It was demonstrated that the change from stratified conditions to natural circulation (and vice versa) is essential for many passive safety systems of the SWR 1000. It would be useful if these flow phenomena could be studied by means of computer code analyses. But in many cases, suitable computer codes are not yet available and development of such codes to serve as a basis for actual decision-making would be too time-intensive.

Designers of new nuclear power plant concepts normally cannot wait until suitable computer codes are ready in order to find solutions to problems. Basic decisions are often made using only a calculator and sound engineering judgement. At the moment it is still easier for the designer to prove its preliminary decisions by way of experimental testing rather than calculational analyses. One can only hope that such computer tools will be available prior to entering the plant design licensing period and that computed results are in good agreement with the results of experimental testing.