Ft. Calhoun Geo-Testing Shows A Dangerous Potential

Public records requests by Clean Nebraska were able to obtain portions of the initial geologic testing report for Ft. Calhoun. The report itself was large, what it contained has mostly not been part of the public discussion about Ft. Calhoun from either OPPD or the NRC. The review here is quite long but it has been broken into sections to facilitate reading. The short of this is there are problems or potential problems, some of them with the ability to be major and they reside under the containment, spent fuel pool, auxiliary building and turbine building.

Erosion issues
Ft. Calhoun was “significantly challenged” by the 2011 record flood according to plant owner OPPD. The post flood reviews initiated by the NRC included a request for geologic testing at the site. OPPD has released portions of the first geo testing report upon a request by Clean Nebraska for the documents. What was found in a review of the available document shows widespread unresolved and potentially dangerous problems at Ft. Calhoun. These problems involve various types of erosion and geologic formations at the site.

Ground fill
When Ft. Calhoun was originally built back in the 1960’s the site by the river was lower than it is today. About 10 feet of backfill dirt was piled up on site to raise the level of the plant. This backfill is susceptible to erosion and other types of movement under certain conditions. The report cited the backfill to be mostly clay, silt and sand composition. Bedrock is 69-75 feet below the plant. During the soil testing done at Ft. Calhoun OPPD instructed the testing company to not do certain testing on the top 10 feet of soil. OPPD’s claimed concern was that they didn’t want any possible underground cables to be cut. They had the testing company instead use a type of water drilling that makes the hole by pumping water and pulling out the soil. This makes testing the soil in that level impossible. The types of testing that could be done on the top 10 feet of soil frequently found problems described as soft spots, voids or other types of instability in testing locations. While OPPD wished to ignore the top 10 feet of soil at the plant the testing showed there is a considerable problem with that top 10 feet of soil and it has been creating damage at the plant since the 1990’s. The 2011 flood made these problems worse and created many new problems around the site. HDR does concede that the top 10 feet of soil “may have been disturbed” by the flood.

backfill in blue

Types of Erosion & Testing
HDR, the contracted company used Ft. Calhoun’s existing design and “as built” documents as the basis for their work. It has become known in recent months that both the design plans and the “as built” plans are incorrect and incomplete on a large scale. This creates a situation where all of the assumptions done by HDR may be built on incorrect information related to the building specifications. As they found out while looking for underground piping at the turbine building. Over 100 feet of underground pipe were not documented and most of the pipe locations on the “as built” plans did not match where underground pipes actually were. If HDR used Ft. Calhoun records that are incorrect it is a situation of “garbage in garbage out“. HDR also sorted potential problems based on probability. If they thought a problem was less likely to happen it was ruled out and not investigated further, creating a situation where a problem could have been overlooked. Visual inspection also led much of the additional inspection creating the potential for problems to go unaddressed because they had no outward signs. HDR implemented an attempt to track the elevation of structures to check for movement but declared is mostly to be unreliable to to margins of error.

HDR made a list of possible flood induced “mechanisms” that could cause damage at the plant. These included various types of erosion from multiple causes. Also mentioned in the report was the issue of existing karst formations under the plant. Karst formations are dissolved rock voids that can result in unstable land and commonly sinkholes, with some being large enough to swallow whole buildings. HDR considers the karst formation to be a credible issue and cited the potential for a foundation pile to punch down through a karst void if the right conditions happened. HDR also raised the potential of sink holes but couched this with the idea that the karst formations, if filled with water might prevent certain failure problems. These karst formations were known by OPPD even before they broke ground on Ft. Calhoun. The selection of the site for Ft. Calhoun was apparently a point of contention among the higher ups at OPPD making those decisions. The Dames & Moore 1967 geologic report shows multiple hazards in the area including “karst” features of the “Winterset Member” of the Dennis Formation. Karst formations can grow over time, Ft. Calhoun has been at this location for over 40 years giving time for changes to the existing karst voids. It is unclear why the AEC allowed a nuclear reactor to be built over land with questionable stability. The drawings below from the 1st geo-testing report shows the below ground structures. It shows a rather large void, fissure or karst formation directly under the reactor. It is not clear from HDR’s report or the drawing what the exact nature of the large section in blue is. It states “infill decomposed limestone”  but does not say if this was naturally full of decomposed limestone or if the area was filled in with decomposed limestone during construction. There is also no mention in the report to the nature of this filled in area.

The seismic investigation conducted found “low velocity” areas (softer or less dense) in the bedrock. The HDR report cites the possibility of karst features including voids, clay or water filled cavities or “solution” widened fractures and joints or zones of weak rock. The area above bedrock had similar soft areas that were assumed to be loose areas of sand and they found evidence of this in the boring work. Boring work found multiple voids down as low as 70 ft in the paved access area (area around the main buildings of the reactor).



illustration not to scale

Turbine Building
Considerable erosion was found under the turbine building and this seemed to be the epicenter of the concerns at the plant, or at least the most obvious evidence. Pipes running below the foundation slab were broken in multiple places and are drawing in considerable amounts of groundwater from the land under the building.Much of it is pouring into a sump pit in the turbine building basement.  Many of these pipes were found to be filled with sand. Water flowed through these pipes even when the plant was not discharging any water through them. This problem has been known since 1993 with little done to deal with it. In the 1990’s an attempt to inject concrete into an 8ft x 1ft void under the building failed. The concrete migrated and didn’t fill in the void. The turbine building has not been tested for seismic loading by HDR. This all puts the turbine building foundation slab, support piles and underground utilities at risk. These broken pipes could have also created an entry point for flood waters into the building. “Loss of lateral support for pile” foundation is cited as a credible possible problem underneath the turbine building. HDR found voids under the turbine building that were .5 to 11 inches at 16 locations under the turbine building. Soil “lacking pre-construction density” were found at all 26 testing points. they ranged from .1 foot to 7.1 feet. Some of these zones were as far down as 13.9 feet below the turbine building floor. 17 holes had NAS zones “below the bottom elevation of the pile caps”.

The containment building sits on steel pilings into bedrock, that are filled with sand and concrete. The mat foundation is 10-12 ft thick with 2 layers of reinforcing material. The interior is all cast in place. The containment building is steel lined inside and made of pre-stressed concrete. The 1968 piling plan was used for design assumptions for the containment building. So far no soil testing under containment has been done or reported. “Loss of lateral support for pile” foundation is cited as a credible possible problem underneath containment. HDR admits this erosion can not be ruled out as a “triggering mechanism” on the containment building. The foundation piles where they run into “solution cavities” go past the cavity to find a stopping point for the foundation pile. The newest soil testing for this structure is 1968 according to the report. The missile shield room had .8 feet of water inside as seen by the water line. Various utility conduits extend vertically from the ground here.  A sand boil or “piping” (erosion) void found was 3.5 wide by 1 foot deep in the SW corner of missile shield room. A stressing gallery tunnel below the containment base mat had water inside when HDR inspected months after the flood.  The water was clean but the source is unknown. They don’t know if this is a larger issue yet. Tests by Geotechnology Inc. outside the containment structures found “deep anomalies that could be gravel, soft clay, loose sand or possibly voids.” “The results of these additional forensic investigations show that soils in the vicinity of the Containment Building have been negatively affected by this triggering mechanism, and that the possibility exists that the soil under the Containment Building has also been negatively affected.” HDR suggested actual testing under containment be done by a 3rd party contractor.

Auxiliary Building
So far no soil testing under the auxiliary building has been done or reported. “Loss of lateral support for pile” foundation is cited as a credible possible problem underneath the auxiliary building. HDR admits this erosion can not be ruled out as a “triggering mechanism” on the auxilary building. The foundation piles where they run into “solution cavities” go past the cavity to find a stopping point for the foundation pile. The newest soil testing for this structure is 1968 according to the report. Below grade walls had water lines on them in the auxiliary building. The aqua dam failure allowed water 2ft high into the dock room and room 24A, water came in through cracks in walls and floors. The foundation piles are 25 feet below grade, but the voids under the turbine building have the potential to continue under the auxiliary building. The compacted soil and deep foundation rule out obvious failures like the maintenance building but there could be voids under the auxiliary building. HDR suggested a further 3rd party investigation underneath the auxiliary building that was beyond their abilities. HDR cited the potential for a lateral foundation pile failure that needs to be ruled out by inspection under this building. Additional forensic investigations showed the soils immediately adjacent to the auxiliary building have been negatively impacted by what they think is the erosion under the turbine building. The auxiliary building includes the spent fuel pool.

Maintenance Building
A concrete column in the maintenance building was found to be cracked and sunk. The floor drains in the maintenance shop were blocked apparently by the same infiltration as the pipes in the turbine building. The maintenance shop column has been sinking since before the flood and the area is bad enough the nearby mens room door no longer opens and closes. This included the column, the slab flooring and the partition wall between this building and the turbine building. HDR considers that the turbine building erosion issue could have continued on under the maintenance building. Ground Penetrating Radar Inc. found voids under the maintenance building column. Foundation footings for the maintenance building are on fill dirt. The 1977 geo-testing report before the maintenance building was constructed indicated 7 to 9.5 feet of fill material had been placed on that site. The maintenance shop “under building voids” were up to 8.5 inches in size and focal towards the failed column location. HDR cites no flood damage here but prefaces that with the disclaimer that they didn’t study the first 10 feet of soil. Of course that is the location of most of the problems.

Sunken pavement and voids were found between the intake building and the “service” building. Water seepage at a manhole, intake structure, water hydrant failure and voids under the road pavement were found.  HDR did not inspect these voids, OPPD repaired the concrete and did no further work on the area. The erosion situation under the turbine building could be either continued out to these other areas or similar ones could be going on there. The lowering of the river level as the flood receded could have caused some of this according to HDR. The Intake system is required for fire fighting at Ft. Calhoun. The Intakes have ongoing groundwater infiltration via cracks in the structure and was said have some flood leaking due to cracks. The river side of the intake building was not inspected due to high water levels at the time and the intake analysis was done with very limited data. The top 10 feet of soil again was excluded from the analysis.

Radioactive Storage
The truck bay of the radioactive waste building was flooded when the aqua dam failed. This “class 1” building has cracks in the walls. HDR was unsure if these were caused by the flood or not. Only some rooms were inspected in this building and all assumptions are based on the “as built” design documents that are known to be incorrect in many cases. The sumps of the building are required to store accumulated water from this building but it was openly flooded to the river. It is not clear if this ever posed any contamination risk or not. HDR considers the flooding of the area around the radioactive waste building to be likely caused by dry soil that was saturated for the first time by the flood causing soil collapse. HDR said they did not have enough data to make a more definitive statement about the radioactive waste building. Deep anomalies were found around the outside of the radioactive waste building during soil inspection. There are some foundation pile supports underneath parts of the building, this could cause uneven settling of the building.

Other Structures
The old steam generators that were removed from the reactor building, the cask storage and transmission towers did not have any flood protection according to HDR’s report.
Pipes under the technical support building were “open” and aggregate (small rocks) could be seen in the pipes.
The circulating water system, condensate storage tank and underground utilities were all cited as potentially being at risk due to the underground erosion found. The condensate storage tank is a part of the emergency cooling system. Underground utilities includes raw water, fire protection, fuel oil and the main cable bank.  HDR didn’t completely clarify actual risk or lack of risk for these pieces of the plant. The service building walls were also found to have cracks though no determination was made as to the cause.

Decades with no deadlines
Problems at Ft. Calhoun have been known since before the plant was built. These current erosion issues have been known since the 1990’s. There are many documented NRC mentions of these problems yet Ft. Calhoun was never forced to resolve any of them for decades. The HDR report refers to many of these previous incidents the NRC knew about. Now there is the potential that the entire plant could be at risk. The 1993 discovery of the erosion problem under the turbine building co-incided with a previous Missouri river flood event. Ft. Calhoun flooded a second time 18 years later with the same geologic failures still unresolved.

What it all means
Erosion could extend out creating large voids under the turbine building base slab and potentially under the containment building and other important buildings at the plant. The potential damage includes loss of soil support around foundation piles leading to pile buckling, decreased pile capacity and foundation failure. HDR calls this possible but unlikely, but urges additional inspection to know more. There are clearly problems with the backfill soil that resides under the plant. OPPD’s request that the top 10 feet of soil be largely ignored vs. the problems found when that layer was tested shows there is a problem in that upper soil level. The specter of widespread voids or areas of instability under the plant is too serious to simply dismiss without in depth inspection to gain conclusive findings. The ongoing admitted and found shallow problems at the plant should obviously all be completely resolved without corner cutting before the NRC should even consider a restart. The deeper problems and questions about the areas under the reactor, auxiliary and turbine buildings must be properly determined with a high level of confidence. The idea of a nuclear reactor potentially sitting atop a sinkhole is exactly the kind of high risk low probability event that shocked the industry at Fukushima. But right now the probability isn’t known as not enough information is available about the true conditions under the plant. Ft. Calhoun sits upriver on one of the US’s major water ways that is also used as drinking water throughout the region. The plant has a very small energy output at only 476 mw compared to around 1000 mw for most commercial power reactors and Omaha has been doing fine without it.

Of all of the potential reasons for the extensive damage found at the plant, HDR kept going back to the broken pipes at the turbine building. All other potential causes were quickly ruled out. Sticking to this broken pipe cause conveniently rules out any natural causes that would be impossible to fix. The broken pipe cause creates a scenario where the problems are something that can be managed and resolved, potentially leading to a restart. Of course any private company would be reluctant to damage a client who paid for an expensive report. This shows the problematic nature of relying on investigative reporting that is solicited by the power company. This is something Japan’s new nuclear regulator has identified and addresses. While they still have power companies do their own investigations into issues. They also do their own hands on investigation and rely on a wider array of experts to establish their understanding of things like geologic problems at a facility.

The findings at Ft. Calhoun show that the potential problems should not be shrugged off as unlikely and left unaddressed for another 18 years. Clear answers with valid data and high confidence should be assured before any discussion of restarting Ft. Calhoun is considered.

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