Victor Dricks
Senior Public Affairs Officer
Region IV
Torrential rains have been battering the Gulf Coast since Friday, but have not adversely affected any of the nuclear power plants in Louisiana, Mississippi, or Arkansas.
Though skies have now cleared over Baton Rouge, the area has been especially hard hit by flooding. But this has had no significant impact on the River Bend nuclear power plant, about 25 miles northwest of the city, or the designated routes that would be used to evacuate the public in the event of a nuclear emergency.
The Waterford 3 nuclear plant, located in Killona (about 25 miles west of New Orleans), has been similarly unaffected. “We’ve had some heavy rain here over the weekend but there has not been any real impact on the plant,” said NRC Resident Inspector Chris Speer.
Flooding is one of the many natural hazards that nuclear power plants must be prepared for. Every nuclear power plant must demonstrate the ability to withstand extreme flooding and shut down safely if necessary. Most nuclear power plants have emergency diesel generators that can supply backup power for key safety systems if off-site power is lost.
All plants have robust designs with redundancy in key components that are protected from natural events, including flooding. These requirements were in place before the Fukushima accident in Japan in 2011, and have been strengthened since.
As of Tuesday, Arkansas Nuclear One, in Russellville, has gotten about five inches of rain since Friday, NRC Resident Inspector Margaret Tobin said. “It’s a little muddy at the site, but that’s about it.”
At Grand Gulf plant in Mississippi, 20 miles southwest of Vicksburg, only light rain has been reported. “We actually had very little rain at the site, compared to what was expected,” said Matt Young, the NRC’s Senior Resident at the plant.
The NRC is closely following events and getting periodic updates from the National Weather Service on conditions that might affect any of the Gulf Coast nuclear plants. Additionally, the resident inspectors are monitoring local weather conditions to remain aware of conditions that could affect continued safe operations of the plants.
U.S. NRC Blog 
It is not that extreme hypothetical today and what is in our future?
The Probable Maximum Precipitation is defined as a specific rain event at the site location, and is a hypothetical indication of the extreme upper limit of precipitation events. It does not equate to an average rainfall rate for the given time period. For example, a thunderstorm may have a localized rainfall rate greater than what would be the calculated average rate for the PMP; however, the total rainfall for the duration of the thunderstorm at the site would be considerably less than the Probable Maximum Precipitation.
Victor Dricks
“The calamity struck quickly and ferociously. In one part of Livingston Parish, more than 31 inches of rain fell in 15 hours.”
I get a about a 50 inch in rate in 24 hours out of the above. Both plants are about 70 miles from Livingston.
You would think you would need about a 10 inch limit above 50 inch for conservatism.
What is the hole in my thinking here?
Thanks for the response.
Mike Mulligan
Hinsdale, NH
Waterford 3 is designed for a probable maximum precipitation of 39.4 inches in 24 hours, and River Bend is designed for 47.1 inches. Even though the rainfall this past weekend was substantial in parts of Louisiana, it did not challenge these plants’ design precipitation rates. Waterford 3 had about 4 inches in 24 hours, and River Bend experienced approximately 5 inches in the same time period. While both plants are designed to withstand external flooding, neither plant experienced abnormal ponding of water that impacted the sites’ safety equipment, operation, or emergency response capability.
Both Waterford 3 and River Bend recently re-evaluated potential precipitation and flooding scenarios using the NRC-approved methods as described in NUREG/CR-7046 (November 2011), “Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America,” and NRC Interim Staff Guidance to confirm the adequacy of the plants’ design following the Fukushima events.
There was no flooding at River Bend or Waterford, but as frequently occurs following heavy rains, there was some pooling of water at various places at each site, but nothing that has interfered with daily operations.
Victor Dricks
What is the design maximum hourly and total rainfall at River Bend and Waterford? I keep thinking about the corroded diesel generator diesel day tank tubing on the roof at Waterford the NRC discovered recently. There were all sorts of talk about the design precipitation rates and the maximum ponding on
the roofs, if the roof drain line clogs up in the violation process.
That was a great catch by the NRC and negligence on Entergy part with never inspecting the safety related tubing on the roof. I believe nobody ever in the history of the plant ever went up on the roof before the NRC trooped onto the roof in an engineering inspection. .
Does this storm (rainfall) and all the flooding challenge the plant design maximum precipitation rates and total?
Was there any abnormal local flooding and ponding of water anywhere on the sites of these two facilities?
How do we come up with plant design precipitation rates and are they valid in todays world?
I get 6″ to 10″ per hour at some location and in media reports?
Mike Mulligan
Hinsdale, NH