05000317/LER-2014-004, Regarding Unfused 250 Vdc Circuits Result in 10 CFR Part 50 Appendix R Unanalyzed Condition Due to Original Design Did Not Adequately Address Fire Protection Requirements
| ML14126A603 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 05/01/2014 |
| From: | Flaherty M Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 14-004-00 | |
| Download: ML14126A603 (8) | |
| 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 |
| 3172014004R00 - NRC Website | |
text
Exelon Generation.
Mark Flaherty Plant Manager Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Lusby, MD 20657 410 495 5205 Office 410 495 5444 Fax 443 534 5475 Mobile www.exeloncorp-com rnark.flaherty@exeloncorp.com 10 CFR 50.73 May 1, 2014 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Calvert Cliffs Nuclear Power Plant Unit Nos. 1 and 2; Docket Nos. 50-317 and 50-318; Facility Operating License Nos. DPR 53 and DPR 69
Subject:
Licensee Event Report 2014-004, Revision 00 Unfused 250 VDC Circuits Result in 10 CFR Part 50 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.
Respectfully, Mark D. Flaherty Plant Manager MDF/KLG/bjd
Attachment:
As stated cc:
NRC Project Manager, Calvert Cliffs NRC Regional Administrator, Region I NRC Resident Inspector, Calvert Cliffs S. Gray, MD-DNR 0o~
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 [01-2014)
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 regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53),
LICENSEE EVENT REPORT (LER)
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 RegulatoryAffairs, NEOB-10202, (3150-0104), Office (See Page 2 for required number of of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB digits/characters for each block) control number, the NRC may not conduct or sponsor, and a person is not I required to respond to, the information collection.
- 3. PAGE Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 1 OF 7
- 4. TITLE Unfused 250 VDC Circuits Result in 10 CFR Part 50 Appendix R Unanalyzed Condition Due to Original Design did not Adequately Address Fire Protection Requirements
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE 1
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR FACILITY NAME DOCKET NUMBER NUBER" NO.
CCNPP, Unit 2 05000318 FACILITY NAME DOCKET NUMBER 10 2014 2014 - 004 -
00 05 01 2014 05000 D. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply) 1 [1 20.2201(b) 0l 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
[I 50.73(a)(2)(vii) ol 20.2201(d)
[I 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A) 0- 20.2203(a)(1) 0l 20.2203(a)(4) 0 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B) 0_ 20.2203(a)(2)(i) 0l 50.36(c)(1)(i)(A)
C3 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL [I 20.2203(a)(2)(ii) 0l 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
[I 50.73(a)(2)(x) 100 [1 20.2203(a)(2)(iii)
[] 50.36(c)(2)
[I 50.73(a)(2)(v)(A)
El 73.71(a)(4)
[I 20.2203(a)(2)(iv) 0l 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5)
[I 20.2203(a)(2)(v) 0l 50.73(a)(2)(i)(A)
[3 50.73(a)(2)(v)(C)
[3 50.73(a)(2)(vii)
[I 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
[E 50.73(a)(2)(v)(D)
Specify in Abstract below or in =
- 1.
DESCRIPTION OF EVENT
A.
PRE-EVENT PLANT CONDITIONS:
On March 10, 2014, Unit 1 was in Mode 5 while conducting a refueling outage and Unit 2 was operating at 100 percent power. There were no inoperable systems, structures, or components that would have impacted this event.
B.
EVENT:
On March 10, 2014 at 1653, as a result of a review of industry's operating experience regarding the potential impact of unfused Direct Current (DC) circuits, Calvert Cliffs identified that an unanalyzed condition with respect to 10 CFR Part 50 Appendix R analysis requirements existed.
Following identification of the existence of an unanalyzed condition, an eight hour Emergency Notification System report was generated.
The review identified ten 250 VDC circuits which were susceptible to causing an 10 CFR Part 50 Appendix R fire in one area being spread to another 10 CFR Part 50 Appendix R fire area. The ten circuits involved are:
250V Battery Charger #15 Ammeter circuit 250V Battery Charger #25 Ammeter circuit 11 Steam Generator Feed Pump Emergency Lube Oil Pump control circuit 12 Steam Generator Feed Pump Emergency Lube Oil Pump control circuit 21 Steam Generator Feed Pump Emergency Lube Oil Pump control circuit 22 Steam Generator Feed Pump Emergency Lube Oil Pump control circuit U-1 Turbine Auxiliaries Emergency Lube Oil Pump control circuit U-1 Generator Auxiliaries Emergency Hydrogen Seal Oil Pump control circuit U-2 Turbine Auxiliaries Emergency Lube Oil Pump control circuit U-2 Generator Auxiliaries Emergency Air Side Seal Oil Pump control circuit The battery charger ammeter control circuits are unfused. The emergency lube oil and seal oil pump circuits have fuses but the fuses are sized (200 amp) solely to protect the motors. There are no fuses to provide over current protection for the emergency lube oil and seal oil pump control circuits. The cables from all these circuits run from the Turbine Building through their respective Cable Spreading Room (CSR) and up to the Control Room. These susceptible 250 VDC circuits are run through cable trays that also contain safety-related cables of equipment needed to ensure safe shutdown of the units.
Specifically at Calvert Cliffs the unanalyzed condition involves a postulated fire in the Control Room or either unit's CSR that could cause one of the susceptible 250 VDC circuit wires to hot short to ground. Then if concurrently the fire also causes another DC wire of the opposite polarity on the same circuit to short to ground, a ground loop through the unfused DC wire would exist. This could cause the wire to draw excessive current and overheat. The resulting overheating of these 250 VDC circuits could cause a secondary fire in another 10 CFR Part 50 Appendix R fire area and could potentially adversely affect multiple safe shutdown equipment and cause the loss of ability to safely shutdown per 10 CFR Part 50 Appendix R. The potential to impact safe shutdown equipment in multiple areas 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.
Following discovery of this unanalyzed condition Operations began compensatory actions to conduct hourly fire watch tours of both units' CSRs and behind the operating panels in the Control Room. Restrictions were also placed on hot work permits within these same rooms.
These fire tours were ended following completion of a Probabilistic Risk Assessment of the increased risk associated with this unanalyzed condition. These evaluations showed that the increase in Core Damage Frequency to be white for Unit 1 and green for Unit 2. Based on this input, combined with the Fire Protection Program's existing daily and weekly transient combustible loading walk downs, the decision was made to end the hourly fire tours. However the hot work permit restrictions were maintained in Unit 1 CSR based on its higher risk factor and in the Control Room.
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
March 10, 2014 A review based on industry operating experience determined the existence of a 10 CFR Part 50 Appendix R unanalyzed condition for ten 250 VDC circuits that run from the Turbine Building in cable trays up to the respective unit's CSR and then to the Control Room. It was determined that a postulated fire in the Control Room or either CSR could cause a short circuit in these susceptible unfused 250 VDC circuits. The overheating of the circuit could cause a secondary fire to occur in a separate fire area and potentially adversely affect multiple safe shutdown equipment. This results in the loss of ability to conduct a safe shutdown as required by 10 CFR Part 50 Appendix R.
Upon determination that an unanalyzed condition existed at Calvert Cliffs, Operations initiated compensatory action consisting of hourly fire tours and placed restrictions on hot work permits within the affected rooms.
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 and behind the operating panels in the Control Room as a compensatory action. An additional compensatory action was taken to place additional restrictions on hot work permits within these rooms.
H.
SAFETY SYSTEM RESPONSES:
There were no demands for safety system actuations during this event.
I1.
CAUSE OF EVENT
This event is documented in the site's Corrective Action Program under CR-2014-002667. The apparent cause of the event was determined to be that the original design of these 250 VDC 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 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 the industry design standards at that time did not require a fused circuit for this type of indicator.
The control circuits for the backup emergency lube oil and seal oil pumps were not fused as the vendors determined that no fuses should be put in these circuits due to the high monetary value of the non-safety related equipment these backup emergency lube oil and seal oil pumps were meant to protect.
In 1980 the 10 CFR Part 50 Appendix R rule was issued. Between 1980 and 1982 Calvert Cliffs performed the 10 CFR Part 50 Appendix R analysis for Unit 1 and Unit 2. This original analysis analyzed all fused circuits. As a result these 250 VDC circuits were not included in that analysis. Calvert Cliffs' considered all equipment, including the 250 VDC 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 all DC equipment met original design and 10 CFR Part 50 Appendix R requirements.
The potential for the ground plane to become a conductor was recently determined to be a credible fault mechanism as published in NUREG/CR-7100, Direct Current Electrical Shorting in Response to Exposure Fire (DESIREE-FIRE), dated April 2, 2012. Prior to this fire testing, fire safe shutdown analysis did not consider the effects of the DC shorts through the ground plane.
Since this is recent testing, this failure mode previously was not considered credible and not taken into account in previous safe shutdown circuit analysis.
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, many plants have identified issues where their DC ammeter circuits and control 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 250 VDC circuits.
II1.
ANALYSIS OF EVENT
On March 10, 2014, Calvert Cliffs determined an unanalyzed condition existed in regards to ten unfused 250 VDC 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 fire area thus affecting Calvert Cliffs' ability to conduct a safe shutdown. An Emergency Notification System report was made at 2243 on March 10, 2014 within the required eight hours 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 Nuclear Regulatory Commission 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 for this issue is conservatively assessed at approximately 5E-06 for Unit 1 and 8E-07 for Unit 2. These values would be non-red using the Significant Determination
Process. The values provided are 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 Fire Protection Program's existing daily and weekly transient combustible loading walk downs, and continued limitations on hot work permits in Unit 1 CSR and the Control Room were commensurate to the core damage risk.
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.
After this unanalyzed condition was identified, hourly fire tours in both Units 1 and 2 CSR and behind the operating panels in the Control Room in addition to limitations on hot work permits in all of these rooms were initiated. After a Probabilistic Risk Assessment analysis quantified the risk associated with this unanalyzed condition, a decision was made that the risk would be adequately managed through the Fire Protection Program's existing daily and weekly transient combustible loading walk downs, and continued restrictions on hot work permits in Unit 1 CSR and the Control Room.
B.
ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:
- 1.
Calvert Cliffs is evaluating the fix for the ten susceptible methods to eliminate 250 VDC circuits to eliminate this unanalyzed condition. A supplemental report will be submitted once the method to eliminate this unanalyzed condition is determined.
V. ADDITIONAL INFORMATION
A.
FAILED COMPONENTS:
There were no failed components in this event.
B.
PREVIOUS LERS ON SIMILAR EVENTS:
A similar licensee event report (LER 317/2013-002) at Calvert Cliffs was submitted on December 17, 2013, identifying that an unanalyzed 10 CFR Part 50 Appendix R condition existed due to unfused 125 VDC ammeter circuits associated with the 125 VDC batteries and their respective battery chargers. While the extent of condition actions taken in regards to the LER included assessing the non-safety-related DC ammeter and control circuits, Calvert Cliffs failed to recognize that the ten 250 VDC circuits ran beyond the Turbine Building. However, Calvert Cliffs continued to monitor new industry operating experience associated with this issue.
Subsequent industry operating experience on non-safety-related DC circuits led Calvert Cliffs to
take a second look at the non-safety-related DC circuits which led to the identification of these ten 250 VDC circuits as causing a 10 CFR Part 50 Appendix R unanalyzed condition to exist.
C.
THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION IDENTIFIER AND SYSTEM NAME OF EACH COMPONENT OR SYSTEM REFERRED TO IN THIS LER:
COMPONENT DC Ammeter & Control Circuits IEEE 803 FUNCTION ID WEL IEEE 805 SYSTEM ID El D.
SPECIAL COMMENTS:
None.