05000206/LER-1990-001, :on 900120,dc Bus Feeder Breakers Opened During Dc Ground Troubleshooting,Resulting in Violation of Tech Spec 3.3.1.Ground Attributed to Degraded Cable Installation & Corrosion Conduit Joint.Ground Cleared

:on 900120,dc Bus Feeder Breakers Opened During Dc Ground Troubleshooting,Resulting in Violation of Tech Spec 3.3.1.Ground Attributed to Degraded Cable Installation & Corrosion Conduit Joint.Ground Cleared

ML13331A358
Person / Time
Site:	San Onofre
Issue date:	02/20/1990
From:	Morgan H SOUTHERN CALIFORNIA EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-001, LER-90-1, NUDOCS 9003010408
Download: ML13331A358 (7)

LER-1990-001, on 900120,dc Bus Feeder Breakers Opened During Dc Ground Troubleshooting,Resulting in Violation of Tech Spec 3.3.1.Ground Attributed to Degraded Cable Installation & Corrosion Conduit Joint.Ground Cleared

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(x)
2061990001R00 - NRC Website

text

Southern California Edison Company SAN ONOFRE NUCLEAR GENERATING STATION P. 0 OX 128 SAN CLEMENTE. CALIFORNIA 92672 H.E. MORGAN TELEPHONE STATION MANAGER February 20, 1990 (714) 36a-6241 U. S. Nuclear Regulatory Commission Document Control Desk Washington, D.C.

20555

Subject:

Docket No. 50-206 30-Day Report Licensee Event Report No.90-001 San Onofre Nuclear Generating Station, Unit 1 Pursuant to 10 CFR 50.73(d), this submittal provides the required 30-day written Licensee Event Report (LER) for an occurrence involving the voluntary entry into Technical Specification 3.0.3 during the troubleshooting of a DC ground. Neither the health and safety of plant personnel or the public was affected by this occurrence.

If you require any additional information, please so advise.

Sincerely,

Enclosure:

LER No.90-001 cc:

C. W. Caldwell (USNRC Senior Resident Inspector, Units 1, 2 and 3)

J. B. Martin (Regional Administrator, USNRC Region V)

Institute of Nuclear Power Operations (INPO)

S 6

F

.St

LICENSEE EVENT REPORT (LER)

FacitLity Name (1)

Docket Number (2)

Pa qe 3 SAN ONOFRE NUCLEAR GENERATING STATION, UNIT 1 01 51 Oj 01 01 1 1

of 0 6

Title (4)

VOLUNTARY ENTRY INTO TECHNICAL SPECIFICATION 3.0.3 DURING DC GROUND TROUBLESHOOTING FVFNT eATF

()

IFR RellMRFn

()I RFPRT DATF (7)

OTHFR FACTI TTTFR TNVflIVFD (A)

Month Day Year Year eSequentia Rev n

Month Day Year Facility Names Docket Number(s)

NONE 0l 51 0l 0l Of 1I 0 1 1 210 90910 01011 001022 90 NE 5000 THIS REPORT IS SUBMITTED PURSUANT TO HE REQUIREMENTS OF 10CFR OPERATING (Check one or more of the foLowing) (11)

MODE (9) 1

___20.402(b) 20.405(c) 50.73(a)(2)(iv) 73.71(b)

POWER

___ 20.405(a)(1)(i) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c) 20.405(a)(1)(ii)

X 50.36(c)(2) 50.73(a)(2)(vii)

Other (Specify in 101 9

1 20.405(a)(1)(iii) _L 50.73(a)(2)(i) 50.73(a)(2)(viii)(A)

Abstract below and 20.405(a)(1)(iv) 50.73(a)(2)(ii) 50.73(a)(2)(viii)(B) in text) 20.405(a)(1)(v) 50.73(a)(2)(iii) 750.73(a)(2)(x)

LICENSEE CONTACT FOR THIS LER (12)

Name AA TELEPHONE NUMBER Name AREA CODE H. E. Morgan, Station Manager 7 1 1 l 4 31 61 81 -I 61 21 41 1 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE

SYSTEM COMPONENT MANUFAC-REPORTABLE

CAUSE

SYSTEM COMPONENT MANUFAC-REPORTABLE TURER TO NPRDS

////

TURER TO NPRDS

////f I

Ill III

////

IIIL Ill.+/-

////

SUPPLEMENTAL REPORT EXPECTED (14)

Expected Month Day Year Submission Yes (If Yes. complete EXPECTED SUBMISSION DATE) lXXi NO Date (15)

ABSTRACT (Limit to 1400 spaces, i.e., approximately fifteen single-space typewritten lines) (16)

At 2229 on 01/19/90, with reactor power at 91.5%, a ground indication was received on DC Bus No. 2. Locating the ground requires opening the DC bus feeder breakers which de-energize control power to Safety Injection (SI) components subject to Technical Specification (TS) 3.3.1.

TS 3.3.1 does not explicitly permit inoperability of these components for any period of time and therefore, opening of such breakers constitutes entry into TS 3.0.3. DC feeder breakers to SI components were opened on six occasions from 0227 to 0236 on 01/20/90. On each occasion, the breaker was open only momentarily in accordance with administrative controls. Consequently, the total time SI components were inoperable was less than the one hour permitted by TS 3.0.3.

The ground was due to the presence of water inside a conduit that contains the power supply cable for the No. 2 Sequencer. The ground has been attributed to a combination of: 1) degraded cable insulation; 2) possible underground conduit corrosion or faulty conduit joint; and 3) the presence of a conduit seal which permitted ground water to collect inside the conduit.

For two days prior to the appearance of the ground on DC Bus No. 2, heavy rain was experienced at San Onofre. The ground cleared on 01/21/90. On 01/24/90, the conduit seal was removed and the water drained from the conduit. It has been determined that this seal serves no purpose and it was not reinstalled. The power supply cable for the sequencer was determined to be acceptable for continued use based on satisfactory megger tests.

Additional sealed conduits will have their seals removed and an inspection for water intrusion will be performed. The results of this inspection will be evaluated to address concerns regarding the protection of electrical components from water intrusion. A TS amendment request, which would permit inoperability of one SI train for up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, is in the process of preparation and will be submitted in the near future.

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION SAN ONOFRE NUCLEAR GENERATION STATION DOCKET NUMBER LER NUMBER PAGE UNIT 1 05000206 90-001-00 2 OF 6 Plant: San Onofre Nuclear Generating Station Unit: One Reactor Vendor:

Westinghouse Event Date: 01-20-90 Time: 0227 A.

CONDITIONS AT TIME OF THE EVENT:

Mode:

1, Power Operation at 91.5%

B.

BACKGROUND INFORMATION

Ground Troubleshooting:

When a DC Bus [BUI ground alarm [ALM] is received in the Unit 1 Control Room, operators initiate troubleshooting in accordance with Abnormal Operating Instruction (AOI) S01-2.6-8, "125 VDC System Grounds or Faults."

The ground is located by momentarily opening breakers [BKR] in a systematic manner and observing the response of the ground indicator [GI].

First, main supply breakers, each feeding several breakers to various safety-related and non-safety-related loads, are opened briefly one at a time until the branch containing the ground is identified. Next, breakers to individual loads are opened in a similar manner and/or leads are lifted until the ground is located. This process may require the removal of DC control power to components associated with one train of Safety Systems such as Safety Injection (SI) [BQ], which is subject to Technical Specification (TS) 3.3.1. TS 3.3.1 does not permit inoperability of one train of SI for any period of time while the plant is in Modes 1 or 2.

Therefore, opening a DC feeder breaker to SI equipment as described above constitutes an entry into TS 3.0.3.

C.

DESCRIPTION OF THE EVENT:

1.

Event:

On 01/19/90, at 2229, with Unit 1 at 91.5% power, a ground alarm on DC Bus No. 2 was received. In the process of attempting to locate the ground in accordance with AOI 501-2.6-8, it was necessary on six occasions (once each), from 0227 to 0236 on 01/20/90, to open the DC feeder breakers to the following SI components: the control circuit to the Train "A" SI Hydraulic Valves (HV), DC control power to the 4160V Bus 2C [EB], DC control power to 480V Bus 2 [ED], DC control power to containment isolation valves [ISV], SIS/LOP Lock Out relays [86], and DC control power to 480V Bus 3. On each occasion, the breaker was only open briefly in accordance with administrative controls. Consequently, the total time SI components were inoperable was less than the one hour permitted by TS 3.0.3.

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION SAN ONOFRE NUCLEAR GENERATION STATION DOCKET NUMBER LER NUMBER PAGE UNIT 1 05000206 90-001-00 3 OF 6 At 0238 on 01/20/90, the ground was located in the power supply cable for the No. 2 Sequencer and the AOI SO1-2.6-8 was exited. On 01/21/90 at 0538, the ground cleared. During troubleshooting efforts on 01/24/90, a Bisco type seal in the conduit which contained the sequencer power supply cable was removed, and water was found in the conduit. The water was drained from the conduit and the conduit was dried.

2.

Inoperable Structures, Systems or Components that Contributed to the Event:

None.

3.

Sequence of Events:

DATE TIME ACTION 01/19 2229 Ground alarm received on DC Bus No. 2.

01/20 0227 TS 3.0.3 entered momentarily on six thru occasions.

0236 01/20 0238 The ground was determined to be in the power cable to the No. 2 Sequencer.

01/20 0248 TS 3.0.3 and AOl S01-2.6-8 were exited.

01/21 0538 Ground cleared on DC Bus No. 2 power feeder cable.

4.

Method of Discovery

Receipt of DC Bus No. 2 ground alarm in the Control Room.

5.

Personnel Actions and Analysis of Actions:

During the ground investigation, operators were effective in minimizing the total time that TS 3.0.3 was entered by limiting the duration of breaker opening, in each case, to that necessary to determine if the ground existed on a particular circuit. Timely identification of the source of the ground was accomplished in accordance with procedures.

6.

Safety System Responses:

None.

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION SAN ONOFRE NUCLEAR GENERATION STATION DOCKET NUMBER LER NUMBER PAGE UNIT 1 05000206 90-001-00 4 OF 6 D.

CAUSE OF THE EVENT

1.

Immediate Cause:

The ground on DC Bus No. 2 was caused by a ground fault on the power feeder cable to the No. 2 Sequencer.

2.

Root Cause:

The root cause of the DC bus ground has been attributed to a combination of: 1) degraded cable insulation; 2) possible underground conduit corrosion or faulty conduit joint; and 3) the presence of a conduit seal which permitted ground water to collect inside the conduit.

Root Cause Discussion:

For two days prior to the appearance of the ground on DC Bus No. 2, heavy rains were experienced at San Onofre. The ground subsequently cleared after a period of no rain.

The subject conduit, which is buried and encased in concrete, runs between two electrical vaults located in the ground. When inspected, no water was found in either vault. One of the vaults is located approximately six feet lower in elevation than the other.

The opening of the conduit into this lower vault was sealed with a Bisco type seal [SEAL]. The seal was removed and a significant amount of water drained from the conduit. The water had a stagnant like odor and appearance. Three other conduits in this vault were found similarly sealed. All four conduit seals are not reflected in any design drawings and have no apparent purpose.

The presence of water in the conduit is indicative of either a faulty conduit joint or conduit corrosion, which permits ground water to flow into and out of the conduit. As a result, once the ground water level rises above the conduit breach, the water level in the conduit will also rise. As the water level in the conduit rose, it came in contact with a portion of the cable where it is believed the cable insulation is degraded. At this time, the cable became grounded and the ground alarm annunciated. After the rain stopped, the ground water level decreased below the breach in the conduit. Subsequently, the water level in the conduit decreased below the fault in the cable and the ground cleared.

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION SAN ONOFRE NUCLEAR GENERATION STATION DOCKET NUMBER LER NUMBER PAGE UNIT 1 05000206 90-001-00 5 OF 6 E.

CORRECTIVE ACTIONS

1.

Corrective Actions Taken:

a.

The bisco seal on the conduit that contained the grounded power cable was removed, thereby eliminating the potential for submergence of this cable. The accumulated water was drained and vacuumed from the conduit.

b.

Electronic Characterization and Diagnostics System (ECAD) equipment was used to determine the location of the fault and the cable condition. The cable was determined to be acceptable for continued service even with the degraded insulation, based on satisfactory megger values.

2.

Planned Corrective Actions

a.

The other sealed conduits located in the electrical vault that contained the conduit discussed above will have the seals removed and an inspection for water intrusion will be performed. The inspection results will be evaluated by the SONGS Availability Improvement Task Force, which will initiate actions, as necessary, to address concerns regarding the protection of electrical components from water intrusion.

b.

A TS amendment request, which would permit inoperability of one SI train for up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, is in the process of preparation and will be submitted in the near future.

F.

SAFETY SIGNIFICANCE OF THE EVENT:

There were no safety consequences to this event since at least one SI train remained operable at all times. Additionally, the ground did not affect operability of SI components except for the momentary troubleshooting periods.

G.

ADDITIONAL INFORMATION

1.

Component Failure Information

Not applicable.

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION SAN ONOFRE NUCLEAR GENERATION STATION DOCKET NUMBER LER NUMBER PAGE UNIT 1 05000206 90-001-00 6 OF 6

2.

Previous LERs for Similar Events:

LER 1-86-014, Revision 1, reported an event involving a ground on DC Bus No. 2. Brief TS 3.0.3 entries were required during troubleshooting the ground, because TS 3.3.1 did not contain explicit action statements for opening the DC Bus No. 2 feeder breakers or lifting leads to components required for Train A SI.

LER 1-87-001 described an event which concerned a ground on DC Bus No. 1. Brief TS 3.0.3 entries were required during troubleshooting the ground, because TS 3.3.1 did not contain explicit action statements for opening the DC Bus No. 1 feeder breakers or lifting leads to components required for Train B SI.

LER 1-87-018 reported an event involving a ground on DC Bus No. 2.

Brief TS 3.0.3 entries were required during troubleshooting the ground, because TS 3.3.1 did not contain explicit action statements for opening the DC Bus No. 2 feeder breakers or lifting leads to components required for Train A SI.

3.

Results of NPRDS Search:

Not applicable.