05000335/LER-2003-002, St.Lucie Unit 1 Regarding Invalid 4.16V Bus Undervoltage Condition During Maintenance Caused EDG Start
| ML031190221 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  (DPR-067) |
| Issue date: | 04/16/2003 |
| From: | Jefferson W Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2003-084 LER 03-002-00 | |
| Download: ML031190221 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3352003002R00 - NRC Website | |
text
0 FPL Florida Power& Light Company, 6501 S. Ocean Drive, Jensen Beach, FL 34957 April 16, 2003 L-2003-084 10 CFR § 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Re:
St. Lucie Unit 1 Docket No. 50-335 Reportable Event: 2003-002-00 Date of Event: February 17, 2003 Invalid 4.16kV Bus Undervoltage Condition During Maintenance Caused EDG Start The attached Licensee Event Report 2003-002 is being submitted pursuant to the requirements of 10 CFR § 50.73 to provide notification of the subject event.
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NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 EXPIRES 7-31-2004 (7-2001)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the Information collection
- 1. t-AL;ILI I Y NAMEz
. IUUtKhl NUMlktIz
' :. PAJht~
St. Lucie Unit 1 05000335 Page 1 of 3
- 4. TITLE Invalid 4.16kV Bus Undervoltage Condition During Maintenance Caused EDG Start
- 5. EVENT DATE 11
- 6. LER NUMBER 11 7. REPORT DATE 11
- 8. OTHER FACILITIES INVOLVED MONTH DAY Y
EAR Y
EAR NTIAL I REVISION MONTH DAY YEAR rL;IU NM EAR INUMBER NUMBIER YA F
]
FACIUTY NAME DOCKET NUMBEHt 02
'17 2003 2003 002 00 04 16 2003
- 9. OPERATING I. THISREPORTS IIITTE P
NT TO THI-I REQUIREMENTS OF 10 CFR §: (Check one or more)
MODE 1
20.2201(b) 20 2203(a)(3)(o) 50 73(a)(2)(ii)(B) 50 73(a)(2)(ix)(A)
- 10. POWER 1
20.2201(d) 20 2203(a)(4) 50 73(a)(2)(m) 50 73(a)(2)(x)
LEVEL 100 20 2203(a)(1) 50 36(c)(1)(i)(A)
X 50 73(a)(2)(fv)(A) 73 71 (a)(4) 20 2203(a)(2)(i)
_ 50 36(c)(1)(ll)(A) 50 73(a)(2)(v)(A) 73 71 (a)(5) 20 2203(a)(2)(e 50 36(c)(2) 50 73(a)(2)(v)(B) 20 2203(a)(2)(le) 50.46(a)(3)(ii) 50 73(a)(2)(v)(C)
Specify in Abstract below or In 20 2203(a)(2)(lv) 50 73(a)(2)(1)(A) 50 73(a)(2)(v)(D) 20 2203(a)(2)(v)
=
50 73(a)(2)(i)(B) 50.73(a)(2)(vu) 20 2203(a)(2)(vi) 50 73(a)(2)()(C) 50 73(a)(2)(v)(A) 20 2203(a)(3)(i)
I 50.73(a)(2)(l)(A) 50 73(a)(2)(vte)(B) 3
- 12. LICENSEE CONTACT FOR THIS LER NAME I I LLP-1UN NUMuK (luce Area CoaeJ Kenneth W. Frehafer, Licensing Engineer (772) 467 -
7748 es, complete EXPECTED SUBMISSION DATE) iBSTRACT (Limt to 1400 spaces, e, a On February 17, 2003, St. Lucie Unit 1 was in Mode 1 at 100 percent reactor power.
While St. Lucie maintenance personnel were performing the replacement of a failed 1B3 4.16kV bus undervoltage (UV) relay, a bus UV shed signal was generated.
This resulted in momentary loss of the 1B3 4.16kV bus while loads were stripped and reloaded to the 1B emergency diesel generator.
During the event all safety equipment operated as designed.
FPL could not definitively determine whether the event was caused by personnel error or spurious operation of the UV protection relay.
The defective relay was replaced and FPL plans to replace the existing 1B3 4.16kV switchgear relays with a different model relay during the next refueling outage.
NRU t-UHM;366U.S NUCLEAR REGULATORY COMMISSION (7-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1) ll I
LER NUMBER (6) l PAGE (3)
.R SEQUENTIAL REVISION NUMBER NUMBER St. Lucie Unit 1 05000335 Page 2 of 3 2003 002 00 TE)Cr (if more soace is required, use additional copies of NRC Form 366A) (17)
Description of the Event On February 17, 2003, St. Lucie Unit 1 was in Mode 1 at 100 percent reactor power.
St. Lucie maintenance personnel were in the process of replacing a failed 1B3 4.16kV bus undervoltage (UV) relay [EIIS:EA:2).
However, during the maintenance activity a bus UV shed signal was generated.
This resulted in momentary loss of the 1B3 4.16kV bus while loads were stripped and reloaded to the 1i emergency diesel generator (EDG).
During the event all safety equipment operated as designed.
The 4.16kV bus undervoltage protection scheme monitors for loss of voltage or degraded grid voltage conditions on the 4.16kV busses.
The protection scheme utilizes two-out-of-two coincident logic for both loss of voltage protection and degraded grid protection. The UV relays are set to trip at approximately 70 percent of nominal bus voltage with a nominal time delay of 1 second.
The degraded grid voltage relays are set to actuate at approximately 92 percent of nominal bus voltage with a nominal time delay of 18 seconds.
The function of the relays is to initiate the automatic disconnection of the affected bus from its offsite source, load shed the affected bus, start the EDG, and sequence loads on to the affected bus.
In addition, a second set of UV relays is provided for each 4160 volt Class 1E bus, set to actuate at approximately 95 percent of nominal bus voltage with a nominal time delay of 23 seconds.
These relays provide annunciation and are used to alarm the undervoltage condition in the control room.
Cause of the Event
The circuit that performs the 1B3 bus UV shed signal is comprised of two (normally open) series contacts of the Agastat DSC timing relays (tag numbers 2X-1 and 2X-2).
Normally, both timing relays are required to operate to perform the shed function.
On January 16, 2003, the 2X-2 relay failed to operate.
In accordance with Technical Specification 3.3.2.1.b, Table 3.3-3, Functional Unit 6.a ACTION 12, the failed relay was placed in "trip" condition by placing a jumper across its relay output contacts.
Therefore the circuit coincidence logic changed from two-out-of-two to one-out-of-one, and operation of the 2X-1 relay or closure of its contact would result in generation of the bus UV shed signal.
In order to support the replacement of the failed relay, the work sequence specified the installation of a jumper between a terminal strip and the 2X-1 relay.
This jumper would electrically duplicate the existing jumper that was added to the 2X-2 relay after its failure on January 16, 2003.
However, as the last connection was landed at the 2X-1 relay, a UV shed signal was generated on the 1B3 4.16kV bus.
The most likely cause of the event was either inadvertent contact with adjacent terminations of the 2X-l relay or spurious operation of the 2X-l relay.
FPL could not definitively determine which of the above caused the event.
Analysis of the Event
Although the planned work package and pre-job briefs acknowledged the possibility of an inadvertent EDG start during the maintenance activity, an EDG start was not definitely expected to occur.
Therefore, in accordance with NUREG-1022, Revision 2, and 10 CFR 50.73(a)(2)(iv)(A), this is reportable as an event that resulted in the manual or automatic actuation of the emergency AC electrical power system.U.S. NUCLEAR REGULATORY CUMM (7-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1) lNUMBER LER NUMBER (6)
PAGE (3)
- 1) YEAR lSEQUENTIAL REVISION St. Lucie Unit 1 05000335 N
NU, Bl Page 3 of 2003 -
002 00 TEXT (if more space is required, use additional copies of NRC Form 366A) (17)
Analysis of Safety Significance Although no UV condition existed on the 1B3 4.16kV bus, all equipment responded to the 1B3 4.16kV bus UV signal as required.
There was no adverse effect on the reactor operation.
Therefore, this event had no impact on the health and safety of the public.
FPL reviewed previous Agastat DSC relay failures and the events surrounding their replacement.
This review indicated that, in this application, the preventive maintenance replacement frequency for the Agastat DSC relays is not conservative in that relay failures occur prior to the established 8-year replacement cycle.
Once a UV/degraded grid relay failure occurs, the design configuration of the relays and high density of terminations are such that there is little room to perform a replacement without a high probability of contact with adjacent terminations.
Only the 1B3 4.16kV bus utilizes DSC type relays for UV/degraded grid timing functions.
The 1A3 bus has been replaced with a newer series NTS812 relay that provides a longer qualified life (20 years) and an improved distance between terminations.
This change to the newer relay was dictated by the obsolescence of the DSC type relay.
FPL plans to replace the DSC relays with a different relay style.
Corrective Actions
- 1. The failed 2X-2 timing relay was replaced and all UV/degraded grid relays were tested successfully.
- 2. FPL issued work orders for the replacement of the UV/degraded grid relays 2X-1 through 2X-6 in the IB-3 4.16kV switchgear during the SL1-19 refueling outage.
These replacements will utilize a different style relay.
Additional Information
Failed Components Identified Component:
1B3 4.16kV bus UV timing relay Manufacturer: Agastat Model Number: DSCXX0125DPBXAA
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