Weld repairs at Flamanville 36 February 2020
The viability of Flamanville 3 steam generators depends on weld repairs. Rumyana Vakarelska reviews repair plans.
PROBLEMS WITH EIGHT DEFECTIVE WELDS connected to the steam generators at the Flamanville 3 EPR in France were revealed during testing and future operation will depend on the success of weld repairs that will continue for at least the next three years, according to EDF.
The weld problems were initially revealed on 21 March 2018, when a quality deviation was discovered during the initial comprehensive inspection, including the legally required examination of the welds in the primary and secondary systems, a report by French nuclear regulator ASN said. This is the reference inspection for the state of the plant before it begins operating. Further weld deviations were subsequently detected. Last July, in a further update, EDF said a total of 33 welds had been found to have quality deficiencies and that they will be repaired. A further 20 welds would also have to be repaired even though they do not have any defects, according to ASN.
EDF’s proposed solution to the problems was first revealed in September 2019, and the company said in a detailed statement on 9 October that repairs will cost around €1.5 billion and that robots will be used to do the repair.
French nuclear regulator ASN said in a report analysing EDF’s proposed repairs that “it is considered that repair of the welds concerned before commissioning of the reactor is the baseline solution” to the problem. ASN is expected to validate repair work by the end of 2020, according to an EDF statement.
EDF said it expects fuel loading to start at the end of 2022, allowing commercial operations to start six months later. But if ASN does not approve EDF’s suggested weld repair method, an alternative plan developed by EDF will cost an extra €400 million and delay the start of operations until 2024.
Penetration weld repair most complex
Repairs to eight welds that connect the main steam transfer pipes that penetrate the two walls of the reactor containment are by far the most complex and costly of those required, according to ASN and EDF.
A London-based energy analyst said in an interview November 29 that the penetration welds “presented a challenge to EDF that is potentially open-ended. That is why the company had asked first to repair the welds after commissioning or even to try to find a solution where the problem would be mitigated, but the welds remained in place unchanged.”
ASN in its technical report noted that in 2018 EDF had, “proposed an approach aiming to justify maintaining these welds as they were. ASN then considered that the outcome of such an approach was uncertain and had asked EDF to begin preparatory operations prior to repair of the welds located between the two walls of the reactor containment.” Flamanville 3 was initially planned to start generating power in 2013 but is now expected to start operations about a decade behind schedule in late 2023 and at a total cost of around €12.4 billion.
Separately, EDF is also warning that additional delays are possible at the two EPRs at Hinkley Point C in England, adding £2.9 billion to their cost.
The welding problems at Flamanville are just one of a series of problems that have beset construction of the 1650MW reactor. They include cracking in the concrete dome of the containment, which were first discovered following tests in 2014.
An EPR at Olkiluoto 3 in Finland has also suffered delays of well over a decade and cost overruns of around three-times the initially planned budget due to a series of construction and engineering issues. However, the Taishan 1&2 EPRs in China started commercial operation on time and on budget in December 2018 and September 2019, respectively, after nine years of construction.
France must “exercise” nuclear capabilities
EDF chairman Jean-Claude Levy said that the French industry must “regularly exercise” its nuclear power capabilities if it wishes to remain a nuclear leader. Levy was speaking during a Senate economic affairs committee hearing on a government-commissioned report on Flamanville 3’s construction, and recent announcements by EDF and the French government about potential reorganisation of the company.
The report said a loss of skills during a gap in construction contributed to the lengthy delays and cost overruns at Flamanville. Also at fault were an overly complex construction and engineering process, with several French state companies and a number of international groups which all had competing visions for different parts of the construction programme. Since only one new reactor has been built in France in the last 25 years and the workforce in the country was either very old or very inexperienced.
Consequences of a pipe break
According to ASN the consequences of a main steam line break include:
- the release of large quantities of steam and energy which could damage equipment or buildings;
- mechanical loading that could damage equipment near or connected to the affected pipe;
- significant loads on the internal structures of the steam generators due to a pressure wave resulting from the break;
- sudden loss of cooling to the primary system, leading to an input of reactivity into the core and fuel damage.
About the author: Rumyana Vakarelska is a journalist covering the energy and environmental sectors