05000321/LER-2009-004, Regarding IRM Signal Spike Caused by Electrical Noise Results in Reactor Scram
| ML091730188 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 06/19/2009 |
| From: | Madison D Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-09-0993 LER 09-004-00 | |
| Download: ML091730188 (4) | |
| 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 |
| 3212009004R00 - NRC Website | |
text
Dennis R. Madison Southern Nuclear Vice President - Hatch Operating Company, Inc.
Plant Edwin I Hatch 11028 Hatch Parkway North Baxley, Georgia 31513 Tel 912.537.5859 Fax 912.3662077 SOUTHERN'\\
COMPANY June 19, 2009 Docket No.:
50-321 f\\lL-09-0993 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin I. Hatch Nuclear Plant Licensee Event Report IRM Signal Spike Caused by Electrical Noise Results in Reactor Scram Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50.73(a)(2)(iv)(A), Southern Nuclear Operating Company is submitting the enclosed Licensee Event Report (LER) concerning a reactor scram resulting from electrical noise on an Intermediate Range Monitor.
This letter contains no NRC commitments. If you have any questions, please advise.
Sincerely, D. R. Madison Vice President - Hatch DRM/M..IK/
Enclosure: LER 1-2009-004 cc:
Southern Nuclear Operating Company Mr. J. T. Gasser, Executive Vice President Ms. P. M. Marino, Vice President - Engineering RTYPE: CHA02.004 U. S. Nuclear Regulatory Commission Mr. L. A. Reyes, Regional Administrator Mr. R. E. Martin, NRR Project Manager - Hatch Mr. J. A. Hickey, Senior Resident Inspector - Hatch
NRC FORM 366 (9-2007)
PRINTED ON RECYCLED PAPER NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME Edwin I. Hatch Nuclear Plant Unit 1
- 2. DOCKET NUMBER 05000 321
- 3. PAGE 1 OF 3
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL NUMBER REV NO.
MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 05000 5
10 2009 2009 - 004 -
0 06 19 2009 FACILITY NAME DOCKET NUMBER 05000
- 9. OPERATING MODE 1
- 10. POWER LEVEL 008
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply) 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(A) 73.71(a)(4) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)
OTHER 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)
Specify in Abstract below or in NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER FACILITY NAME Edwin I. Hatch / Kathy Underwood, Performance Improvement Supervisor TELEPHONE NUMBER (Include Area Code) 912-537-5931 CAUSE SYSTEM COMPONENT MANU-FACTURER REPORTABLE TO EPIX
CAUSE
SYSTEM COMPONENT MANU-FACTURER REPORTABLE TO EPIX
- 14. SUPPLEMENTAL REPORT EXPECTED YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
NO
- 15. EXPECTED SUBMISSION DATE MONTH DAY YEAR ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On May 10 at 1041 EDT, Unit 1 was in run at 224 CMWT, 8 percent power. At this time a reactor startup from a planned maintenance outage was in progress. Upon placing the reactor mode switch to the run mode as part of normal startup activities, a full reactor scram was initiated. Intermediate Range Neutron Monitoring (IRM) upscale trips were received in each of the two Reactor Protection System (RPS) scram channels. Investigation revealed that the 1A IRM (Bus A) and the 1H IRM (Bus B) had spiked upscale when the mode switch was taken to run.
The cause of the scram was an electrical noise spike transmitted into the IRMs. The noise signal was sufficient to cause IRM A and H to trip on "high-high" neutron flux level.
Replacing degraded cables, and connections, as well as improving grounding of the neutron monitoring system improved noise levels in the system. In addition ferrite beads were installed on each cable entering and/or exiting the preamplifier NEMA enclosures on each of the eight IRM channels.
(If more space is required, use additional copies of NRC Form 366A)
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EIIS Code XX).
DESCRIPTION OF EVENT
On May 10 at 1041 EDT, when the Unit 1 reactor mode switch was taken to the run mode following a planned maintenance outage a full reactor Scram was initiated. The following alarms were received in conjunction with the Reactor Scram: "IRM BUS A UPSCALE TRIP OR INOP", "IRM BUS B UPSCALE TRIP OR INOP" and "IRM UPSCALE. Investigation revealed that the 1A IRM (Bus A) (EIIS Code IG) and the 1H IRM (Bus B) had spiked upscale when the mode switch was taken to run, resulting in a reactor scram. The plant had been experiencing increased noise on the IRMs since the morning of May 6, 2009. Multiple corrective actions had taken place to reduce and eliminate noise on the IRMs which had been experienced with plant component manipulations prior to the startup and subsequent scram.
CAUSE OF EVENT
The cause of the scram was an electrical noise spike transmitted into the IRMs. The noise signal was sufficient to cause IRM A and H to trip on "high-high" neutron flux level.
The scram occurred simultaneously with the movement of reactor mode switch from Start-Up to Run. Post-incident testing revealed that IRM noise spikes were being induced by RPS (EIIS Code JC) relay actuations which generated electro-magnetic interference (EMI).
It is concluded that noise induced spikes from the RPS relay actuations caused the scram.
REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT This event is reportable in accordance with 10 CFR 50.73 (a)(2)(iv)(A), which requires the licensee to report any event or condition that resulted in a manual or automatic actuation of any Engineered Safety Feature (ESF), including the Reactor Protection System (RPS).
The IRM scram function provides for reactor protection during startup, shutdown, and low power operations. Because the IRM "high-high" neutron flux trips were due to electrical noise introduced to the instrumentation, no actual over power event occurred. The safety function of the IRMs was not diminished. There were no safety consequences as a result of this event. All control rods (EIIS Code AA) inserted and plant systems operated as expected following the scram. There were no systems or components inoperable during the event that could have contributed to the event. The reactor scram posed no safety consequences to the health and safety of the general public or plant personnel.
Based on this analysis, it is concluded that this event had no adverse impact on nuclear safety. This analysis is applicable to all power levels and operating modes in which a LOCA is postulated to occur. (9-2007)
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET U.S. NUCLEAR REGULATORY COMMISSION
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE YEAR SEQUENTIAL NUMBER REVISION NUMBER Edwin I. Hatch Nuclear Plant Unit 1 05000321 2009 004 0
3 OF 3
PRINTED ON RECYCLED PAPER
CORRECTIVE ACTIONS
Extensive investigation and repair activities to correct degraded cables and connections and to improve the grounding of the neutron monitoring system improved the noise response of the IRMs.
The plant installed five ferrite beads (Fair-Rite Type 31 material) on each cable entering and/or exiting the preamplifier NEMA enclosures on each of the eight IRM channels. These ferrite beads were positioned in close proximity to the preamplifiers. The ferrite bead works to add common mode impedance to IRM cables, thereby causing EMI to be reflected toward its source. The ferrite bead responds to the magnetic field produced by the common mode current carried on the conductors within the ferrite bead. The ferrite bead does not affect the differential mode signal (current) within the cable on which the ferrite bead was placed.
Post-installation testing prior to restart demonstrated that noise spikes from RPS relay actuations into the IRM instruments were of much lower amplitude.
ADDITIONAL INFORMATION
Other Systems Affected: None
Failed Components Information
None Commitment Information: This report does not create any new permanent licensing
commitments
Previous Similar Events
There are no similar events within the past two years in which a reactor scram was initiated due to electrical noise spike on the nuclear instrumentation.