05000255/LER-2011-005, Regarding Service Water Pump Shaft Coupling Failure
| ML112760550 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 10/03/2011 |
| From: | Vitale A Entergy Nuclear Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| PNP 2011-066 LER 11-005-00 | |
| Download: ML112760550 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 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 |
| 2552011005R00 - NRC Website | |
text
Entergy Nuclear Operations, Inc.
Palisades Nuclear Plant
~Enterg,i 27780 Blue Star Memorial Highway Tel 269 764 2000 Anthony J Vitale Site Vice President PNP 2011-066 October 03, 2011 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
SUBJECT:
Licensee Event Report 2011-005, Service Water Pump Shaft Coupling Failure Palisades Nuclear Plant Docket 50-255 License No. DPR-20
REFERENCES:
10 CFR 50.73, 10 CFR 21.21
Dear Sir or Madam:
Licensee Event Report (LER) 2011-005 is enclosed. This LER is being submitted in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by the plants Technical Specifications and 10 CFR 21.21(c) for reporting defects, and failures to comply, associated with substantial safety hazards for dedicated items.
This letter contains no new commitments and no revisions to existing commitments.
Sincerely, AJV/tad Enclosure: Licensee Event Report 2011-005 CC Administrator, Region Ill, USNRC Project Manager, Palisades, USNRC Resident Inspector, Palisades, USNRC
NRC FORM 366 APPROVED BY 0MB NO. 3150-0104 EXPIRES 1013112013 U.S. NUCLEAR REGULATORY COMMISSION (10-2010)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
(See reverse for required number of digits/characters_for_each_block)
- 3. PAGE PALISADES NUCLEAR PLANT 05000255 1
of 4
- 4. TITLE:
Service Water Pump Shaft Coupling Failure
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL REV FACILITY NAME MONTH DAY YEAR YEAR NUMBER NO MONTH DAY YEAR FACILITY NAME 08 09 2011 2011 005 00 10 03 2011
- 9. OPERATING MODE II. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
El 20.2201(b)
U 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii)
~
El 20.2201(d)
U 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
U 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
[]
20.2203(a)(2)(i)
U 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
U 50.73(a)(2)(iv)(A)
U 50.73(a)(2)(x)
U 20.2203(a)(2)(iii)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 73.71(a)(4)
,~
U 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5)
IUV U
20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
~
OTHER Specify in Abstract below or in El 20.2203(a)(2)(vi)
~__50.73(a)(2)(i)(B)
El__50.73(a)(2)(v)(D)
NRC_Form_366A
- 12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (Include Area Code Terry Davis (269) 764-2117 I
. COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT AUSE SYS EM COMPONENT FACTURER REPORTABLE
CAUSE
SYSTEM COMPONENT FACTURER PORTABLE B
BI CPLG H331 Y
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPE~..TED MONTH DAY YEAR SUBMISSION El YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
~
NO DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines On August 9, 2011, at 1202 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.57361e-4 months <br />, service water system (SWS) pump, P-7C, failed to deliver discharge pressure. As a result, a 72-hour limiting condition for operation (LCO) was entered in accordance with Technical Specification (TS) 3.7.8 condition A, due to one or more SWS trains being inoperable. The TS 72-hour LCO was exited after approximately 63 hours7.291667e-4 days <br />0.0175 hours <br />1.041667e-4 weeks <br />2.39715e-5 months <br /> on August 12, 2011, at 0309 hours0.00358 days <br />0.0858 hours <br />5.109127e-4 weeks <br />1.175745e-4 months <br /> when repairs and testing on P-7C had been completed.
Investigation into the failure revealed a broken pump shaft coupling. The failure mechanism of the coupling was determined to be intergranular stress corrosion cracking (IGSCC). A past operability evaluation concluded that, based on the failure mechanism of the coupling, P-7C would have been unable to operate satisfactorily for the required 30-day mission time. Therefore, P-7C was inoperable from July 10, 2011, until the coupling failed on August 9, 2011. During the period P-7C was considered inoperable, SWS pumps P-7B and P-7A were removed from service, on separate occasions for brief periods of times, for the performance of routine maintenance activities. The requirement of TS 3.7.8 condition C, that 100% of the required post accident SWS cooling capability be available, was met at all times during the 30-day period when P-7C was considered inoperable.
The cause of the IGSCC was due to inadequate coupling design specifications. P-7A and P-7B shaft couplings were replaced using newly designed couplings. Replacement of the shaft couplings on P-7C, with the new design, is scheduled. This event is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS and 10 CFR 21.21(c) for reporting defects, and failures to comply, associated with substantial safety hazards for dedicated items.U.S. NUCLEAR REGULATORY COMMISSION (10-2010)
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE SEQUENTIAL REVISION YEAR NUMBER NUMBER PALISADES NUCLEAR PLANT 05000255 2011 005 00 2
OF 4
PLANT CONDITIONS
On August 9, 2011, at the time service water system (SWS) [BI] pump [P], P-7C, failed, the plant was in Mode 1, operating at approximately 100% power.
INTRODUCTION
The SWS provides a heat sink for the removal of process and operating heat from safety-related components during a design basis accident or transient. During normal operation or a normal shutdown, the SWS also provides this function for various safety-related and non-safety-related components. During post-accident conditions, with all other SWS and related system components operable, 100% of the required SWS post-accident cooling capability can be provided by any one SWS pump.
The SWS consists of three pumps, P-7AIBIC connected in parallel, taking suction from a common intake structure supplied by Lake Michigan. The discharge of the pumps flow into a common header before splitting into three headers (two critical headers for safety-related equipment and a single non-critical header for non safety-related equipment). The return piping from the three headers join into a common line and discharge to the cooling tower makeup basin.
The three SWS pumps are comprised of a two stage pump end with stainless steel (SS) impellers. The pump end is coupled to the motor through six line shafts, a packing shaft, and a motor shaft connected by eight couplings all of the same design.
The design specification of the line shaft couplings for the three SWS pumps was changed in December 2007. The design specification included information from previous engineering evaluations that changed coupling material from carbon steel to 416SS. The line shaft couplings for P-7A were replaced in April 2009. The line shaft couplings on P-7B were replaced in May 2010. The line shaft couplings for P-7C were replaced in June 2009.
On September 29, 2009, P-7C failed to deliver discharge pressure. The investigation into the failure revealed a broken coupling between the top line shaft and the packing shaft. An analysis determined that the coupling failed from intergranular stress corrosion cracking (IGSCC). There are three parameters that must be present for couplings to fail by the mechanism of IGSCC; susceptibility of material for IGSCC, a corrosive environment, and a stress intensity that exceeds the threshold for IGSCC on the pump shaft coupling. Inherent to the Palisades design is the corrosive environment (lake water) and the stress applied during pump operation. The failed coupling was determined to have been improperly heat treated, based on the high hardness value of the 41 6SS coupling, rendering it susceptible to IGSCC. Improper heat treatment was a result of issues within the quality control program of the vendor, HydroAire Services Inc.
EVENT DESCRIPTION
On August 9,2011, at 1202 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.57361e-4 months <br />, P-7C, failed to deliver discharge pressure. A 72-hour limiting condition for operation (LCO) was entered in accordance with Technical Specification (TS) 3.7.8 condition A, due to one or more SWS trains being inoperable. Work to restore P-7C began immediately. During disassembly, it was determined that the line shaft coupling [CPLG] failed similarly to the failed coupling in the same pump in September, 2009.U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
CONTINUATION_SHEET
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE SEQUENTIAL REVISION YEAR NUMBER NUMBER PALISADES NUCLEAR PLANT 05000255 2011 005 00 3
OF 4
Replacement couplings from inventory stock were installed. The TS 72-hour LCC was exited after approximately 63 hours7.291667e-4 days <br />0.0175 hours <br />1.041667e-4 weeks <br />2.39715e-5 months <br /> on August 12, 2011, at 0309 hours0.00358 days <br />0.0858 hours <br />5.109127e-4 weeks <br />1.175745e-4 months <br /> when repairs and testing on P-7C had been completed. The requirement of TS 3.7.8 condition C, that 100% of the required post accident SWS cooling capability be available, was met at all times during the 30-day period when P-7C was considered inoperable.
CAUSE OF THE EVENT
Investigation into the December 2007 design specification change, the September 2009 coupling failure, and industry operating experience (CE) revealed several causes for the IGSCC failure of the coupling in 2011.
The 2007 design change specification to use 416SS in the Palisades SWS operating environment was faulted. Personnel involved in the design change process did not have sufficient metallurgical knowledge. Palisades did not obtain an adequate technical review by personnel with expertise in metallurgy.
The root cause conducted after the 2009 coupling failure did not sufficiently investigate the base material properties of 41 6SS. Specifically, the toughness properties of the material in the corrosive environment of Lake Michigan water were not investigated. The coupling material is a quenched and tempered 416 martensitic SS with low toughness properties. This makes it particularly susceptible to IGSCC when subjected to the tensile stress and a corrosive environment (due to the presence of chlorides).
Ineffective use of CE. Since 2004, there have been several examples of nuclear industry CE linking IGSCC susceptibility with high Rockwell hardness values and/or low material toughness in type 416SS when exposed to fresh water. Palisades did not translate this CE into effective specification, contract, inspection, testing, or oversight actions.
CORRECTIVE ACTIONS TAKEN After the August 2011 failure, Palisades completed an engineering change (EC) to change the material of the service water pump couplings from 41 6SS to I 7-4PH SS. This EC was based on a report provided to Palisades, by an independent vendor that evaluated similar failures in the industry, and recommendations from a team of metallurgy and pump experts.
A new design specification using 1 7-4PH SS for the material of the SWS pumps shaft couplings was developed and approved for all three SWS pumps. The new design specification for the coupling material was changed in order to minimize susceptibility to IGSCC. The 4165S shaft couplings on P-7A and P-7B were replaced with the 17-4PH SS design.
Past operability evaluations performed for P-7A and P-7B, due to the shaft coupling on the pumps being constructed of the same 41 6SS material, concluded the pumps could have met the required 30-day mission time. An independent laboratory confirmed there were no indications of IGSCC on the number 5, 6, and 7 couplings, those couplings considered to be most susceptible to IGSCC, removed from P-7A. There were indications of IGSCC identified on the number 5, 6, and 7 couplings removed from P-7B. However, the evaluation concluded the cracking on the couplings had not propagated to the point where P-7B would have been unable to meet the required 30-day mission time.U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
CONTINUATION_SHEET
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE SEQUENTIAL REVISION YEAR NUMBER NUMBER PALISADES NUCLEAR PLANT 05000255 2011 005 00 4
OF 4
CORRECTIVE ACTIONS TO BE TAKEN Replacement of the 416SS shaft couplings that remain on P-7C with the 17-4PH SS design couplings.
Creation of an Engineering Standard that clearly identifies station requirements and expectations for material changes affecting installed plant equipment.
ASSESSMENT OF SAFETY CONSEQUENCES
No actual safety consequences resulted from this event. Operating service water pumps continued to meet all critical, non-critical and containment service water system cooling loads. Potential safety consequences of this event are of low safety significance: the equipment necessary to safely shutdown the reactor and maintain safe shutdown conditions under normal and emergency circumstances remained intact and available.
PREVIOUS SIMILAR EVENTS
LER 2010-001, Service Water Pump Shaft Coupling Failure.