ML14178A519
| ML14178A519 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 12/17/1993 |
| From: | Christensen H, William Orders NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML14178A518 | List: |
| References | |
| 50-261-93-35, NUDOCS 9401040383 | |
| Download: ML14178A519 (6) | |
See also: IR 05000261/1993035
Text
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REG(,,
UNITED STATES
NUCLEAR REGULATORY COMMISSION
REGION 11
101 MARIETTA STREET, N.W., SUITE 2900
ATLANTA, GEORGIA 30323-0199
Report No.:
50-261/93-35
Licensee:
Carolina Power and Light Company
P. 0. Box 1551
Raleigh, NC 27602
Docket No.:
50-261
License No.: DPR-23
Facility Name: H. B. Robinson Unit 2
Inspection Conducted: November 22 - December 3, 1993
Lead Inspector:
W. T. Orders, Senior Resident Inspector
Date Signed
Other Inspectors: C. R. gle, Resident Inspector
Approved by:
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H. 0. Christensen, Chief
Dafe
igned
Reactor Projects Section 1A
Division of Reactor Projects
SUMMARY
Scope:
This special inspection consisted of a review of an event which occurred on
November 22, 1993, in which your "A" diesel generator did not achieve the
required voltage when started and the "B" diesel generator would not start
during testing.
9401040383 931220
PDR ADOCK 05000261
G
REPORT DETAILS
1.
Persons Contacted
- R. Anderson, Vice President Brunswick Nuclear Plant
- S. Billings, Technical Aide, Regulatory Compliance
- B. Clark, Manager, Maintenance
- T. Cleary, Manager, Technical Support
- A. McCauley, Manager, Electrical Systems, Technical Support
- M. Pearson, Plant General Manager
- R. Wallace, Manager, Licensing
Other licensee employees contacted included technicians, operators,
engineers, mechanics,and office personnel.
- Attended Exit Interview
2.
Event Summary
On the morning of November 22, 1993, the licensee was performing a
routine surveillance test on the "A" emergency diesel generator (EDG).
They discovered that the generator voltage regulator was mis-adjusted to
440 volts as opposed to the required 480 volts. The licensee adjusted
the voltage regulator and successfully completed the test. Later that
morning the licensee attempted to perform the same test on the "B" EDG
when it was discovered that the engine would not roll when starting air
was applied.
The licensee failed to determine how the voltage regulator on the "A"
EDG became mis-adjusted,_ but concluded that two of the six pilot air
valves in the air start distributor on the "B" diesel had seized, which
had prevented starting air from being injected into two cylinders, and
had resulted in the engine's failure to start. Ultimately, the air
start distributor was repaired and the diesel returned for service on
November 29, 1993.
3.
System Description
Engineered safety features (ESF) equipment is connected to 480 volt
emergency buses El and E2.
Each emergency bus has a dedicated EDG;
diesel "A" for bus El and diesel "B" for bus E2.
The EDGs are Fairbanks Morse twelve cylinder, opposed piston engines
coupled to 2500 KW, 480 VAC generators. Engine starting is accomplished
with compressed air applied to the first six cylinders of the engine.
The starting air is applied to the individual cylinders through the
operation of six air start check valves on the air start header. The
air start check valves are actuated by pneumatic signals from pilot
valves contained in the air start distributor.
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The diesels are designed to start and reach rated speed and voltage
within 10 seconds. The EDGs are designed to start 900 hp of motor load
within a single load block and to pick up full rated load within 45
seconds.
The EDGs are designed to start automatically on receipt of a safety
injection (SI) signal, sensed undervoltage on the associated 480 volt
bus, or a manual start command.
4.
Event Details
During the conduct of safeguards systems testing on October 25, 1993,
the "B" EDG failed to start. Initial troubleshooting efforts failed to
detect the cause for this failure. The engine was started twice without
incident on October 26. Subsequent troubleshooting revealed that the
springs for the air start distributor pilot air valves associated with
cylinders 2, 4, and 6 were broken. The broken springs were sent to the
Carolina Power and Light Environmental and Education Center for
evaluation to determine the failure mechanism. At the end of this
inspection, that evaluation had not been completed.
On October 27, the diesel was successfully started after temporary
replacement springs were installed. (The springs were obtained from the
training diesel, were not qualified, and were therefore considered
"temporary".)
Later that day, the diesel successfully started during
performance of a scheduled technical specification required surveillance
test.
Two days later on October 29, the diesel was again successfully started
during post maintenance testing after all the pilot air valve springs
were exchanged with new qualified replacements. The diesel was
successfully started again on November 8 during routine surveillance
testing.
On November 12, 1993 the licensee initiated a startup of the reactor
following the completion of refueling outage 15.
On November 14,
following completion of low power physics testing, the unit was placed
on line and reactor power increased to 30 percent power.
On November 16, the licensee detected that a weld on a main feedwater
drain valve was leaking. Ultimately the licensee was forced to shut the
unit down on November 17, to repair the leak.
On the morning of November 22, 1993, the licensee performed a routine
surveillance test on the "A" EDG. They discovered that the generator
voltage regulator was mis-adjusted to 440 volts as opposed to the
required 480 volts. The licensee adjusted the voltage regulator and
successfully completed the test. The licensee initiated an evaluation
to determine if the diesel generator could perform its intended safety
function with the voltage regulator mis-adjusted. At the conclusion of
this inspection, that evaluation was not complete.
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Later on the morning of November 22,
the licensee attempted to perform
the same surveillance test on the "B" EDG when it was discovered that
the engine would not roll when starting air was applied. The licensee
declared the machine inoperable, quarantined the diesel generator rooms,
and assembled a team to evaluate the failure of the diesel.
On the following day, November 23, the licensee requested vendor
assistance. The licensee, aided by the vendor representative, concluded
that the number 2 and 6 pilot air valves had bound and that the failure
was most probably due to debris.in the system. The debris was believed
to be from other corrosion products in the pilot valve caps, or
fragments of the aforementioned broken springs.
The next day, November 24, a cleanliness inspection of air start
distributor was performed including blowing air through the associated
system piping but no attempt was made to capture debris. Later that day
repairs were completed and operations personnel successfully tested the
diesel.
It should be noted that when the EDG was tested, the licensee
determined that, similar to the "A" EDG, the generator voltage regulator
was mis-adjusted to 450 volts as opposed to the required 480 volts. The
licensee is also evaluating the "B" diesel generator to determine if it
could perform its intended safety function with the voltage regulator
mis-adjusted. At the conclusion of this inspection, that evaluation was
incomplete.
On November 28, after operations personnel performed fast and slow speed
starts of the EDG and licensee management had reviewed the maintenance
actions that had been performed, the "B" diesel was declared operable.
5.
Conclusions
a.
Technical Specification 3.7.1.d requires, in part, that the
reactor shall not be made critical unless two diesel generators
are operable.
Implicit in the definition of "operable" is the
requisites that the diesel generators, start, achieve the design
rated speed and produce the required voltage output.
On November 22, 1993, the licensee determined that the "A" EDG
would produce only 440 volts as opposed to the required 480 volts
and that the "B" EDG would not start. By definition, this implies
that both EDGs were inoperable.
The EDGs were previously tested and known to be operable on
November 8, 1993. Between November 8 and November 22, 1993,
the
reactor was made critical and operated at power levels up to 30
percent for a period of 5 days.
Given the above, it appears that both EDGs were inoperable
simultaneously when the unit was at power. This is an apparent
violation of the above referenced Technical Specification.
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b.
During the conduct of safeguards systems testing on October 25,
1993, the "B" EDG failed to start. Subsequent troubleshooting
revealed that the springs for the pilot air valves associated with
cylinders 2,4, and 6, in the air start distributor were broken.
The springs were replaced and the EDG was returned to service.
On the morning of November 22, 1993, the licensee was performing a
routine surveillance test on the "B" EDG when it was discovered
that the engine would not roll when starting air was applied.
The licensee concluded that the numbers 2 and 6 pilot air valves
had bound and that the failure mode was most probably due to
debris in the system. The licensee believes that the debris was
either corrosion products in the pilot valve caps, or fragments of
the aforementioned broken springs. Either of these two causes are
indicative of inadequate corrective action related to the event of
October 25 and as such is an apparent violation of 10 CFR 50,
Appendix B, Criterion XV1.
6.
Exit Interview
The inspection scope and findings were summarized on December 2, 1993,
with those persons indicated in paragraph 1. The inspectors described
the areas inspected and discussed in detail the inspection findings
listed below and in the summary. There were no dissenting comments from
the licensee. The licensee did not identify as proprietary any of the
materials provided to or reviewed by the inspectors during this
inspection.
Item Number
Apparent Violation
93-35-01
Both EDGs Inoperable Simultaneously
When Unit Was at Power.
93-35-02
Inadequate Corrective Action Related
to Event of October 25, 1993.
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