CONCRETE CANCER | COVER STORY
Above: ASR cannot be ‘remediated’ so that the expansion stops, to do so requires complete replacement
staff had previously said that the NRC has identified three findings, which NRC described as being “of very low safety Significance,” but highlight the fact that “continued focus is warranted”. For example, the Containment Enclosure Building had
deformed towards the Emergency Feedwater Pumphouse until they touched and a ‘seismic gap’ was lost. A separate containment internal structure issue dates
back to 2021, discovered during Seabrook’s autumn refuelling outage. The NRC inspectors became aware of cracking and spalling in the reactor cavity pit area of the containment internal structure – normally inaccessible during operation as a locked high-radiation area. There were visual indications that there was ASR on the other side of the wall. As an interim test, the licensee applied reasonable ASR loads and concluded the structure is still able to withstand the effects of ASR. Later root cause analysis required the development of finite element models. In March 2024, NRC staff were able to go on-site and review the root cause studies as well as the completed structural evaluations. NextEra wanted to understand the distresses that they were seeing in the containment internal structures, including spalling and cracking in the reactor cavity pit, and also distresses in other areas of the containment internal structure.
The C-10 group asked the NRC to make more data on
the issue public, saying that without it “any assessment of ASR’s impact is incomplete and potentially misleading”. Maintaining expertise on ASR was a concern for both the citizen group and for NRC. C-10 wanted to know the NRC and NextEra’s plans to
expand and preserve their technical understanding of the ASR issue, suggesting that early understanding of the issue had been relatively simplistic and that NRC have very few staff expert in the issue. There had also been changes in the ACRS since its members were last briefed on the issue in 2022.
The NRC staff had also made note of the issue and the
need to have people in post “who must be cognizant of the ASR degradation mechanisms present at the site and how the effects manifest throughout the structures”. They highlighted on-site visits where the team included extra people who had joined the Civil and Structural Engineering Branch and were there to be brought up to speed on ASR, for ‘knowledge transfer’ purposes. The fact remains that as Seabrook is the only US nuclear
reactor to have to manage ASR, retaining institutional knowledge over the long term is a challenge. NRC and the plant operator have to keep a watching brief over their expertise and knowledge with the same care needed to manage the ASR itself. ■
Summary of the ASR Licence Conditions ● Assess expansion behaviour to confirm it is comparable to the large-scale test programme and check the margin for future expansion.
● Corroborate, using Seabrook field data, the concrete modulus to expansion correlation used to calculate pre-instrument through-thickness expansion.
● Conduct a volumetric expansion check for control extensometers every six months. ● Develop a monitoring programme to ensure that rebar failure or yielding does not occur, or is
detected if it has already occurred, if the structural evaluations indicate rebar stress may exceed yield.
● If the ASR expansion rate significantly exceeds 0.2 mm/m (0.02%) through-thickness expansion per year, NextEra will perform an engineering evaluation focused on the continued suitability of the six-month monitoring interval.
● Each core extracted from Seabrook Unit 1 will be subjected to a petrographic analysis to detect internal microcracking and delamination.
www.neimagazine.com | June 2025 | 19
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47
