05000220/LER-1917-002, Regarding Manual Reactor Scram Due to Pressure Oscillations
| ML17143A228 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 05/18/2017 |
| From: | Kreider R Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NMP1L3157 LER 17-002-00 | |
| Download: ML17143A228 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(iv)(B), System Actuation |
| 2201917002R00 - NRC Website | |
text
Exelon Generation NMP1L3157 May 18, 2017 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Nine Mile Point Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR-63 Docket No. 50-220 10 CFR 50.73
Subject:
NMP1 Licensee Event Report 2017-002, Manual Reactor Scram Due to Pressure Oscillations In accordance with the reporting requirements contained in 1 O CFR 50.73(a)(2)(iv)(A), please find enclosed NMP1 Licensee Event Report (LER) 2017-002, Manual Reactor Scram Due to Pressure Oscillations.
There are no regulatory commitments contained in this letter.
Should you have any questions regarding the information in this submittal, please contact Dennis Moore, Site Regulatory Assurance Manager, at (315) 349-5219.
~/.
Robert E. Kreider Jr.
Plant Manager, Nine Mile Point Nuclear Station Exelon Generation Company, LLC REK/RSP
Enclosure:
NMP1 Licensee Event Report 2017-002, Manual Reactor Scram Due to Pressure Oscillations cc:
NRC Regional Administrator, Region I NRC Resident Inspector NRC Project Manager
Enclosure NMP1 Licensee Event 2017-002, Manual Reactor Scram Due to Pressure Oscillations Nine Mile Point Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR-63
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2017)
, the htt1;1:1/www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
NRG 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 6
- 4. TITLE Manual Reactor Scram Due to Pressure Oscillations
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.
MONTH DAY YEAR NA NA FACILITY NAME DOCKET NUMBER 3
20 17 2017 -
02
. - 00 5
18 17 NA NA
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: {Check all that apply)
D 20.2201 (bl D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
. 1 D 20.2201 (dl D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)(1)
D 20.2203(aJ(4l D 50.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1 )(i)(A)
[gJ 50. 73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
D 50.36(c)(1 )(ii)(A)
D 50. 73(a)(2)(v)(A)
D 73.71 (a)(4)
D 20.2203(a)(2J(iiil D 50.36(c)(2)
D 50.73(a)(2)(v)(B)
D 13.11 (a)(5l D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 13.11(a)(1) 004 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 13.11(a)(2J(il D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 13.11(a)(2)(iil D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in
D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES
March 19, 2017 19:25 - Operations transfers Reactor Pressure Control from the Turbine Mechanical Hydraulic Control System's Electronic Pressure Regulator (EPR) to the Mechanical Pressure Regulator (MPR) in support of reactor shutdown for 2017 refueling outage.
20:01 - Operations commences reactor shutdown March 20, 2017 00:01 - With the reactor at approximately 24% power the Main Turbine was taken offline.
00:38 - In support of surveillance testing the first of two turbine overspeed tests was performed. Reactor power was 18.8% at the time of the overspeed trip. Throughout the overspeed trip test the MPR responded as expected and reactor pressure oscillations were well within procedural limits.
02:06 -The second turbine overspeed test, "Back-up Overspeed Trip Test", was performed. Reactor power was at approximately 13.5% at the time of the second overspeed trip. The MPR response resulted in 2.0 to 2.5 psig reactor pressure oscillations.
02: 10 - Operators entered the special operating procedure for Pressure Regulator Malfunction, due to reactor pressure oscillations of 2-3 psig.
02:27.- Operators inserted a manual scram of the reactor due to pressure oscillations exceeding procedural limits.
E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED
None
F. METHOD OF DISCOVERY
Control Room Operations were closely monitoring the MPR and its associated critical parameters during and after turbine overspeed testing. The pressure oscillations and turbine bypass valve movement was promptly identified and Control Room Operations quickly verified that the indications were not the result of any ongoing field work.
G. MAJOR OPERATOR ACTION:
YEAR 2017 SEQUENTIAL NUMBER 002 Based on the monitoring of plant conditions and in accordance with station procedures Control Room Operators performed a manual scram of the reactor.
H. SAFETY SYSTEM RESPONSES:
All safety systems responded as expected.
IL
CAUSE OF THE EVENT
REV NO.
00 The apparent cause of this event was a partial blockage within the MPR sensing line coupled with hysteresis found within the cylinder stroke of the Mechanical Hydraulic Control (MHC) Bypass Relay.
Crud collecting in the MPR pressure sensing bellows line resulted in overdamped feedback signals to the MPR. Overspeed testing performed at 13.5% power caused large pressure swings in the sensing lines, resulting in transport of crud through the pressure sensing bellows line. The over damped feedback caused the MPR to exhibit limit cycle behavior (pressure oscillations).
Additionally, there was hysteresis within the MHC Bypass Relay caused as the bypass relay linkage passed through a worn bushing resulting in a friction induced sticktion.
The partial blockage within the MPR sensing line and the Bypass Relay hysteresis, when combined with normal pressure oscillations at low power levels, lead to reactor pressure swings outside the procedurally acceptable limits.
III.
ANALYSIS OF THE EVENT
This event is reportable under 10 CPR 50.72 (b)(2)(iv)(B) and 10 CPR 50.73(a)(2)(iv)(A) as any event or condition that resulted in a manual or automatic actuation of any of the systems listed in 10 CPR 50.73(a)(2)(iv)(B). Due to pressure oscillations exceeding the procedurally required limit, the RPS system was manually actuated, resulting in a reactor scram. There were no nuclear safety consequences or concerns associated with this event. All safety systems and balance of plant equipment responded as expected.
IV.
CORRECTIVE ACTIONS
A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:
- 1. The pressure sensing bellows line was replaced and the associated piping was flushed
- 2. The bypass relay was repaired.
B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:
- 1. Implementation of a two year preventive maintenance activity for routine flushing and filling of the pressure sensing bellows line and associated piping with contingencies to replace when required.
- 2. Revision of associated procedures to include steps to flush and backfill sensing lines.
- 3. Revised the Turbine Trip Tests procedure to ensure turbine overspeed testing is completed above 21 percent power to minimize the possibility of pressure oscillations as a result of the overspeed test.
v.
ADDITIONAL INFORMATION
A. FAILED COMPONENTS:
Mechanical Hydraulic Control (MHC) Bypass Relay Mechanical Pressure Regulator (MPR)
Pressure sensing bellows line B. PREVIOUS LERS ON SIMILAR EVENTS:
99 "Reactor Scram Due to Mechanical Pressure Regulator Suppressor Valve Failure and Mode Switch Position not in Conformance with Technical Specifications". The cause of the reactor scram was the failure of the MP~ pressure suppressor valve (a J. A. Campbell Company Micro-Bean Valve). The vendor treated the valve with excessive corrosion inhibitor which led to an internal blockage in the MPR feedback loop.
A. 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 IEEE 805 Mechanical Pressure regulator (MPR)
RG JJ Electric Pressure Regulator RG JJ Mechanical Hydraulic Control Bypass Relay RLY JJ Main Turbine TRB JJ Rea.ctor Vessel RPV AD Suppressor Valve v
JJ B. SPECIAL COMMENTS:
None
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