Nuclear accidents and developments in nuclear safety and radiation protection • 29 “The stress tests prove that things can move forward when everyone does their bit. It was a new idea and everyone bought into it. It is all the more miraculous given that it is never easy to reach a consensus in international bodies.” Olivier Gupta ASN Director General since 2016 “One of the remarkable things in the wake of Fukushima, was the stress tests episode. After the accident, WENRA held a meeting in Helsinki. Commissioner Günther Oettinger stated: “We have to conduct stress tests”. He undoubtedly had no idea what they were, but he thought that it was a good way of bothering the others… That was clear. During a WENRA meeting in Helsinki, I proposed to my colleagues to anticipate things by setting up a working group on the spot, to start thinking about what the content of the stress tests could be. It was led by Olivier Gupta (see opposite) who started to work that very evening in Helsinki! Fairly rapidly we had a stress tests project. It was subsequently reworked, but it nevertheless served as a basis for the process as a whole. I have warm memories of that period. We reproduced a process somewhat similar to the one created at the start of WENRA, concerning the obligations to be imposed on the Eastern European countries joining the European Union… When you take an initiative, you take it through to its conclusion!” André-Claude Lacoste ASN Chairman from 2006 to 2012 Stress tests The aim of the stress tests is to determine to what extent the NPPs have safety margins that guarantee their operational safety, even in situations of extreme emergency. Birth of the stress tests concept The concept emerged during a meeting of WENRA, the Western European Nuclear Regulators' Association, held in March 2011 in Helsinki, a fortnight after the Fukushima Daiichi NPP accident. The term stress tests was taken from the financial sector, in reference to the bank stress tests following the 2008 financial crisis. Olivier Gupta was present as Chairman of the WENRA Reactor Harmonization Working Group (RHWG). He recalls the scene: "The word has just been pronounced by Günther Oettinger, European Commissioner for Energy. Nobody had asked anything of us, but we said to ourselves: it's up to us to give him some intelligent content to try to do something with it. The idea was to say: finally, what happened at Fukushima? They lost all the external cooling sources, what we call the heat sink. They lost all the external and internal power supplies. And there were core meltdowns”. The incidents at Fukushima were caused by the tsunami and it is highly improbable that this would happen in Europe. It was not a question of thinking about why things happened, but just considering the input data: total loss of electricity, loss of cooling, and core meltdown, as a starting point for the reflection. There were numerous questions: what would happen in the European NPPs? How much margin do we have? That is to say how far are we from a situation that becomes catastrophic with massive releases? How much time do we have to act? There you have the basic philosophy of the stress tests, these are the questions that one asks. "I started out with a blank sheet of paper and two words – stress tests, rather like when you sit a philosophy exam. Everything was finished in about three weeks. This "miracle" reflects the context specific to WENRA. Year after year, we have established sufficient confidence between the participants at the difference levels to be able to move forward on difficult subjects such as this one, without conflict in a concerted and constructive manner”.
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