and others like to talk about “problems in the aggregate,” or a
big-picture view of the issues. But that phrase is taking on new meaning
in the case of the Seabrook nuclear power plant, where there are concerns involving the aggregate used in the concrete.
specifically, the problem at the New Hampshire facility is the
intrusion of moisture into the foundation walls of certain structures,
resulting in the degradation of some of the concrete.
exact term for what is occurring at Seabrook is alkali silica reaction,
or ASR, which involves the hydroxide ions in the pore solution in
cement paste and the reactive silica in aggregate. (Aggregates are inert
granular materials, such as sand, gravel or crushed stone that, along
with water and cement paste, are an essential ingredient in concrete.)
The main byproduct of ASR is a gel, which can expand and may cause
micro-cracks in the concrete.
the extent of the problem is still being evaluated, structures
identified as being affected by ASR are considered “operable but
exactly does that mean? In layman’s terms, it means the NRC – while far
from done with reviews of the issue – has determined the structures can
continue to safely perform their function based on the following
1. Conservative safety load factors, or the extra safety margin that was included when the structures were designed and built;
2. Visual observations by qualified NRC inspectors;
3. The fact that the ASR is limited to localized areas; and
4. Because progression of the concrete degradation is occurring slowly.
determination, contained in an NRC inspection report issued on March
26, was the result of reviews carried out by six of our inspectors over
many months, dating back to last September. Among other things, we made
use of concrete/structural integrity expertise at our headquarters
office. We also had an inspector in our Region III office, in suburban
Chicago, observe lab tests performed in Northfield, Ill., on concrete
core samples taken from Seabrook.
important next step for the NRC’s review of the Seabrook concrete
degradation will be a public meeting scheduled for Monday, April 23, at
our headquarters office in Rockville, Md. During that meeting, the NRC
staff will discuss with NextEra, the plant’s owner and operator, its
analysis of the issue, planned corrective actions and dates to fully
correct the problem, as well as other details.
on the outcome of that session, the NRC will determine its next steps
regarding the issue. One thing we have already made clear is that no
decision will be made by the agency on a license renewal application for
the plant until the extent of the concrete degradation is fully
of the public who would like to listen in on the meeting but cannot
travel to NRC headquarters will be able to do so by phone bridge. What’s
more, the slides to be used during the session will be available via an