05000220/LER-2012-001, Regarding Automatic Reactor Scram Due to Electronic Pressure Regulator Failure
| ML12312A015 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 09/17/2012 |
| From: | Philippon M Constellation Energy Nuclear Group, EDF Group, Nine Mile Point |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 12-001-00 | |
| Download: ML12312A015 (9) | |
| 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) 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 |
| 2202012001R00 - NRC Website | |
text
Michel A. Philippon Plant General Manager P.O. Box 63 Lycoming, New York 13093 315.349.5205 315.349.1321 Fax CENG.
a joint venture of OComstellaion eD NINE MILE POINT NUCLEAR STATION U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 September 17, 2012 ATTENTION:
SUBJECT:
Document Control Desk Nine Mile Point Nuclear Station Unit No. 1; Docket No. 50-220 Licensee Event Report 2012-001, Automatic Reactor Scram due to Electronic Pressure Regulator Failure In accordance with 10 CFR 50.73(a)(2)(iv)(A), please find attached Licensee Event Report 2012-001, Automatic Reactor Scram due to Electronic Pressure Regulator Failure.
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, 4~/K2J~
MAP/KJK
Attachment:
Licensee Event Report 2012-001, Automatic Reactor Scram due to Electronic Pressure Regulator Failure cc:
NRC Project Manager NRC Resident Inspector NRC Regional Administrator
ATTACHMENT LICENSEE EVENT REPORT 2012-001 AUTOMATIC REACTOR SCRAM DUE TO ELECTRONIC PRESSURE REGULATOR FAILURE Nine Mile Point Nuclear Station, LLC September 17, 2012
NRC 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 05000220I1 of 7
- 4. TITLE Automatic Reactor Scram due to Electronic Pressure Regulator Failure
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER SEQUENTIAL REV MONTH DAY YEAR YEAR NUMBER NO.
MONTH DAY YEAR NA NA FACILITY NAME DOCKET NUMBER 07 17 2012 2012 001 0
09 17 2012 NA NA
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
[I 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
[E 50.73(a)(2)(vii)
N E] 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
F] 50.73(a)(2)(viii)(A)
E] 20.2203(a)(1)
El 20.2203(a)(4)
[E 50.73(a)(2)(ii)(B)
[I 50.73(a)(2)(viii)(B)
- 10. POWER LEVEL E] 20.2203(a)(2)(i)
[I 50.36(c)(1)(i)(A)
[] 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
E] 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(ivXA)
[I 50.73(a)(2)(x)
[] 20.2203(a)(2)(iii)
El 50.36(c)(2)
[I 50.73(a)(2)(v)(A)
E] 73.71(a)(4) 100
[] 20.2203(a)(2)(iv)
F] 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
E] 73.71(a)(5)
E] 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)
[I 50.73(a)(2)(v)(D)
Specify in Abstract below or in When the EPR was placed in service on June 26, 2012, the MPR paddle gap and the MPR/EPR servo indication difference were found outside of the ODMI monitoring plan limits. The MPR paddle gap was adjusted to within the ODMI monitoring plan limits; however, the indicated MPRJEPR servo indication difference was low outside of the ODMI monitoring plan limits. The initial data from when the EPR was placed in service and the MPR paddle gap adjusted was identified in a condition report. From June 26 to July 17, 2012 the MPR/EPR servo difference indications increased, back into the band, while visually maintaining the MPR paddle gap within the ODMI monitoring plan limits.
The initial data from when the EPR was placed in service and the increasing servo difference readings were logged in the monitoring plan.
When DT-1 failed, and the TCVs closed, the MPR was not set close enough to take control from the EPR prior to the high neutron flux scram being received. Contributing to the MPR not taking control in time was the speed at which the TCVs were closed by the EPR. The EPR servomotor (hydraulic cylinder) stroke time must be limited to ensure satisfactory operation. The stroke time must be fast enough to provide good EPR response; however, the stroke time must be slow enough to prevent undesirable mechanical problems, such as pressure oscillations.
The combination of the EPR response timing set fast and the MPR paddle gap setting resulted in the MPR not being close enough to take control of reactor pressure when the EPR failed.
The HiPCI system actuation signal on low RPV level is an expected occurrence following a reactor scram due to water level shrinkage. The H:PCI system is an operational mode of the feedwater system and is not an Emergency Core Cooling System (ECCS).
There was no impact on Nine Mile Point Unit 2 (NMP2) from this event.
This event involved the automatic actuation of the Reactor Protection System (RPS), which resulted in a reactor scram, and the automatic initiation of the HPCI system due to reactor low water level.
The notification per 10 CFR 50.72(b)(2)(iv)(B) for RPS actuation and 10 CFR 50.72 (b)(3)(iv)(A) for HPCI initiation were completed on July 17, 2012 at 1323 (Event Number 48110).
C. INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED TO THE EVENT:
There were no inoperable components or systems that contributed to this event.
D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES
6/26/2012; 1800 -
EPR placed in service. Monitoring plan implemented.
6/26 to 7/16/2012 -
Monitoring of EPR and MPR parameters completed every shift. MPR paddle gap is verified within ODMI monitoring plan limits for all log readings after initial adjustment. MPR to EPR servo difference indications trend upward, indicating a widening MPR paddle gap.
7/17/2012; 1118-NMP1 is at 100% power with the EPR operating normally controlling pressure, with the MPR as backup, when DT-1 fails. The failure of DT-1 causes an erroneous feedback input into the EPR circuitry. The EPR responds to the failure by sending a close signal to the hydraulics. The TCVs closed, resulting in a pressure increase followed by a neutron flux increase and corresponding Average Power Range Monitor (APRM) high flux scram signal from the RPS, initiating an automatic scram.
7/17/2012; 1118 -
HPCI mode of operation initiates on low reactor water level.
7/17/2012; 1119 -
Reactor water level is restored above the low water level set point.
7/17/2012; 1125 -
HPCI mode of operation secured.
E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED
None
F. METHOD OF DISCOVERY
This event was discovered by the operators when the annunciators for high neutron flux and RPS initiation of the reactor scram alarmed in the control room.
G. MAJOR OPERATOR ACTION:
After the scram, the operators verified all rods fully inserted. No other actions were required to support shutting down the reactor.
H. SAFETY SYSTEM RESPONSES:
All safety systems responded per design. There was no loss of offsite power to the onsite emergency buses, the HIPCI system initiated as designed, and the ECCS systems were available, but not called upon to support the safe shutdown of the reactor.
II. CAUSE OF THE EVENT
The root cause of this event is the station staff did not treat the ODMI checklist and associated monitoring plan with the appropriate level of importance when alert conditions were exceeded. The contributing cause of DT-I's failure is attributed to age related degradation of the LVDT.
Exceeding the ODMI monitoring plan action parameters was not properly communmcated to the issue manager or station management.
The EPR and MPR are integral subsets of the pressure regulator for the NMP1 turbine mechanical hydraulic control (MHC) system. The MPR is designed to be a back up for the EPR at NMPl.
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I I s I
NMP2 turbine controls use an electrohydraulic control system; thus, NMP2 is not susceptible to the type of failure that occurred at NMP1.
This event was entered into the Nine Mile Point Nuclear Station (NMPNS) corrective action program (CR-2012-006792).
III. 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). Both the RPS and HPCI system (an operating mode of the feedwater system) were actuated during this event. Both systems are listed in 10 CFR 50.73 (a)(2)(iv)(B).
Except for the failure of the DT-1 servo position feedback to the EPR circuitry, there were no equipment failures associated with this event. All other plant systems performed per design. Plant parameters, other than the reactor water level, remained within normal values throughout the event.
There was no loss of offsite power to the onsite emergency buses, HPCI initiated as designed, and the ECCS systems were available, but not called upon to support the safe shutdown of the reactor.
Had a design basis accident occurred coincident with this event, plant systems would have responded per design to mitigate the accident. Based on the above considerations, the safety signpificance of this event is very low, and the event did not pose a threat to the health and safety of the public or plant personnel.
This event affects the NRC Regulatory Oversight. Process (ROP) Index for Unplanned Scrams. Due to this scram, the Unplanned Scrams Index value will be 0.8 compared to the Green-to-White threshold value of greater than 3. This reduction will not result into entry into the "Increased Regulatory (White) Response Band."
IV. CORRECTIVE ACTIONS
A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:
- 1. The EPR was removed from service pending replacement of the EPR electronics and DT-l in the NMP1 refueling outage planned for early 2013. The plant was returned to full power on July 21, 2012.
B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:
- 1. The Operational Decision Making procedure is being revised to ensure that a review of open ODMI checklists is completed when operating conditions change and when the alarm or alert criteria in implementation plans are reached.
- 2. The Monitoring and Contingency Planning for Abnormal Conditions procedure is being revised to require detailed action statements and notification of the issue manager and Operations Manager of any parameters outside of alert ranges.
I
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- 3.
Replacement of the EPR electronics and DT-1 is scheduled for the 2013 NMP1 refueling outage.
This modification includes all LVDTs and servo position indicators associated with the EPR, as well as the other electronic components.
- 4. The maintenance procedure for calibrating EPR hydraulic components is being revised to update the speed setting for the EPR servomotor stroke time.
V. ADDITIONAL INFORMATION
A. FAILED COMPONENTS:
The DT-1 servo position feedback to the EPR circuitry is the only component that failed during this event.
B. PREVIOUS LERs ON SIMILAR EVENTS:
Three previous LERs for NMP1 were submitted due to similar EPR failures.
LER 1987-014, Electrical Pressure Regulator Servo-Valve Malfunction Results in Reactor Scram, High Pressure Coolant Injection Mode of Feedwater and Main Steam Isolation Valve Closure. The cause of this event was failure of the EPR servo-valve due to binding of internal components. The servo-valve was replaced.
LER 1992-003, Reactor Scram on High Neutron Flux Caused by Failures in the Electronic Pressure Regulator. The cause of this event was loose, oxidized and intermittent electrical connections at one of the EPR's four LVDTs and electrical noise between adjacent field wiring. The terminal boards were cleaned and electrical connections tightened.
LER 1994-005, Reactor Scram on High Neutron Flux Caused by an Electrical Pressure Regulator Malfunction. The cause of this event was a malfunction of either the steam line resonance compensator or the operational amplifier. Both components were replaced and the EPR calibrated.
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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 COMPONENT IDENTIFIER IEEE 805 SYSTEM IDENTIFICATION Linear Variable Differential Transformer Electronic Pressure Regulator High Pressure Coolant Injection System Reactor Protection System Electrohydraulic Control System Turbine Control Valve Mechanical Pressure Regulator D. SPECIAL COMMENTS:
N/A PC N/A N/A N/A PCV PC IT TG BJ JC TG TG TG None I