ML16148A840
| ML16148A840 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 10/29/1993 |
| From: | Harmon P, Lesser M, Poertner W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML16148A839 | List: |
| References | |
| 50-269-93-29, 50-270-93-29, 50-287-93-29, NUDOCS 9311160103 | |
| Download: ML16148A840 (5) | |
See also: IR 05000269/1993029
Text
R REGL1
UNITED STATES
NUCLEAR REGULATORY COMMISSION
REGION II
101 MARIETTA STREET, N.W., SUITE 2900
ATLANTA, GEORGIA 30323-0199
Report Nos.:
50-269/93-29, 50-270/93-29 and 50-287/93-29
Licensee:
Duke Power Company
422 South Church Street
Charlotte, NC 28242-0001
Docket Nos.: 50-269, 50-270, 50-287, 72-4
License Nos.:
DPR-38, DPR-47, DPR-55, SNM-2503
Facility Name:
Oconee Nuclear Station
Inspection Conducted: October 19 - 27, 1993
Inspector:
____t___
P. Harmon, Senior Resident Inspector
Date Signed
W. Poertner, Resident Inspector
Date Signed
Approved by:_
/
1)
/f3
M. Lesser, Section Chief
Date Signed
Projects Section 3A
Division of Reactor Projects
SUMMARY
Scope:
This special inspection was conducted to review the events
associated with a component failure which caused inoperability of
one of the emergency power sources which was initially discovered
in September, 1992.
Results:
One apparent violation was identified involving a lack of prompt
corrective action to resolve a previously identified deficiency.
A component essential to the operation of the emergency power
distribution system was found to have never been adequately
tested. Corrective action was not timely and when testing
ultimately was performed, it was discovered to have been
inoperable for an indeterminate period.
9311160103 931029
PDR ADOCK 05000269
G
REPORT DETAILS
1.
Persons Contacted
Licensee Employees
- H. Barron, Station Manager
S. Benesole, Safety Review Manager
D. Coyle, Systems Engineering Manager
J. Davis, Safety Assurance Manager
T. Coutu, Operations Support Manager
B. Dolan, Manager, Mechanical/Nuclear Engineering
W. Foster, Superintendent, Mechanical Maintenance
- J. Hampton, Vice President, Oconee Site
D. Hubbard, Component Engineering Manager
C. Little, Superintendent, Instrument and Electrical (I&E)
- M. Patrick, Regulatory Compliance Manager
B. Peele, Engineering Manager
- S. Perry, Regulatory Compliance
- G. Rothenberger, Operations Superintendent
R. Sweigart, Work Control Superintendent
Other licensee employees contacted included technicians, operators,
mechanics, and staff engineers.
NRC Resident Inspectors
- P. Harmon
t
Poertner
- Attended Exit Interview
2.
Background
During accident conditions concurrent with the loss of offsite power,
the emergency power supply for Oconee Nuclear Station is the two Keowee
Hydrostation units.
The two hydroelectric generators provide the
emergency power through two separate and independent paths.
One path,
the overhead path, is a 230 kv transmission line to the Oconee station
230 kv switchyard yellow bus, which will supply each unit's startup
transformer. The other path is an underground feeder to the Oconee CT-4
transformer. The Keowee units are normally lined up with one unit
aligned to the overhead path, and the other aligned to theunderground
path.
No particular precedence is established for which Keowee unit is
aligned to which path.
Automatic start of both Keowee units occurs on a loss of the grid, an
engineered safety features actuation, or loss of vol'
tage on an Oconee
unit's main feeder bus.
On loss of offsite power, the Keowee unit
assigned to the overhead path will connect to the yellow bus after the
yellow bus has been disconnected from the grid.
When Keowee unit 2 is
aligned to the overhead path, this connection is viansa
ACB-2.
Confirmation that the yellow bus has been disconnected from the grid,
2
and is ready for connection to Keowee unit 2 is accomplished by relay
27T2X, a Westinghouse MG-6 relay. If this relay does not operate, the
ACB will not close in and the Keowee unit will not provide power to the
yellow bus.
3.
Event Description
On September 29, 1992, at approximately 10:00 p.m., technicians were in
the process of performing post-modification tests on ACB-2. When ACB-2
did not close as required, the licensee investigated and discovered that
an MG-6 relay, 27T2X, was set with an improper gap of one half inch
instead of seven sixteenths as required by the manufacturer.
Technicians found a plastic armature stop nut was broken. The relay was
repaired and the post-modification test was performed successfully.
The licensee performed a root cause investigation and determined that
the ACB-2 failure was caused by the failed MG-6 relay. The exact time
of the failure is indeterminate, and could have existed since original
installation. The MG-6 relay had not been modified, inspected or tested
since original installation.
The licensee submitted Licensee Event Report LER 269/92-14 on October
29, 1992 to document the event. The LER concluded that Keowee Unit 2
had been inoperable for an indeterminate period of time prior to
discovery during the periods when Keowee unit 2 was aligned to the
overhead path. When called upon in that configuration, Keowee Unit 2
would not have been available to supply emergency power to the Oconee
units.
As previously stated, the MG-6 relay and consequently the Keowee
overhead path were inoperable for an indeterminate period of time. The
time is indeterminate for the following two reasons:
A.
The overhead path through ACB-2 was inoperable only when Keowee
Unit 2 was aligned to the overhead path. Swapping of Keowee Units
between overhead and underground paths is done routinely.
B.
Neither the specific MG-6 relay nor the Keowee overhead path had
ever been tested according to the licensee. The relay and
consequently the overhead path could have been inoperable since
initial installation. Periodic testing of either the relay or the
overhead path would have identified the problem.
The inspectors had discussed the issue regarding the lack of direct
testing of the overhead path with the licensee prior to this event. The
licensee had acknowledged the inspectors' concern, and stated that they
were in the process of devising a test to prove that the overhead path
would work if called upon. The licensee's test, as required by T.S.
4.6.5, was limited to testing the External Grid Protection System Logic.
This test is a logic continuity test and does not directly test the
Keowee overhead function.
3
Oconee T.S. 4.6.2.a requires that the Keowee Hydro units will be started
annually using the emergency start circuits in each control room. This
is to verify that each hydro unit and associated equipment is available
to carry load within 25 seconds of a simulated requirement for
engineered safety features. The licensee conforms to this requirement
by performing PT/O/A/0620/16, Keowee Hydro Emergency Start Test. This
performance test verifies operability of the Keowee emergency start
circuitry, and demonstrates that both Keowee units can supply 25 MW of
power within 25 seconds of emergency start initiation. The test does
not verify operability of the MG-6 feature of ACB-2. The inspectors
questioned whether MG-6 is included as "associated equipment" referred.
to in T.S. 4.6.2.a. The licensee stated that they do not consider this
to be the intent of the T.S. In effect, the licensee had never tested
the actual path emergency power would have to take from Keowee to the
Oconee emergency buses via the overhead line.
The inspectors
documented their concerns in NRC Inspection Report 50-269, 270, 287/92
24 as Unresolved Item 92-24-01.
The inspectors determined that in January, 1991, the licensee completed
a Design Baseline Determination (DBD) on the Keowee Emergency Power
System. The published results included a Test Acceptance Criteria (TAC)
which listed the specific test requirements necessary to provide
assurance of operability of the system. The TAC includes specific
requirements to test the overhead path, and to test the ACB-1 and ACB-2
breaker functions. The licensee performed some preliminary work on
devising tests to satisfy the TAC requirements, but had not fully
developed the tests when the failure was discovered on September 29,
1992.
The Code of Federal Regulations, 10 CFR 50, Appendix B, Criterion XI
requires that a program be established to assure that all testing
required to demonstrate that structures, systems and components will
perform satisfactorily in service is identified and performed.
The Code of Federal Regulations, 10 CFR 50, Appendix B, Criterion XVI,
Corrective Action, requires that measures shall be established to assure
that conditions adverse to quality are promptly identified and
corrected. In the instance described above, the licensee had identified
deficiencies in the test program relative to full functional testing of
the emergency power path. However, corrective actions were not pursued
in a timely manner to devise and perform the required tests.
Specifically the test inadequacy was discovered in January 1991 and
corrective action was not implemented until September 1992, some 20
months later. Prompt corrective action to devise and perform the
required tests would have identified that the overhead emergency power
path was inoperable prior to the discovery date. This apparent
violation is being considered for escalated enforcement action, 50-269,
270, 287/93-27-01: Untimely Corrective Action for Test Program
Inadequacy Causes Keowee Unit 2 Inoperability for Indeterminate Time.
4
4.
Exit Interview
The inspection scope and findings were summarized on October 27, 1993,
with those persons indicated in Paragraph 1. The inspectors described
the areas inspected and discussed in detail the inspection finding. The
licensee did not identify as proprietary any of the material provided to
or reviewed by the inspectors during this inspection nor did they
provide any dissenting comments.
Item Number
Description/Reference Paragraph
50-269,270,287/93-29-01
(Apparent Violation) Untimely Corrective
Action for Test Program Inadequacy Causes
Keowee Unit 2 Inoperability for
Indeterminate Time (paragraph 3).