05000220/LER-2010-001, Regarding Reactor Scram Due to Inadequate Post Maintenance Testing
| ML110190231 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 01/07/2011 |
| From: | Lynch T Nine Mile Point |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 10-001-00 | |
| Download: ML110190231 (10) | |
| 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 10 CFR 50.73(a)(2)(iv)(B), System Actuation |
| 2202010001R00 - NRC Website | |
text
Thomas A. Lynch Plant General Manager P.O. Box 63 Lycoming, New York 13093 315.349.5205 315.349.1321 Fax CENG.
a joint venture of Constellation r
SE nergy '
- I eD F NINE MILE POINT NUCLEAR STATION January 7, 2011 U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 ATTENTION:
SUBJECT:
Document Control Desk Nine Mile Point Nuclear Station Unit No. 1; Docket No. 50-220 Licensee Event Report 2010-001, Reactor Scram Due to Inadequate Post Maintenance Testing In accordance with 10 CFR 50.73(a)(2)(iv)(A), please find attached Licensee Event Report 2010-001, Reactor Scram Due to Inadequate Post Maintenance Testing.
There are no regulatory commitments in this submittal.
Should you have questions regarding the information in this submittal, please contact John J. Dosa, Director Licensing, at (315) 349-5219.
Very truly yours, TAL/JMT
Attachment:
Licensee Event Report 2010-001, Reactor Scram Due to Inadequate Post Maintenance Testing cc:
Regional Administrator, NRC Project Manager, NRC Resident Inspector, NRC zr~~
ATTACHMENT LICENSEE EVENT REPORT 2010-001 REACTOR SCRAM DUE TO INADEQUATE POST MAINTENANCE TESTING Nine Mile Point Nuclear Station, LLC January 7, 2011
ýNRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Nine Mile Point Unit 1 05000220 1 OF 8
- 4. TITLE Reactor Scram Due to Inadequate Post Maintenance Testing
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR None NA NUMBER NO-.oeN FACILITY NAME DOCKET NUMBER 11 10 2010 2010 001 00 01 07 2011
'None NA
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
[] 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii)
NA El 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
[__ 20.2203(a)(1)
El 20.2203(a)(4)
[I 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
- 10. POWER LEVEL
[] 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)
E] 20.2203(a)(2)(ii)
[] 50.36(c)(1)(ii)(A)
Z 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
E:
20.2203(a)(2)(iii)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 73.71(a)(4) 100 El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5)
El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER El 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 spring in relay 12K74 caused a half Channel 12 isolation signal. In this configuration, only Channel 11 of the one-out-of-two taken twice logic needed to be completed for an MSIV isolation to occur.
During performance of surveillance test N1-ISP-036-004, the induced Channel 11 low-low level completed the Channel 12 isolation signal and deenergized the Channel 12 MSIV SOVs.
Together with the two preexisting conditions, the performance of the surveillance test resulted in closure of the outboard MSIVs and the subsequent scram on MSIV position.
Following the scram, N1-SOP-1, Reactor Scram, and N1-EOP-2, RPV Control, were entered and executed. Reactor vessel pressure was controlled using Emergency Condenser 11 until use of the main heat sink (condenser) was reestablished. The High Pressure Coolant Injection (HPCI) System initiated, as designed, on a low reactor water level signal.
C.
INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED TO THE EVENT:
Relay 12K74 was found to have a misaligned contact spring and evidence of electrical arcing on the contact that provides input to the Channel 12 reactor vessel isolation logic.
SOV-01-04D and SOV-01-03D, the Channel 11 MSIV SOVs, were each found to have misaligned connector pins in their respective Grayboot splice connectors. However, the MSIVs remained operable in that the two preexisting conditions would not have prevented the MSIVs from closing.
D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES
4/25/2005 -
The Grayboot splice connectors associated with Channel 11 MSIV solenoid operated valves SOV-01-04D and SOV-01-03D were installed in 2005. Nine Mile Point Nuclear Station, LLC has determined that the connecter pins in the Grayboot connectors have been misaligned since their installation.
8/12/2010 -
Relay 12K74 was cycled for surveillance testing on August 12, 2010. The contact associated with the low-low reactor vessel isolation logic remained in an open state since performance of this test.
11/10/2010 -
At 1056 on November 10, 2010, NMP1 scrammed from full power operation due to closure of outboard MSIVs 01-03 and 01-04. Valves 01-03 and 01-04 closed following receipt of an invalid low-low reactor level signal.
E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED
No systems or secondary functions were affected by this condition. This event did not affect Nine Mile Point Unit 2.
NRC FORM 366 (10-2010)
F. METHOD OF DISCOVERY
The reactor scram was self-revealing via multiple control room indications.
G. MAJOR OPERATOR ACTION:
Following the scram, Operations confirmed that all control rods had fully inserted. N1-SOP-1, Reactor Scram, and N1-EOP-2, RPV Control, were entered and executed. Plant operators took manual control of RPV level control and stabilized level between 53 and 95 inches. Reactor vessel pressure was controlled by manually initiating Emergency Condenser 11 until the main heat sink (condenser) was reestablished. Emergency Condenser 11 was then secured. The HPCI System initiated, as designed, on a low reactor vessel water level signal. The HPCI System was then secured following restoration of normal water level.
H. SAFETY SYSTEM RESPONSES:
Nine Mile Point Unit 1 outboard MSIVs 01-03 and 01-04 closed as expected with both Channel 11 and 12 SOVs deenergized due to a combination of preexisting plant conditions and performance of the low-low reactor water level surveillance test. All control rods fully inserted as designed on closure of the MSIVs. Partial closure of MSIVs in both main steam lines produces a scram so the reactor is not operated without its main heat sink. Reactor vessel pressure was controlled by manually initiating Emergency Condenser 11 until the main heat sink (condenser) was reestablished by reopening MSIVs 01-03 and 01-04. The HPCI System initiated, as designed, on a low reactor vessel water level signal. At NMP1, HPCI initiation on a reactor low level signal is an expected occurrence due to water level shrinkage following a scram.
I1. CAUSE OF EVENT:
The November 10, 2010 scram was the result of the combination of two latent preexisting plant conditions and performance of a quarterly instrument channel surveillance test. The first preexisting condition was misaligned connector pins on the Grayboot splice connectors found in the power circuit of the outboard MSIV Channel 11 SOVs. The cause of the misalignment has been determined to be insufficient rigor in the behaviors and knowledge (training) used in determining the appropriate post maintenance testing (PMT) in 2005 for redundant/complex control circuits.
Following replacement of the SOVs (which included installation of the Grayboot connectors), the PMT identified and performed was cycling the outboard MSIVs per surveillance procedure.
However, since each MSIV is designed with two redundant SOVs, each capable of porting air to or away from the MSIV, the test performed was not adequate to identify the failed Grayboot connection or the deenergized SOV. A contributing cause was inadequate technical guidance in the maintenance procedure and vendor manual regarding inspection and testing of the Grayboot connectors.
The second preexisting condition was a misaligned contact spring in isolation logic Channel 12 relay 12K74 which was installed in April 2005. The cause of the misalignment has been determined to be excess material (plastic) left on the contact spring holding peg during fabrication of the relay's NRC FORM 366 (10-2010)
movable contact holder. The excess material allowed the position of the contact spring to change and uneven forces to be applied to the movable contact. Consequently, the contact associated with the low-low level isolation logic remained open since the relay was cycled during the previous surveillance test performed in August, 2010.
The misaligned connector pins and contact spring, together with insertion of a reactor vessel low-low water level signal for surveillance testing, resulted in an MSIV closure and subsequent reactor scram on MSIV position.
Condition Report 2010-011008 applies to this LER.
I1l. ANALYSIS OF THE EVENT:
This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph 10 CFR 50.73(a)(2)(iv)(B). On November 10, 2010, closure of outboard MSIVs 01-03 and 01-04 resulted in a reactor scram and initiation of HPCI.
The SOV Grayboot splice connectors were left in a misaligned position since 2005. However, this misalignment resulted in the subject SOVs being left in a deenergized state (i.e., the required state to port air away from the MSIVs) and therefore would not have prevented the MSIVs from closing.
Relay 12K74 failed in a position such that one path of the Channel 12 reactor vessel isolation logic was completed. Therefore, its failure would not have prevented the MSIVs from closing and performing their safety function.
The November 10, 2010 scram is bounded by the NMP1 Updated Final Safety Analysis Report (UFSAR) analyzed transient delineated in UFSAR Chapter XV, Section A.3.5, Main Steam Isolation Valve Closure, (With Scram). The analyzed event assumes the reactor is at rated power, an MSIV closure occurs and that a scram is initiated automatically by MSIV position. The UFSAR also states that the Electromatic Relief Valve (ERV) set pressures are low enough to prevent lifting of the Reactor Pressure Vessel (RPV) safety valves. No ERVs lifted during this event.
A walkdown of the Main Steam System was performed per procedure and identified no evidence of damage to snubbers or supporting structural members.
Based on the above, it is concluded that the safety significance of this event is low and the event did not pose a threat to the health and safety of the public or plant personnel.
This event does impact the NRC Regulatory Oversight Process (ROP) Index for Unplanned Scrams. Due to this scram, the Unplanned Scram Index value will be 0.8 compared to a Green-to-White threshold value of greater than 3.
NRC FORM 366 (10-2010)
IV. CORRECTIVE ACTIONS
A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:
Reactor vessel pressure was controlled using Emergency Condenser 11 until the main heat sink (condenser) was reestablished; the Emergency Condenser was then secured. The HPCI System initiated, as designed, on a low reactor vessel water level signal following the scram.
HPCI was secured following restoration of normal water level.
The Channel 11 Grayboot splice connector misaligned connector pins were repaired and an appropriate PMT performed to assure proper operation of the SOVs. Channel 12 relay 12K74 was replaced and tested to assure proper operation.
B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:
Actions which were taken or are planned to be taken include the following:
Grayboot Splice Connector
- 1) Immediate actions were to repair the Channel 11 Grayboot splice connectors.
- 2) Training will be provided to planning personnel to ensure an adequate understanding of complex/redundant circuits for the proper determination of PMT requirements.
- 3) Procedure/manuals governing Grayboot connector maintenance activities will be revised to include additional post assembly inspections and testing. This will include a continuity check following each Grayboot installation.
General Electric (GE) Relay 12K74
- 1) Immediate action was to replace Channel 12 relay 12K74 and inspect two other CR305 relays.
- 2) Four additional CR305 relays from the same lot as the failed relay will be inspected. If additional deficiencies are found, additional corrective actions will be initiated.
V. ADDITIONAL INFORMATION
A. FAILED COMPONENTS:
Relay 12K74 was found to have a misaligned contact spring and evidence of electrical arcing on the contact that provides input to the Channel 12 reactor vessel isolation logic.
NRC FORM 366 (10-2010)
SOV-01-04D and SOV-01-03D, the Channel 11 MSIV SOVs, were each found to have misaligned connector pins in their respective Grayboot splice connectors.
B. PREVIOUS LERs ON SIMILAR EVENTS:
None C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION IDENTIFIER AND SYSTEM NAME OF EACH COMPONENT OR SYSTEM REFERRED TO IN THIS LER:
COMPONENT IEEE 803 FUNCTION IDENTIFIER IEEE 805 SYSTEM IDENTIFICATION Plant Protection System Reactor Vessel Isolation System Emergency Condenser Main Steam Isolation Valve Relay Connector Solenoid Operated Valve D. SPECIAL COMMENTS:
None COND ISV RLY CON FSV JC JM BL SB JC SB SB NRC FORM 366 (10-2010)
0 cj.~
0 NRC FORM 366 (10-2010)