B14043, Provides Erosion/Corrosion Program Update Info as Committed in
| ML20090B315 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 02/24/1992 |
| From: | Opeka J NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES |
| To: | Martin T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| B14043, NUDOCS 9203030308 | |
| Download: ML20090B315 (7) | |
Text
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1 NORTHEAST UTILITIES
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. -.m February 24, 1992 Docket No. 50-423 B14043 Mr. Thomas T. Martin Regional Administrator, Region i U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406
Dear Mr. Martin:
Millstone Nuclear Power Station, Unit No. 3 Erosion / Corrosion Proaram Update and Unit Restart Introduction Northeast Nuclear Energy Company (NNECO), on behalf of Millstone Unit No. 3, herebysubmitserosion/ corrosion (E/C)iprogramupdateinformationascommitted in a letter dated January 3, 1992.z This letter will also confirm that NNEC0 has fulfillek2jts commitments at Millstone Unit No. 3, as stated in the November 18, 1991, Northeast Utilities (NU) E/C program letter prior to returning the unit to service on February 6, 1992.
Additionally, NNECO is hereby providing selected E/C program information, as appropriate, to clarify and support related topical discussions between various NRC Staff and NNEC0 personnel, flackaround In a letter dated November 18,1991,(3) NNEC0 provided a brief overview of our E/C program that evolved from the Millstone Unit No. 3 moisture separator drain line pipe rupture. As a result of the November 6, 1991, Millstone Unit No. 2 moisture separator reheater (MSR) drain line rupture event, the NU E/C program, then in the process of being upgraded, was accelerated and enhanced.
We further stated that our units would not be returned to service until (1)
J.
F. Opeka letter to the U.S. Nuclear Regulatory Commission, "Haddam Neck Plant, Millstone Nuclear Power Station, Unit Nos.
1, 2,
and 3, Erosion / Corrosion Program Update, Response to NRC Region I Augmented Inspection Team Report," dated January 3, 1992.
(2)
J. F. Opeka letter to the U.S. Nuclear Regulatory Commission, "Haddam Neck Plant, Millstone Nuclear Power Station, Unit Nos.
1, 2,
and 3, Erosion / Corrosion Programs," dated November 18, 1991.
(3)
Ibid.
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Mr. Thomas T. Martin B14043/Page 2
- February 24, 1992 comprehensive component inspections had been completed, all indications of observed degradation had been evaluated and dispositioned as required, and where necessary, component / piping would be repaired or replaced.
On November 22, 1991, a contingent of NU personnel presented the restart E/C program to the NRC Region I Staff.
This comprehensive presentation included not only a discussion of the Millstone Unit No. 2 pipe rupture event, but more importantly, it focused on the enhanced E/C programmatic issues.
A significant portion of the presentation covered NU's screening approach to identify locations susceptible to E/C.
This was primarily based upon use of the CHECMATE computer program and broad industry experience.
The explicit organizational structure delineating inspection, implementation, resolution / review, and acceptance responsibilities was presented.
Programmatic documentation (program manual) and controls were also discussed.
Shortly following the presentation to Region 1 Staff, key NU corporate engineering management personnel relocated to the Millstone site to coordinate and assist in the restart E/C program.
This organization provided focused and coordinated resource allocation during all phases of program implementation.
. Current Millstone Unit No. 3 Status At Millstone Unit No. 3, all actions necessary to return the unit to service have been completed.
Comprehensive inspections of susceptible components identified utilizing CHECMATE, current industry experience, and unit specific history have been completed, or exempted where appropriate, as explained later in this section.
The corrective actions 1 Region 1 Augmented Inspection Team Report,(4)isted in Section 4.2 of the NRC regarding numbers of inspections and analyses have either-been met or exceeded.
All indications of observed degradation have been evaluated and dispositioned per program requirements.
l
. The repair and replacement of components / piping have been completed.
l The Millstone Unit No.
3-E/C restart program resulted in extensive inspections.
The total numoer of inspection -locations selected for the Millstone Unit No. 3 E/C restart program was 863.
The number of required inspection locations based on industry experience consisted of 221 large bore (2" or greater) and 149 small bore (less than 2") locations.
A total of 74 l
large bore inspection locations were established based on the CHECMATE l
analysis.
In addition, 69 large and small bore inspection locations were l
identified by_walkdowns as well as 22 additional inspection locations from the plant-specific experience data base.
Lastly, as a result of the inspection findings, a -total of 328 additional large and small bore piping inspection locations were included in the E/C restart program using the sample expansion criteria.
(4)
M. W. Hodges letter to J. F. Opeka, "NRC Region 1 Augmented Inspection Team Report (50-336/91-81)," dated December 12, 1991.
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- Mr. Thomas T. Martin B14043/Page 3 February 24, 1992 The E/C restart program inspection requirements were implemented by completing 830 new inspections during the current outage and by taking exemptions for 33 locations.
A summary of the exemptions taken is provided in Attachment 1.
Exemptions were taken based on duplicate identified points (17 locations),
credit for recent previous examinations (2
locations),
and component inaccessibility and/or inconsequential damage considerations (14 locations).
A total of 57 component repairs were accomplished, 55 of which were identified as requiring repair or replacement as part of the E/C restart inspection program. All repairs or replacements were completed prior to startup.
One finding was of particular note during the current E/C pror
.i inspections at Millstone Unit No. 3.
A component in a 16-inch, extrac.on steam line, immediately downstream of the high pressure turbine, was.aund to be worn significantly enough to require immediate replacement.
This finding occurred on December 17, 1991, approximately one day before a pipe rupture in a 14-inch, extraction steam line downstream from the high pressure turbine at a nuclear facility in Spain.
Although the particular Millstone Unit No. 3 piping component was initially identified for inspection based on " industry experience," CHECMATE also correctly " flagged" the component for inspection.
The wear rates predicted by CHECMATE and engineering predicted values for this particular component correlated favorably.
The engineering predicted wear rate in this particular area was approximately 65 mils / year, and the CHECMATE initial prediction was approximately 58 mils / year. The actual inspection data were then fed back into CHECMATE, per the E/C program technical requirements, to further improve the wear rate correlation.
We believe that the E/C restart program was comprehensive and effective based on the scope of inspections, including the sample expansions, and the repairs and/or replacements completed prior to startup.
l Additional E/C Proaram Information The NU E/C program has already demonstrated itself to be comprehensive and L
effective, as all four NU units will be subjected to thorough and systematic piping / component inspections.
A copy of the E/C Technical Requirements for Restart document, previously discussed (and requested by NRC Staff) during the November 22, 1991, Region I Staff meeting, was provided as_ Attachment I to the January 3, 1992, letter. This E/C technical requirements document, applicable for our four nuclear units, was developed in conjunction with industry standards and in collaboration with Electric Power Research Institute (EPRI) l personnel.
It has undergone not only internal review and approval, but has also been independently reviewed by EPRI.
Brie fly, the component inspection locations, in susceptible systems, are l
identified from the following four sources:
(1) CHECMATE--The computer code developed by EPRI to predict pipe wall thinning in systems without sufficient historical inspection data.
l Mr. Thomas T. Martin B14043/Page 4 February 24, 1992 (2)
Industry Experience Locations--Components which industry experience indicates are particularly susceptible to E/C (e.g.,
those downstream of flow control
- valves, orifices / flow meters, exit nozzles, and feed pumps).
(3) Plant-Specific Experience locations--Component locations within the specific plant where previous thinning has required repair or replacement.
(4)
Engineering Based /Walkdown Selections--Certain systems and pipe segments have usage and flow rates which cannot be accurately quantified because demand greatly varies or are controlled by a remote level, pressure, or temperature signal and will not be analyzed in CHECMATE.
The results of these inspections for Millstone Unit No. I and the Haddam Neck Plant will be reported to the NRC Staff in subsequent correspondence, As of this writing, we anticipate that approximately 488 and 865 inspections will be conducted at these units, respectively.
Information Sharino with Industry Our recent E/C experience and findings have been and will continue to be shared with the industry utilizing the Nuclear Network System.
On November 7, 1991, we communicated the Hillstone Unit No. 2 MSR drain line rupture to the industry on the Nuclear Network System.
On December 12, 1991, a supplemental notice was electronically transmitted as Technical Support Information Exchange, describing the NU E/C e f forts to comprehensively enhance and accelerate completion of our E/C-program.
On December 16, 1991, that message was reclassified as Operating Plant Experience.
We have since received several telephone follow up inquiries as a result of this information sharing.
On December 30,
- 1991, another Nuclear Network electronic message was transmitted in which the Millstone Unit No. 3 extraction steam line inspection finding was discussed.
We will continue to share information with the industry as appropriate.
Conclusion We completed the NU E/C program manual technical requirements for restart, at Millstone Unit No. 3, with the previously noted exceptions, prior to returning the unit to service.
NNEC0 believes the E/C Restart Program provides a high degree of assurante that each unit will operate until the next refueling outage without experiencing an E/C related piping rupture.
Our E/C program activities at the other two units are in various stages of completion. We will remain in periodic contact with the NRC Staff and provide i
e-
-Mr. Thomas T. Martin
-B14043/Page 5 february 24, 1992 additional program updates as more informction becomes available.
Please do not hesitate to contact us if you have any questions.
Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY
(8 l. L :x(,-
t J. F Ope _khi G
Executive Vice President cc:
V. L. Rooney, NRC Project Manager, Millstone Unit No. 3 W. J. Raymond, Senior Resident Inspector, Millstone Unit Nos. 1, 2, and 3 U.S.- Nuclear Regulatory Commission Attention:
Document Control Desk Washington, DC 20555
i e
Docket No. 50-423 EllEU Attachment No. 1 Millstone Nuclear Power Station, Unit No. 3 Erosion / Corrosion Program Update Millstone Unit No. 3 Erosion / Corrosion Program Exemptions February 1992
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