Belgian Federal Agency for Nuclear Control (FANC) director-general Jans Bens has called for careful inspection of all 430 nuclear facilities globally.

The Belgian regulatory chief issued the recommendation after detection of multiple cracks in critical components of two reactors, Doel 3 and Tihange 2. Meanwhile the UK’s nuclear regulator told PEi that its nuclear facilities are unaffected by the problems discovered in Belgium.

Jan Bens of FANC
Steel nuclear reactor pressure vessels in Doel 3 and Tihange 2 plants were found to be affected in 2012, which had initially been dismissed as manufacturing defects by the operator of the reactors, Electrabel.

“What we are seeing in Belgium is potentially devastating for nuclear reactors globally due to the increased risk of a catastrophic failure.”

Further tests in 2014 at the facilities indicated advanced embrittlement of the sample steel vessels. Unexpected cracking in the vessels can be caused due to corrosion from normal operation.

The presence of highly radioactive nuclear fuel cores in the vessels raises the risk of accidents during malfunction, and it is assumed that this could be an issue with all nuclear power generation facilities worldwide.

A spokesperson for the UK nuclear regulator said it had no cause for concern at what it maintained is the only nuclear facility relevant to the Belgian case: EdF’s Sizewell B plant.

Jo Debank of the Office for Nuclear Regulation (ONR) told Power Engineering International, “The ONR is aware of recent developments from a programme of materials properties testing for the steel Reactor Pressure Vessels (RPVs) of the Doel 3 and Tihange 2 plants in Belgium.  The only operational civil nuclear plant in the UK with a steel RPV is Sizewell B.”

“The site licensee EdF Energy performed a safety review of the Sizewell B manufacturing and inspection records and concluded that the RPV was manufactured in such a way as to minimise the risk of occurrence of hydrogen-flakes, and the RPV was inspected rigorously during manufacture such that, in the unlikely event that hydrogen flakes occurred, they would have been detected and recorded.”

ONR considers that these conclusions are not challenged by the recent developments in the Doel 3 and Tihange 2 nuclear plants in Belgium.  The safety case for operation at Sizewell B, is therefore unaffected.  ONR will continue to monitor developments relating to this matter through cooperation with international regulators.”

The problem was initially discovered in the summer of 2012 and both the Doel 3 and Tihange 2 reactors were shut down since March 24th, 2014 after additional tests revealed an unexplained advanced embrittlement of the steel of the test sample. The integrity of the pressure vessel must be absolute due to the radioactive releases that would result if this component were to fail.

FANC has subsequently issued a statement confirming that the additional tests conducted in 2014 revealed 13,047 cracks in Doel 3 and 3,149 in Tihange 2. On February 15th the nuclear reactor operator, Electrabel (GDF/Suez) announced that it would be prepared to ‘sacrifice’ one of its reactors to conduct further destructive tests of the reactor pressure vessel in order to study this poorly understood and extremely concerning damage phenomenon. 

Material scientists who investigated the site said their findings indicate that the problem could be far beyond manufacturing. If confirmed, it means that the safety of every nuclear reactor on the planet could be significantly compromised.

During ultrasonic, material properties and structural integrity tests, the scientists found a fracture toughness test revealing unexpected results, which suggested that the mechanical properties of the material were more strongly influenced by radiation than experts had expected. As a precaution both reactors were immediately shut down again. Electrabel launched a test campaign to find an explanation for the unexpected test results.

Subsequent tests proved to be able to detect flaw indications in the wall of the RVP.

Currently a 4th irradiation campaign is being executed in the research reactor and the results of this irradiation campaign and of the subsequent material tests are expected by April 2015.

Meanwhile, the Belgian security authorities need time to look into this new information and will continue their analysis during the first months of 2015. They are also calling in the help of international experts who are specialized in damage mechanisms caused by radiation and in mechanical resistance tests.

This international expert panel (International Review Board) met for the first time in Brussels at the start of November 2014. The main conclusion of this meeting was that the methodology used by Electrabel was not yet sufficiently developed to make a well-grounded judgment.

The international experts have formulated some suggestions for further actions and studies. Based on these suggestions and on the documents already analyzed, the Belgian security authorities have passed a series of additional demands and suggestions to Electrabel, so that the licensee can adjust its methodology and validate the underlying hypotheses of its arguments.

In April 2015, the FANC will organize a new meeting of the international panel of experts to obtain their advice on the results of the new material tests and on the new data provided by Electrabel.

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