05000499/LER-2013-001, Regarding Manual Reactor Trip Due to Dropped Rods M8 and D8

Regarding Manual Reactor Trip Due to Dropped Rods M8 and D8

ML130720684
Person / Time
Site:	South Texas
Issue date:	02/28/2013
From:	Koehl D South Texas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NOC-AE-13002974, G25, STI: 33661623 LER 13-001-00
Download: ML130720684 (6)

LER-2013-001, Regarding Manual Reactor Trip Due to Dropped Rods M8 and D8

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)(iv)(B), System Actuation
4992013001R00 - NRC Website

text

Nuclear Operating Company South Texas Project Electric Generating Station PO. Box 289 Wadsworth, Texas 77483

/

February 28, 2013 NOC-AE-13002974 File No.: G25 10 CFR 50.73 STI: 33661623 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 South Texas Project Unit 2 Docket No. STN 50-499 Licensee Event Report 2-2013-001 Unit 2 Manual Reactor Trip Due to Dropped Rods M8 and D8 Pursuant to 10 CFR 50.73, STP Nuclear Operating Company (STPNOC) submits the attached Unit 2 Licensee Event Report (LER) 2-2013-001 to address the Unit 2 Manual Reactor trip that occurred on January 4, 2013.

This condition is considered reportable under 10 CFR 50.73(a)(2)(iv)(A), any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of this section.

This event did not have an adverse effect on the health and safety of the public.

There are no commitments contained in this LER. Corrective actions will be implemented in accordance with the STP Corrective Action Program.

If there are any questions on this submittal, please contact either Jamie Paul at (361) 972-7344 or me at (361) 972-7800.

Dennis L. Koehl President and CEO/CNO JLP Attachment: LER 2-2013-001

NOC-AE-1 3002974 Page 2 of 2 cc:

(paper copy)

(electronic copy)

Regional Administrator, Region IV U. S. Nuclear Regulatory Commission 1600 East Lamar Blvd Arlington, Texas 76011-4511 Balwant K. Singal Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North (MS 8B13) 11555 Rockville Pike Rockville, MD 20852 Senior Resident Inspector U. S. Nuclear Regulatory Commission P. 0. Box 289, Mail Code: MN1 16 Wadsworth, TX 77483 C. M. Canady City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704 A. H. Gutterman, Esquire Morgan, Lewis & Bockius LLP Peter Nemeth Crain Caton & James, P.C.

John Ragan Chris O'Hara Jim von Suskil NRG South Texas LP Kevin Polio Richard Pena City Public Service C. Mele City of Austin Richard A. Ratliff Texas Department of State Health Services Alice Rogers Texas Department of State Health Services Balwant K. Singal U. S. Nuclear Regulatory Commission

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO, 3150.0104 EXPIRES: 10/31/2013 (10-2010)

, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to the information collection.

3. PAGE South Texas Unit 2 05000499 1 OF4

4. TITLE Unit 2 Manual Reactor Trip Due to Dropped Rods M8 and D8

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER NO.

___N/A N/A 01 04 2013 2013 001 0

02 28 2013 N/A N/A

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10CFR§: (Check allthat apply)

El 20.2201(b)

[D 20.2203(a)(3)(i)

[

50.73(a)(2)(i)(C)

D] 50.73(a)(2)(vii)

[] 20.2201 (d)

[_1 20.2203(a)(3)(ii)

[]

50.73(a)(2)(ii)(A)

[]

50.73(a)(2)(viii)(A)

__ 20.2203(a)(1)

Wj 20.2203(a)(4)

Wj 50.73(a)(2)(ii)(B)

[1 50.73(a)(2)(viii)(B)

10. POWER LEVEL D 20.2203(a)(2)(i)

Z 50.36(c)(1)(i)(A)

W 50.73(a)(2)(iii)

[1 50.73(a)(2)(ix)(A) 100%

20.2203(a)(2)(ii)

[

50.36(c)(1)(ii)(A) 50.73(a)(2)(iv)(A)

[1 50.73(a)(2)(x)

[_1 20.2203(a)(2)(iii)

Ej 50.36(c)(2)

[]

50.73(a)(2)(v)(A)

[_1 73.71 (a)(4)

El 20.2203(a)(2)(iv)

Ej 50.46(a)(3)(ii)

[]

50.73(a)(2)(v)(B)

El 73.71(a)(5)

El 20.2203(a)(2)(v)

El 50.73(a)(2)(i)(A)

[-

50.73(a)(2Xv)(C)

El OTHER El 20.2203(a)(2)(vi)

El 50.73(aX2)(i)(B)

El 50.73(a)(2)(v)(D)

Specify in Abstract below or in NRC Form 366A

12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (Include Area Code)

Jamie Paul, Licensing Supervisor 361-972-734414. SUPPLEMENTAL RESPONSE EXPECTED fr YES (if yes, complete 15. EXPECTED SUBMISSION DATE)

ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

At 07:05 on 1/4/2013, Unit 2, while at 100% power, commenced surveillances 0PSP03-RS-0004 and 0PSP03-RS-0001 tc satisfy the monthly requirements of Technical Specification 4.1.3.1.2. and to demonstrate the shutdown and control rods are Operable by movement of at least 10 steps in any one direction.

During testing, two rods on shutdown bank E (SBE) dropped to the bottom of the core and a manual reactor trip was required. The dropped rods on SBE occurred while inserting shutdown bank C (SBC) rods in 6 steps. After SBE rod M-8 dropped, rod motion was stopped. While validating the dropped rod, a second rod, D-8, in SBE dropped. At 09:41, once both dropped rods were validated by diverse indications of power, flux, and rod positions, a manual reactor trip was performed. Troubleshooting identified the problem as high resistance on Rod Holdout Mode Selector (RHMS) switch contacts in Rod Control Power Cabinet SCDE when the contacts should have been closed. This blocked the multiplexing signal to the SBE Stationary Regulation card resulting in dropped rods.

This condition is considered reportable under 10 CFR 50.73(a)(2)(iv)(A), any 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). There were no personnel injuries, no offsite radiological releases, and no damage to safety-related equipment associated with this condition. This condition did not have an adverse effect on the health and safety of the public.

NRC FORM 366 (10-2010)

SUMMARY OF THE EVENT At 07:05 on 1/4/2013, Unit 2, while at 100% power, the control room commenced OPSP03-RS-0001 "MONTHLY CONTROL ROD OPERABILITY", and OPSP03-RS-0004 "CONTROL ROD OPERABILITY (6 AND 10 STEPS)". Surveillances OPSP03-RS-0004 and OPSP03-RS-0001 test the shutdown and control rods not fully inserted in the core in order to satisfy the monthly requirements of Technical Specification 4.1.3.1.2. and also provide instructions for demonstrating the shutdown and control rods not fully inserted in the core are Operable by movement of at least 10 steps in any one direction.

During testing, two rods on shutdown bank E (SBE) dropped to the bottom of the core and a manual reactor trip was required per OPOP04-RS-0001, "CONTROL ROD MALFUNCTION". The dropped rods on SBE occurred while inserting shutdown bank C (SBC) rods in 6 steps. When SBC demand reached 255, one rod in SBE dropped (M-8) while the rest of the rods in SBE transitioned from 258 to 252/246 on Digital Rod Position Indication (DRPI). Rod motion was stopped and while validating the dropped rod, a second rod in SBE dropped (D-8). At 09:41, once both dropped rods were validated by diverse indications of power, flux, and rod positions, a manual reactor trip was performed.

This event resulted in a reactor trip from 100% power. The Unit was stabilized in Mode 3 with all systems necessary to maintain shutdown conditions, remove decay heat, control the release of radioactive material, and mitigate the consequences of an accident available.

Troubleshooting identified that the problem was isolated to the Rod Holdout Mode Selector (RHMS) switch in Rod Control Power Cabinet SCDE. This is a five-position, seven deck rotary Grayhill switch used to interface with the Rod Holdout Sequencing card and other power cabinet components to accomplish the rod lockout function for rapid refueling. Switch Pin 7 to common C2 on deck F was found to have a high resistance (-300Mohms) while in the "OFF" position.

FORM 366 (10-2010)LICENSEE EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMISSION CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE YEA SEQUENTIAL RE.No South Texas Unit 2 05000499 YUEN RNF 1

2013 001 00 The Rod Holdout Mode Selector switch in Rod Control Power Cabinet SCDE was replaced. To address extent of condition in Unit 2, the four other Rod Holdout Mode Selector switches in the other Rod Control Power Cabinets were tested.

E.

METHOD OF DISCOVERY

The two dropped rods on shutdown bank E requiring a manual reactor trip were self-revealing.

II. EVENT-DRIVEN INFORMATION A.

SAFETY SYSTEMS THAT RESPONDED All required safety systems responded as expected except that one of two Nuclear Instrument Source Range detectors, N32, did not energize automatically. This was identified and the function performed manually. In addition to failing to automatically energize, the source range audio count rate on N32 also failed to function. These conditions have been entered into the Corrective Action Program.

B.

DURATION OF SAFETY SYSTEM INOPERABILITY

N/A C.

SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT There was no impact to radiological safety, safety of the public, or safety of station personnel during this event.

The Incremental Conditional Core Damage Probability (ICCDP) for the Reactor Trip in Unit 2 on 1/4/2013 is 1.12E-07. The resulting Incremental Conditional Large Early Release Probability (CLERP) is 5.92E-08.

Ill.

CAUSE OF THE EVENT

The cause of this event has been determined to be high resistance circuit on the RHMS from the C (common) contact in switch position 7 on deck F due to contamination. Even though offsite failure analysis did not reproduce the high resistive contact nor did it find evidence of contamination that could have caused this condition, enough evidence exists from other failure analysis and industry experience to conclude that contamination is the cause.

The cause of this contamination could be due to:

The low current that flows through these contacts is not enough to burn through corrosion/carbon deposits that builds up on the contacts over time.

Solder flux on contact surfaces.

Grease or other contaminants.

FORM 366 (10-2010)LICENSEE EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMISSION CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE YEAR SEQUENTIAL REV. NO South Texas Unit 2 05000499 NUMBER 4OF4 2013 001 00

IV. CORRECTIVE ACTIONS

Corrective actions will be implemented in accordance with the STP Corrective Action Program. The Rod Holdout Mode Selector switch in Rod Control Power Cabinet SCDE was replaced. Corrective actions to prevent future failures will include either a design change to address the vulnerability associated with the RHMS switch contacts or replacement of existing switches with newly manufactured switches.

V. PREVIOUS SIMILAR EVENTS

There have been no similar reportable events at STP within the last three years. The Rod Holdout Mode Selector (RHMS) switches in the Rod Control Power Cabinets interface with the Rod Holdout Sequencing card and other power cabinet components to accomplish the rod lockout function for rapid refueling. There are no previous similar industry events as South Texas Project (STP) is the only plant that uses rapid refueling.

VI. ADDITIONAL INFORMATION

N/A FORM 366 (10-2010)