– Gov’t: Erosion is “undermining foundation” of major dam upstream of US nuclear plants — “Extensive network” of seepage paths found — “Water flowing through from multiple sources & multiple directions” — Nuclear plants doing Problem Evaluation Reports on ‘complex and urgent’ situation (VIDEO) (ENENews, July 30, 2015):
TVA’s Boone Dam repair announcement, Jul 30, 2015 (emphasis added):
- 2:30 — The location of this sinkhole and the presence of the sediment… really raised the possibility of a safety concern with the dam… The initial investigation showed that we had internal erosion. A phenomenon called ‘piping’ where voids from water flowing through the dam — more of a stream-like effect — than just seepage. Internal erosion is one of the leading causes of dam failures around the world. So we knew that we had to do something here to protect the safety of the public… particularly downstream risk… Around the clock inspectors [are] keeping surveillance on the dam [and we have] sensors to monitor movements that might occur in the dam itself.
- 4:00 — One of the key findings so far is that water is flowing through the foundation from multiple sources, and in multiple directions. It’s actually seeping through porous rock — rainwater upstream, through porous rock, through the dam…
- 9:15 — There’s still a lot of unknowns as we move into the project.
- 21:30 — There’s only 3 companies in the world that do this kind of remediation. That’s the complexity we’re talking about.
- 24:00 — Reporter: You said that water was coming from multiple sources and moving in multiple directions. To the people who are watching… I would think they would think that seems like an impossible task to do. There are some… in this community who think… that Boone Dam can’t be fixed… Is there a possibility that these solutions that you’re proposing won’t work?
TVA’s Boone Dam Investigation and Analysis Summary: [There is] “internal erosion,” in which voids develop within a dam and/or its foundation because of the action of flowing groundwater… one of the leading causes of dam failures… March of 2015, TVA discovered a well-developed, complex network of groundwater seepage paths coming from sources other than the reservoir… surface runoff flows underneath the dam and is a leading contributor to the observed seepage and sinkhole… Further investigation has confirmed that deterioration of the cutoff trench has occurred as seepage flows continue to undermine the foundation of the embankment dam… If left unaddressed, continued internal erosion may lead to enlargement of the network of voids at which time a large influx of water into the voids could cause rapid acceleration of internal erosion and eventual breaching of the dam. Due to the complex and urgent nature of the situation at Boone Dam, TVA has complemented its own dam safety engineers with nationally recognized experts… In its current state, the dam cannot be relied upon to serve the functions for which it was constructed. In the unlikely event of a dam failure, risks to the public would include: … loss of critical infrastructure [and] potential loss of life… [We are] engaging local and state emergency management officials… developing specific plans to address potential emergencies and conducting mock exercises to execute those plans. TVA has also initiated efforts to reinforce downstream facilities in a way that will minimize potential risks from an unlikely failure of Boone Dam.
TVA’s Boone Dam Weekly Update, Jun 23, 2015: Our investigation has shown that more water is seeping through the foundation of the dam than would typically be expected. A contributor to the seepage is the high water table from the area just east of the dam. Both sources of seepage and subsequent erosion have created an extensive network of seepage paths beneath the dam… TVA Dam Safety experts [are] working to understand the extent of the seepage and erosion…
Sequoyah Nuclear Plant – NRC Integrated Inspection Report (pdf), Feb 4, 2015: For the five operability evaluations described in the problem evaluation reports (PERs) listed below, the inspectors evaluated the technical adequacy of the evaluations… The inspectors completed five samples [including] PER 952079 – Functional Evaluation of Boone Dam Sinkhole.
Watts Bar Nuclear Plant – NRC Integrated Inspection Report (pdf), Feb 9, 2015: The inspectors reviewed the operability evaluations affecting risk-significant mitigating systems listed below [including] PER 952103 for the discovery of a sinkhole and tailwater sediment at the Boone Dam.