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24 June 2011. New York Times report, 24 June 2011, on flooding disputes between NRC and nuclear plant operators along the Missouri River:

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Cooper Nuclear Station Missouri River Flood 1994



March 31, 1994

                               LOCAL AREA FLOODING


All holders of operating licenses or construction permits for nuclear power


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to emergency preparedness, equipment operability
and radiological control problems that may result from local area flooding.
It is expected that recipients will review the information for applicability
to their facilities and consider actions, as appropriate, to avoid similar
problems.  However, suggestions contained in this information notice are not
NRC requirements; therefore, no specific action or written response is


The Cooper Nuclear Station is located between Nemaha and Brownville, Nebraska
and is adjacent to the Missouri River.  The facility floor and plant grade
elevations are about 275 meters [903 feet] above mean sea level.  The
elevation of the area surrounding the plant is about 271.3 meters [890 feet]
and the area is protected by a levee to an elevation of 274.9 meters
[902 feet].  The normal groundwater table is 267.9 meters [879 feet].  The
level for the 1000-year flood and the 10,000-year flood are predicted to be
274.3 and 274.9 meters [900 and 902 feet], respectively.  During this event,
the Missouri River peaked at 274.6 meters [900.8 feet].

Description of Circumstances

During the months of June and July 1993, the State of Nebraska and several
surrounding states experienced record rainfalls that caused flooding over
extensive areas.  In accordance with plant flood procedures, the licensee for
the Cooper Nuclear Station had placed barriers around the entrances to the
reactor building, the radwaste building, the turbine building and the diesel
generator rooms when the water level in the Missouri River reached 273.4
meters [897 feet].  On July 21, the licensee began a reactor startup from a
scheduled refueling and maintenance outage.  At that time, the river level was
273.1 meters [896 feet] and decreasing.

On July 22 and 23, the river level rose rapidly and, at 10:35 a.m. on July 23,
the licensee decided to shut down the reactor.  At 6:19 p.m. on July 23, the

9403250222.                                                             IN
94-27                                                              March 31,
1994                                                              Page 2 of 3

licensee declared a Notice Of Unusual Event when the water level in the
Missouri River reached 274.0 meters [899 feet].  The river level continued to
rise and subsequently peaked at 274.6 meters [900.8 feet].  The elevated river
level caused the closure of several area roads including a portion of
Interstate 29 and Route 136 in the State of Missouri which isolated one of the
planned emergency evacuation routes.

Subsequent to the reactor shutdown, the licensee noted increased inleakage.
The vital area rooms outside of the radiologically controlled areas were
relatively dry with only a minor amount of water leaking in through the
concrete walls below ground elevation.  However, some of the below-grade rooms
inside radiologically controlled areas in the turbine building and the reactor
building, had extensive inleakage.  In some cases, the inleakage significantly
challenged the capacity of the floor drains.  Examples of this problem were:
(1) a lower hallway in the turbine building where standing water was found and
water was leaking in around safety-related cable trays and (2) the
turbine-driven feedwater pump rooms where water was dripping on control boxes,
and the floor drain system had backed up so that standing water from within
areas known to be radiologically contaminated had migrated out into designated
clean areas.  The NRC inspectors observed that plant personnel had not taken
actions to identify the areas where inleakage was occurring and had not
established measures to divert the water away from important components.  The
turbine building inleakage was eventually stopped when the licensee pumped out
the underground cable tunnels that encircled the plant.  The heavy rains had
flooded the cable tunnels and water was covering the manways and storm drains
at grade level.

Similar problems were observed in the reactor building quadrant rooms and
torus room.  Water leaking into the reactor core isolation cooling (RCIC) pump
room was impinging on RCIC electrical components.  Subsequently, an
annunciator lit up indicating a ground in the RCIC 250-V dc circuitry.  This
ground was apparently caused by water that had entered into some of the RCIC
circuitry.  The water leaking into the torus room was impinging on junction
boxes and other electrical components.  The inleakage in these areas was not
appreciably reduced when the licensee pumped out the cable tunnels and storm
drains.  However, the inleakage did decrease as the river level dropped.


This event demonstrates that flooding problems and degradation of equipment
may be caused by water inleakage even though flood waters are not above grade
elevations.  Water leaking through underground walls may impinge on electrical
equipment or may enter radiologically controlled areas and spread
contamination to other areas.  Underground cable and pipe tunnels may become
flooded and serve as pathways for water to enter plant buildings.  Management
and plant personnel attention to these conditions is important to ensure that
equipment is protected and unsafe facility conditions are not created.  The .
IN 94-27                                                              March
31, 1994                                                              Page 3
of 3

NRC previously discussed problems caused by water leakage through conduit
seals into plant buildings in NRC Information Notice 92-69, "Water Leakage
From Yard Area Through Conduits Into Buildings."

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.

                                         Brian K. Grimes, Director
                                         Division of Operating Reactor Support
                                         Office of Nuclear Reactor Regulation

Technical contacts:  W. B. Jones, RIV
                     (817) 860-8147

                     J. L. Birmingham, NRR
                     (301) 504-2829

List of Recently Issued NRC Information Notices

Page Last Reviewed/Updated Wednesday, February 16, 2011