05000275/LER-2007-003, Emergency Diesel Generator Actuation Due to a Transient Undervoltage Condition
| ML072150377 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 07/27/2007 |
| From: | Becker J Pacific Gas & Electric Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| DCL-07-076 LER 07-003-00 | |
| Download: ML072150377 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2752007003R00 - NRC Website | |
text
11 "8, Pacific Gas and Electric Company' July 27, 2007 James R. Becker Diablo Canyon Power Plant Vice President P. 0. Box 56 Diablo Canyon Operations and Avila Beach, CA 93424 Station Director 805.545.3462 Fax: 805.545.4234 PG&E Letter DCL-07-076 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Diablo Canyon Unit 1 Licensee Event Report 1-2007-003-00 Emergency Diesel Generator Actuation Due To A Transient Undervoltage Condition
Dear Commissioners and Staff:
In accordance with 10 CFR 50.73 (a)(2)(iv)(A) Pacific Gas and Electric Company is submitting the enclosed Licensee Event Report regarding an emergency diesel generator actuation due to a transient undervoltage condition. This event was reported under Emergency Notification System report Event Number 43393 in accordance with 10 CFR 50.72 (b)(3)(iv)(A) on May 29, 2007.
This event did not adversely affect the health and safety of the public. There are no new or revised regulatory commitments in this report.
swh/2246/A0699162 Enclosure cc/enc:
Terry W. Jackson, NRC Senior Resident Inspector Bruce S. Mallett, NRC Region IV Alan B. Wang, NRR Project Manager Diablo Distribution INPO A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak
- Diablo Canyon
- Palo Verde
° South Texas Project
- WolfCreek
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 06/30/2007 (6-2004)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the digits/characters for each block) information collection.
- 3. PAGE Diablo Canyon Unit 1 05000275 7
1 OF 6
- 4. TITLE Emergency Diesel Generator Actuation Due To A Transient Undervoltage Condition
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE 1
- 8. OTHER FACILITIES INVOLVED 0 28 20I I
IIFACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR FAITYNMDOKTUBE NUMBER NO.
FACILITY NAME DOCKET NUMBER 05 28 2007 2007 - 003 -
00 07 27 2007
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
El 20.2201(b)
[I 20.2203(a)(3)(i)
F1 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii)
[1 20.2201(d)
El 20.2203(a)(3)(ii)
E] 50.73(a)(2)(ii)(A)
[I 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
[E 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
El 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL
[] 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
Z 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
El 50.36(c)(2)
[E 50.73(a)(2)(v)(A)
El 73.71(a)(4)
El 20.2203(a)(2)(jv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5) 8 El 20.2203(a)(2)(v)
[I 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER [I 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (include Area Code)
Lawrence M. Parker - Senior Regulatory Services Engineer (805) 545-3386CAUSE SYSTEM COMPONENT MAU EOTBE
CAUSE
SYSTEM COMPONENT FACTURE R
TOEPORTBL FACTURER TO EPIX FACTURER TO EPIX No
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR SUBMISSION El YES (if yes, complete 15. EX(PECTED SUBMISSION DATE)
[I NO DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On May 28, 2007, at 2250 PDT, with Unit 1 at approximately 8 percent power, preparations were being made to parallel the Main Generator to the grid. All 12kV and 4160V electrical busses had been transferred to the Startup-Standby power supply (230kV System).
Operations started Circulating Water Pump 1-2, a large 12kV motor. Starting this motor caused a transient voltage dip in the Startup Standby System voltage. The voltage dip duration was sufficient to time-out the undervoltage diesel generator start time delay relay on the 4160V Vital Bus 'G,' causing a start of the associated Emergency Diesel Generator (DG) 1-2. The 4160V Vital Bus 'G' continued to be powered by the Startup-Standby power source; loads were not transferred and DG 1-2 remained in operation unloaded. DG 1-2 was verified not to be required and returned to its normal standby condition.
On May 29, 2007, at 0501 PDT, an eight-hour nonemergency report was made pursuant to 10 CFR 50.72 (b)(3)(iv)(A) via the Event Notification System (ENS 43393).
Corrective actions to prevent recurrence include incorporation of precautions in plant operating procedures to minimize the transient voltage effects due to the start of large motors.
NRC FORM 366 (6-2004)
PRINTED ON RECYCLED PAPER NRC FORM 366 (6-2004)
PRINTED ON RECYCLED PAPER
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL NUMBER REVISION NUMBER DiabloCanyonUnit 051 010101 2 7 5 2007 0 10 1 3 0 10 2
OF16 TEXT
- 1.
Plant Conditions
The Pacific Gas and Electric Company's (PG&E) Diablo Canyon Power Plant Unit 1 was in Mode 1 (Power Operation) at approximately 8 percent reactor power prior to the event.
II.
Description of Problem A.
Background
The circulating water system [KE] provides a continuous ocean water cooling supply to the main condenser [COND], condensate cooler [CLR],
service water cooling system [KG], and intake cooling system [KE]. Each unit has two single-stage circulating water pumps (CWPs). The CWPs are nominal 12kV, 13,000 horsepower motors and can derive their power from the 230kV Startup-Standby System [EA] or the Unit Auxiliary Power System to their respective nonvital 12kV buses. Each unit has two nonvital 12kV Buses; nonvital Bus D provides power to CWP 1-1, Reactor Coolant Pumps (RCPs) 1-2 and 1-4, and nonvital Bus E provides power to CWP 1-2, RCPs 1-1 and 1-3.
Each unit has three 4160V vital buses that can be powered from the Startup-Standby, Unit Auxiliary, or emergency diesel generators [DG]
[EK]. Should a sustained low voltage condition be experienced on any of these buses, undervoltage relays will initiate a DG start signal and if undervoltage is of sufficient magnitude/duration, the bus will separate from the offsite power source and transfer to the DG for subsequent loading.
Three undervoltage relays are provided on each 4160 Class 1E vital bus for detecting sustained degraded voltage condition or a loss of bus voltage. A relay will generate a loss of power (LOP) signal (first level undervoltage relay (FLUR) setpoint) if the voltage is below 75 percent for a short time.
The second level undervoltage relay (SLUR) actuates at approximately 3785V or below, approximately 91 percent, but above the setpoints of the FLURs, the following SLUR actions occur automatically:
(1) After a less than or equal to 10 second time delay, the respective diesel generators will start.
(2) After a less than or equal to 20 second time delay, if the undervoltage condition persists, the circuit breakers for all loads to
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL NUMBER REVISION NUMBER DiabloCanyonUnit 051 01010121 1 5 2007.0 01 3 01 0 3 OF6 TEXT the respective vital 4160V buses, except the 4160-480V load center transformer, are opened and sequentially loaded on the DG.
B.
Event Description
On May 28, 2007, at 2250 PDT, with Unit 1 at approximately 8 percent power, preparations were being made to parallel the Main Generator to the electrical transmission grid. All 12kV and 4160V electrical busses had been transferred to the Startup-Standby power supply (230kV System).
Operations started CWP 1-2, a 13,000 horsepower 12kV motor. Since the 12kV System feeds the 4kV System when aligned to Startup, the resultant voltage dip propagated throughout the Startup Standby System. The voltage transient duration of approximately 8 seconds was sufficient to time out the SLUR on the 4160V Vital Bus 'G,' causing a start of that bus's DG 1-2. The 4160V Vital Bus 'G' voltage recovered to above the SLUR voltage setpoint prior to timing out the load shed timer. Thus the bus continued to be powered by the Startup-Standby power source; loads were not transferred and DG 1-2 remained in operation unloaded.
Immediately after the component actuation, DG 1-2 was verified not to be required to respond to the voltage transient event, was shut down, and returned to its normal standby condition.
On May 29, 2007, at 0501 PDT, an eight-hour nonemergency report was made using the Event Notification System (ENS 43393) pursuant to 10 CFR 50.72 (b)(3)(iv)(A).
C.
Status of Inoperable Structures, Systems, or Components that Contributed to the Event None.
D.
Other Systems or Secondary Functions Affected
None.
E.
Method of Discovery
The automatic actuations were immediately known to licensed plant operators in the control room by alarms and indications.
I
.1 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL NUMBER REVISION NUMBER Dibononnti0 0 0 10 12 171 5 20071-0 3 1 0 10 4 1OF6 TEXT F.
Operator Actions
Plant operators responded to alarms and indications provided in the control room, confirmed that continued DG 1-2 operation was not required, shut down the DG, and returned it to its standby status.
G.
Safety System Responses DG 1-2 automatically started when a transient undervoltage condition was sensed on the 4160V Vital Bus 'G', causing DG 1-2 to start, but did not cause it to load. Since the 4160V Vital Bus 'G' continued to be powered by the Startup-Standby power source, loads were not transferred to DG 1-2. The magnitude/duration of the voltage transient on the 4160V Vital Bus 'F' and 4160V Vital Bus 'H' was similar, but due to the relay settings being closer to 10 seconds, these relays did not time out and the DG 1-1 and DG 1-3 did not start.
I1l.
Cause of the Problem A.
Immediate Cause The duration of a 4kV undervoltage transient resulting from the start of a 13,000 horsepower CWP pump motor, while both the associated 12kV bus and the 4kV Vital Bus G were aligned to the Startup offsite power source, exceeded the setpoint of the second level undervoltage DG start time delay relay, starting DG 1-2.
B.
Root Cause Plant procedures did not clearly identify precautions necessary for the subject plant configuration to minimize voltage transient conditions that could result in an inadvertent DG start.
C.
Contributing Causes
Prior engineering recommendations were not captured in plant procedures.
IV.
Assessment of Safety Consequences
There were no actual safety consequences involved in this event since the safety-related plant electrical systems responded as designed. All vital
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL NUMBER REVISION NUMBER DiabloCanyonUnitl 0150101 0 1 2 17 15 2007 i0 10 13 0 0 5 OF 6
TEXT equipment remained aligned to the Startup-Standby power source for the duration of the event.
Final Safety Analysis Report (FSAR) Update, Section 15.2.9, "Loss of Offsite Power to the Station Auxiliaries," previously analyzed the total loss of offsite power, and bounds the transient undervoltage conditioned experienced in this event. The FSAR Update concluded that "for the loss of offsite power to station auxiliaries event, all safety criteria are met."
This condition is not considered a Safety System Functional Failure as the transient undervoltage condition is a previously analyzed condition and anticipated operational occurrence that does not create a significant condition adverse to safety. The lowest voltage experienced on 4160V Vital Bus 'G' was seen as approximately 85.6 percent; the FLUR setpoint is at 75 percent and the SLUR setpoint is at approximately 91 percent. The setpoints for the FLURs and SLURs are based on ensuring sufficient margin is available so that loads are not stripped from the bus and reloaded on the DGs. In addition, The SLUR setpoints have been selected to ensure that the technical specification allowable values are not exceeded due to normal instrument drift. The methodology used provides margin by accounting for inaccuracies, biases, and uncertainties of components including calibration equipment.
Therefore, the event is not considered risk significant and it did not adversely affect the health and safety of the public.
V.
Corrective Actions
A.
Immediate Corrective Actions
Following confirmation that the DG start was due to the CWP start voltage transient, DG 1-2 was shut down and returned to its standby status.
B.
Corrective Actions to Prevent Recurrence
- 1. PG&E revised the CWP starting procedure OP E-4:l to add a precaution to minimize the voltage transient condition due to the large motor start.
- 2. PG&E will revise the RCP starting procedure OP A-6:1 to add a precaution to minimize the voltage transient condition due to the large motor start.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (1)
DOCKET NUMBER (2)
LER NUMBER 16)
PAGE (3)
YEAR SEQUENTIAL NUMBER REVISION NUMBER DiabloCanyonUnitl 0 51 0 0 0 2 171 5 2007 -
o0 0 3 0
o0 6
1F TEXT VI.
Additional Information
A.
Failed Components None.
B.
Previous Similar Events
None.