05000317/LER-2013-002, From Calvert Cliffs Nuclear Power Plant Regarding Unfused Ammeter Circuits Result in Appendix R Unanalyzed Condition

From Calvert Cliffs Nuclear Power Plant Regarding Unfused Ammeter Circuits Result in Appendix R Unanalyzed Condition

ML13353A171
Person / Time
Site:	Calvert Cliffs
Issue date:	12/17/2013
From:	Flaherty M Constellation Energy Nuclear Group
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 13-002-00
Download: ML13353A171 (8)

LER-2013-002, From Calvert Cliffs Nuclear Power Plant Regarding Unfused Ammeter Circuits Result in Appendix R Unanalyzed Condition

Event date:
Report date:
Reporting criterion:	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)(iv)(A), System Actuation 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
3172013002R00 - NRC Website

text

Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Lusby, Maryland 20657 CENGS.

a joint venture of Constellation 6j9aeDF O Energy, I'

CALVERT CLIFFS NUCLEAR POWER PLANT December 17, 2013 U.S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:

Document Control Desk

SUBJECT:

Calvert Cliffs Nuclear Power Plant Unit Nos. I and 2; Docket Nos. 50-317 and 50-318; License Nos. DPR 53 and DPR 69 Licensee Event Report 2013-002, Revision 00 Unfused Ammeter Circuits Result in Appendix R Unanalyzed Condition The attached report is being sent to you as required by 10 CFR 50.73.

There are no regulatory commitments contained in this correspondence.

Should you have questions regarding this report, please contact Mr. Douglas E. Lauver at (410) 495-5219.

Very truly yours, Mark D. Flaherty Plant General Manager MDF/KLG/bjd

Attachment:

As stated cc:

N. S. Morgan, NRC Resident Inspector, NRC W. M. Dean, NRC S. Gray, DNR

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-20 10)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

l3. PAGE Calvert Cliffs Nuclear Power Plant, Unit 1 05000 3171 1 OF 07

4. TITLE Unfused Ammeter Circuits Result in A pendix R Unanalyzed Condition

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

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

CCNPP' Unit 2 05000318 FACILITY NAME DOCKET NUMBER 10 18 2013 2013 - 002 -

00 12 17 2013 05000

9. OPERATING MODE

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

El 20.2201(b)

El 20.2203(a)(3)(i)

[I 50.73(a)(2)(i)(C)

[1 50.73(a)(2)(vii) 1 El 20.2201(d)

[I 20.2203(a)(3)(ii)

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

[I 50.73(a)(2)(viii)(A)

El 20.2203(a)(1)

El 20.2203(a)(4)

Z 50.73(a)(2)(ii)(B)

El 50.73(a)(2)(viii)(B)

__ 20.2203(a)(2)(i)

El 50.36(c)(1)(i)(A)

[I 50.73(a)(2)(iii)

El 50.73(a)(2)(ix)(A)

10. POWER LEVEL El 20.2203(a)(2)(ii)

-] 50.36(c)(1)(ii)(A)

[I 50.73(a)(2)(iv)(A)

El 50.73(a)(2)(x)

[I 20.2203(a)(2)(iii)

[I 50.36(c)(2)

[I 50.73(a)(2)(v)(A)

[1 73.71(a)(4)

El 20.2203(a)(2)(iv)

El 50.46(a)(3)(ii)

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

El 73.71(a)(5) 100 [E 20.2203(a)(2)(v)

[I 50.73(a)(2)(i)(A)

El 50.73(a)(2)(v)(C)

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

El 50.73(a)(2)(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)

Kenneth L. Greene, Licensing Engineer 410-495-4385CAUSE SYSTEM COMPONENT MANU-REPORTABLE

CAUSE

SYSTEM COMPONENT MANU-REPORTABLE FACTURER TO EPIX FACTURER TO EPIX B

EJ WEL Y

14. SUPPLEMENTAL REPORT EXPECTED

15. EXPECTED MONTH DAY YEAR SUBMISSION El YES (If yes, complete 15. EXPECTED SUBMISSION DATE)

Z NO DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

On October 18, 2013, a review of industry operating experience determined an unanalyzed condition existed with respect to 10 CFR Part 50 Appendix R analysis requirements. The unanalyzed condition involved a postulated fire in Unit 1 Cable Spreading Room (CSR) that could cause an unfused direct current (DC) ammeter circuit to become grounded. If the fire also caused another DC wire of the opposite polarity on the same component to become grounded, a ground loop through the unfused DC ammeter wiring could exist. This ground loop could draw excessive current and could overheat. Because the affected DC ammeter circuits run through both unit CSRs on the way to the Control Room, a secondary fire could occur in Unit 2 CSR. Fire in both CSRs is not an analyzed condition under the 10 CFR Part 50 Appendix R program. Review determined that only three unfused DC ammeter circuits were susceptible to this condition. The apparent cause was determined to be that the original design of the DC ammeter circuits did not adequately address fire protection program requirements.

On November 11, 2013 technicians lifted the leads to the affected ammeter circuits which eliminated this unanalyzed condition. A modification to install fuses on the affected DC ammeter circuits is planned.

NRC FORM 366 (10-2013)U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL I

REV YEAR NUMBER NO Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 2013

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1.

DESCRIPTION OF EVENT

A.

PRE-EVENT PLANT CONDITIONS:

On October 18, 2013, Unit 1 was operating at 100 percent power and Unit 2 was operating at 99.5 percent power. There were no inoperable systems, structures, or components that would have impacted this event.

B.

EVENT:

On October 18, 2013, a review of recent industry operating experience regarding the potential impact of unfused Direct Current (DC) ammeter circuits in the Control Room (CR) and the Cable Spreading Rooms (CSR) identified that an unanalyzed condition existed at Calvert Cliffs with respect to 10 CFR Part 50 Appendix R analysis requirements. Following identification of the existence of an unanalyzed condition, Calvert Cliffs generated an eight hour Emergency Notification System report.

The review identified that the ammeter circuits for each of the station DC batteries and their associated battery chargers contain a shunt in the current wiring. The shunt contains two leads that run to an ammeter in the CR. The small difference in the voltage between the two taps off of the shunt is enough to deflect the ammeter in the CR when current flows from either a station DC battery or a DC battery charger. The ammeter wiring attached to the shunt does not contain a fuse. Therefore, if one of the ammeter wires shorts to ground at the same time as another DC wire of the opposite polarity on the same battery or battery charger also shorts to ground, a ground loop through the unfused ammeter wire could occur. The potential exists that the overloaded ammeter wiring could draw excess current, overheat, and damage wiring leading to other equipment needed to conduct safe shutdown of the units.

Specifically at Calvert Cliffs the unanalyzed condition involves a postulated fire in Unit 1 CSR that could cause one of the DC ammeter wires to hot short to ground. Then if concurrently the fire also causes another DC wire of the opposite polarity on the same equipment (DC battery or DC battery charger) to short to ground, a ground loop through the unfused DC ammeter wire would exist. This could cause the wire to draw excessive current and overheat. Because certain DC ammeter wires run from Unit 2 CSR through Unit I CSR on their way to the CR, the ground loop could cause a secondary fire to start in Unit 2 CSR. This secondary fire could then adversely affect the ability of safe shutdown equipment to operate in Unit 2 CSR. The potential to impact safe shutdown equipment in both CSRs places Calvert Cliffs in an unanalyzed condition with respect to 10 CFR Part 50 Appendix R analysis requirements. Since 10 CFR Part 50 Appendix R analyses are based on demonstrating the ability to withstand a single common enclosure fire scenario, a condition that could propagate a fire beyond a single common enclosure is an unanalyzed condition.

At Calvert Cliffs, DC ammeters were installed during initial construction in the CR for each DC battery and DC battery charger in addition to local ammeters in the CSR. Each ammeter circuit contains a shunt which allows a small amount of current to flow to the ammeter wheneverU.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

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SEOUENTIAL I

REV YEAR NUMBER NO.

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of 07 current flows from their associated battery or battery charger. The ammeter wires were unfused as was allowed by the industry codes and standards in place at the time.

A thorough review of all DC ammeter circuits for Unit 1 and Unit 2 demonstrated that only three circuits contain all of the conditions necessary to make them potentially susceptible to this postulated failure scenario. The susceptible circuits are:

Circuit ZB2D103M - Runs from DC Bus 21, 2BUS2DO1, to CR Panel 1C24A.

Circuit ZB1 D13B - Runs from DC Battery Charger 13, 1CHGR13, to CR Panel 1C24A.

Circuit ZB2D21A - Runs from DC Battery Charger 21, 2CHGR21, to CR Panel 1 C24A.

Each of these circuits runs from Unit 2 CSR through Unit 1 CSR on their way to the panel in the CR. Thus a postulated fire in Unit 1 CSR could be spread to Unit 2 CSR should any of these DC circuits become grounded and a ground loop be developed.

Following discovery of this unanalyzed condition, Operations began a compensatory action to conduct hourly fire tours in both CSRs. On November 11, 2013, technicians lifted the leads in Unit 2 CSR for each of the three susceptible remote DC ammeter circuits which removed the 10 CFR Part 50 Appendix R unanalyzed condition. Local current indication remained available in Unit 2 CSR for each of the three circuits.

C.

INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED TO THE EVENT:

There were no inoperable structures, components, or systems that contributed to this event.

D.

DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES

October 18, 2013 Engineering determined an unanalyzed condition existed at Calvert Cliffs with respect to 10 CFR Part 50 Appendix R analysis requirements. This determination was made as the result of a review of recent operating experience from Palo Verde Nuclear Generating Station of a postulated fire causing a ground loop in their unprotected DC ammeter wiring.

This could then result in excessive current flow (heating) in the ammeter wiring to the point of causing a secondary fire. The secondary fire could adversely affect safe shutdown equipment and potentially cause loss of ability to conduct a safe shutdown as required by 10 CFR Part 50 Appendix R.

After determination that an unanalyzed condition existed at Calvert Cliffs, Operations initiated the compensatory action of conducting hourly fire tours in both Unit 1 and Unit 2 CSRs.U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL REV YEAR NUMBER NO.

Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 2013

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of 07 November 11,2013 Technicians lifted the leads in Unit 2 CSR for the three susceptible DC ammeter circuits.

Lifting the leads eliminated the unanalyzed condition for Calvert Cliffs. As a result, Operations discontinued their hourly fire tours in the CSRs. Lifting the leads also removed the ammeter capability in the CR for these three circuits but local ammeter readings in Unit 2 CSR remained.

E.

OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED

No other systems or secondary functions were affected by this condition.

F.

METHOD OF DISCOVERY

This unanalyzed condition was discovered through a review of recent industry operating experience at other nuclear power plants. The review determined Calvert Cliffs was susceptible to a postulated fire resulting in an unanalyzed condition at Calvert Cliffs with respect to 10 CFR Part 50 Appendix R analysis requirements.

G.

MAJOR OPERATOR ACTION:

Upon determining an unanalyzed condition existed, Operations began hourly fire tours in both Unit 1 and Unit 2 CSRs as a compensatory action. Operations continued these fire tours until the unanalyzed condition was terminated by lifting of the leads of the susceptible DC ammeter wires.

H.

SAFETY SYSTEM RESPONSES:

There were no demands for safety system actuations during this event.

II.

CAUSE OF EVENT

This event is documented in the site's Corrective Action Program under CR-2013-008305. The apparent cause of the event was determined to be that the original design of the DC ammeter circuits did not adequately address fire protection program requirements. This led to a condition that was not conservative in regards to the potential of unfused DC ammeter circuits to cause an unanalyzed 10 CFR Part 50 Appendix R condition.

Calvert Cliffs Unit 1 and Unit 2 were designed and built in the 1970s using the industry codes and standards in effect at that time. The DC ammeter circuits were designed without fuses as Institute of Electrical and Electronics Engineers 384, 'Trial Use Standard Criteria for Separation of Class IE Equipment and Circuits,' did not require an 'isolation device' for DC ammeter wiring as long as the circuit was considered associated with the safety train. In 1980 10 CFR Part 50 Appendix R rule was issued. Between 1980 and 1982 Calvert Cliffs performed the Appendix R analysis for Unit 1 and Unit 2. This original analysis analyzed all fused circuits. As a result theU.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

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of 07 DC ammeter circuits were not included in that analysis. Calvert Cliffs analysis was accepted by the Nuclear Regulatory Commission and the site considered all equipment, including the DC ammeter circuits, met original design and 10 CFR Part 50 Appendix R requirements. In 2006 Calvert Cliffs initiated a commitment to implement the performance based, risk informed National Fire Protection Association 805 approach. As part of the National Fire Protection Association 805 project, the DC analyses were not reanalyzed because no discrepancies were found in the existing calculations and configurations. At that time Calvert Cliffs still considered the DC equipment met original design and Appendix R requirements.

Over time, with additional AC and DC cable testing, industry's understanding of the potential for a grounded, unfused DC loop to result in a loss of capability to conduct a safe shutdown as required by 10 CFR Part 50 Appendix R, has evolved.

As a result, industry has begun to determine that the original analyses, and subsequent interpretation of evolving regulations, were not conservative in regards to treatment of unfused.

DC circuits and the potential for causing an unanalyzed condition. Since late 2011, several plants have identified issues where their DC ammeter circuits did not meet current understanding of the regulations and have issued operating experience reports. Review of these industry operating experience reports led Calvert Cliffs to determine an unanalyzed condition existed at Calvert Cliffs in regards to the unfused DC ammeter circuits. A thorough review was able to determine that only three of the DC ammeter circuits at Calvert Cliffs were susceptible to a grounded loop caused by a fire that could result in a secondary fire resulting in the plant being unable to conduct a safe shutdown.

Ill.

ANALYSIS OF EVENT

On October 18, 2013, Calvert Cliffs determined an unanalyzed condition existed in regards to selected unfused DC ammeter. circuits that were susceptible in a postulated fire to become grounded and draw excessive current. This could result in the fire to spread to a second room thus affecting Calvert Cliffs ability to conduct a safe shutdown. An Emergency Notification System report was made at 1405 on October 18, 2013 within the required eight hour requirement in accordance with 10 CFR 50.72(b)(3)(ii)(B).

This event is also reportable via a written 60 day report under 10 CFR 50.73(a)(2)(ii)(B) as "Any event or condition that resulted in... The nuclear power plant being in an unanalyzed condition that significantly degraded plant safety."

There were no actual consequences associated with this event. This event was reviewed pursuant to the criteria of NRC Enforcement Policy, "Interim Enforcement Policy Regarding Enforcement Discretion for Certain Fire Protection Issues (10 CFR 50.48)," to ensure the criteria were satisfied. Specifically, Calvert Cliffs identified and corrected this issue as part of the transition to National Fire Protection Association 805, the issue was entered into the corrective action program, compensatory measures were implemented in a reasonable time commensurate with the risk significance, and the violation was not willful. A bounding probabilistic risk assessment analysis showed the core damage frequency risk increase wouldU.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL REV YEAR NUMBER NO.

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of 07 be a maximum of 9E-06. This value would be non-red using the Significant Determination Process. The value provided is bounding and further resources and detailed analysis would likely reduce the overall increase in core damage probability. The probabilistic risk assessment staff have assessed that the initial compensatory measures implemented, which included hourly fire tours, were commensurate to the core damage risk. After the leads were lifted, the risk from this issue was negligible.

This event had no impact on any Nuclear Regulatory Commission Reactor Oversight Process Performance Indicator for either Unit 1 or Unit 2.

IV.

CORRECTIVE ACTIONS

A.

ACTION TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:

1. The leads for the three DC ammeter circuits susceptible to this unanalyzed condition were lifted. Lifting these leads removed the possibility of a grounded loop in these circuits allowing a fire in Unit 1 CSR to be spread to Unit 2 CSR.

B.

ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

1. Implement a modification to install fusing in the three susceptible DC ammeter circuits to eliminate the potential for a fire to be spread from Unit 1 CSR to Unit 2 CSR.

V. ADDITIONAL INFORMATION

A.

FAILED COMPONENTS:

There were no failed components in this event.

B.

PREVIOUS LERS ON SIMILAR EVENTS:

A review of recent licensee event reports was performed and it was determined that no similar conditions had been identified.

C.

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 FUNCTION ID SYSTEM ID DC Ammeter Circuits WEL EJ DC Station Batteries BTRY EJ DC Battery Chargers BYC EJU.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL REV YEAR NUMBER NO.

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of 07 D.

SPECIAL COMMENTS:

None