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Hydrogen Cracks in Belgian Nuclear Reactor Pressure Vessels: Five Years After Their Discovery

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Elaborates on some reported findings and identifies possible mechanisms and risks for further growth of defects in the reactor pressure vessel walls in the Belgian nuclear power reactors Doel 3 and Tihange 2 – which were restarted in 2015 after inspection found “thousands” of “hydrogen flaws”.

Product Number: 51317--9457-SG
ISBN: 9457 2017 CP
Author: Walter Bogaerts
Publication Date: 2017
Industry: Energy Generation
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$20.00

Hydrogen Cracks in Belgian Nuclear Reactor Pressure Vessels:Five years after their discovery – An updateIn June-July 2012 “thousands” of fissures were discovered in the Reactor Pressure Vessel (RPV) of the Belgian nuclear reactor Doel 3 during an ultrasonic inspection (UST). In September 2012 similar defects but fewer in number were also found in the reactor Tihange 2. Both RPV forgings were produced by the same fabricator which also delivered some 10 vessels to US nuclear plants.“Hydrogen flakes” originating from the processing of the original RPV ingots were identified as the root cause of the problem. After an initial series of investigations the reactors were authorized to re-operate until a number of anomalous embrittlement results were found in irradiation experiments on similar materials. After the stop of the reactors new UST inspections in 2014 indicated the presence of a total of 13047 “hydrogen flaws” in Doel 3 and 3149 in Tihange 2. However some three years after the first detection of these “thousands of hydrogen flaws” in the RPV shells and after new investigations both reactors received authorisation to restart in December 2015. Since then the affected reactors have been plagued by a number of scrams and unforeseen shutdowns.In view of all this the potential problem of (hydrogen-related) crack-growth in the RPVs and the related longer-term aging problems of the reactors are still imminent and deserve further attention; probably more than ever.This paper briefly elaborates on some findings and new research results and identifies possible mechanisms and risks for further growth of the defects in the reactor pressure vessel wall. The current study shows that – despite a number of counter-arguments – there are for instance significant potential risks or at least uncertainties about the role(s) of process-generated hydrogen (e.g. originating from corrosion radiolysis etc…). Also the more recent finding of similar UST-results in the Swiss reactors Beznau 1 (and 2) is a matter of concern.

Key words: nuclear, RPV, cracks, hydrogen

Hydrogen Cracks in Belgian Nuclear Reactor Pressure Vessels:Five years after their discovery – An updateIn June-July 2012 “thousands” of fissures were discovered in the Reactor Pressure Vessel (RPV) of the Belgian nuclear reactor Doel 3 during an ultrasonic inspection (UST). In September 2012 similar defects but fewer in number were also found in the reactor Tihange 2. Both RPV forgings were produced by the same fabricator which also delivered some 10 vessels to US nuclear plants.“Hydrogen flakes” originating from the processing of the original RPV ingots were identified as the root cause of the problem. After an initial series of investigations the reactors were authorized to re-operate until a number of anomalous embrittlement results were found in irradiation experiments on similar materials. After the stop of the reactors new UST inspections in 2014 indicated the presence of a total of 13047 “hydrogen flaws” in Doel 3 and 3149 in Tihange 2. However some three years after the first detection of these “thousands of hydrogen flaws” in the RPV shells and after new investigations both reactors received authorisation to restart in December 2015. Since then the affected reactors have been plagued by a number of scrams and unforeseen shutdowns.In view of all this the potential problem of (hydrogen-related) crack-growth in the RPVs and the related longer-term aging problems of the reactors are still imminent and deserve further attention; probably more than ever.This paper briefly elaborates on some findings and new research results and identifies possible mechanisms and risks for further growth of the defects in the reactor pressure vessel wall. The current study shows that – despite a number of counter-arguments – there are for instance significant potential risks or at least uncertainties about the role(s) of process-generated hydrogen (e.g. originating from corrosion radiolysis etc…). Also the more recent finding of similar UST-results in the Swiss reactors Beznau 1 (and 2) is a matter of concern.

Key words: nuclear, RPV, cracks, hydrogen

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