ML20096G020
| ML20096G020 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 05/18/1992 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 92-287, NUDOCS 9205220123 | |
| Download: ML20096G020 (11) | |
Text
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VinoixA F.u:nute Axn l'own:n Co>iem ltscunosu.vsuunner ununs May 18,1992 U. S. Nucitar Regulatory Commission Serial No.
92 287 Attn.: Document Control Desk NL&P/TAH: R4 Washington, D.C. 20555 Docket Nos.: 50 338 50 339 License Nos.: NPF 4 NPF-7 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 SERVICE WATER SYSTEM RESTORATION ACTIVITIES Virginia Electric and Power Company is planning extensive refurbishment activities for restoration of certain portions of the existing buried and concrete encased Service Water headers at North Anna Power Station. The three principle activities involved are: 1) enhancing the current chemical treatment to control sulfate reducing bacteria in the system,2) cleaning, repairing, and coating of large bore concrete encased piping, and 3) replacing certain portions of the buried piping. These activitios continue the repair and replacement project already initiated on the smaller boro Service Water distribution piping and the Service Water reservoir spray arrays. Additional details of this portion of the Service Water project are provided in the attachment.
Implementation of this portion of the Service Water repair and replacement project will require removing the surrounding earth and/or concrete encasement of certain portions of the normally buried and protected Service Water headers, electrical system ductbanks, and the emergency diese! generators fuel oil supply piping to gain access to the Service Water headers. As a result, the normal d6 sign basis protection against natural phenomena afforded by the earth and/or concrete encasement will be temporarily removed which will require specific exemption from the applicable re0ulations. It is our Intent to request specific exemption in accordance with the criteria specified in 10 CFR 50.12. The exemption is intended to support work planned for the Unit 1 steam generator replacement outage currently scheduled to begin in January 1993, the Unit 2 refueling outage currently scheduled to begin in September 1993, and the time Interval between the outages.
Specific exemption will be requested from 10 CFR Part 50, Appendix A, Criteria 2 (GDC-2) " Design basis for protection against natural phenomena." Exemption from this requirement will be necessary during the excavation of the main and auxiliary Service Water supply and return headers, and during the excavation of the Service Water supply and return lines for the Unit 1 and Unit 2 Containment Recirculation Spray heat exchangers. We anticipate that the GDC-2 exemption will be needed on three separate occasions as this work will he performed in three distinct stages.
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Dochet Nos.: 50 338&S0 339 Sorial No.
92 207 Page 2 of 3 The first occasion requiring exemption will extend from thirty days prior to the initiation of tne Unit 1 steam generator replacement outage through thirty days after the outa0e and will support the work on the Service Water supply and return linos for the Unit 1 Recirculation Spray heat exchangers. The second occas!on will be for approximately 120 days between the Unit 1 steam generator replacement outage and the 1993 Unit 2 refueling outage. The exemption will support the installation of new access ports on the thirty six inch main Service Water headers. Finally, the third occasion will be from thirty days prior to the initiation of the 1993 Unit 2 refueling outage through thirty days alter the outage. The exemption will support the work on the Service Water supply and return lines for the Unit 2 Recirculation Spray heat exchangers.
As described in 10 CFR 50.12(a)(2), special circumstances must be present for the NRC to consider granting an exemption.
Two of the examples of special circumstances stated in the regulation apply in this case.
The first special circumstance is that the exemption provides only temporary relief from the applicable regulation and that the licensee has made good faith efforts to comply with the regulation. The second special circumstance is that compliance would result in undue hardship c' other costs that are significantly in excess of thoto contemplated when the regulatb as adopted.
The first special circumstance is met in that each occasion for exemption from GDC 2 will be only temporary J.nd have specific duration dates. Concerning the second special circumstance, we have marf9 a good faith effort in considering alternatives to an exemption request and have concluded that the project could only be conducted without an exemption if both units are shutdown and defueled. As there are no dual unit outages planned or scheduled, we believe that this alternative represents an undue hardship, and this falls within the scopo of the second special circumstance.
apact of scheduling such a dual unit os.tage and simultaneously defueling both u,
would have potentially significant consequences in terms of power supply, fuel sto me capacity and replacement power costs. We believe that it was never the intent of tl. 'ulation to require such actions to ecsure compliance with the regulation.
Also, the ochedule that we are proposing for this portion of the Service Water project will accelerate the timetable for restoring the portions of the Service Water system that have become degraded. We conclude thet the undue hardship and other cost criterion described in the second special circumstance is met.
Because of time and schedular restraints, we will submit separate, specific detailed exemption requests for each stage of the construction effort. The first detailed exemption request will address the scope of work to be performed in conjunction with the North Anna Unit 1 steam generator replacement outage. The Service Water activities will require exemption for a period beginning thirty days prior to the outage and ending thirty days after the outage, it is our intent to submit this detalled exemption request by July 15, 1992. To support the current project and outage I
schedules, we will request your approval of the exemption by November 13,1992.
This initial exemption request will also provide achedule for the submittal, and requested approval dates, for the remaining exempoon requests.
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Docket Nos.: 50 338&50 339 SedalN1 92 287 Page 3 of 3 PrF to submitting each exemption request, we will complete a safety analysis to i
er. ore thet the effects resulting from the implementation of each of the temporary namptions will be acceptable.
As part of this effort, we will develop specific
,/
antingency measures and compensatory actions to provide added assurance of the 4
safe operation of the facility during each exemption period. We wi!! submit detailed descriptions of these measures and ac1ons as part of the exemption requests.
addition, in order to implement the Service Water system restoration project, we also n
. rd to rely on Technical Specification 3/4.7.4.1 which pumits us to remove one Water header for up to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> in support of tervice Water upgrade 2
,, s. Our current schedule will require four entries into the 168 hour0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> Action f1 S:o a ent during the first and third ctages of tha project with two entrias taking place at m.,
eginnhg of each stage and two at the end. Two entries will be required for the and stage. Also, once the first stage has be6n entered, conditions may require an Mnal two entries during the Unit 1 steam gcnerator replacement outage.
iore, over a period of apcroximate!y one year, we anticipate er.tering the ActMa Sta..nent a maximum of twelve times.
?P Because multiple entries into the Actirn Statement will be required, we will develop appropriate composatory and contingency measures to ensure availability of required safety functions. These compensatory and contin.gency measures will be i
available for NRC review. As part of our safety evaluation ?upporting the restoration project. we will review and confirm that the analyses and assumptions supporting Technical Specification 3/4.7.4.1 remain valid.
If you have enc que.eCons or require additionalinformation, please contact us.
\\ m truly youc s
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ik Mhs W. L. Stewart Senior Vice President - Nuclear Attachment 1
pc: U.S. Nuclea: Reguiatory Commission Region 11 101 Marietta Street, N.W.
Suite 2900 Atlanta, Gnrgia 90323 Mr. M. S. Lesser NRC Senior Resident inspector North Anna Pwer Station
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Docket Nos.: 50 338850-339 4
Serial No, 92 287
. Anachmed Page 1 of 5 SERVA ? WATER SYSTEM RESTORATION PROJECT - PHASE I HQBTH ANNA POWER STATION
1.0 BACKGROUND
Virginia-Electric and Power Company has recently completed an extensive
. evaluation of the mat;fial condition of the North Anna Power Station Units 1 and
- 2 Service Water System and has developed a comprehensive action plan to: 1) address and attempt to eliminate the root cause of the existing corrosion damage,.2) prolong the remaining life of currently acceptable portions of the n
-system and 5) provide repair and/or replacement designs for degraded sections.
The existence of pitting corrosion in the system has been known for some tirce.
Only recently, hows m have we been able to more accurately charactenze microbiolo0 cally:in.w;ed corrosion (MIC) pitting depths and densities in i
representative areas oi ine system. By using dynamic ultrasonic (UT) scanning techniques and physical hands-on measurements where possible, Engineering personnel have baen able to calculate general and pitting corrosion rates.
Current rates cf corrosion on uncoated carbon steel materials are estimateu at 0-6 mils per year (mpy) (0.001 - 0.006 ;nches per year) for general corrosion wall loss _and,120 mpy-(0.001 - 0.020 inches per year) for pitting corrosion wall loss.
_These values represent average. wall loss over the life of the system. Current rates in specific areas can be higher depending on location,. flow ccr.ditions and the random nature of pitting. attack. The 24 inch lines have been the most
- susceptible to general and pitting corrosion largely due to the stagnant and low flow conditions present. Of particular concern are the inaccessible 24 inch lines, i.e., those that are direct buried or encased in concrete.
Virginia Electric and Power Company is planning an extensive refurbishment program for the_ existing uncoatedi buried and concrete encased 24 inch Service Water pipe sections. This program will consist-of a combination of in-place Ecleaning / assessing / repairing and/or internal coating of certain pcrtions and replacement of other portions as described in the following paragraphs.-
2.0 SERVICE WATER SYSTEM DESCRIPTION i
3 The Service Water System uses a spray pond (Service Water reservoir) as its normal source of water and its heat sink. Makeup Ter evaporation, wind c: rift, and blowdown is provided from Lake Area. In the event of a failure in the function of the reservoir, Lake _ Anna provides a bac'Kup source of cooling water. Together,
- the reservoir and Lake Anna form the station's ultimate heat sink. There are four Service Wawr pumps located in the Service Water Pump House which utilize the the reservoir as their heat sink. The Service Water pumps and reservoir provide L
the required cooling in the event of a LOCA in one unit and a safe shutdown and cooldown of the unaffected ;mit assuming the most limiting single failure.
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6 Docket Nos.: 50 333&50-333 Serial No.92-287 Attachment Page 2 of 5 The Service Water System is a shared system common to both Unus 1 and 2.
Service Wa..
is pumped from the reservoir to various ety related systems and components via.edundant supply headers and back to the reservoir via redundant return headers and spray systems. The reservoir water is chemically treated with corroslon inhibitors and b!ocides whicii are injectec ci the supply headers near the Service Water Pump House. Makeup water added to the reservoir (from Lake Anna as described above) is not treated prior to mixing with treated reservoir water.
The Service Water System pavides a supply M cooling water to various safety related and non safety related components. Th vstem operates during normal plant operation, shutdown operation, and during and after accident situations.
Service Water also serves as a backup supply source for the Auxiliary Feedwater System and backup cooling for certain components normally cooled by the closed Component Cooling water system.
q There are two Service Water loops (one supply and one return header each) that provide Service Water to both units. Two loops are used to increase the reliability of the system as each loop has 100 percent capacity.
The two supply headers consist of 36 inch diameter lines which run from the Service Water Pump House to the main power block of the station. Various size branch lines off of these headers feed the components. The 36 inch headers are internally coated r d are externaHy coated and/or wrapped where direct buried.
Lines 24 nich ano smaller are not internally coated but were externally protected when buried.
The two return headers collect the Service Water from the plant components and systems and return it to the reservoir via the Service Water Valve House. As with the supply headers, these lines are 36 inch diameter, internally coated and externa lly coated and/or wrapped. The lines reduce to 32.25 inches diameter r
from the Sw!ce Water Tie-in Vault to the Service Water Valve House and are externally coated but are mt internally coated. Service Water can also be returned to the Unit 2 discharge tunnel when Service Water is being supplied from Lake Anna by the Auxiliary Service water Pumps.
3.0 RECENT IMPROVEMENTS AND MODIFICATIONS Numerous upgrades have been implemented over tha last decade it - 1sponse to the initial discovery of system corrosion problems These have included the replacement of smaller distribution lines, redesign and replacement of the spray arrays and headers in the reservoir, mechanical and chemical cleaning of T
Service Water piping, and improvements in chemical addition and control in the Service Water system.
Docket Nos.: 50 338650 339 Serial No.
92 287 Attachment Page 3 of 5 These efforts have contributed to significant improvements in the condition of Service Water system components and in the quality of water chemistry However, in spite of these efforts, additional work is required to address the effects of corrosion on the larger uncoated header piping which is buried in soil and encased in concrete. Plans for refurbishment of these lines are outlined in Section 4.0, 4.0 PLANNED IMPROVEMENTS AND U.ODIFICATIONS Plans for the current system ugrade have beba divided into two categories, designated as Phase I and Phase ll. The specific gograde activities were ranked based on such factors as safety significanco, p9rceived benefits, current condition of components, cost and schedule. Those activities viewed as a high priority are grouped into Phase I, with lower priority items being Phase ll. Phase I activities are the focus of this submittal. Phase 11, which includes potential reservoir relining, internal recoating o1 the 36 inch headers (which are currently coated), and repair and/or replacement of other accessible piping, will be evaluated and pursued in the future as necessary.
Phase i includes an enhancement to the current Service Water chemical treatment program. - Addition of an improved microblocide is being implemented to specifically control sulfate-reducing bacteria (SRB), considered to be the significant contributor to pitting of the carbon steel Service Water piping. The objective is to appreciably reduce the pitting corrosion rate caused by these SRBs and thereby prolong the remaining life of the system piping.
The priraipal Phase I effort consists of an extensive cleaning, assessing, repairing, internal coating,and replacement program for over 2100 linear feet of buried or concrete encased 24 inch diameter lines. Approximately 1500 feet will be repaired and coated, and 600 feet will be replaced. The pipM orimarily consists of the stagnant supply and return headers to the Unit
'J Unit 2 Recirculation Spray Heat Exchangers, the auxiliary supply and retun headers from Lake Anna, and the normally flowing supply and return headers to the Unit 1 and Unit 2 Component Cooling heat exchangers.
The major difficulty to be encountered in addressing these pipe sections is a lack of access. The only built-in access ports into the 24 inch piping are located in the basement of the Auxiliary Building. The rest of the piping has no provision for access except via removal of certain expansion joints or valves. Personnel safety iscues and confined area entry requirements make entries into the pipe for visualinspections or in-situ repairs difficult and time consuming activities.
The overall objective of this effort is to clean and restore internal pipe curfaces as required to assure continued structuralintegrity and apply a protective coating to i
minimize or eliminate further corrosion, in general, the refurbishment process which is discussed below will only be used on concrete encased pipe sections.
Pipe sections which are F act buried (24 inch diameter) will be replaced with l
new piping similarly coa d internally and protected externally from corrosion.
i New accesses will also be added in strategic locations to facilitate pipe repair and coating as well as future inspections and maintenance.
Docket Nos.: 50-338&50 339 Serial No.92-287 l
Attachment Pago 4 of 5 The following sequence outlines the individual work activities required to perform interior restoration and coating work on these pipe sections. The activities required for the interior restoration and coating work will be verified by a full-scale fabricated mock-up that will demonstrate under simulated conditions that the procedures, techniques, equipment and personnel can accomplish the objectives of the project. The mock-up will also be used to qualify application personnel and stress personnel safety requirements. The sequence of activities presented below details tne four major processes involving initial cleaning and surface preparation, corrosion assessment, repairing, and coating application and inspection.
- 1. Initial cleaning and surface preparation will involve a combination of hydrotazing (high pressure water blasting) and abrasive blasting.
The hydrolazing will remove the gross deposits of dirt, mud, silt, debris and corrosion products.
After removing any remaining water and drying, a production abrasive blast cleaning will be oerformed to facilitate assessing the pipe interior for general conAion and corrosion damage.
- 2. A manual and/or remote condition assessment technique will be used to accurately assess the actual pipe condition following cleanup. The technique will be based on the following considerations: personnel safety, technique accuracy and repeatability, relative ease of implementation, and overall cost effectiveness. A comprehensive internal examination will be carried out to assess overall pipe conditions and identify the need for repairs based on required minimum wall thickness criteria.
- 3. Areas identified by the corrosion assessment as requiring base metal repair will be filled by welding.
- 4. Following required weld repairs and final surface preparation, a coating
[
system will be applied. Application of an epoxy patch compound will be applied to pits and other surface irregularities requiring filling to assist in the subsequent application of epoxy coating. Two coats of epoxy coating will be applied over the prepared substrate. Final coating operations will include final dry film thickness readings to verify achievemat of minimum thicknesses and final cure of the coating system.
in parallel with the pipe refurbishment program, an evaluation of the Service Water pumps will be performed. This effort will focus on the condition vf critical pump components and determining the need for rebu;lding or replacing them.
Modifications or upgrades will then be implemented as appropriate.
4 It is possible that certain areas may lend themselves to a different type of repair than simple weld metal buildup. Should this arise, an alternative " engineered" repair may be preferred from a design and/or construction perspective. We would propose to submit these permanent repair altern::.ms for relief from code requirements under 10 CFR SC.55a only in cases where the benefits are obvious.
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Docket Nos.: 50-338&50-339 Serial No.
92 287 Attachment Page 5 of 5
' 5.0 IMPLEMENTATION SCHEDULE - PHASE I Repair and/or replacement of the uncoated buried or concrete encased 24 inch lines will be implemented in stages over the next four years during planned Unit 1 and Unit 2 outages. The work will begin during the 1993 Unit 1 Steam Generator Replacement outage with repair of the concreto encased portions and replacement of the direct buried portions of the four lines to and from the Unit 1 Recirculation Spray heat exchangers. Subsequent outages will address the four lines to the Unit 2 Recircu!ation Spray heat exchangers (1993 and 1995), two auxiliary Service Water supply lines (1994) and the four lines to the Unit 1 and Unit 2 Component Cooling heat exchangers (1994 and 1995).
Enhanced chemical treatment is nearing implementation. Service Water pumo work will be initiated following the Unit 1 steam generator replacement outage (1993).
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