ABSTRACT
The methodical issues concerning analysis of the experimental data on fission product (FP) release from irradiated fuel are considered to derive constants required for predicting FP behaviour in accident situations. The features of the analysis are compared in terms of the diffusion and activation models of FP behaviour as well as of the one-group FP release model used for the analysis of accident situations.
In the analysis of FP release from the fuel in accident situations the authors use the activation FP release model where the release rate is meant as the superposition of FP releases from two groups of defects with the activation energies ℰ > K O T and ℰ < K O T https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003070344/f17fe9b1-c951-4506-931a-f509d40bc783/content/eq372.tif"/>
the fraction of the products in each group being determined by the spectral characteristic “m” The relation between the basic constants of the diffusion one-group and activation models of FP behaviour is established.
On example of the amalysis of the experimental data on Cs release in heating irradiated fuel it is shown that use of the traditional models for determination of the radionuclide release in the accident may lead to inaccurate conclusions on predicting the evolution of the radionuclide release and quantitative estimates of the fission product balance in the damaged reactor.
The release evolution in a severe NPP accident is analyzed in terms of the activation model of FP behaviour in the fuel.
A two–stage character of the release is substantiated. Por determination of temperature fields in the fuel and in the reactor allowance is necessary for transfer of FP, sources of the radioactive decay energy.
Specific features of an express method for evaluating quantitative characteristics, radionuclide composition, and release dynamics basing on the analysis of characteristic nuclide fractionation coefficient are considered. Use of the model in predicting the dynamics of the radionuclide release at the Chernobyl–4 accident realized at the accident initial stage is discussed.
The results are presented and the explanation is given of some features typical of an accidental release radionuclide composition which cause the presence of cesium spots and in fall-outs, “hot” particle etc.
Proposals are made on organizing the system of the initial express evaluation of the accident parameters, and also on the sampling methodology.
