05000285/LER-2015-006

LER-2015-006, AIMMM MEIN
nom.
Omaha Public Power District
10 CFR 50.73
LIC-15-0128
December 11, 2015
U.S. Nuclear Regulatory Commission
Attn: Document Control Desk
Washington, DC 20555-0001
Fort Calhoun Station, Unit No. 1
Renewed Facility Operating License No. DPR-40
NRC Docket No. 50-285
Subject: Licensee Event Report 2015-006, Revision 0, for the Fort Calhoun Station
Please find attached Licensee Event Report 2015-006, Revision 0. This report is being submitted
pursuant to 10 CFR 50.73(a)(2)(ii)(B). There are no new commitments being made in this letter.
If you should have any questions, please contact Brad Biome, Manager, Site Regulatory
Assurance, at (402) 533-7270.
Louis P. Cortopassi
Site Vice President and CNO
LPC/epm
Attachment
c: M. L. Dapas, NRC Regional Administrator, Region IV
C. F. Lyon, NRC Senior Project Manager
S.M. Schneider, NRC Senior Resident Inspector
444 SOUTH 16TH STREET MALL • OMAHA, NE 68102-2247
-
reusi oProartmire
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION
(02-20,4)
,f ; W, r i
'!1"4!'"If LICENSEE EVENT REPORT (LER)
(See Page 2 for required number of
digits/characters for each block)
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018
Estimated burden per response to comply with this mandatory collection request: 80 hours.
Reported lessons :earned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections
Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by
internal e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and
Regi;latory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC
20503. If a means used to impose an information collection does not display a currently valid OMB
control number, the NRC may not conduct or sponsor, and a person is not required to respond to,
the information collection.
1. FACILITY NAME
Fort Calhoun Station
2. DOCKET NUMBER
05000285
3. PAGE
1 OF 5
Unanalyzed Fire Vulnerability Due to Inadequate Design

Fort Calhoun Station
Event date:	10-21-2015
Report date:	12-11-2015
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
Initial Reporting
ENS 51487	10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition
2852015006R00 - NRC Website

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3153-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

BACKGROUND

Fort Calhoun Station (FCS) is a two-loop reactor coolant system (RCS) of Combustion Engineering design. The pressurizer is designed to maintain adequate RCS pressure. The 36 pressurizer heaters are 480 VAC immersion heaters with an output of approximately 25 (23.6) kilowatts (kw) each. One group of heaters operates in the proportional mode of operation, and the second group operates in the backup mode of operation. The six proportional heaters (17percent of the heaters) operate with a variable power input (proportional controllers) as required to offset steady-state heat losses and to maintain a specific steam pressure in the pressurizer. These heaters are normally energized. The backup heaters are controlled by the Pressurizer Pressure Control System. The backup heaters (30 total)(750 kw) are operated in four heater banks: 6 heaters in banks 2 and 3, and 9 heaters in banks 1 and 4.

The four backup heater banks are controlled by four-position switches on control board (CB)-1, 2, 3.

The OFF and ON positions provide manual control of the heaters, while the AUTO position allows automatic heater control. Backup heater bank 4 can be controlled by a handswitch located on motor control center Motor Control Center (MCC)-4C1 in the upper electrical penetration room. The handswitch has two positions, OFF and ON, and is used for manual control of bank 4 backup heaters if the Control Room becomes inaccessible. The local/remote switch on Alternate Shutdown Panel Al-185 must be selected to LOCAL to operate bank 4 heaters at the MCC.

The safety-related function of the alternate shutdown panels is to provide a means for shutting down and maintaining the reactor in a safe condition if access to the main control room is lost due to fire or other cause. Alternate shutdown capability must be independent of cabling in the cable spreading room and the main control room in order to preserve safe shutdown capability in the event of a fire in either of those two areas. In addition, the systems must be able to maintain reactor coolant inventory, achieve and maintain hot shutdown conditions for an extended period of time. Auxiliary Feedwater Panel Al-179 provides instrumentation and controls for the turbine driven auxiliary feedwater pump to supply both steam generators from the emergency feedwater storage tank supply. Alternate shutdown capability is independent of cabling in the cable spreading room and the control room because of the most limiting event, which is a fire. The design makes this assumption and other controls necessary for alternate shutdown capability are located near their respective equipment, but away from the control room. These local controls include the following:

• Emergency diesel generator DG-2 start at local control panel

• Low Pressure Safety Injection (LPSI) pump SI-1B operation at its breaker on bus 1A4

• Main turbine-generator trip at Al-325, Turbine Trip Pushbuttons in the Turbine Building

• Pressurizer heater operation at MCC-4C1 Pressurizer pressure is controlled by monitoring its indication on Al-179 and cycling the backup heaters at MCC-4C1.

Reported lessons learned are incorporated info the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to Impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Fort Calhoun Station

EVENT DESCRIPTION

On October 21, 2015, at 1315 CDT, while conducting design reviews, it was discovered that the isolation function, when transferring control from the Main Control Room to the Alternate Shutdown Panel (Al-185) for pressurizer heater bank 4, had been identified as a potential circuit failure.

Identification of the potential circuit failure vulnerability is for pressurizer heater bank 4 when isolated from Alternate Shutdown Panel (Al-185) and operated locally from MCC-4C1 for Alternate Shutdown Fire Areas 41 (Cable Spreading Room) and 42 (Main Control Room).

The vulnerability involves an external hot short affecting the conductor connecting to the control room switch which may keep the 94/10 relay energized and defeat MCC control of the heaters. In a postulated event, a fire in the control room could prevent the heaters from energizing when demanded, or cause the heaters to unintentionally energize.

The vulnerability has been added to the pre-existing NFPA 805 Fire Protection compensatory measure for Fire Area 41. For Fire Area 42, the Main Control Room is continuously staffed, which has been credited as the compensatory measure.

The Headquarters Operations Office (H00) was notified of the event at 1833 CDT per 10 CFR 50.72(b)(3)(ii)(B). (Event Number (EN) 51487) This report is being submitted per 10 CFR 50.73(a)(2)(ii)(B). Condition Report (CR) 2015-12195 was written to document the event.

CAUSE OF THE EVENT

FCS designed the Alternate Shutdown Panel (ASP) Al-185 under MR-FC-78-056 (Engineering Change (EC) 9120) which was installed in 1980. Alternate shutdown capability was designed as required by NRC Staff Position Safe Shutdown Capability letter dated September 18, 1979. As part of the safe shutdown requirements, pressurizer backup heater bank 4 is required to maintain normal pressurizer operating temperature and pressure while bringing FCS to hot shutdown.

Control circuits were required to have isolation devices; however, hot shorts and grounds were not specifically noted in the NRC position letter. MR-FC-78-056 did not provide isolation of the pressurizer backup heater bank 4 control circuit. Rather, FCS would isolate the control circuit at the MCC through manual action.

Reported lessons leaned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOlA, Pdvacy and Information Collectors Branch (T-5 F53), U.S. Nuclear Regulatory Ccmmission, Washington, DC 20555-0001, or by internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Informatoc and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503.1 a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

On February 20, 1981, the NRC issued Generic Letter 81-12 (NRC-81-0027), "FIRE PROTECTION RULE" (45 FR 76602, November 19, 1980). The letter reiterated (in part) that, "Paragraph 50.48(b) of 10 CFR Part 50, which became effective on February 17, 1981, requires all nuclear plants licensed to operate prior to January 1, 1979 to meet the requirements of Sections I II.G, III.J and 111.0 of Appendix R to 10 CFR Part 50 regardless of any previous approvals by the Nuclear Regulatory Commission (NRC) for alternative design features for those items. This would require each licensee to reassess all those areas of the plant where cables or equipment, including associated non-safety circuits, that could prevent operation or cause maloperation due to hot shorts, open circuits or shorts to ground...

FCS provided a response per letter LIC-81-0037 dated March 19, 1981, which states, "Omaha Public Power District has reviewed the requirements of Appendix R to 10 CFR 50 and the Commission letter dated February 20, 1981, and feels that our existing fire protection system meets the intent of Appendix R. Therefore, no modifications are planned by the District.

On April 8, 1982, NRC sent FCS letter NRC-82-0060 requesting information on 3 open items from the Safety Evaluation Report. One of which is "Modification must be made to the plant such that no wiring changes or pulling of fuses is necessary to achieve and maintain hot standby.

FCS responded in letter LIC-82-0206 on May 25, 1982, stating, "...necessary wiring changes will be made to provide means for isolation of heater control circuits from the fire area (cable spreading room and control room)." MR-FC-82-066 was designed and approved on December 14, 1982, to comply with 10 CFR 50 Appendix R and installation was completed on December 17, 1983. The purpose of the modification was the isolation of pressurizer backup heaters 4 control circuits and local starting of the pressurizer backup heaters 4 at Al-185. The technical error was first introduced in MR-FC-82-066 as the design did not fully isolate the control circuit.

In 1985, NRC Information Notice (IN) 85-09, "Isolation Transfer Switches and Post-fire Shutdown Capability" was issued. Fort Calhoun evaluated IN 85-09 and identified vulnerabilities in the alternate shutdown circuits. Modification MR-FC-85-080 installed redundant fuses in the control circuit for the pressurizer backup heater bank 4. Although pressurizer backup heater bank 4 control circuit had a vulnerability which required redundant fuses to be installed, the review did not identify that the pressurizer backup heater bank 4 control circuit was not fully isolated from the control room as described in CR 2015-12195. As a result, the technical error introduced in MR-FC-82-066 was not identified in MR-FC-85-080.

In 2009, FCS began transitioning the Fire Protection Program from 10CFR50 Appendix R to NFPA 805. The NFPA 805 project for cable selection and circuit analyses was completed by Engineering Planning & Management (EPM) Inc. This review resulted in engineering analyses EA-FC-010-036 "NFPA 805 Safe Shutdown Model Development" and EA-FC-10-037 "NFPA 805 Safe Shutdown Cable Selection/Location".

Fort Calhoun Station Reported lessons !earned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by Internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

The circuit analysis was completed by EPM to verify that proper isolation of the pressurizer backup heater bank 4 control circuit had been established in the fire event in the control room or cable spreading room. However., the analysis and review of the pressurizer backup heater bank 4 control circuit completed in the 2009 timeframe did not identify the vulnerability identified in CR 2015-12195.

The apparent causes of this event were:

1) The preparers and reviewers of MR-FC-82-066 and MR-FC-85-080 did not apply adequate technical rigor to fully understand the isolation of the pressurizer backup heater bank 4 control circuit at A1-185 from the control room in the event of a control room or cable spreading room fire.

These are latent human performance errors.

2) During the EPM 2009 circuit analysis review for the transition from 10CFR50 Appendix R to NFPA 805, EPM did not apply adequate technical rigor to identify the vulnerability of control circuit isolation of the pressurizer backup heater bank 4 at Al-185 from the control room in the event of a control room or cable spreading room fire.

CORRECTIVE ACTIONS

Short Term Corrective Actions The vulnerability has been added to the pre-existing NFPA 805 Fire Protection compensatory measure for Fire Area 41. For Fire Area 42, the Main Control Room, is continuously staffed which has been credited as the compensatory measure.

An Extent of Condition (EOC) review of the Alternate Shutdown capability control circuits to determine proper isolation from the control room at the alternate shutdown panels has been completed. No additional issues were identified.

Long Term Corrective Actions Additional action to resolve latent error to fully isolate the pressurizer backup heater bank 4 control circuit will be implemented by the corrective action program.

SAFETY SYSTEM FUNCTIONAL FAILURE

This does not represent a safety system functional failure in accordance with NEI 99-02, Revision 7.

PREVIOUS EVENTS

There have not been any previous incidents of this type at the station.