10.06.2019 change 10.06.2019

Polish researcher investigates the impact of turbulence on nuclear reactor safety

Photo: Fotolia Photo: Fotolia

The impact of turbulence in the flowing cooling material on the safety of nuclear reactors is the subject of research of Tomasz Kwiatkowski, a PhD student from the National Centre for Nuclear Research. He will present his research during the competition for scientists dealing with nuclear safety.

Doctoral project of MSc. Tomasz Kwiatkowski from the Department of Nuclear Power and Environmental Analysis of the National Centre for Nuclear Research has been nominated by the international association NUGENIA to be presented in a competition for young scientists at the world conference FISA 2019/EuradWaste`19, which begins on June 4 in Romania, the National Centre for Nuclear Research informs in a press release.

Virtually all currently used nuclear reactors are cooled with liquid or gas flowing around the reactor core and receiving heat. In power reactors, this heat is used to generate steam that drives the turbines that generate electricity. The most common reactor coolant is water, but there are also installations that use liquid metals or gases. The coolant - regardless of its type - does not flow smoothly through the space inside the core. The actual flow is full of disturbances in the form of local turbulences.

We know the phenomenon well from everyday life: when turbulence occurs in home water supply pipes, it is usually accompanied by characteristic, often unpleasant sounds. They are caused by the vibrations of the pipe material, induced by the turbulence. In nuclear reactors, the most important effect is uneven cooling of the fuel elements and reactor vessel walls. Turbulences may lead to large local temperature differences, local pressure differences, and, as a result, stresses and faster material fatigue, which may result, for example, in undesirable microcracks. The material, from which the installation is made, must be resistant to such phenomena. The scale of unfavourable processes should also be as small as possible.

Reactor designers usually make certain assumptions as to the required resistance of construction materials to all kinds of disturbances. The "safety margin" is very large, but scientists and engineers still strive to minimize the scale of the unknowns. This knowledge can be significantly expanded by using mathematical models and harnessing huge computing powers to perform calculations.

"We would like to be able to model flows using the computational fluid dynamics (CFD) tools in the area of the whole reactor vessel" - says Tomasz Kwiatkowski, quoted in the press release. "Currently, to a limited extent, we are able to carry out analyses for individual fuel cartridges, inter-rod spaces or simplified models of the entire vessel. Such calculations have been done in our team. The correctness and effectiveness of the models we used was confirmed in situations where it was possible to compare the theoretical predictions with measurement results. For example this year, together with Dutch partners, we published a numerical analysis of the following phenomena, when suddenly, in an emergency mode, additional coolant should be injected into the reactor vessel, as the working coolant was lost. The calculations could be confronted with the measurement performed earlier at the Helmholtz Zentrum Dresden Rossendorf on the actual model of the vessel made on the appropriate scale. It turned out that the results of our calculations carried out together with colleagues from the Nuclear Research and Consultancy Group (NRG) in the Netherlands accurately described what had been measured in the experiment" - he says.

"Plant builders need a tool that will allow to quickly and reliably describe and assess a specific situation" - says Kwiatkowski. "The project, which I will present in the competition during the FISA/EuradWast conference in Pitesti, Romania, assumes checking simplified models and possibly proposing improvements based on a comparison with the advanced model. That will allow to use a simplified model without fear that the results will not reflect the reality. Work in the project will be carried out together with colleagues from NRG, with whom we have been cooperating for some time, and we will carry out calculations in the Świerk Computing Centre (CIŚ - Centrum Informatyczne Świerk) and with the support of local specialists" - he adds.

The FISA 2019 / EuradWaste`19 conference, the largest periodic European meeting of experts in the field of nuclear safety, organised for the ninth time, takes place on 4-6 June at the nuclear facility in Pitesti, Romania. Romania organises this year`s conference in connection with its current presidency in the EU. The competition for young scientists will be settled on June 6 after all candidates have made their presentations.

PAP - Science in Poland

ekr/ zan/ kap/

tr. RL

Copyright © Foundation PAP 2019