Some important data for accident analysis

Design basis accidents (DBAs) are those accidents chosen by the deterministic method or with the help of probabilistic considerations, in order to design all the plant systems, but particularly the safety ones. Some of the following considerations are of interest for DBAs and for the other accidents. Most of the quoted data are taken from examples of typical 1000 MWe pressurized plants. 

It is well recognized that the Doppler coefficient is one of the most important counter-reactions during reactivity excursions. The increase of the fuel temperature causes an increase in the amplitude of the uranium-238 neutron capture resonances and, therefore, a decrease in the core reactivity. In some transients, it is conservative to assume a most negative Doppler coefficient (when a higher power 

Origin of fast shutdown Trigger level in the analyses Time delay (s) 

High level in steam generator, feedwater pumps stop, feedwater system valves shut-off, turbine trip 2 

According to the two curves, at practically zero initial power, an increase in power until 10 per cent causes a reduction in reactivity ranging from —0.1 per cent to —0.2 per cent. 

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