CNS Status

3/24/2019 - 4:01 p.m.
Nebraska Public Power District and Cooper Nuclear Station management announced at 4:01 p.m. Sunday, March 24, the plant had exited the emergency classification of a Notice of Unusual Event (NOUE) status it entered early Friday morning, March 15.

Missouri River water levels near Cooper have dropped to 896 feet mean sea level, three feet below 899 feet MSL – the level at which Cooper was required to enter the emergency classification status. Weather forecasts and U.S. Army Corps of Engineers expected upstream dam releases indicate the river’s level at Brownville will slowly continue to drop. The plant operated safely while under a NOUE.

Utility officials made the decision after several days of river elevations consistently dropping below the 899-feet sea level mark and discussing the decision with county and state agencies. Plant staff also conducted a thorough assessment of the site’s emergency preparedness plan before making the decision to exit the NOUE.

The station made the notification as part of the station’s emergency preparedness plan that includes procedures to follow when flooding conditions are in effect. Cooper was in the Notification of Unusual Event status for nine days.

There was no threat to plant employees or the public throughout the event. A Notification of Unusual Event is the lowest and least serious of four emergency classifications established by the Nuclear Regulatory Commission for nuclear power plants.

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Is NPPD's nuclear power plant, Cooper Nuclear Station, safe from the Missouri River floods?

Cooper initiated its flood procedure plan earlier this week and is following a series of steps that involve proactively preparing the site for potential flooding.

The plant was designed to withstand various natural disasters, including flooding. For example, the site was built 13 feet above the natural grade to an elevation of 903 ft. mean sea level (MSL) to accommodate the maximum, probable flooding event.

How do we know Cooper can withstand flooding conditions?

Cooper began commercial operation in 1974. A flood occurred in 1984, when water levels reached 897.7’ mean sea level and also in 2008, when flooding conditions caused water levels to reach 896.7’ MSL.

In 1993, localized flooding occurred in the area and heavy rains caused extensive damage to many roadways in the 10-mile zone around Cooper. Water levels reached 900.8’ MSL.

On June 22, 2010, water levels at Cooper reached 899.4’ MSL, and, as it did in 2011, NPPD declared a Notification of Unusual Event. The station exited its emergency classification on June 25, when flooding conditions subsided below 899’ MSL.

This past Friday morning, Cooper issued a Notification of Unusual Event when river levels reached above the 899 MSL. 

What actions have Cooper Nuclear Station personnel taken to protect the plant from flood waters?

Nebraska Public Power District officials do not expect floodwaters to impact vital plant equipment, but have installed various methods of barriers to protect buildings and structures from flooding.

Protection is also achieved through the station’s redundant power supply and safety systems and through operational staff’s adherence to daily procedures in its emergency preparedness plan. A supplemental plan is also in place to ensure response organizations are staffed and personnel are available to meet the needs of the station on a 24-hour basis.

What is a "Notification of Unusual Event" and why did NPPD declare one at Cooper Nuclear Station?

A Notice of Unusual Event or NOUE is the lowest level of emergency classification for a nuclear power facility as designated by the Nuclear Regulatory Commission. Cooper Nuclear Station declared at NOUE on Friday, March 15, due to flood waters reaching a mean sea level greater than 899 feet. There is no release of radiation and no threat to the public as a result of entering this NRC classification level.

Cooper Nuclear Station stores spent fuel rods at the plant. If the Missouri River rises high enough, could they be flooded over and contamination be carried downstream?

No, contamination could not be carried downstream. Fuel rods at the plant are stored in safe, secure facilities.

There are two methods of storage for spent fuel rods that have been used in the reactor at Cooper Nuclear Station – one is a dry cask storage facility and the other is the spent fuel pool.

The dry cask storage facility is located on a concrete pad on the north side of the facility. It is designed to withstand earthquakes, tornadoes and flooding. When fuel is taken from the spent nuclear fuel pool, it is placed into specially designed, NRC approved steel canisters which are pressurized and welded shut after loading. The steel canister keeps radiation from the environment, although there is some heat being generated by the natural radioactive decay of the fuel rods.

The canister, which has been decontaminated, is placed inside a horizontal storage module (HSM), which are large concrete structures that weight 160 tons each. The HSM is designed to allow air movement around the canisters to reduce residual heat generated by the decay of the used fuel.Water could flow around the canisters but would not contain any radioactive material. The storage facility is built to the plant grade and the modules are designed to withstand flood waters that reach 50 feet above it. The storage units require no electricity to operate.

The second storage facility is known as the spent fuel pool, which contains the majority of used fuel that has been removed from the reactor during refueling outages. This pool contains water, which is excellent at suppressing radiation and transferring heat. In the event off-site power is lost, safety systems would be initiated and would continue to bring cooling water into the reactor. 

If flood waters rise, can it flood Cooper Nuclear Station's reactor building?

It is highly unlikely that Missouri River water would ever reach the reactor building. Barricades have been placed both outside and inside the building to keep the water away, and these barricades are built four feet tall. The water would have to be above 907 feet mean sea level before it could enter the building. That would be a seven-foot rise above the river’s current water level. Even if water reached the reactor building, it would be directed to floor drains.

Can or will a nuclear emergency, such as what happened at Japan, occur in Nebraska?

The Midwest is NOT susceptible to a tsunami. The plant is designed against flooding from the Missouri River, and NPPD is working with a number of entities to monitor the flooding conditions. 

Cooper Nuclear Station has multiple safety and backup systems in place to respond to major, natural disasters or crisis events such as flooding, earthquakes or tornadoes. In addition, the site has a“beyond-design-basis” strategy, which addresses accident sequences that were not considered in the design process because they were judged to be too unlikely. They are considered beyond the scope of a design-based accident. To our knowledge, the Japanese do not plan for “beyond the design.”

If Cooper Nuclear Station is shutdown due to flooding, will NPPD be able to meet its customer demand for electricity?

Yes, NPPD relies on a diverse mix of power plants across the state to generate electricity. These power plants use a variety of fuel types ranging from nuclear, to coal, natural gas, hydro, oil, wind and solar. Each of these generating plants also provide a different level of electricity output, but are used in combination to serve customers’ electricity needs in NPPD’s service area.