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NRC NEWS
U. S. NUCLEAR REGULATORY COMMISSION
OFFICE OF PUBLIC AFFAIRS, REGION III
801 Warrenville Road, Lisle IL 60532 |
| CONTACT: |
Jan Strasma (630) 829-9663/e-mail: rjs2@nrc.gov |
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Angela Greenman (630) 829-9662/e-mail: opa3@nrc.gov |
NEWS ANNOUNCEMENT: RIII-96-44 August 7, 1996
CONTACT: Jan Strasma 708/829-9663
Angela Dauginas 708/829-9662
E-mail: opa3@nrc.gov
NRC INSPECTION TEAM ISSUES REPORT ON FOAM SEALANT MATERIAL
FOUND IN EQUIPMENT COOLING SYSTEM AT LASALLE NUCLEAR POWER
STATION
A Nuclear Regulatory Commission Augmented Inspection
Team has issued its report on the foam sealant material found
in the equipment cooling water system, resulting in the
shutdown in late June of both units at the LaSalle Nuclear
Power Station.
The LaSalle Station, which has two reactors, is operated
by Commonwealth Edison Co. near Seneca, Illinois.
The NRC inspection was conducted July 1-17, and the
team's preliminary findings were discussed in a July 17
meeting, which was open to the public.
In May and June, a utility contractor repairing cracks
in concrete at the plant's water intake building injected a
foam sealant material in the cracks. Some of this material
entered a large water-filled tunnel beneath the floor of the
building and, in two instances, reduced the water flow into
systems which cool various plant components.
Initially, the utility believed that the foreign
material would not affect any plant safety systems because it
would float at the top of the tunnel. Subsequently, the
sealant material was found in the lower part of the tunnel
where it could affect the cooling system for safety-related
components.
When it was discovered that safety systems might be
affected, the utility shut both reactors down on June 28-29.
The units resumed operation after the foreign material was
removed and plant systems were thoroughly inspected and
tested.
The NRC team found that the cause of the foreign
material entering the cooling system was poor control of the
concrete crack repairs. The contractor was permitted to
perform the work with no knowledge of the potential impact of
the work, no approved procedures, and inadequate oversight.
In addition, once water flow in the equipment cooling
system was affected, the utility failed to rigorously pursue
the cause of the problem and to appreciate its significance.
The NRC team's function was to gather information about
the problem, its causes, and the utility's corrective
actions. Further NRC reviews will determine what violations
of NRC requirements occurred, if any, and what enforcement
action is appropriate.
The executive summary of the inspection report is
attached.
# # # # #
(NOTE: The full report may be obtained from the NRC Region
III Office of Public Affairs. It is also available on the
NRC's internet web site at the following address:
http://www.nrc.gov/OPA/reports.
# # # # #
NRC AUGMENTED INSPECTION TEAM REPORT EXECUTIVE SUMMARY
On June 19, 1996, with both units [at the LaSalle Nuclear
Power Station] operating at 100% reactor power, non-essential
service water discharge pressures began to decrease due to
high differential pressures across the in-line strainers.
Actions were successfully taken by the operators to backwash
the strainers and restore normal discharge pressures. On
June 24, 1996, the same problem recurred and a diesel fire
pump concurrently experienced high coolant temperatures
during routine surveillance testing.
The licensee's root cause determination following the initial
event on June 19 was inadequate and focussed on sandblasting
material that the licensee believed had become entrained in
the non-essential service water system and fouled the
strainers. Subsequent to the June 24 event, the licensee
determined that the cause of both events was injectable
sealant being used to repair cracks in the structure of the
safety-related service water intake tunnel. The intake
tunnel provides a common water source for both Unit 1 and
Unit 2 non-essential and emergency service water systems.
The crack repair activities resulted in a large amount of the
sealant getting into the tunnel and a portion of it being
drawn into the non-essential service water strainers.
Following the June 19 and 24 events, the licensee incorrectly
concluded that the material that fouled the non-essential
service water system could not affect the emergency service
water systems. On June 28, during service water intake
tunnel cleaning operations, divers found sealant in the
tunnel that could compromise operability of the emergency
service water systems. After some delay, the licensee then
declared the emergency service water systems inoperable and
shut down both units.
Subsequent to the events the licensee developed and
effectively implemented a plan to clean the sealant from the
intake tunnel and inspect selected system components. After
discussion with licensee management regarding NRC concerns on
the scope and direction of the licensee's actions, additional
plans were developed by the licensee which included the
inspection and cleaning of all emergency service water
strainers and performance of additional testing to ensure
that all emergency systems functioned and to demonstrate
emergency system strainer backwash capability. These
additional inspections and tests were satisfactorily
performed and resulted in the discovery of several
significant issues.
The AIT concluded that the root cause of the strainer fouling
was poor control of work on a safety-related structure. The
staff responsible for assigning and controlling this work
lacked sufficient facility knowledge to appreciate the
potential consequences of this work. As a result, a
contractor was permitted to seal cracks in the safety-related
service water intake tunnel structure with no knowledge of
the potential impact of the work, no approved procedures, and
inadequate oversight. Control room operator performance and
command and control in the control room during event response
were good. However, operators responding to the Lake Screen
House lacked appropriate knowledge regarding non-essential
service water strainer operation.
The AIT also concluded that an inadequate assessment of the
root cause of the June 19 and 24 events, as well as the
failure to develop a comprehensive and thorough inspection
and recovery plan, permitted repeated challenges to key
safety systems and the availability of the ultimate heat
sink. Loss of the function of those safety systems, and the
resultant loss of the ultimate heat sink, would have
significantly impacted the licensee's ability to respond to
analyzed accidents. Had the root cause evaluation for the
initial event been thorough, the event of June 24 could have
been avoided, reducing the time that the emergency service
water systems for both units were threatened.
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