05000366/LER-2011-003, Regarding Manual Reactor Scram During Startup Due to Too Few Operable Intermediate Range Monitors
| ML113550524 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 12/21/2011 |
| From: | Ajluni M Southern Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NL-11-2469 LER 11-003-00 | |
| Download: ML113550524 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 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)(8) 10 CFR 50.73(a)(2)(viii)(8) 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)(8) 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(8) |
| 3662011003R00 - NRC Website | |
text
Mark J. Ajluni. P.E.
Southern Nuclear Nuclear Li censing Director Operating Company. Inc.
40 Inverness Cente r Parkway Post Office Box 1295 Birmingham, Alabama 35201 T81205.992.7673 Fax 205.992.7885 December 21, 2011 SOUIHERN '\\
COMPANY Docket Nos.: 50-366 I\\IL-11-2469 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin I. Hatch Nuclear Plant - Unit 2 Licensee Event Report 2011-003 Manual Reactor Scram During Startup Due to Too Few Operable Intermediate Range Monitors Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50.73(a)(2)(i)(A) and 10CFR 50.73(a)(2)(iv)(A), Southern Nuclear Operating Company (SNC) is submitting the enclosed licensee event report (LER) concerning a required reactor shutdown accomplished with a manual reactor scram due to having too few intermediate range monitors (IRMs) operable.
This letter contains no NRC commitments. If you have any questions, please contact Doug McKinney at (205) 992-5982.
Respectfully submitted, M. J. Ajluni Nuclear Licensing Director MJAlsbtllac Enclosure: Licensee Event Report 2011-003 cc: Southern Nuclear Operating Company Mr. S. E. Kuczynski, Chairman, President & CEO Mr. D. G. Bost, Chief Nuclear Officer Ms. P. M. Marino, Vice President - Engineering Mr. B. L. Ivey, Vice President -Regulatory Affairs RTYPE: CHA02.004
U.S. Nuclear Regulatory Commission NL-11-2469 Page 2 U. S. Nuclear Regulatory Commission Mr. V. M. McCree, Regional Administrator Mr. P. G. Boyle, NRR Senior Project Manager - Hatch Mr. E. D. Morris, Senior Resident Inspector - Hatch
Edwin I. Hatch Nuclear Plant - Unit 2 Licensee Event Report 2011-003 Enclosure Manual Reactor Scram During Startup Due to Too Few Operable Intermediate Range Monitors
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMS: NO. 3150-0104 EXPIRES: 10/31/2013 1 ()'201 0)
Estimated burden per response to comply with this mandatory collection request 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments re~arding burden estimate to the Records and FOIAIPrivacy Service Branch ( *5 F53). U.S.
LICENSEE EVENT REPORT (LER)
Nuclear Re~ulatory Commission, Washington, DC 20555*0001, or by internet e*mail to in ocollects.resources@nrc.gov, and to the Desk OHicer, Office of Information and Regulatory Affairs, NEOB*10202, (3150'{)104), Office of Mana~ement and Budget, Washington, DC 20503. If a means used to impose an in ormation collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to rescond to. the information collection.
r. PAGE Edwin I. Hatch Nuclear Plant Unit 2 05000366 1 OF 3
~. TITlE Manual Reactor Scram During Startup Due to Too Few Operable Intermediate Range Monitors 5, EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER SEQUENTIAL REV MONTH DAY YEAR YEAR MONTH DAY YEAR NUMBER NO.
05000 FACILITY NAME DOCKET NUMBER 10 24 2011 2011 - 003 -
0 12 21 2011 05000
~. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply) o 20.2201(b) o 20.2203(a)(3)(i) o 50.73(a)(2)(i)(C)
D 50.73(a)(2)(vii) 2 o 20.2201(d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
D 20.2203(a)(1)
D 20.2203(a)(4) o 50.73(a)(2)(ii)(8)
D 50.73(a)(2)(viii)(8)
D 20.2203(a)(2)(i)
D 50.36(c)(1 )(i)(A) o 50.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(ii)
D 50.36(c)(1 )(ii)(A)
~ 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
D 20.2203(a)(2)(iii) o 50.36(c)(2)
D 50.73(a)(2)(v)(A)
D 73.71 (a)(4)
D 20.2203(a)(2)(iv) o 50.46(a)(3)(ii) o 50.73(a)(2)(v)(8) o 73.71 (a)(5) 0 D 20.2203(a)(2)(v)
~ 50.73(a)(2)(i)(A) o 50.73(a)(2)(v)(C) o OTHER
- 10. POWER LEVEL o 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(8)
D 50.73(a)(2)(v)(O)
Specify in Abstract below or in NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER FACILITY NAME I~ELEPHONE NUMBER (Indude Area Code)
Edwin I. Hatch / Steven Tipps - Principal Engineer - Licensing 912-537-5880 MANU*
REPORTABLE MANU*
REPORTABLE
CAUSE
SYSTEM COMPONENT
CAUSE
SYSTEM COMPONENT FACTURER TO EPIX FACTURER TO EPIX
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR SUBMISSION 2
12 2012
~ YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
DNO DATE A8STRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On October 24, 2011, at approximately 0% power during startup from a scheduled maintenance outage, the 'A' intermediate range monitor (IRM) signal exhibited increasing levels of electrical noise while on Range 1. A spike in the signal resulted in a half-scram signal that prompted Operations personnel to bypass the 'A' IRM and declare it inoperable. The 'C' IRM subsequently began exhibiting erratic behavior and slowly drifted downscale while on Range 7. Operations personnel "ranged" down the 'C' IRM; however, its signal continued to display the same erratic behavior. Operations personnel then declared the 'C' IRM inoperable, resulting in no operable IRM channel in one quadrant of the reactor core. Further control rod withdrawal to maintain the core critical was prohibited. Accordingly, Operations personnel were directed to insert a manual scram signal and shutdown in accordance with Tech Spec 3.3.1.1, Action G.1.
Testing revealed degraded signal cable shielding at undervessel connectors in six of eight IRM channels allowing electrical noise to couple to the signal conductor. The noise was caused by a consistent low frequency signal on the preamplifier signal input and output cables and by degraded connectors.
Connectors were replaced and post maintenance testing confirmed noise had been reduced to acceptable levels. Additional long term actions are being considered.
NRC FORM 366 (1 ()'201 0)
3
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EllS Code XX).
DESCRIPTION OF EVENT
On October 24, 2011, while in Mode 2 (startup) at approximately 0% power, following a Unit 2 scheduled maintenance outage, the 'A' intermediate range monitor (IRM) signal exhibited increasing levels of electrical noise while on Range 1. A spike in the signal resulted in a half-scram signal that prompted Operations personnel to bypass the 'IRM' and declare it inoperable. The noise slowly subsided as control rods were pulled to achieve criticality, and as power on the IRMs increased.
During this time the 'A' IRM remained bypassed and inoperable.
Approximately three hours later, the 'C' IRM subsequently developed erratic behavior and slowly drifted down scale while on Range 7. Operations personnel "ranged" down the 'C' IRM in an attempt to get it to stay on scale; however, its signal continued to display the same erratic behavior.
Operations personnel then declared the 'C' IRM inoperable, resulting in no operable IRM channel in one quadrant of the reactor core. The station's Technical Requirements Manual (TRM) prohibits control rod withdrawal with no operable IRM channels in a core quadrant. As a result further control rod withdrawal to counter the negative reactivity effect from the increasing reactor coolant temperature and maintain the core critical was prohibited. Rather than allowing the increasing reactor coolant temperature to take the core subcritical, Operations personnel were directed to insert a manual scram signal to comply with the Technical Specifications 3.3.1.1, Action G.1, requiring the reactor to be placed in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> of loss of both IRMs in the affected quadrant.
CAUSE OF EVENT
Testing by a third-party vendor revealed degraded signal cable shielding at under-vessel connectors in six of the eight IRM channels. The degraded shielding allowed electrical noise to couple to the signal conductor rather than being shunted to ground as designed. The source of the noise has not yet been determined, but it appears to be a consistent, low frequency signal that is not blocked by ferrite beads since they primarily filter high frequency signals and had been previously installed on the preamplifier signal input and output cables for that purpose. The IRM preamplifiers increased the signal noise (as well as the neutron flux signal) and transmitted it to the rest of the IRM signal processing circuit.
The IRM channels performed acceptably during three previous unit startups in 2011; thus, it appears the signal cable shielding degraded, at least in part, from stresses and wear experienced during those three startups. Testing to detect and repair shielding degradation is performed during each refueling outage (once every two years) but was not required prior to each startup.
REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT This event is reportable in accordance with 10CFR50.73(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). Additionally, when IRMs 'A' and
'C' became inoperable, both IRMs in the same quadrant of the reactor core were inoperable. The required action by the Technical Specifications was to be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Completion of the shutdown required by the Technical Specifications is reportable in accordance with 10CFR50.73 (a)(2)(i)(A).
The IRMs monitor neutron flux levels from the upper range of the source range monitor (SRM) to the lower range of the average power range monitors (APRMs). The IRMs are capable of generating trip signals that can be used to prevent fuel damage resulting from abnormal operating transients in the intermediate power range.
In this power range, the most significant source of reactivity change is due to control rod withdrawal. The IRM LICENSEE EVENT REPORT (LER) u.s. NUCLEAR REGULATORY COMMISSION (10*2010)
CONTINUATION SHEET
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE Edwin I. Hatch Nuclear Plant Unit 2 05000366 YEAR J SEQUENTIAL NUMBER IREVISION J NUMBER 3
OF 3
2011 03 0
mitigates control rod withdrawal error events and is diverse from the rod worth minimizer (RWM), which monitors and controls the movement of control rods at low power. The IRM System is divided into two groups of IRM channels, with four IRM channels inputling to each trip system. An analysis performed by General Electric (GE) assumes that one channel in each trip system is bypassed. However, a more recent analysis performed by GE in April 2002 revealed that, with two IRMs operable per trip system, adequate protection is provided for reactivity events in the intermediate range. This trip is active in each of the 10 ranges of the IRM, which must be selected by the operator to maintain the neutron flux within the monitored level of an IRM range.
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 IRM's was not diminished. There were no safety consequences as a result of this event. All control rods (EllS 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.
CORRECTIVE ACTIONS
Maintenance personnel replaced the six degraded under-vessel connectors for the affected IRMs.
Post maintenance testing confirmed that the noise coupling to the signal conductor had been reduced to acceptable levels. The reactor resumed startup activities on October 28, 2011 with only a minor noise problem remaining on the 'A' IRM signal. Actions continue to find and eliminate the low frequency noise on the 'A' IRM channel.
Long-term corrective actions being considered include requiring neutron monitoring system signal path testing prior to each startup and increased trending and monitoring of IRM signals prior to startup in order to detect the presence of noise. Current plans are to perform the signal path testing for the Unit 2 IRMs prior to startup from a maintenance outage planned for December 2011.
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
LER 1-2009-004 was reported June 19, 2009, in which an IRM signal spike due to electrical noise the resulted in a reactor scram. The cause of the signal spike was high frequency electrical noise coupled to the IRM signal conductors through degraded connector shielding.
Degraded cables and connections were replaced, improvements made on the grounding of the neutron monitoring system and ferrite beads were installed on each cable entering and/or exiting the preamplifier NEMA enclosures on each of the eight channels.
No actions such as IRM signal path testing prior to each startup or increased monitoring of IRM signals prior to startup to detect the presence of noise were put into place for this event. There is a potential that implementation of additional actions for this event in 2009 could have precluded entry into this condition in 2011.