal operation of the reactor (Fig. 3-5) which determines the contamination of the primary circuit and thus the source term in case of a depressurization or a water ingress accident has again identified silver to be the nuclide with the largest release fraction. 

After the severe accidents at the Three Mile Island and Chernobyl nuclear power stations, new designs with improved safety features have been proposed focusing on more intensive consideration of passive safety characteristics. A much more far-reaching demand for the introduction of innovative nuclear power plants in the future is made on a design such that fission product release is made impossible or, at least, restricted to the plant itself. 

II. Reactor Accidents in Relation to Fission Product Release... 

II. REACTOR ACCIDENTS IN RELATION TO FISSION PRODUCT RELEASE... 

At the present state of the art, a corner of an article about evaluation of population hazards is hardly an appropriate place in which to attempt an exposition of reactor safety. Nevertheless, we may contrive a brief description of these types of reactor accidents which, it is thought, could lead to fission product release. The intention is to illustrate ways in which fuel could be damaged and then release fission products ultimately to the atmosphere. Though gas-cooled reactors, water-cooled reactors, and sodium-cooled fast reactors will be discussed, no comparisons, invidious or otherwise, are intended between the safety of these systems. 

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 release of fission products under accident conditions will clearly... 

Large-scale experimental releases of fission product activity are clearly ruled out because of the implications on the safety of the public, described in Section V,F, as are also the smaller scale releases referred to earlier in Section V. Therefore, for verification of our conclusions we have to rely on limited experience from those few accidents that have occurred and that have released fission products (see Section I,D), but much more on our store of knowledge of all the factors involved, i.e., types of reactor accidents (Section II) through fission product release (Section III) and dispersion of a release in the atmosphere (Section IV), to analysis of the radiation and radiobiological hazards and risks to exposed members of the population. In view of these several steps involved in the estimation of hazard, it is reassuring that the many different authors who have written on the topie reach conclusions which are generally similar and differ only in limited areas. 

A. General Design Criterion 41 (Reference...) as it relates to containment atmosphere cleanup systems being designed to control fission product releases to the reactor containment following postulated accidents. 

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. 

As a final barrier against fission product release, a containment system is one of the important Engineered Safety Features (ESF) in a current nuclear power plant. It consists of a containment structure and several systems to maintain the integrity of contaminant during accident scenarios. This system is very expensive. Recently, along with the development of advanced nuclear power plant, especially for more innovative reactor designs, the concept of a containment is also getting development. For example, a vented confinement concept... 

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