ML20087G342
| ML20087G342 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 03/30/1995 |
| From: | Ohanlon J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20087G346 | List: |
| References | |
| 95-147, NUDOCS 9504040158 | |
| Download: ML20087G342 (23) | |
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I VIRGINIA ELECTHIC' ann Pownu COMPANY Ricuxoxu,V noIx A 2020I March 30, 1995 U.S. Nuclear Regulatory Commission Serial No.95-147' Attention: Document Control Desk NL&P/JBL R1 Washington, D.C. 20555 Docket Nos.
50-338 50-339 Ucense Nos. NPF-4 NPF-7 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 i
PROPOSED TECHNICAL SPECIFICATIONS CHANGES Pursuant to 10 CFR 50.90, the Virginia Electric and Power Company requests amendments, in the form of temporary changes to the Technical Specifications, in
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Facility Operating License Numbers NPF-4 and NPF-7 for North Anna Power Station Units 1 and 2, respectively. The proposed temporary changes would allow one of the two service water loops to be isolated from the component cooling water heat exchangers (CCHXs) during power operation in order to refurbish the isolated service water headers. The proposed temporary changes would be valid for two periods of up to 49 days each for Implementation of the service water system upgrades associated with the repair / replacement of the 18-inch,20-inch, and 24-inch service water supply and retum piping to/from the CCHXs.
A discussion of the proposed Technical Specifications changes is provided in..
The proposed Technical Specifications changes are provided in.
It has been determined that the proposed Technical Specifications changes do not involve an unreviewed safety question as defined in 10 CFR 50.59 or a significant hazards consideration as defined in 10 CFR 50.92. The basis for our determination that the changes do not involve a significant hazards consideration is provided in Attachment 3. The proposed Technical Specifications changes have been -
reviewed and approved by the Station Nuclear Safety and Operating Committee and the Management Safety Review Committee.
NRC approval of the proposed Technical Specifications changes by September 1, 1995 is requested to support conducting refurbishment of the affected service water i
headers during the fourth quarter of 1995. Should you have any questions or require additional information, please contact us.
Very truly yours, Lw ames P. O'Hanlon Senior Vice President - Nuclear Attachments 95o4o40158 95o33o hj DR ADOCK 050o 9
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"U S. Nuclear Regulatory Commission Region ll 101 Marietta Street, N.W.
Suite 2900 Atlanta, Georgia 30323 Mr. R. D. McWhorter NRC Senior Resident inspector North Anna Power Station Commissioner Department of Radiological Health Room 104A 1500 East Main Street Richmond, Virginia 23219
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f COMMONWEALTH OF VIRGINIA )
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COUNTY OF HENRICO
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The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by J. P. O'Hanlon, who is Senior Vice President -
Nuclear, of Virginia Electric and Power Company. He is duly' authorized to execute and file the foregoing document in behalf of that Company, and the statements in the document are true to the best of his knowledge and belief.
Acknowledged before me this.86N ay of
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My Commission Expires:
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0 Notary Public (SEAL)
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ATTACHMENT 1 DISCUSSION OF CHANGES a
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VIRGINIA ELECTRIC AND POWER COMPANY 1
2 Discussion of Changes introduction Pursuant to 10 CFR 50.90, Virginia Electric and Power Company requests temporary changes to Technical Specifications 3.7.3.1, " Component Cooling Water Subsystem -
Operating," and 3.7.4.1, " Service Water System - Operating," for North Anna Power Station Units 1 and 2. The proposed Technical Specifications changes will allow one of the two service water loops to be isolated from the component cooiing water heat exchangers during power operation in order to refurbish the isolated service water headers.
This refurbishment activity is part of Virginia Electric and Power Company's extensive service water system restoration project at North Anna Power Station. This project has been the subject of numerous correspondence to the NRC regarding requests for temporary relief from certain regulations to facilitate the pipe refurbishment process. A summary of this related correspondence is included under the heading " Reference Documentation" later in this discussion.
Service water pipe refurbishment work to date has been implemented by using the current Action Statement "d" of Technical Specification 3.7.4.1 which allows one of the two redundant service water loops to be removed from service for up to 168 hours0.00194 days <br />0.0467 hours <br />2.777778e-4 weeks <br />6.3924e-5 months <br /> (7 days) for " service water system upgrades." This action statement has primarily been used to install temporary code-qualified pipe plugs or blanks to isolate the portion of the system to be refurbished from the operable portion of the system for extended durations. Upon completion of the work, the action statement would then be re-entered to remove the plug or blank, thuc returning the system to its normal configuration.
The section of service water piping being addressed by this proposed Technical Specifications change request presents a special challenge. The design of this portion of the service water system does not permit isolation within the currently allowed outage time specified for service water system upgrades. Therefore, Virginia Electric and Power Company is requesting temporary changes to the applicable Technical Specifications, i.e., one-time for each service water loop. The purpose of this proposed change request is to allow temporary changes to the existing service water (SW) and component cooling water (CC) Technical Specifications to permit safe and efficient conduct of the pipe refurbishment project during two-unit power operation. This proposed change request is supported by both deterministic and probabilistic evaluations.
The work activities to be performed and the various system alignments required during the refurbishment project were evaluated using the Individual Plant Examination (IPE)
Page 1 of 19 l
t Probabilistic Safety Assessment (PSA) model for North Anna Power Station. The total effect of this pipe refurbishment project was estimated by a sensitivity analysis resulting in only a slight non-risk significant increase in CDF. Compensatory actions, contingency measures, and increased minimum system availability requirements will be put in place to reduce risk of damage to the operating SW header and to provide backup means of cooling equipment.
Since this project does not affect the containment or any other accident mitigation systems, there is no significant change in dose consequences. As a result of these evaluations, it has been determined that the system refurbishment activities, described herein, will not result in an increase in probability or consequences of any accident previously evaluated.
The proposed changes to the Technical Specifications requirements provide operational flexibility needed to perform necessary repairs. Implementation of these repairs will not introduce any new accident initiators nor affect the performance of accident mitigation systems. Hence, the activities associated with the proposed changes do not create the possibility for an accident or malfunction of a different type than any previously evaluated.
The Technical Specifications continue to require the SW and CC systems to remain functional during the period with a single SW supply to the component coc!!ng water heat exchangers (CCHXs). The effect of this pipe refurbishment project on CC system reliability was estimated by a sensitivity analysis to be less than a 1E-6 per year increase in core damage frequency. This has been determined not to be a significant roduction in margin of safety.
ased on the evaluations summarized above, it has been determined that operation of the North Anna Units 1 and 2 as allowed by the requested temporary Technical Specifications changes would not involve an unreviewed safety question.
Background
The SW system restoration project, which began in 1992, has three objectives: 1) to minimize corrosion,2) to prolong the remaining service life of currently acceptable portions of the piping system, and 3) to provide for the repair and/or replacement of degraded piping sections. The project plan consists of two phases, i.e., Phase I and Phase ll. The principal Phase I project activities include an extensive cleaning, assessing, repairing, internal coating, and replacement program for over 2100 linear feet of 24-inch diameter buried or concrete encased piping. Phase il includes other long-term system upgrades including repair and/or replacement of accessible piping.
l To date, our efforts have concentrated on Phase I of the project. The stagnant and j
low-flow conditions in these sections of 24-inch diameter pipe create an ideal environment for corrosion. Therefore, refurbishment of these sections has been the Page 2 of 19 l
highest priority. Phase I work is still in progress and will continue for the next several j
years.
In parallel with the Phase I refurbishment, other portions of the SW system continue to be monitored to confirm our priorities and maintain an aggressive and proactive approach to total system refurbishment. Results from this continued monitoring have shown that portions of the Phase 11 piping are approaching critical wall thickness and j
should be addressed at this time. This involves the refurbishment of the exposed 18-inch,20-inch, and 24-inch diameter SW piping to/from the Units 1 and 2 CCHXs.
This piping is located in the lowest level of the Auxiliary Building and is accessible for refurbishment. However, the design of this portion of the SW system does not permit isolation and refurbishment within the currently allowed outage times specified in the Technical Specifications for the CC and SW systems.
Project Discussion The service water piping configuration at the CCHXs is a complex interconnection of piping, valves, and supports. Figure 1 shows a schematic view of the SW piping serving the four CCHXs (two per unit). From the figure, it can be seen that each of the four CCHXs can be aligned to either of the "A" or "B" main SW loops. This provides an adequate level of operational flexibility during normal operating and outage conditions. However, the existinD Technical Specifications do not permit isolation of this portion of the SW system for more than a 168-hour (7-day) period and this is insufficient time to perform the necessary repairs / replacements.
Several alternative approaches of plant conditions and system configurations were evaluated as a means to avoid an extended period of operation with only one SW header providing cooling to the CCHXs. One alternative evaluated was to perform the pipe refurbishment activities during a two-unit shutdown. However, there are no two-unit outages planned for North Anna and to schedule such an outage would present substantial undue hardship on the Company in terms of power supply and replacement power costs. Installation of a temporary pipe jumper (i.e., a temporary parallel supply and return header to/from the CCHXs) was also evaluated as an alternative approach. However, this alternative requires an even more complex piping configuration than that which is currently installed. In addition, the need to design, procure, and install such a jumper to the appropriate safety-related criteria would be cost prohibitive. Therefore, requesting the temporary changes to the Technical Specifications to allow this portion of the SW system to be isolated for two extended periods of time (one time for each header) was determined to be the appropriate approach.
Even with the proposed extended periods of time for the service water system upgrades, because of the complexity of this systems interconnection, it is necessary to Page 3 of 19
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perform a precise series of system alignments to isolate and blank-off the necessary portions of the service water piping at the CCHXs. The sequence outlined below identifies the major steps necessary to isolate, refurbish, and return to service piping associated with the main "A" SW header:
i First, it is necessary to isolate and blank the 24 inch header to/from the CCHXs.
This is' accomplished by isolating the entire "A" header using Action Statement "d" (the 168-hour Action Statement) of Technical Specification 3.7.4.1 and j
performing the following in sequence (refer to Figure _1):
1)
Re-align SW system to supply all applicable loads from the "B" main header and enter the 168-hour Action Statement on the "A" main header.
2)
Drain the "A". main supply and return piping.
.j 3)
Remove valves 1-SW-MOV-108A and 1-SW-247.
4)
Install blank flanges in place of above valves.
5)
Refill the "A" main supply and return piping and return the header to service.
6)
Clear the 168-hour Action Statement.-
1 It'should be noted that, during the course of refurbishment, piping which must remain operable will retain its seismic _ qualification along with other governing -
l design basis requirements.
f At this point, both "A" and "B" main SW loops are operating normally except that only the "B" header is available to supply the CCHXs. To prevent unnecessarily -
Isolating the CCHXs, the autoclosure feature of the SW MOVs on the "B" header will be defeated.
Then, with the "A" header isolated to the CCHXs, the following manipulations at.
the individual CCHXs can be performed. This sequence will be repeated for each of the four CCHXs (1-CC-E-1 A,1-CC-E-18,2-CC-E-1 A, and 2-CC-E-1B):
1)
Isolate and drain the CCHX (SW side).
2)
Remove its corresponding isolation valves on the "A" SW header.
3)
Replace the removed valves with code qualified blanks.
4)
Return the CCHX to service.
i By performing this manipulation on each of the four CCHXs, the supply and return i
loop to/from the CCHXs can be isolated for pipe refurbishment activities. The actual pipe cleaning / assessment / repair / coating and replacement would then take place for the section of the "A" header piping'.which is out of service. At the
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conclusion of pipe refurbishment, the "A" main header blanks would be removed by entering the Technical Specifications action statement and the main supply and return valves would be re-installed. Each CCHX would be sequentially Page 5 of 19
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isolated to remove the blanks, re-install the valves, and return the CCHX to service. At this point, the header would be returned to its normal configuration, it is evident that during this entire evolution the CCHXs on both units are being served by only one of the two main SW headers, i.e., the "B" header for the above case. This sequence of system re-alignments and piping refurbishment has been conservatively estimated to require approximately 49 days to accomplish. A second 49-day period would be required to accompiish the same refurbishment activities on the "B" header.
Each 49-day period is based on the following work activity schedule (contingency is included in these durations to accommodate unexpected conditions):
- 1) Approximately 7 days to isolate one main SW loop, remove the supply and return valves to/from the CCHX header, and install the 24-inch blind flanges.
Simultaneously install the cross-connect piping which will provide a bypass flow path for this partially isolated main SW loop. (These activities must be performed within the 168-hour action statement allowed by Technical Specification 3.7.4.1.)
- 2) Approximately 8 days (2 days each) to sequentially isolate the four CCHXs for removal of valves and installation of blind flanges.
- 3) Approximately 21 days for piping refurbishment.
- 4) Approximately 7 days to isolate one main SW loop, remove the 24-inch blind flanges, and reinstall the valves. (These activities must be performed within the 168-hour action statement allowed by Technical Specification 3.7.4.1.)
- 5) Approximatel-6 days (2 days each) to sequentially isolate three of the four
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CCHXs for removal of blind flanges and reinstallation of valves. (Note that one CCHX remains out of service to refurbish its 18-inch and 20-inch piping. The fourth CCHX can be returned to service outside of the 49-day period.)
After completion of the pipe refurbishment activities described above (performed during the two 49-day periods), a small portion of the piping adjacent to each CCHX will require refurbishment. This consists of the 18-inch and 20-inch piping between the CCHX and the four adjacent 18-inch isolation valves.
This piping will be addressed by isolating one heat exchanger at a time. Because these pipe sections l
are relatively short, pipe refurbishment can be performed using the 168-hour Technical Specifications action statements. It should be noted that this 18-inch and 20-inch piping adjacent to the CCHXs can be refurbished without requiring a complete SW header drain down. The 24-inch SW isolation valves to/from the CCHXs will be l
used to isolate the appropriate piping so that the upstream portion of the main SW l
header can remain in service. To complete work on all of this piping, it is projected l
that tweive additional valve alignment changes will be required, i.e., the 24-inch valves will need to be closed and then re-opened a total of twelve times to isolate and then return-to-service piping to/from the CCHXs. These valve alignment changes will be addressed by station administrative controls.
Page 6 of 19 l
1 1
During the various system re-alignments, there will be instances where it will be necessary to operate the facility with only two of the four CCHXs operable. This will occur as heat exchangers are valved in and out to remove valves and install blank flanges and subsequently to remove the blanks and re-install the valves. TS 3.7.3.1 requires three operable CC subsystems during two-unit power operation. Operation with two operable CC subsystems is permitted for up to 7 days per Action Statement "a" of TS 3.7.3.1. This action statement will be used during the course of this project for these valve and blank flange installations and removals to facilitate completion of the pipe refurbishment.
Soecific Chanaes Virginia Electric and Power Company proposes to temporarily change TS 3.7.4.1,
" Service Water System - Operating," to allow operation of the SW system with one independent source of SW to/from the Unit 1 and Unit 2 CCHXs for two periods of up to 49 days each. This proposed change also allows the automatic closure feature of the SW valves to/from the CCHXs to be defeated during the 49-day periods. This request will also temporarily change TS 3.7.3.1, " Component Cooling Water Subsystem - Operating," to allow the CC subsystems to be considered OPERABLE with only one independent source of SW provided to/from the CCHXs during these 49-day periods. The proposed temporary changes allow that the provisions of Specification 3.0.4 would not be applicable during the periods of operation with only one SW loop providing cooling to the CC subsystems.
An evaluation of the impact of these proposed temporary Technica! Specifications changes on other safety systems was performed. The effect of modified operation of the SW and CC systems due to the refurbishment activities on equipment required by other Technical Specifications as well as the effect of other Technical Specification action statements on the operation of the SW and CC systems during the two 49-day periods were evaluated. The proposed temporary Technical Specifications changes discussed below address the conclusions of this evaluation.
These proposed changes apply to both the Unit 1 and Unit 2 Technical Specifications unless noted otherwise.
TS 3.7.3.1 "Comoonent Coolina Water Subsystem - Ooerating" The following paragraph will be added as a footnote for determining the CC subsystems operable:
" For the purpose of service water system upgrades associated with the supply and return piping to/from the component cooling water heat exchangers (CCHXs), the Page 7 of 19
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p component cooling water subsystems shall be considered OPERABLE with only l
one service water loop to/from the CCHXs, provided all other requirements in this
-specification are met. This condition is permitted two times only (once for each SW loop) for a duration of up to 49 days each.' During each period of operation l
with only one SW loop _ available to/from the CCHXs, the provisions of Specification 3.0.4 are not applicable. Upon completion of the work associated j
. ith the second 49-day period, this footnote will no longer be applicable.
L w
Change Unit 1 page number '3/4 7-17a" to page number "3/4 7-17b" and Unit 2 page number '3/4 7-14a' to page number "3/4 7-14b."
Relocate Surveillance Requirement 4.7.3.1 from page number 3/4 7-17 to a new page number 3/4 7-17a (for Unit 1) and from page number 3/4.7-14 to a new page number I
3/4 7-14a (for Unit 2).
TS 3.7.4.1 " Service Water System - Ooeratina" The following paragraph will be added as a footnote to the limiting condition for..
operation for the service water system to temporarily allow one loop of SW to provide cooling to the CCHXs and to specify additional provisions for operation with the SW l
system in this configuration:
l For the purpose of service water system upgrades associated with the supply and
-l return piping to/from the component cooling water heat exchangers (CCHXs),
one of the two service water (SW) loops is permitted to temporarily bypass the l
CCHXs, provided all other requirements in this specification are met. This i
condition is permitted two times only (once for each SW loop) for a duration of up to 49 days each. During each period of operation with only one SW loop available to/from the CCHXs, four.out of four SW pumps (excluding the auxiliary i
SW pumps) shall remain' OPERABLE. With one SW pump inoperable, work may continue provided actions are taken to either restore the pump to OPERABLE i
status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or restore both SW headers to/from the CCHXs to j
OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, or place both units in HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. During l
each period of operation with only one SW loop available to/from the CCHXs, the i
automatic closure feature of the SW valves servicing the CCHXs shall be defeated to ensure SW flow to the CCHXs is not interrupted.- During each period of operation with only one SW loop available to/from the CCHXs, the provisions of Specification 3.0.4 are not applicable, provided two SW loops are capable of providing cooling for all other OPERABLE plant components. Upon completion of the work associated with the second 49-day period, this footnote will no longer be applicable.
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i
' Relocate Action Statement "d" and the associated footnote "*" from page number 3/4 7-18 to page number 3/4 7-18a (for Unit 1) and from page number 3/4 7-15 to page number 3/4 7-15a (for Unit 2).
Safety Significance The SW system refurbishment associated with the supply and return piping to/from the CCHXs and the proposed temporary changes to Technical Specifications 3.7.3.1 and 3.7.4.1 have been evaluated to assess their impact on the normal operation of the SW and CC systems and to ensure that the design basis functions of these system are preserved.
The SW System The SW system is shared between Unit 1 and Unit 2. The SW system is required to function during all normal and emergency operating conditions. During normal plant operation, the SW system provides cooling water to the CCHXs, charging pump coolers, instrument air compressor coolers, and control room chiller condensers of both units. The largest percentage of header flow is directed through the CCHXs with the remaining small percentage directed to the other components listed.
During the proposed refurbishment activities, one of the two SW headers to/from the CCHXs would be blanked-off from the rest of the main SW loop. Concurrently, a temporary cross-connect, with a manually operated butterfly valve, would be installed l
between the supply and return headers of the affected main SW loop to provide a flow l
path bypassing the CCHXs. The installation of a temporary bypass avoids the situation where, during normal operation, the SW pump would be limited to the remaining flow paths on the main SW loop which are small diameter lines, i.e.,
4-inches and under. (Without the temporary bypass, the SW pump on the " partially deadlocked" main SW loop would be subjected to a low flow state approaching pump shut off conditions.) The temporary cross-connect will be opened whenever the corresponding 24-inch SW header to the CCHXs is isolated for repairs, i.e., during the two 49-day periods and during subsequent refurbishment of the piping directly adjacent to each CCHX. This cross-connect will ensure normal operation of the SW pump aligned on this header.
l Operation of the SW system with the cross-connect installed was evaluated for design basis accident (DBA) conditions. The limiting DBA con ition for the SW system is a loss-of-coolant accident (LOCA) on one unit with simultaneous loss-of offsite-power to both units. In response to a LOCA, a safety injection / containment depressurization actuation (SI/CDA) signal would start all four main SW pumps and would isolate SW flow to the CCHXs of the affected unit to ensure adequate flow to the containment recirculation spray heat exchangers (RSHXs) on the accident unit. However, during Page 9 of 19
the two 49-day periods with the CCHXs aligned to a single SW header, this normal response to an accident condition (i.e., isolating SW flow to the CCHXs in response to a CDA signal) may also result in the undesired interruption of CC cooling to the unaffected unit. Therefore, the automatic closure feature of the SW valves servicing the CCHXs shall be defeated to ensure SW flow to the CCHXs is not unnecessarily interrupted. A SW system hydraulic analysis has been performed to verify that adequate flow is provided to the RSHXs with the temporary cross-connect installed and throttled open, assuming the occurrence of the most limiting single failure. During the two 49-day periods with their automatic isolation function defeated, the SW valves on the header aligned to the CCHXs would not be considered " automatic" valves and,
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therefore, would not be subject to the requirements for automatic actuation as required by Technical Specification Surveillance Requirement 4.7.4.1.c.2. The defeating of this automatic valve operation will be addressed by station administrative procedures.
The containment isolation valves in the SW lines to the RSHXs are closed during normal operation. These valves open in response to a CDA signal to provide SW flow to the RSHXs of the affected unit. Should an Si signal be received without a concurrent CDA signal, all four SW pumps will start but the containment isolation valves at the RSHXs will not open. In this case, it may be necessary to manually secure one of the SW pumps on the partially bypassed header to prevent pump operation at low flow conditions since the additional flow is not needed. This variation from normal pump operation will be addressed by station administrative procedures.
During the course of refurbishment, piping which must remain operable will retain its seismic qualification along with other governing design basis requirements. The temporary cross-connect will also be designed, procured, and installed in accordance with applicable safety-related piping design criteria. It will be installed during the same Technical Specifications action statements that isolate and blank-off the 24-inch headers to/from the CCHXs.
The CC System The CC system is shared between Unit 1 and Unit 2. The CC system provides cooling water to various safety-related and non safety-related components, some of which l
may contain primary coolant. The CC system provides cooling water to components located inside the reactor containment building during normal two-unit operation. This component cooling function, along with the air recirculation cooling coils (cooled by the chilled water system), serves to maintain the containment atmospheric air temperature within the required equipment qualification temperature limits.
The CC system also provides cooling water to the residual heat removal (RHR) heat l
exchangers during unit shutdown. The design basis for this CC system function is to achieve fast cooldown of one unit (i.e., to reduce reactor coolant system temperatures Page 10 of 19
from 350*F to 140 F in sixteen hours) while maintaining normal operating loads on the other unit. Fast cooldown is achieved using both trains of RHR pumps and heat exchangers. A slow cooldown can be achieved in 3G hours if one train of RHR and two CC subsystems are used.
Operation of the CC system with one SW header available has been evaluated with hydraulic and heat transfer analyses. The following are the results of these analyses.
- 1) Normal CC heat transfer loads can be met with two CCHXs operated on one SW header with two SW pumps. Hydraulically, up to three CCHXs can be operated on one SW header with up to three SW pumps, if required.
- 2) The fast cooldown heat transfer loads can be met with three CCHXs operated on one SW header with two SW pumps and the SW supply temperature less than or equal to 75 F. For a SW supply temperature between 75 F and 78.5 F, a slow cooldown can be achieved with this same system configuration. If the SW supply temperature is greater than 78.5 F, a third SW pump can be aligned to the SW header supplying the CCHXs to affect a slow cooldown of the unit.
- 3) Containment atmospheric temperature limits can be maintained.
In addition, utilizing only one SW header to supply cooling to the CCHXs has the potential to affect the reliability of the CC system and all of the equipment cooled by the CC system. This is discussed further in the probabilistic safety assessment section below.
The CC system does not function to mitigate the consequences of a DBA. In fact, as the result of a DBA, the CC pumps for the affected unit are deenergized on a CDA signal.
Comoensatorv Actions and Contingency Measures The work activities proposed to be performed to accomplish refurbishment of the exposed 18-inch, 20-inch, and 24-inch diameter SW piping to/from the Unit 1 and Unit 2 CCHXs were evaluated.
As a result, specific compensatory actions and contingency measures were developed to provide added assurance of the safe operation of the facility during this project.
Listed below is a summary of the compensatory actions and contingency measures which will be implemented as part of this project:
- 1) During periods of operation in Action Statement "d" of Technical Specification 3.7.4.1 (168-hour action statement) when the SW system is on one header, the following contingency measures will be in place:
Page 11 of 19
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. a. An alternate, temporary source of cooling water to the charging pumps will be available. Pipe connections are in place for providing cooling water to the charging pumps coolers by utilizing the fire protection (FP) or primary grade
-(PG). water systems should the normal service water supply be interrupted.
Abnormal Procedure 0-AP-12 "Lo ss of Service Water' addresses use of this alternate source of cooling water. This alternate cooling source will be staged during the project and can be placed into service in approximately 10 minutes.-
The procedure _ requires the charging pumps to be cycled to' prevent overheating until one of the' alternate cooling sources can be placed into'-
1 service.. Continued seal injection flow provided by the charging pumps will:
cool the RCP seals and preclude a seal failure due to overheating.-
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- b. An alternate source of cooling water to th's: control room / emergency-switchgear room (CR/ESGR) air conditioning system will.be available. The
. capability of providing bearing cooling (BC) water-as an alternate source'of water to the CR/ESGR cooling system is permanently in place. Abnormal, Procedure 0-AP-12 " Loss of Service Water" addresses use of this alternate-1 source of cooling water,
- c. It should be noted that, as part of their normal licensed operator continuing -
training, operating crews are trained on the simulator in the use of Abnormal Procedure 0-AP-12 for loss of service water. In addition, the operating crews' have been trained on the simulator for operation of the facility in the 168-hour action statement and implementation of contingencies associated with the service water system restoration project.
- 2) During the two 49-day periods, temporary pipe clamps and other emergency repair equipment will be staged in the area of construction in.the Auxiliary.
Building. This equipment is provided to facilitate the capability for emergency.
repair of the SW system piping to assist in recovery from a postulated loss of SW i
system'due to the rupture of the SW system header (s). Procedures and training will be provided to the construction personnel to ensure the effectiveness of this measure.
- 3) During the two 49-day periods when operating with one SW header supplying the CCHXs, no major maintenance or testing shall be planned on the main SW pumps. This is specified to ensure adequate SW flow capability is available in case of a spurious pump failure. To the maximum extent practical, routine periodic tests (e.g., quarterly pump tests) and preventative maintenance work j
(e.g., motor checks) will be scheduled prior to or following the 49-day periods.
Certain tests may have to be performed during the 49-day periods (e.g., during Technical Specification required emergency diesel start tests, the associated SW pump is considered inoperable due to its emergency power supply being inoperable). For tests which render a SW pump inoperable, the 72-hour action Page 12 of 19
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statement (included in the footnote provided as part of this-proposed change request) will be entered for performing the test. If a SW pump on the header supplying the CCHXs is rendered inoperable (for testing or any other reason), an operable SW pump from the other header will be realigned to this header to maintain two operable pumps on the header supplying the CCHXs.-
- 4) The project will be scheduled such that no planned unit outages will occur during i
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the 49-day periods when operating with one SW header supplying the CCHXs.
This is specified to avoid planned RHR. system operation. In the event that an.
unplanned unit shutdown is required, all pipe refurbishment work will be stopped and conditions will be evaluated to determine the best course of action based on the status of the refurbishment.
- 5) During the two 49-day periods when operating with one SW header _ supplying the CCHXs, pipe refurbishment work will be scheduled when SW supply.
1 temperatures can be maintained nominally at 75 F (typically October through April). This is specified to minimize the flow requirements to the CCHXs which are required to ' operate. Higher SW temperatures can be tolerated, but would lengthen a unit cooldown if such an unplanned evolution were required. If SW-supply temperatures exceed 78.5 F, a third SW pump will be aligned to the header supplying the CCHXs only if a unit shutdown is required. The 75 F nominal SW target temperature noted above has no impact on the ability to depressurize the containment as a result of a DBA since the accident analysis ~
ceumo: an initial SW temperature of 95 F.
- 6) During the course of refurbishment, piping which must remain operable will retain its seismic qualification along with other governing design basis' requirements.
Temporary, seismic supports will be used as appropriate.
Probabilistic Safety Assessment i
The activities to be performed during the refurbishment project and the various system alignments required have been evaluated using the Individual Plant Examination (IPE)
Probabilistic Safety Assessment (PSA) model for North Anna Power Station.. This model is used in a manner ' hat is generally consistent with the Nuclear Energy Institute (NEl) / Electric Power Research Institute (EPRI) draft PSA Applications Guide (Revision H). Analysis was done for two-unit operation with both units assumed to be -
operating at 100% power.
In general for IPE PSA evaluations, core. damage _
frequency (CDF) is the annualized probability of component failures leading to heatup-of the reactor core to the point where severe damage is anticipated. The overall effect of the proposed refurbishment activities on the CDF for North Anna, while work is in progress, is a slight non-risk significant increase in CDF. Utilizing only one SW header to supply flow to the CCHXs has the potential to affect the reliability of the CC '
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' system and all of the equipment cooled by the CC system. The effect of providing only one SW header to supply cooling to the CCHXs on the PSA model is a slight increase in the frequency of reactor trips and an increase in the probability of RHR system failure.
The increased frequency of reactor trips is due to the decreased reliability of the CC system to supply cooling to the reactor coolant pump (RCP) motors. When only one SW header is available to the CCHXs, the increased frequency of losing this single header can be conservatively estimated by combining the failure probability of both SW pumps ( approximately 1.5E-4 based on IPE PSA data). Also considered was the frequency of pipe rupture anywhere in the single available header. When the single SW header fails to supply cooling to the CCHXs, the CC system will heatup causing inadequate cooling for sustained operation of the RCPs. Tripping these pumps results in a reactor trip. The second SW header can be expected to supply other equipment with cooling. A sensitivity analysis shows the increase in CDF as a result of the increased reactor trip frequency to be less than 1E-8 per year.
The CC system is also included in the PSA model as a support system for RHR cooling. The RHR system is used to reduce reactor coolant system temperatures from 350 F (hot shutdown) to 140 F (cold shutdown). The only accident initiator that requires the unit to be cooled down and placed on RHR cooling are sequences which are initiated with a steam generator tube rupture. (Note that, for the North Anna plant design, RHR is separate from the safety injection system and the low head safety injection pumps.) The increased probability for the loss of RHR when only one SW header is available to the CCHXs is estimated using fault tree analysis and is dominated by the failure of both SW pumps. The probability for the loss of both SW pumps aligned to the CCHXs is estimated to be 1.5E-4. The effect of this increase in RHR failure probability was determined by adding this probability to the top single event in the RHR function and recalculating the new CDF. The resulting increase in CDF as a result of RHR system failuro following a steam generator tube rupture is less than 1E-8 per year.
The CC system is further included in the PSA model as part of the loss of RCP seal cooling as an initiating event and as a loss of function during other initiating event scenarios. The effect on the probability for a loss of RCP seal cooling due to losing CC cooling to the RCP thermal barriers is negligible due to the high reliability of the charging system to provide seal injection.
The total effect of this pipe refurbishment project was estimated by a sensitivity analysis combining both the change in the reactor trip initiating event frequency and the increased failure probability of RHR resulting in less than a 1E-6 per year increase in CDF. Since this project will not affect the containment systems, there would not be any significant change in off-site dose, except that resulting directly from the increase Page 14 of 19
In CDF. These minor increases in CDF and off site dose are less than what is defined as risk significant in the NEl / EPRI draft PSA Applications Guide.
The following limiting conditions were included in the PSA model as assumptions and will be implemented during the 49-day periods when the CCHXs are supplied from only one SW header. These assumptions must remain valid for this analysis to be applicable:
Neither unit will plan to have RHR in service while only one SW header is available to the CCHXs.
The only equipment with a single SW header will be the CCHXs. All other equipment which normally has two SW headers available will still have two SW headers available.
During single SW header operation, there will always be two normal SW pumps operable and aligned to the SW header supplying flow to/from the CCHXs.
These assumptions will be ensured by station administrative controls. The assumption that neither unit is utilizing RHR while only one SW header is available is due to the inability to quantify CDF associated with shutdown conditions.
PSA experience indicates that this could be an increase in risk. If a steam generator tube rupture occurs, the unit response should be in accordance with approved procedures (including placing the unit on RHR as necessary), and all work on the other header will be stopped to avoid damage of the operating header due to construction mishaps. If RHR is needed for any other reason, then the best course of action for restoring the second SW header and utilizing RHR cooling would be evaluated based on project status.
PSA calculations for previous Phase I project work have evaluated the impact of multiple entries into the 168-hour Action Statement of Technical Specification 3.7.4.1.
This CCHX exposed piping work scope will require that the entire SW system be placed on one-loop operation six times (two times for work on the "A" header, two times for work on the "B" header, and two times for removal of the temporary cross-connects). Evaluation of these entries results in an increase in CDF of less than 2E-8 per year.
Conclusions The purpose of this proposed change request is to allow temporary changes to the existing Technical Specifications requirements to permit refurbishment of the SW piping to the CCHXs during two-unit power operation. The design of the affected section of SW piping does not permit isolation for a sufficient period of time under the Page 15 of 19
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' current Technical Specifications to allow the necessary work to be performed. The proposed changes have been thoroughly evaluated and it has been determined that operation of the North Anna Power Station Units 1 and 2 with the requested temporary Technical Specifications changes would not involve an unreviewed safety question.
- 1) The proposed changes would not increase the probability of occurrence or the consequences of an accident or malfunction of equipment important to safety previously evaluated in the safety analysis report. The proposed changes are only temporary and provide for refurbishment of the SW piping to the CCHXs.
SW system operation with the cross-connect installed and the autoclosure feature of the SW MOVs to the CCHXs defeated was evaluated for design basis accident (DBA) conditions. The DBA condition for the SW system is a loss-of-coolant accident on one unit with simultaneous loss-of-offsite-power to both units. A SW system hydraulic analysis has been performed to verify that adequate flow is provided to the containment recirculation spray heat exchangers (RSHXs) with the temporary cross-connect installed and throttled open, assuming the occurrence of the most limiting single failure. Therefore, there is no increase in probability or consequences of the DBA condition, t
Even so, utilizing only one SW header to supply flow to the CCHXs has the potential to affect the reliability of the CC system and all of the equ:;: ment cooled by CC.
As discussed above, the activities to be performed during the refurbishment project and the various system alignments required were evaluated using the IPE PSA model for North Anna Power Station. The effect on the IPE PSA model is a slight increase in the frequency of reactor trips and an increase in the probability of RHR failure.
The total effect of this pipe refurbishment project was estimated by a sensitivity analysis combining both the change in the reactor trip initiating event frequency and the increased failure probability of RHR resulting in only a slight non-risk significant increase in CDF.
During the course of refurbishment, piping which must remain operable will retain its seismic qualification along with other governing design basis requirements.
Compensatory actions, contingency measures, and system availability requirements would also be provided by station administrative controls. These limitations serve to reduce risk of damage to the operating SW header and provide backup means of cooling equipment. Since this project does not affect l
the containment or any other accident mitigation systems, there is no significant change in dose consequences.
- 2) The proposed changes would not create the possibility for an accident or j
malfunction of a different type than any evaluated previously in the safety analysis
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report.
The proposed changes to the allowed outage times only provide l
operational flexibility needed to perform necessary repaws. During the project, 1
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[there will be a significant time period when all the CCHXs are aligned to one SW:
' loop. The possibility of an interruption of.SW supply to the heat.exchangers-during a DBA is eliminated by defeating the closure of the 24-inch SW isolation MOVs to the CCHXs on a SI/CDA signal. Both SW headers will be available for equipment required for safe shutdown of the units (i.e., RSHXs, charging pumps, and CR/ESGR chillers).
The SW pipe _ repair ' activities and 'the-installation / removal of the SW cross-connect piping do not create the possibility for a malfunction of equipment different than previously evaluated. Therefore,.
implementation of the restoration project and approval of the proposed Technical-Specifications changes will not introduce any new accident initiators nor affect 3
the performance of accident mitigation systems.
- 3) The proposed changes would not reduce the_ margin of safety as defined in the basis for any Technical Specification. The proposed changes to the schedule only provide operational flexibility to perform the required SW pipe refurbishment.
The Technical Specifications continue to require the SW and CC systems to remain functional during the period with a single SW supply to tho_ CCHXs. As L
stated in item 1) above, the SW system is fully capable of performing its DBA function during the course of the pipe refurbishment project with the proposed Technical Specification changes in place. The effect of this pipe refurbishment project on CC system reliability was estimated by a sensitivity analysis combining both the change in the reactor trip initiating event frequency and the increased failure probability of RHR resulting in less than a 1E-6 per year increase in CDF.
Since this project will not affect the containment systems, there would not be any significant change in off-site dose,- except that resulting directly from the increase in CDF. These minor increases in CDF and off site dose are less than what is defined as risk significant in the NEl / EPRI: draft:PSA ' Applications Guide.
Therefore, there is not a significant reduction in margin.of safety. In fact, as a result of the repairs to the SW piping around the CCHXs, the long-term material condition of the SW system will be improved.
Based on the above evaluation, the proposed changes to the Techrxal Specifications wiin aot adversely affect the safe operation of the plant. Therefore, this proposed change request for Norin Anna Units 1 and 2 does not result in an.unreviewed safety
_ question as defined in the criteria of 10 CFR 50.59.
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4 Hgference Documentation Listed below are docketed correspondence which have been issued for previous SW refurbishment work associated with Phase I of the service water restoration project.
These items are listed in chronological order.
Letter Serial No.92-287. dated May 18.1992 This letter informed the NRC of our plans to perform extensive refurbishment activities for restoration of certain portions of the SW system as part of the Phase I project.
Letter Serial No.92-450. dated July 16.1992 This letter provided the basis for temporary exemption from the requirements of 10 CFR Part 50, Appendix A, General Design Criterion 2 (GDC-2), " Design Basis for Protection against Natural Phenomenon," for Stages 1,2,3, and 4 of Phase I of the project.
Letter Serial No. 92-450A. dated Seotember 11.1992 This letter requested an additional temporary exemption from the requirements of 10 CFR 50.49, " Environmental Qualification of Electric Equipment Important to Safety for Nuclear Power Plants," for Phase I / Stage 1 of the project. The scope of Stage 1 addressed the 24-inch lines to and from the Unit 1 recirculation spray heat exchangers. The details of these temporary requests, particularly for Stage 1, were discussed with the NRC at meetings held on August 24, September 28, and November 2,1992.
NRC Letter dated October 30.1992 This NRC letter provided the " Environmental Assessment and Finding of No Significant impact" associated with our ex^mption request.
Letter Serial No. 92-4508. dated Novembo 4.1992 This letter docketed responses to two sets of NRC questions received by fax / phone on September 14,1992 and October 14,1992.
Letter Serial No. 92-450C. dated November 4.1992 This letter provided revised Phase I plans which included deletion of Stage 2 (new 36-inch manways) and revised the schedule for Phase I.
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NRC Letter dated December 3.1992 This letter provided NRC approval of the temporary exemptions from the requirements of 10 CFR Part 50, Appendix A, GDC-2, for North Anna Units 1 and 2, and 10 CFR Part 1
50.49, for North Anna Unit 2, for the Phase I / Stage 1 project.
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' Letter Serial No.93-067. dated February 17.1993 This letter provided the description and basis for just:fication of a temporary exemption from the requirements of 10 CFR Part 50, Appendix A, GDC-2, for North Anna Units 1 and 2 during the Phase I / Stage 3 SW system restoration activities. The scope of Stage 3 was similar to Phase I / Stage 1 in that it addressed the 24-inch lines to and from the recirculation spray heat exchangers on Unit 2.
Letter Serial No. 93-067A. dated Juiv 12.1993 This letter withdrew the GDC-2 exemption request required for Stage 3 due to a change in implementation schedule.
Letter Serial No.93-378. dated Juiv 30.1993 This letter provided the description and basis for justification of a temporary exemption from the requirements of 10 CFR Part 50, Appendix A, GDC-2 for North Anna Units 1 and 2 during Phase I / Stage 4 SW system restoration activities. The scope of Stage 4 involved restoration of the 24-inch auxiliary service water supply lines from Lake Anna to the main service water headers.
NRC Letter dated Seotember 30.1993 This NRC letter provided the " Environmental Assessment and Finding of No Significant impact" associated with our Stage 4 exemption request.
NBC Letter dated December 27.1993 This letter provided NRC approval of the temporary exemption from the requirements of 10 CFR Part 50, Appendix A, GDC-2, for North Anna Units 1 and 2 for the Phase I /
Stage 4 project.
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