Terrorism thrown out of nuclear 'stress tests'

25 May 2011

'Stress testing' of the European Union's 143 nuclear power reactors will not specifically include terrorism after that idea was rejected by national safety regulators. 


Instead, the tests will focus on the aspects of nuclear plant safety highlighted by the Fukushima accident: earthquakes and flooding as natural events, as well as loss of safety functions and severe accident management following any initiating event.


The tests will be applied to the 143 nuclear reactors in the European Union's 27 member states, as well as those in any neighbouring states that decide to take part. Results are to be peer reviewed and shared between regulators, which retain sovereign authority on nuclear safety entirely above any powers of the European Commission or the European Council, which decided to carry out 'stress tests' on 21 March.


Representing the independent regulators of the EU, the European Nuclear Safety Regulators Group (ENSREG) said security issues like terrorism prevention and response were outside its mandate. It nevertheless noted the stress test analyses would be relevant for the eventuality of aircraft crash.


The push to include deliberate criminal attack had been led by Günther Oettinger, a German appointee to the European Commission selected for the energy brief. Despite gaining support from anti-nuclear countries such as Austria and Germany, Oettinger faced vehement opposition from nuclear users like France and the UK on national security grounds. For now, full consideration of security issues such as terrorism has been placed aside to be handled by a special working group of EU states and the EC. The 'mandates and modalities' of this group are to be set by the European Council.


Today Oettinger's staff used finely-tuned language to link the tests with terrorism: "These are comprehensive tests as the Commission has called for which embrace both natural and man made hazards (i.e. effects of airplane crashes and terrorist attacks)." They further emphasised in Q&A documents that aircraft crashes could be included among man-made events. That possibility actually lies with national regulators, which must submit their specifications to nuclear licensees by 1 June.


The tests 


Two 'initiating events' are covered in the scope: earthquake and flooding. The consequences of these - loss of electrical power and station blackout, loss of ultimate heat sink and the combination of both - are to be analysed, with the conclusions being applicable to other general emergency situations.


In accident scenarios, regulators will consider power plants' means to protect against and manage loss of core cooling as well as cooling of used fuel in storage. They will also study means to protect against and manage loss of containment integrity.


Nuclear plant operators are to begin work on a document for each power plant site. This analysis of 'extreme scenarios' will follow what ENREG called a progressive approach "in which protective measures are sequentially assumed to be defeated" from starting conditions which "represent the most unfavourable operational states."


The operators have to explain their means to maintain "the three fundamental safety functions (control of reactivity, fuel cooling confinement of radioactivity)" and support functions for these, "taking into account the probable damage done by the initiating event."


The documents have to cover provisions in the plant design basis for these events and the strength of the plant beyond its design basis. This means the "design margins, diversity, redundancy, structural protection and physical separation of the safety relevant systems, structures and components and the effectiveness of the defence-in-depth concept." This has to put focus on 'cliff-edge' effects, e.g. when back-up batteries are exhausted and station blackout is inevitable


For severe accident management scenarios they must identify the time before fuel damage is unavoidable and the time before water begins boiling in used fuel ponds and before fuel damage occurs. Measures to prevent hydrogen explosions and fires are to be part of this.




Operators should send a progress report on their work to their regulators by 15 August and a final version by 31 October. Regulators are to report progress to the European Commission on 15 September and in full by 31 December.


Information is to be shared among regulators throughout this process before the final reports go to peer-review by teams appointed by ENREG and the European Commission. The final documents will be published in line with national law and international obligations, provided this does not jeopardise security - another area where each country may behave differently.


Researched and written
by World Nuclear News