Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9608280058
NIAGARA MOHAWK
GENERATION
BUSINESS GROUP
NINE MILE POINT NUCLEAR STATION/LAKE ROAD, P.O. BOX 63, LYCOMING, NEW
YORK 13093/ TELEPHONE (315) 349-7263 FAX (315) 349-4753
August 21, 1996
CARL D. TERRY NMP2L 1655
Vice President
Nuclear Engineering
U. S. Nuclear Regulatory Commission
Attn: Document Control Desk
Washington, DC 20555
RE: Nine Mile Point Unit 2
Docket No. 50-410
NPF-69
Subject. Clow Valve Stub Shaft Dowel Pin Failure
Gentlemen:
Pursuant to 10CFR Part 21, Reporting of Defects and Noncompliance,
Niagara Mohawk is reporting a deviation which could have created a
substantial safety hazard. Niagara Mohawk had previously notified the
Commission of this issue on July 23, 1996, via telephone and facsimile.
The attached report contains the information required by
10CFR21.21(c)(4).
Sincerely,
C. D. Terry
Vice President - Nuclear Engineering
CDT/JMT/kap
Attachment
xc: Regional Administrator, Region I
Mr. B. S. Norris, Senior Resident Inspector
Mr. D. S. Hood, Senior Project Manager, NRR
Records Management
ATTACHMENT
1. Name and address of the individual or individuals informing the
Commission.
Mr. Carl D. Terry, Vice President - Nuclear Engineering
Niagara Mohawk Power Corporation
Nine Mile Point Nuclear Station
P. O. Box 63, Lake Road
Lycoming, NY 13093
2. Identification of the facility, the activity or the basic component
supplied for such facility or such activity within the United States
which fails to comply or contains a defect.
Nine Mile Point Unit 2 (NMP2) Standby Gas Treatment System (GTS)
discharge piping isolation valve 2GTS*MOV3B.
3. Identification of the firm constructing the facility or supplying
the basic component which fails to comply or contains a defect.
2GTS*MOV3B was supplied to NMP2 by the Clow Corporation.
4. Nature of the defect or failure to comply and the safety hazard
which is created or could be created by such defect or failure to
comply.
During pre-planned maintenance activities associated with GTS valve
2GTS*MOV3B, the valve's stub shaft dowel pin fell out of its hole
and into the GTS discharge piping. Although the ensuing
investigation did not positively identify a root cause, Engineering
conservatively dispositioned the associated Deviation Event Report
(DER) indicating that the cause of this event was a manufacturing
process deficiency. (Niagara Mohawk believes this is an isolated
event based on the number of Clow valves in service and years of
service without a similar failure.) Specifically, this deficiency
was identified as the failure to fully peen over the dowel pin hole
in the valve disk. Consequently, the valve stub shaft failed to
rotate respective to the main shaft, thus preventing the valve limit
switches from properly displaying valve position. These valve limit
switches are used as input permissives for the GTS train start
logic.
The GTS is designed to prevent leakage of radioactive gases and
particulates to the environment during accidents by maintaining a
negative pressure on the Reactor Building. The GTS consists of two
parallel and redundant air filtration assemblies with associated
duct work, dampers, controls, and exhaust fans. The discharge of
each fan has a normally closed isolation valve (2GTS*MOV3A/3B) which
will open upon
1
receiving a GTS start signal. Once 2GTS*MOV3A/3B is open, the GTS
filter train fans (2GTS*FN1A/1B) are given a permissive signal to
start.
In the event the GTS System was called upon to function, discharge
valve 2GTS*MOV3B would have received an open signal. If the dowel
pin had already fallen out or were to fall out prior to the valve
opening, the valve would still have opened. However, the valve stub
shaft, which positions the valve limit switches, would not have
rotated as the valve moved to the open position. Since limit
switches indicating the discharge valve in the open position is a
permissive to GTS system operation, the respective fan would not
have started resulting in an inoperable GTS. Assuming a single
failure in the redundant GTS train, both trains could be potentially
inoperable. Therefore, a substantial safety hazard existed.
5. The date on which the information of such defect or failure to
comply was obtained.
Niagara Mohawk identified the defect on May 23, 1996 as a potential
Part 21 issue. The defect was determined to be reportable on July
22, 1996.
6. In the case of a basic component which contains a defect or fails to
comply, the number and location of all such components in use at,
supplied for, or being supplied for one or more facilities or
activities subject to the regulations in this part.
Although there are additional Clow valves at NMP2, this defect would
only effect GTS isolation valves 2GTS*MOV3A/3B in a similar manner
(i.e., potentially make the associated system inoperable). As
previously discussed, loss of the dowel pin would have prevented the
associated GTS fan from starting but would not have affected the
ability of the valve to open and close. For the remainder of the
Clow valves, the limit switches do not provide system permissives
but provide valve position indication only. Therefore, the failure
of the shaft to rotate would not have had the same safety
significance.
7. The corrective action which has been, is being, or will be taken;
the name of the individual or organization responsible for the
action; and the length of time that has been or will be taken to
complete the action.
Immediate corrective action by Niagara Mohawk was to reinstall the
pin that fell from 2GTS*MOV3B and to re-peen the dowel hole. The
redundant GTS train was started and verified operable. Both trains
are subject to periodic Technical Specification required
surveillance testing to verify operability. 2GTS*MOV3A will be
inspected in RFO5, scheduled to begin in September 1996, to verify
proper peening. Niagara Mohawk does not anticipate similar problems
in the remaining Clow valves based on the number of Clow valves and
the years of service.
8. Any advice related to the defect or failure to comply about the
facility, activity, or basic component that has been, is being, or
will be given to purchasers or licensees.
None
2
*** END OF DOCUMENT ***
LICENSEE: NIAGARA MOHAWK POWER CORP.
SITE: NINE MILE POINT 2 EN NUMBER:30775
DOCKET: 05000410 EVENT DATE: 07-23-96
RX TYPE: BWR EVENT TIME: 00:00
VENDORS: GE-5 NOTIFY DATE: 07-23-96
EMERGENCY CLASS: N/A REGION: 1 STATE: NY TIME: 09:00
OPS OFFICER: STEVE SANDIN
10 CFR SECTION: CCCC 21.21 UNSPECIFIED PARAGRAPH
UNIT SCRAM RX INIT INITIAL MODE CURR CURRENT MODE
CODE CRIT PWR PWR
2 N Y 100 POWER OPERATION 100 POWER OPERATION
DISCOVERY OF A CONDITION AFFECTING THE OPERABILITY OF CLOW
(MANUFACTURER) VALVES INSTALLED IN THE UNIT 2 STANDBY GAS
TREATMENT SYSTEM
THE LICENSEE DETERMINED THAT CLOW (MANUFACTURER) VALVES IN THE
STANDBY GAS TREATMENT SYSTEM HAVE A DOWEL PIN INSTALLED WHICH IS
NOT PEENED IN PLACE. SHOULD THESE DOWELS COME LOOSE, IT COULD
INTERFERE WITH THE VALVE LIMIT SWITCHES AND PREVENT THE MAKEUP OF
CIRCUIT PERMISSIVES.
