Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
In 86-106
Supplement 2
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
March 18, 1987
Information Notice No. 86-106, SUPPLEMENT 2: FEEDWATER LINE BREAK
Addressees:
All nuclear power reactor facilities holding an operating license or a
construction permit.
Purpose:
Information Notice No. 86-106 provided general information to addressees
about the catastrophic failure of feedwater ping that occurred on December
9, 1986, at Unit 2 of the Surry Power Station and resulted in four
fatalities. Supplement 1 to that notice provided information about thinning
of piping walls which was the cause of the failure of feedwater piping. This
supplement provides addressees with information about potentially generic
systems interaction problems that were caused by release of large quantities
of feedwater. Recipients are expected to review the information provided for
applicability to their facilities and consider actions, if appropriate, to
preclude the occurrence of similar problems. However, suggestions contained
in this information notice do not constitute NRC requirements; therefore, no
specific action or written response is required.
Discussion:
On December 9, 1986, both units at the Surry Power Station were operating at
full power when an 18-inch suction line to a main feedwater pump in Unit 2
failed catastrophically releasing, in the turbine building, large quantities
of hot feedwater which flashed to steam. Condensed steam saturated a
security card reader in the turbine building basement approximately 50 feet
from the failed pipe and shorted out the card reader system for the entire
plant. As a result, key cards would not open doors controlled by the
security system. Controlled-access doors to the control room were blocked
open to provide access for operating, emergency, and management personnel.
Security personnel were posted at the doors and permitted entry of essential
personnel based on personal recognition. Twenty minutes after the failure,
the card reader system was functioning normally.
Water also entered a fire protection control panel through an open conduit
and shorted circuits in the panel. This resulted in the discharge of 62
water sprinkler heads in the fire suppression system within minutes of
failure of the feedwater piping. Actuation of the sprinkler heads did
provide cooling of the atmosphere in the turbine building but added to the
quantity of water in the
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IN 86-106, Supplement 2
March 18, 1987
Page 2 of 3
turbine building basement. Water from the sprinklers outside the Unit 2
cable tray room apparently flowed under the door into the cable tray room,
leaked around foam fire seals in floor penetrations, and dripped into the
control room. The control room serves Units 1 and 2 and is located beneath
the cable tray rooms for these units.
A carbon dioxide fire suppression system is provided for the cable tray
rooms. Water from sprinkler heads located directly over and adjacent to
control panels for this system and water from the failed feedwater pipe
entered the control panels through the ends of several open conduits. Within
a few minutes after failure of the feedwater pipe, shorting of fire
protection control circuits caused the contents of the main carbon dioxide
storage tank to be emptied into the cable tray rooms leaving the station
without carbon dioxide in the event of fire. Carbon dioxide, which is
heavier than air, entered the control room via stairwells and
controlled-access doors which were blocked open. Personnel on the Unit 2
side of the control room complained of shortness of breath, dizziness, and
nausea.
A halon fire suppression system is provided for the emergency switchgear
rooms for Units 1 and 2. These rooms are located below the control room. The
halon system was actuated in the same way that the carbon dioxide system was
actuated. Halon leaked into the Unit 1 computer room through floor
penetrations and from the computer room into the Unit 1 side of the control
room. Halon haze was reported but did not hamper the performance of
operators.
An operator who was in the stairwell behind the control room when the card
readers failed experienced difficulty in breathing. Because of locked doors,
he could not exit through the control room or a switchgear room which
contained halon. The other means of egress was through a cable tray room
which contained carbon dioxide. An operator in the control room heard him
knocking and admitted him.
The security communications system includes radio repeaters that improve the
clarity of reception of low-power hand-held radios used in the plant. A
radio repeater, located in the Unit 1 cable tray room and approximately 5
feet from a carbon dioxide nozzle, was covered with a thick layer of ice as
a result of cooling from the discharge of carbon dioxide. The performance of
the radio repeater was temporarily degraded and may have resulted in the
need for personnel using hand-held radios to move to other locations in
order to communicate effectively.
The licensee intends to seal and shield control cabinets and conduits for
the carbon dioxide and halon fire suppression systems from water sources, as
necessary, to prevent inadvertent actuation of these systems. Penetrations
connecting the computer and emergency switchgear rooms have been sealed, as
necessary, to prevent leakage of halon into the control room. Additional
actions to preclude system interactions may be warranted.
Additional information about the Surry accident and system interactions can
be found in NRC Inspection Reports 50-280/86-42 and 50-281/86-42 dated
February 10, 1987, and in Licensee Event Report 86-020-01 in Docket 50-281
dated January 14, 1987.
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IN 86-106, Supplement 2
March 18, 1987
Page 3 of 3
No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
Regional Administrator of the appropriate NRC regional office or this
office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: Roger Woodruff, IE
(301) 492-7205
Attachment:
List of Recently Issued IE Information Notices
