Closer monitoring required of Seabrook NPP concrete degradation

21 September 2020

The US Atomic Safety and Licensing Board (ASLB), under the Nuclear Regulatory Commission (NRC) has ordered stricter monitoring for Seabrook nuclear power plant's issues involving cracks in its concrete. It was issued in late August and made public 11 September, about a year after a   hearing on the issue.

The board is upholding, as well as expanding, the part of the plant’s licence that stipulates how it should manage the ageing and cracking of its concrete. Seabrook is the only US nuclear plant known to be experiencing this problem, which is caused by a chemical process known as alkali-silica reaction (ASR).

The new conditions require plant owner, Florida-based NextEra, to monitor the problem more closely and frequently.

In 2016, NextEra Seabrook, which operates the single-reactor Seabrook plant, requested the amendment for analysing the concrete degradation’s impact on safety-significant areas of the plant.

The C-10 Research and Education Foundation filed ten proposed contentions regarding the amendment. The ASLB granted a hearing in October 2017 on five contentions, which was consolidated into one – that NextEra’s large-scale concrete testing programme yielded data that are not representative of the reaction’s progression at Seabrook, and that the resulting monitoring, acceptance criteria and inspection intervals are inadequate. The Board held a full hearing on the matter in September 2019.

However, the 207-page ruling on 11 September imposed four additional conditions designed to further address the ASR concrete degradation issues:

  • NextEra will monitor certain devices measuring concrete expansion every six months, rather than starting in 2025 and every 10 years after that;
  • If stress analyses show degradation-related expansion and other forces will exceed the strength of rebar in the concrete, NextEra must monitor the affected rebar to ensure it has not yielded or failed, or detect such failure if it has already occurred;
  • If the degradation-related expansion rate in any area of a “seismic Category I” structure significantly exceeds a certain limit, NextEra will evaluate whether to implement more frequent monitoring; and
  • Each concrete core extracted from Seabrook must undergo a detailed microscopic evaluation to detect degradation-related features.

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