ML20247R850
| ML20247R850 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 05/20/1998 |
| From: | Walter MacFarland ILLINOIS POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| U-602983, NUDOCS 9805290228 | |
| Download: ML20247R850 (25) | |
Text
11tinois Power Cornpany
.el O- Chnton Power Station
- P.O. Box G78 Chnton. IL 61727 l g- Tel 217 935 5623 Fax 217 9354 632 Walter G. MacFarland IV Sensor Vice President and Chief Nuclear officer PMR u.6o29 3 8E.100a An ilhnova Company May 20, 1998 l
Docket No. 50-461 10CFR50.90 10CFR50.59 -
l Document Control Desk Nuclear Regulatory Commission Washington, D. C. 20555
Subject:
Clinton Power Station Proposed Amendment of Facility Operatina License No. NPF-62 (LS-98-008)
Dear Madam or Sir:
Pursuant to 10 CFR 50.90, Illinois Power (IP) hereby requests amendment of Facility Operating License NPF-62 for the Clinton Power Station (CPS). Specifically,
' and pursuant to 10CFR50.59(c), IP requests prompt NRC review and approval of a proposed modification to the CPS auxiliary power system, including associated changes /
proposed for the CPS Updated Safety Analysis Report (USAR), for which it has been f determined that an unreviewed safety question exists. The proposed modification is to /
replace the emergency reserve auxiliary power transformer (ERAT), which provides power to the plant 4.16-kV safety busses from the offsite 138-kV transmission network, with a new transformer having a larger capacity and automatic load tap-changing capability [i.e., with a load tap changer (LTC)].
By letter dated May 4,1998 (IP letter U-602972), and as discussed in more detail in meetings previously conducted with the NRC staff, IP described the modifications currently being pursued or planned to provide the short-term, as well as
(. the long-term, solution to the degraded voltage problem at CPS. These modifications l include the installation of 480/120-volt regulating transformers (to replace selected, l existing non-regulating tre.nsformers in the CPS auxiliary power system), the installation L of static VAR compensators (SVCs) on the secondary (4.16-kV) side of the ERAT and _
L ' on the secondary side of the reserve auxiliary transformer (RAT) (which is associated j with the offsite 345-kV transmission network), and the installation of LTCs to replace L. . the existing fixed-tap RAT and ERAT. The May 4 letter is a license amendment application dedicated to the SVCs.
. c.' i 1
n L ,
L .
_ _m.ii__ _.m _... _.i___..__ ._1._. .J
U4,02983 i
Page 2 of 3 As noted in the May 4 letter, and as discussed in a teleconference between IP and NRC staff personnel on April 1,1998, installation of the SVCs (which were originally intended to be in service for or by this summer) will not be completed until late summer or early fall. In the mean time, i.e., throughout this summer, CPS will remain in a shutdown condition as the current outage continues. However, in light of the intermittent low grid voltage conditions observed last summer (1997) during periods of peak load demand, when one of the two offsite electrical power sources intermittently could not support the minimum required voltage for CPS, installation of the ERAT LTC is currently proceeding on a priority basis. (In lieu of the SVCs being ready for service, installation and use of the ERAT LTC was the next, most immediately available option, as it had already been purchased. The RAT LTC is not available, since it was not planned to be installed until much later than the ERAT LTC.) Installation of t he ERAT LTC as soon as possible will ensure that, even without the SVCs installed, an gerable offsite power source can be maintained throughout the summer such that the Technical Specification requirements for having at least one operable offsite source operable during shutdown conditions (Modes 4 and 5) can be met.
Because installation of the ERAT LTC and the associated changes required for the US AR involve an unreviewed safety question, NRC approval per 10 CFR 50.90 (i.e., via a license amendment) is required prior to implementation. It should be emphasized that this application for amendment supports use of the ERAT LTC to regulate voltage from the 138-kV offsite source this summer (and beyond) while the plant is in a shutdown condition and only one ofrsite source is required to be operable per the plant Techni:a!
Specifications. On this basis, IP's evaluation of this proposed amendment, which is included in Attachment 2 to th" letter, is limited in scope to the use of the ERAT LTC to support one offsite source for US (i.e., the 138-kV system) during plant shutdown conditions. The attached evaluation primarily addresses operation of the ERAT LTC in its automatic mode of operation, due to consideration of potentially more limiting failure modes when the LTC is operating automatically under control ofits associated controller.
Ilowever, the ERAT LTC may also be operated in a manual mode, during which the ERAT LTC is not subject to the limiting failure modes evaluated for the automatic mode of LTC operation. Thus, although manual operation of the ERAT LTC may be evaluated under 10CFR50.59, and therefore would not involve an unreviewed safety question, for the cake of completeness in addressing LTC operation, an evaluation for manual operation of the ERAT LTC is included in Attachment 2.
It should also be emphasized that this application supports installation and operation of the ERAT LTC alone (when operating in its automatic mode) to provide voltage support for the plant while the plant is in a shutdown condition. Similarly, IP's May 4,1998 application for the SVCs only addresses installation and operation of the SVCs by themselves to provide voltage support for the facility, except that it supports SVC operation with the plant operating or in a shutdown condition. As noted in the previous meetings with the NRC, IP's longer-term plans call for the SVCs and LTCs to be operating together and automatically to provide both steady-state and transient voltage support to the plant based on long-term projections. However, to simplify and expedite
. s l 5 U-602983 L Page 3 of 3 evaluation of the ERAT LTC for its immediate use this summer, this application only supports operation of the ERAT LTC without concurrent operation of the SVCs (unless the LTC is operated in the manual mode). Further evaluation is required to support operation of the SVCs with the LTCs in their automatic mode, and therefore, a submittal to support such operation will be provided at s later date.
Additional information and documents to support this application are provided as attachments to this letter. An affidavit supporting the facts set forth in this letter and its attachments is provided as Attachment 1. Attachment 2 contains a description of, and justification for, the ERAT LTC modification and the associated USAR changes, additional background information, and an evaluation of the proposed change, including i the basis for no significant hazards consideration. A failure analysis of the ERAT LTC is I provided in Attachment 3. In addition, marked-up pages from the CPS USAR to reflect the required changes are provided in Attachment 4, and an evaluation for environmental impact consideration is provided in Attachment 5.
i In light of the immediate need for use of the ERAT LTC to provide plant voltage support this summer, IP respectfully requests that this application for amendment be reviewed with the highest possible priority and as promptly as possible. IP currently estimates that the ERAT LTC can be installed and ready for testing at the end of June.
Therefore, approval in that timeframe is requested. Please notify IP as soon as possible for any additional information that may be required to support your review, so that it may be provided in a timely manner to support your prompt approval.
Sincerely Yours, k}
Walter G. MacFarland, IV
'b "
Senior Vice President and ChiefNuclear Officer TBFJmlh l
Attachments cc: NRC Clinton Licensing Project Manager NRC Resident Office, V-690 NRC Regional Administrator, Region III Illinois Department of Nuclear Safety
I l
. 6 Attachment I to U-602983 LS-98 008 Page1of1 Walter G. MacFarland, IV, being first duly sworn, deposes and says: That he is Senior l
Vice President and ChiefNuclear Officer for Clinton Power Station; that this appli::ation l for amendment of Facility Operating License NPF-62 has been prepared under his supervision and direction; that he knows the contents thereof; and that to the best of his knowledge and belief said letter and the facts contained therein are true and correct.
j f
Date: This 20 day ofMay 1998.
]
Signed: M ' ~
.I Walter GiMacFarland IV 1
l 1
STATE OF ILLINOIS l SS. f . MFm M
- l f Jeequerme 8.MenNos ? j b d ++ COUNTY J Notary Pubic,Stee of IEnols
! MycomminaionEgbes11MIDDI 1
i L _ _
7-I Subscribed and sworn to before me this 20 day ofMay 1998.
I t
mood $t 8 8,w&
' [(Notary Public)/
-- ------------_--________)
. a Attachment 2
~ toU402983 LS-98-008 Page 1 of 9 Backarou'nd -
As more fully described in IP's May 4,1998 application for amendment of the CPS Operating License to address degraded voltage concerns at Clinton Power Station (CPS),
i and as discussed in meetings previously conducted with NRC staff personnel, CPS has experienced degradation of the voltage available to the CPS auxiliary power system from either (or both) of the offsite electrical power sources required by 10 CFR 50 Appendix A L General Design Criterion (GDC) 17, " Electric Power Systems." This was observed, for
, example, last summer (1997) when voltage on one of the offsite sources was not able to be maintained above the minimum required value conservatively established for CPS, for frequent but short periods of time, with CPS in a shutdown condition.
( As also described in IP's May 4 amendment application, several plant modifications are planned or underway for resolving the degraded voltage issue at CPS. Modifications that l are currently underway include the installation of 480/120-volt regulating transformers to replace selected non-regulating 480/120-volt transformers used in the CPS auxiliary j power system, and the installation of static VAR compensators (SVCs) for connection to the secondary side of the following important transformers:
- 1. The reserve auxiliary transformer (RAT), which is in the offsite 345-kV circuit connection to the CPS auxiliary power system, and J
- 2. The emergency reserve auxiliary power transformer (ERAT), which is in the offsite 138-kV circuit connection to the CPS auxiliary power system.
1 Planned modifications include replacement of the fixed-tap RAT and ERAT with transformers having automatic load tap changer (LTC) capability. The RAT has been scheduled to be replaced with its LTC at a distant future date since that replacement is only required to meet projected long-term needs for the facility.
Because the SVCs will not be ready for service this summer (as originally planned),
installation of the ERAT LTC was moved ahead ofits original schedule so that it can be available to provide the voltage support needed for the facility this summer, particularly during periods of peak load oemand. This will avoid the situation experienced last summer, as it will ensure that, even without the SVCs installed, an operable offsite power
> source can be maintained in accordance with the Technical Specification requirements for having at least one offsite source operable during plant shutdown conditions.
i s
ERAT Modification and LTC Desian Features The new ERAT has a higher load carrying capacity, as it is rated at 18/24/30 MVA OA/FA/FA @ 65'C rise, in comparison to the current ERAT rating of 15.12 MVA, OA
~ therefore will accommodate higher and lower voltages than previously allowed from the j 132-kV system as it regulates voltage to the plant auxiliary system. i
Attachment 2 p
to U-602983 LS-98-008 Page 2 of 9 The tap changer mechanism for the LTC is located in a separate enclosure alongside and attached to the transformer. A drive motor charges a spring-loaded mechanism to rotate the tap changer to increase or decrease the number of transformer windings in service. In the automatic mode, the tap changer is given comm uds to raise or lower the tap setting by the tap changer controller located on the transformer. The tap changer can also be operated in a manual control mode, for which the drive motor is still utilized. Otherwise (in the event of drive motor failure or a loss of power to the drive motor), a hand crank can be utilized to mechanically efTect a tap change via the spring-loaded mechanism.
With regard to automatic operation, the ERAT LTC is also provided with a backmp control unit. The backup control unit prevents the LTC tap changer control, in the unusual event of a failure, from running the secondary voltage outside the desired upper and lower limits. It also prevents the line drop compensator from raising the voltage too high under full or overload conditions.
l Similar LTC transformers are in use at other NRC-licensed facilities including Limerick, Peach Bottom, Salem, Hope Creek, Sequoyah, Browns Ferry, North Anna, Surry, Diablo l Canyon, Susquehanna, Oyster Creek, TMI 1 and Indian Point 2. Based on contacts with each of these licensees, LTC transformers in nuclear power applications are providing safe and reliable operation.
Proposed Channes to the CPS USAR To reflect the incorporation of the ERAT LTC into the CPS design, the changes described below and indicated on the attached marked-up pages from the CPS USAR (per Attachment 4) are proposed:
l
- USAR Section 8.3.1.1.1 is being revised to describe the addition of a nonsegregated t
bus duct section tie to the existing duct run.
- USAR Section 8.3.1.1.2 is being revised to indicate that the ERAT has automatic load tap changing capability and that an optimum tap setting (for a fixed-tap transformer design)is no longer applicable.
t
- USAR Figure 8.3-1 is being revised to reflect the new ERAT LTC and its rating of 18/24/30 MVA OA/FA/FA @ 65*C rise.
- I.
- Attachment 2 to U-602983 LS-98-008 Page 3 of 9 The USAR changes described above are those which have been determined to be appropriate at this time. Further changes are anticipated to reflect the long-term configuration that will be in place when the SVCs are installed and are capable of operating in conjunction with the ERAT (and RAT) LTC(s) operating in the automatic mode.
Evaluation of Proposed ERAT LTC Modification Scope ofEvaluation As noted previously, the immediate purpose of the ERAT LTC modification is to ensure that voltage support for CPS is in place at the onset of high summer load demand. By providing automatic adjustment of the voltage required by the CPS auxiliary power system from the offsite 138-kV system, the ERAT LTC will ensure continued operability of this offsite source. This will ensure continued compliance with the requirements of Technical Specification 3.8.2, "AC Sources - Shutdown," which requires CPS to have at least one of its two offsite electrical power sources operable during shutdown conditiors (Modes 4 and 5).
In addition, the proposed replacement of the ERAT with an LTC to support plant voltage from the 138-kV transmission system is consistent with the requirements of 10CFR 50 Appendix A, GDC 17. Although GDC 17 addresses design requirements for two offsite electrical power sources (as well as the onsite electrical power sources), consideration should be given to the requirements that apply to a single offsite source when only one w offsite source is required (per the Technical Specifications). Specifically, GDC 17 requires I consideration to be given to minimizing the probability oflosing electric power from the offsite supplies (supply) as a result of, or coincident with, the loss of power generated by the nuclear power unit. Accordingly, while CPS is in a shutdown condition, when only one source of offsite power is required, employment of the ERAT LTC will minimize the probability of a transfer to the diesel generator (s) in the event of high plant load that could otherwise cause a trip of the plant undervoltage relays. This has a positive effect on plant risk, since risk is generally increased when electric power source availability is reduced to just the diesel generators.
The above describes the immediate purpose of the ERAT LTC modification. However, as also noted previously, long-term modification plans for the two CPS offsite electrical power sources call for replacement of the RAT and ERAT with LTCs, as well as installation of an SVC for each circuit. Thus, a configuration for each offsite source (or L more specificeWar each circuit connection between the associated offsite transmission system and tha CPS auxilidy power system) will be attained in which the LTC and SVC
- are' operating together and automatically to provide steady-state and transient voltage L i control capability for normal plant operation as well as accident conditions. This D configuration, however, will require further evaluation including, for example, evaluatian
- of the interaction between the LTC and the SVC, which is beyond the scope of the limmediate configuration irvolving only replacement of the ERAT with its LTC. It should therefore be emphasized that the proposed changes addressed by this submittal, including l
l
f f' l' .
Attachment 2 to U 602983 l-l LS-98-008 Page 4 of 9 l
ifs evaluation of the ERAT LTC modification, are applicable only to the ERAT LTC replacement, specifically to operation of the ERAT LTC without the SVCs in service and with the plant in a shutdown configuration, unless (as explained later) the ERAT LTC is simply operated in the manual mode.
10CFR50.59/ Failure Modes Evaluation In support of the ERAT LTC modification and the associated changes to the CPS USAR, IP has evaluated the modification pursuant to the requirements of 10CFR50.59. From that evaluation, which includes evaluation of the potential failure modes or malfunctions associated with the ERAT LTC, and as noted in the cover letter, IP has determined that the proposed change involves an unreviewed safety question. This conclusion results from i answering yes to the question ofwhether the proposed change creates thepossibility for a malfunction of a different type than any evaluated previously in the safety analysis report
[Ref.: 10CFR50.59(a)(2)(ii)]. IP has determined that this particular question must be answered yes due to the possibility of an overvoltage condition that could be created by a malfunction of the LTC controller, as further explained below. (Malfunction of the LTC controller could also produce an undervoltage condition, but such a condition has been previously evaluated.)
By design, when operating in its automatic mode, the LTC raises and lowers volt ge by i operation of the tap changer via the LTC controller. The controller monitors load and source voltage to create an " error" signal based on load demand, which changes the tap setting when required so that voltage is controlled to within the desired bandwidth. IP has evaluated the potential failure modes of the LTC and its control system, and the results of that evaluation are provided in Attachment 3. Of most concern is the possibility for the controller to fail in a manner that could cause the tap changer to suddenly run voltage up to an unacceptable level, especially under light load conditions. (This was deemed to be more possible than a failure of the tap changer mechanism itself. The latter would not likely fail in a manner to suddenly run voltage up to a high, fixed level, by itself.) The sustained high voltage that could result from this kind of malfunction of the LTC controller could damage plant safety systems or components connected to the busses at the time of the failure. Further, since all of the required plant safety busses could be aligned to the ERAT (as it may be the only circuit connection to an operable offsite source during the summer) such damage could occur to plant safety systems or equipment in multiple divisions. Such a common-mode malfunction has not been previously evaluated in the CPS safety analyses (i.e., the USAR).
In consideration of this potential malfunction, and as described previously, a backup control unit is supplied for the LTC. This feature significantly reduces the probability of a spurious, sustained high voltage condition that could result from a malfunction of the LTC controller as described above, since such a condition would have to involve a failure of both the LTC controller and the backup controller.
_ _ - _ _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ __ -__,.___m__._____ _ _ _ J
l o
o Attachment 2 to U.602983 LS-98-008 Page 5 of 9 Other LTC failure modes or malfunctions that could lead to an overvoltage condition are
~ those identified in Attachment 3 that result in the tap changer failing to change the tap setting when expected, i.e., the tap setting remains "as is." This can result from a failure of the controller when the LTC is operating in the automatic mode, or from a failure of the drive motor within the LTC (including a loss of power to the drive motor) when the LTC is operating in either the automatic or manual mode. In either case, an overvoltage (or undervoltage) condition could be created if grid voltage changed subsequent to the failure.
For example, if the failure occurred during the afternoon of a day when high summer load demand existed, a high tap setting could lead to a high voltage condition later that evening when load demand diminishes and grid voltage increases. In such cases, however, the
! condition would evolve relatively slowly, the magnitude of the resultant change in voltage would be limited to what the change in grid voltage produced, and operators could take action to mitigate or correct the condition, including monitoring voltage to determine whether any further action is required. In the case of a controller failure, an operator could place the LTC in the manual mode and change the tap settino,if required. In the case of a drive motor failure, an operator can use the hand crank to mechanically the change the tap setting if required.
Of the various failure modes identified in Attachment 3, the above fail-as-is failure modes (i.e., wherein the tap changer fails to change the tap setting on demand) are the most likely, compared to the controller failure that causes the tap setting to be run up (or down) to an undesirable setting. This is consistent with the results obtained from an informal survey conducted by IP of various utilities employing LTCs at their nuclear power plants.
The survey revealed no reported instances of an LTC controller spuriously running voltage to an extreme value. Instances of LTCs failing "as-is" (as described above) were reported, but in many cases, either voltage did not reach levels that demanded immediate action, or operator action was able to be taken to mitigate the situation. There were no reported instances of equipment failures resulting from LTC failure.
Thus, of the evaluated LTC failure modes most likely to occur (i.e., the fail-as-is type),
such failure modes are casily mitigated, slowly evolving, and/or their consequences are minimal. On the other hand, for the failure mode potentially yielding the greatest change in voltage (i.e., the controller failure resulting in an unwanted extreme tap setting), such a failure is the least likely to occur. Regardless, even for this type of failure, the degree of voltage change would be limited, as determined by such factors as the existing grid. voltage and the operating limits of the LTC. The point at which equipment damage would occur is difficult to determine. In general, however, overvoltage is considered to be a long-term equipment degradation condition and not usually an immediate equipment failure condition. In the PRA evaluation that follows, the overvoltage condition resulting from LTC failure is conservatively treated as a condition that may lead to equipment damage with a certain degree of probability.
Attachment 2 to U 602983 LS-98-008 Page 6 of 9 PRA Evaluation - 1
'As noted previously, the scope of the evaluation performed for the ERAT LTC is limited to plant shutdown conditions. During such conditions, the probability of occurrence of an l
accident like a DBA LOCA is greatly reduced. . As stated in the TS Bases for TS 3.8.2, wherein the basis for reduced requirements during shutdown is described, "...Many design basis accidents that are analyzed in MODES 1,2, and 3 have no specific analyses in MODES 4 and 5 because the energy contained within the reactor pressure boundary, reactor coolant temperature and pressure, and the corresponding stresses result in the probabilities of occurrence being significantly reduced or eliminated, and minimal consequences." Events of most concern with respect to the reactor during shutdown conditions are those involving, or which could lead to, a loss of core decay heat removal.
To evaluate plant risk with respect to the ERAT LTC modification, IP has performed a probabilistic risk assessment (PRA) of the plant configuration with the ERAT LTC in place'and with the plant in a shutdown condition. The analysis includes the probability of occurrence for an ERAT LTC failure that can result in damage to safety equipment, including the safety-related decay heat removal systems, with a subsequent probability of r _ failure to employ alternate decay heat removal capability, followed by fuel damage.
Although the P.RA assumes a low decay heat load (consistent with the current, extended plant shutdown), conservative assumptions include the following:
L (1) Operating / reliability data from the vendor was used to support a reasonable estimate for the probability of a malfunction of the LTC that causes overvoltage.
Specifically, for a population of LTCs constituting approximately 2000 service years, the vendor reported no LTC failures requiring the associated transformer to be de-energized. IP conservatively assumed one failure for this population with a 50% chance that the failure produces a significant overvoltage condition.
(t r.,ause an overvoltage condition would not be expected to cause immediate L quipment failure, and because some of the plant safety systems or equipment would be in a standby status, i.e., not connected to the bus at the time of the overvoltage condition, a 20% success probability was assigned to operator action to detect and correct overvoltage condition before equipment damage.
Based on ths PRA, the probability of an event involving an LTC malfunction that leads to
. safety-relhted equipment damage due to overvoltage, including the loss of decay heat removal capability, and which culminates in fuel damage, is conservatively evaluated as 4
2 x 10 per year.
- f. This probability has been determined to be acceptable for supporting the ERAT LTC b modification. In consideration of this result, and in consideration of the plant being in a
- shutdown condition (for which the probability of many design basis events and conditions is reduced), IP believes that the proposed change (i.e., the modification and associated
[.
change to the CPS USAR) is justified, particularly in light of the safety benefit to be
~
l gamed by the voltage support capability provided by the ER . I LTC. Further, although
Attachment 2 to U-602983 LS-98-008 Page 7 of 9 IP determined that the proposed change involves an unreviewed safety question based on introducing the possibility of a new malfunction not previously evaluated, IP does not believe that the proposed change introduces the possibility of a new accident not previously evaluated. This conclusion, too, is based on the PRA result concurrent with the plant being in a shutdown condition.
Evaluation for Mcnual Operation of the ERAT LTC The above evaluation of the ERAT LTC is focused on the ERAT LTC operating in the automatic mode, i.e., with the LTC tap changer being automatically controlled by the associated controller. This mode of operation was addressed in particular because of the potential for the controller to fail in a manner that could cause the tap changer to run voltage up (or down) to unacceptable levels. Consideration of this failure mode constituted the basis for the unreviewed safety question. Accordingly, the provisions or limitations imposed on or by IP's evaluation of the ERAT LTC are based on automatic operation of the LTC.
As noted previously (and in the cover letter), however, the ERAT LTC may also be operated manually. In this mode, the LTC is released from control of the associated controller, and is not subject to the potential for voltage to be run up (or down) to unacceptable levels in an uncontrolled manner due to controller failure. (With regard to the potential for misoperation of the tap changer during manual operation of the LTC, tap changes performed locally and manually by plant personnel will be controlled in accordance with prepared and approved plant procedures.) For manual operation,
- therefore, the limitations imposed on or by the evaluation for automatic operation of the ERAT LTC do not apply, and any changes related thereto will be evaluated per 10CFR50.59, as required. For example, operation of the ERAT LTC in the manual mode would not be restricted to the plant being in a shutdown configuration. This includes, upon NRC approval of the proposed license amendment for use of the SVCs, operation of the ERAT LTC (in the manual mode) in conjunction with the SVCs, during which the plant may be in operation or in a shutdown condition.
Evaluation for Significant Hazards Consideration P In accordance with 10CFR 50.92, a proposed change to the operating license involves no significant hazards consideration if operation of the facility in accordance with the proposed change would not: (1) involve a significant increase in the probability or consequences of any accident previously evaluated, (2) create the possibility of a new or L different kind of accident from any accident previously evaluated, or (3) involve a significant reduction in a margin of safety. The proposed change, i.e., the proposed modification to replace the ERAT with an LTC, and associated changes proposed for the CPS USAR, is evaluated against each of these criteria below:
I
~
4 Attachment 2 to U-602983 LS-98 008 Page 8 of 9 (1) Installation of the new ERAT with automatic LTC capability (and increased capacity) will support operability of the 138-kV source for CPS, thus maintaining at least one operable source of offsite electrical power in accordance with Technical Specification 3.8.2. The voltage support provided by the new ERAT LTC will also minimize the probability of a transfer to the onsite emergency diesel generator (s) in the event of high plant load (including a real or inadvertent actuation ofESF systems). These positive effects from the voltage regulation provided by the ERAT LTC support operation of safety systems required for decay heat removal and maintaining the plant in a safe condition, as well as may be required for mitigation of accidents that could occur during plant shutdown conditions.
At the same time, (and as further addressed below) employment of the ERAT LTC introduces the possibility of a new malfunction that could cause plant equipment important to safety to be subjected to overvoltage. However, since the ERAT LTC incorporates a primary and backup means of preventing voltage extremes (high or low), the potential for damage to plant equipment (or an unnecessary trip of the undervoltage relays) is low. The PRA performed for this potential overvoltage condition, under plant shutdown conditions, showed that an event involving overvoltage caused by LTC/LTC-controller failure and which leads to equipment failure and subsequent fuel damage, is not credible.
L On the basis of the PRA evaluation, and in consideration of the safety benefit associated with the voltage support provided by the ERAT LTC, IP believes that employment of the ERAT LTC during plant shutdown conditions has no significant b adverse impact to plant safety systems. Therefore, the proposed does not involve a significant increase in the probability or consequences of any accident previously evaluated.
(2) In consideration of the potential adverse impacts that the ERAT LTC may have on plant systems, structures or components, such impacts are primarily confined to potential electrical faults or abnormal conditions. With respect to potential adverse !
electrical impacts, the potential electrical failure modes or abnormal conditions applicable to the ERAT LTC mainly include the same failure modes or conditions that applied to the ERAT as a fixed-tap transformer, except for the potential malfunction of the LTC controller that could cause voltage to be run up or down to excessively high or low values. As noted previously, however, this potential is greatly reduced by the backup controller provided with the ERAT LTC (For an undervoltage condition, plant equipment would be additionally protected by the plant safety bus degraded voltage relays.
c l
l
_ - . _ - _ _ _ _ - _ _ - - _ _ _ _ _ _ _ _ - _ _ _ - _ . - _ _ _ _ = _ _ - -
i4- Attachment 2 to U-602983 LS-98-008 Page 9 of 9 With respect to a potential LTC malfunction that may cause an overvoltage condition, further evaluation by PRA (for plant shutdown conditions) has shown that the probability of an event involving an LTC malfunction that causes an overvoltage condition leading to damage of safety-related equipment and subsequent fuel damage is 2 x 10#per year. This makes such an event incredible. Further, the potential for overvoltage from an LTC malfunction to lead to a new or unanalyzed accident is reduced by the plant being in a shutdown condition, as previously described.
Thus, although the use of the ERAT LTC introduces the possibility of a new equipment malfunction not previously evaluated, based on the above, it does not -
introduce the possibility of a new or different accident not previously evaluated.
(3) As noted previously, incorporation of the ERAT LTC into the CPS auxiliary power system will regulate plant bus voltage for the 138-kV offsite source. As such, the ERAT LTC will compensate for reduced margin that has occurred or may occur in the near term (especially during peak summer load demand), with respect to the difference between the voltage required for plant safety loads and the minimum expected offsite vohage. The ERAT LTC also has a significantly higher load capacity than the current ERAT, thus further enhancing the capability and capacity of the 138-kV offsite source.. This increased margin also reduces the probability of a transfer to the' diesel generator (s) (that are intended to be an emergency electric power source) in the event of high plant load with low offsite source voltage.
Based on the above, and with respect to voltage requirements for plant loads the proposed ERAT replacement does not involve a significant reduction in the margin ofsafety.
In summary, based on evaluation of each of the above criteria, IP has concluded that the proposed change, i.e., the ERAT LTC modification and associated changes to the CPS USAR, does not involve significant hazards consideration.
S
-- __ m________________a
3 3
= 8 8 2 d e 9 a d o h=0@i n 2 T T l
c 68 9 s r
= U S p t
n e
g A A t
e r R R AtoLh l a E E m s t t m a n e
n e
o h r r
r r
C T u u A c c s
Ry s Ei tc a a e e wa e p m a
m a
Nc a S S d d a a s l o l o
e r r t
a fe f e
l o s s s n n i a a e
s n t r t r
n o oec oec o
p i
t t r
t r
a c
e t
n o o u n ou os s
R o r r i
t s i t
i s pe c e c e y at at l
a da rm r a r a n s onr onr A e r l oof t a e t a e 3 u r s e
r t el a r t el a v n t e l p p n r i a a e
m l
i u F Ot r Ot o Ot o h
a c F r a C e t
t T m r
A L fo t t T s u p
u p
n e A a r g t
u t
u R T a o o E t lt r r c o e e a
p v m m t r r m u p fo f o
I t s s u n n o ar a
r t t d f f e o o c
u s s d s s e o o R L L n
r n i t
e i s r e m t
r g ogs r r o hi on hs n u f sd d dn i
l i s n a n ei ni F t a
r h r s
a w uw o
r r pe ge m - -
r d e- ao t o mr t o mr t
ef
- o - o ef gl r s s s s n e a n a n ov L o h ar Pt h ar Pt
[i iI '
3 k- k- -
3 6 t
6 n8 0f e9 3 2 6 1
6 1 1 1 m6 0 o 2
hc -68 2 4 4 4 4 n
s n n n 9 e t o o o o tau S- ag t n e t t t t c
At3 LP c c c a a m a p
a p p p m m m m m o i i i i C e s
e s
e s
e s
r r r r e e e e v s v s v s v s d e d e d a se da es a s a s s o su o su o su o Nb Nb Nb Nb u s
e r e to d s
s d s n l
s e n u s l oy ri e rk n iB r a r ona r i
a a( t l n e to C yi ul t
i u
q nTla qe in r t t i i n a o n .
i n a one
.l s cor e oLur o c e r e
s miit mie ut t i p ga mec nf ai mlau f i n
o r e s r id s o a mg o na g p o p le ptoo kl c o t l npoi n t n
s l
l op l
o pd b a v r or oet e t t on m tt i e r a r a ef e i it e e s R t nt t
nt r ri d n t
c/d d op s c s oe oe e s a n aU p cl b
clb sf rodu ro a mta r o .e te a
s pa pa nt el e t e utpraa r an t
a r agaug a g r
u k ut p k et r a gn pl an a n e c c et e nls )p et a c re ei l c c pl a i
a o F
a Ba c Ba a gf t a r i
Ovmh c Ov o h c
C T r e L r e og og e ( at ( a e g el e r el t e r
g a go go u a l t
a vl i u a v i l t
o l t
oifd a l
t d a t lo v oi f c
a vr r
e vrg g v r gr g p e d r
ef i n ef n n
i v vi I
m o u viw o) e o o) e w o e e s
e gl s
l eg s
l l
s u u ut af o ut af o a
c n o a no al c ve os al c o se c i d rv g i
t di t Ji d r g d d l e an l e n u n l
t n ud ud a Cc o o Cc oo Cuc o nh Cu o n hc o g t
i n
g s ng o n nn n o r ai su "s it ti ioi t
t t
i t o c s ct e c e c ( )t a n s n s n "s s s" up fup f ui- s l
on e f a l ial i latr a a s a l
r a ta f u med med m"g ororem ri l
e r s e wde r i
a r t le id a le e n ot F l o
r r e on e l l o
r on o e l
l ot r e i
t moo e mtg s
t nso t
t t t n so t t
n p v on ot pn c ot c pn o ct a i
r t d r t i
t mn mn e e s Ce Tt h e Ce Tt h e Cp Te e Cw To p t a L a w t La w ' k Lpt l
Attachment 4 to U<>02983 LS-98-008
' 8' I of X Attachment 4 Proposed Changes to CPS USAR
ll 1!li ll
')
- ^
x . , . . ,
NT
. OR i'!f- fLp I O S TPE E pQ. met'N
+ R
' N AR U t/, x T S T C
d - / D SIS U l~ g .
.'i r
~
e t x\ ('.
x \. "
R Y 3-L A 21 EN1TE R
T S
4y-
' t
. N
.- g -\Y O e ~ .
WAYRE E I T
OTUH _
f' [O - O \
\
\
y s
PE F IG S T A
S-ky: !g
{j tgT 7
-l
.l7j L, (i, ( \
l NS AF L P
A OD I C
=
t-
,l
\
}
g.. TET NA N
I R
P LPD I
il'
= j! - ; "
e
- CU
%N .I ks 4l o*
s/,
n o
e r.
] L m E" .
] aG p s
a
/ m".- .-
~ _
- E w
/. m"*.. ~
wO
=
=
m .
~
N f+"'x~
~ - w a,, S" ., =_
m
~ _ ' e .
c u .
s n '"
~ 7J~ 9 J_ "'
- s. . .
r e
I f _ _.
e, m
N m
O
=. I T
A
- i ' - -
1 f= '
x ./ M I
E l
4-
.1 a-
._7 i
n E k' k- ,
/n C
N E
F E
C N
A S
0/
- 1
" 2 _
h[._- . I
- . U I
= w, l"1_
=i sc __
y gp, c
M f
_ d[O;:
/'
N R
O F
- ti ' 3 \ 2 _
. {l, ~ ( T b
_E -F E f.wlT
- ! , ilji ig \ E f
i S
,T - M - .
_ ~
3
)= . ~
,.' . 2 t
E N R U
G
~ s-I F
i E
E S
~
_'_l . ' l E r,
- ~ T
- .~ , ';/ O N
g=g
= ' - .
= _
,m"~ ,2,. f' /
-q f
A'~i f,~, - 'p -
./
m u_\ '.,t33h ub ~
- jM._Am.s.U'-
/ l yW:,.
- . '/ -
C= =
3~..
[
.%Wj._n.gg'.
y_.
[
' / -
- m _
6s
/.
up jd _.
$ e]{:yvs%!l%9,js3_i r' ,p.M*,p.f. 5 3i \ f f _
\ )g'"
, .I ,
I 7 '
- .fI I
.[ .l\
fg*MWk-
- u
/ N e/ /.'",'.! -
/
r 1f\ s 8 '
. , P v ._ I~ t *
' 'g u M a.s R_ $ :,'t. hV, /j
, ,. - ~ , //
l,llllll l1l
CPS-USAR Revision 7
- May 1997
- c. 6900-V switchgear 1A and IB,
\
- d. 4160-V switchgdar 1A and 1B, 's
- e. 480-V unit substations,
~
- f. 4.80-V motor control centers, 9 480/277-V lighting distribution cabinets, and
- h. uninterruptible power supplies 1A and 1B.
The primary 6900- and 4160-V power sources for the unit auxiliary a-c power system are the two UAT's associated with the unit. Each UAT is rated 22.4/29.9/37.4 OA/FA/FA, 650C rise.
Each UAT is nominally sized to carry one-half of the full-load requirements of the unit. Each UAT is connected by cable to the main generator bus duct. The cable'is sized to carry the full load of the transformer winding to which it is connected.
l The main power transformer bank is rated 1041 MVA, FOA, 650C rise. Maximum loading supplied to the Main Power Transformer bank is below the rated value. . Loading is administratively limited to 1041 MVA when unit auxiliary transformer loading is reduced due to transferring of unit auxiliary buses.
l The secondary source of power for the unit auxiliary aec power system is the RAT. For cycle 7 operations, the Reserve .)
Auxiliary Transformer will be the normal power source for the unit auxiliary 4.16 kV loads to ensure proper voltage levels are maintained on the Class 1E a-c distribution system when it is being supplied by the Reserve Auxiliary Transformer. The RAT is rated 38/50.7/63.4 MVA OA/FA/FOA, 650C rise. The RAT is sized to carry the startup load of the unit in addition to the total coincidental-LOCA load of the unit. The RAT is connected to the i 345-kV switchyard by an overhead transmission line.
Both the UAT's and RAT are connected to 4.16- and 6.9-kV switchgear by bus duct. The main bus duct connections to the 4.16- and 6.9-kV windings of the transformers are sized to carry the full load of the transformer windings. Each branch connection from the main bus duct to 4160- and 6900-V switchgear is sized to carry a load equal to the maximum switchgear continuous rating.
-emeatg to rienseyty. fed bus M Men W mr
- The Emerge racy Reserve Auxiliary Transformer (ERAT) secondary l
' leads aredunderground in a concrete encased duct run deesn-Mae l
+eenefemee to the Control Building termination for the nonsegregated bus connection, which then distributes to the j
- Class 1B buses, the main run being located in the Control and i Auxiliary Buildings. The Reserve Auxiliary Transformer
- secondary leads are outdoor and indoor nonsegregated buses which distribute to the Class 18 and non-Class 1E buses, and main , !
indoor run being located in the Turbine and Radwaste Buildings. ' l The Generator Main Transformer connections are Isolated Phase 8'.3-2.
- y. NE I
T
/
LA CD P u
1 T [- 1 3,
8 G
// P ~p g
3V dN _ZN XF
.. - E 1- US E I
b Tmu AN S..A S
SLO p G& AT t
CS wD F' U t i
- > . {, N L L - I A : T A R i
f N N
A C
L B
A C
Y a C mV( cv OC y
Y C A R A E R O R L P F P E S S -
C,r r
}O -
r >
I p ,
1 l
,,Il , l Y.
i E
C. @ h i)
C Nx EuF GAS TM I
R M R .N )C -
SE L B
P c
o P
O O
E 5A T -
FT L D'D MER RT (L t '
FY dCSm I
V V C k k E
E OS L E
2 1
1 1
VR * -
V 3 s _O( $m KE -
. e
- d SW S >O 4 [d r l e
w
' CPS-USAR Revision 7 e
May 1997 degraded voltage causing the 15-second time delay relay to time out, the system automatically trips the offsite sources causing lo'ad shedding and the " slow" transfer to the onsite power s source. )
All undervoltage, time delay and auxiliary relays used in the scheme are qualified for Class 1E use and are located at the respective Class 1E 4160 V buses.
A voltmeter in the control room piloted from the same set of potential transformers as the second level undervoltage relays allows the control room operator to determine the undervoltage sensing PT's voltage output during power operation.
Test switches allow the relay operation to be verified during full power operation. This is accomplished by opening the test switches or lifting a lead and observing that the relay operates on loss of voltage. Since all undervoltage relays on the bus are required to operate before automatic transfer is initiated, testing of one relay will not cause spurious tradsfer of the system operation.
to the onsite source during the relay check during power There are no bypasses incorporated in the design, consequently, no bypass annunciation is'provided in the control room. CPS Technical Specifications include.the information concerning limiting conditions for operations, surveillance requirements, and pickup and dropout allowable values for the second-level voltage protection sensors and associated time delay devices )
required by STS as applicable to Clinton. The pickup trip and dropout setpoints with maximum and minimum limits are in the Operational Requirements Manual (ORM).
The starting time of the largest 1E motor, with offsite voltage at the minimum expected value, is approximately 10 seconds or less. Based on this information, the timer is set at 15 seconds. Motor starting time has been verified. After this timer has timed out, the loads will automatically transfer to the onsite power source. Instrumentation and controls will not be damaged by this degraded voltage for this short time period.
The basis for establishing the setpoints of these relays is to select a voltage high enough at the 4160 V level to ensure all Class 1E equipment down to the 120-V level will start and continue to operate properly while minimizing the possibility of spurious transfer to the diesel generators.
The minimum expected voltages at the 4160 V level were determined by a voltage analysis that determined the voltage levels at the 1460-V and 480-V Class 1E buses for maximum and minimum level conditions expected for the anticipated voltage range of the offsite sources. The optimum tap settings of the Emergency neccrve .'.=iliary Transformer (ERAT) and Lim Reserve l j
Auxiliary Transformer (RAT) were found to be 9%"1fff8 + 2-1/2%.
recpectivcip.
WuS )
- '> [n se.rt 6.N.c hed 8.3-6
_ _ _ _ _ _ _ _ l
2 (Add to bottom of page 8.3-6)
The ERAT has on-load tap changing capability. That is, the number of effective primary windings can be varied over a range of 1.06 pu to 0.81 pu by a load tap changer (LTC) mounted on the ERAT to provide a consistent 4160-V output.
The LTC can be operated in a manual or automatic mode. In the manual mode, an operator can make tap changes locally at the ERAT, and may be made with the ERAT in service. In the automatic mode, a controller in the LTC raises or lowers the tap setting in response to grid voltage. A backup controller provides oversight of the primary controller, preventing tap movement above or below prescribed setpoints.
j
,+ , ,
- IS/n/30 MA dl/FAlfM&S *C ItEVISION 7 - -
1 an,, g,g,.,, APIllL 1997 i
, um O K) b' i A=i=I7M 5% E-~ =43 72.._ _
- I'~~~~j7771 il 4C =aC m ;--
) I!! .! N,. f
... ,_ , _ - m .,.-
J_ s -~ , I
} A e ,,_ , , {A g ,' ,, its
.L . ..m-H. 4 ,{t 4
[ h di * ;li illiIlP -- ckh=h 11I il~ - kE@ i.$~.5 ~* _I i Lt_t_t_ t f i i-I lh. l qigr,ia. =..= n lilh I !llI T_ IT[ j'jjli i)fgh -- j ( E52=L.-._ ;
- ll;!!!
_c=L' i
-t-t-t-t-t-t-t ^-t-t-t-t- (i -????**?"l
^
I i l $ !I J
,1 li 0: I L r,g:r.l.e.n=. =. _ __ _
g, . -i r ~ f, a I
..x.
=== 1 >'" a=rcT'_"
a.w 4 y] :::" = _f_t_t_f_t_t_t_t t_t-t_t-t !D . r d ". m a , l iiiiiiiii iiiii Lj-t_t-t-t-t t t t t-t t l!Il!kk ikik!! !I!I!!I ; j j
~\Eev X - . ._ ,
i - . _ . _ . _ . _ ! l i-t-t-t_i-f-f-f!
' N=be.: ' ijilil j!! Ig rg g> f,L IN T O N POWER STATIO N e $elll I h( !si a IDATED SAFETY AN Al.YSIS REPORT
~
g (.. . FIGURE 8.3-1 I[ ELECTRICAL LOADING DIAGRAM
----_a- -------_-- - - - -
r
*f.
E Attachment 5 to U-602983 LS-98-008 Page i of 3 l .,. Environmental Assessment i
Background
Clinton Power Station (CPS) was designed to have two "immediate access" sources of offsite power. These offsite sources are associated with the 345-kV and 138-kV offsite transmission systems. The 345-kV system provides power to the CPS auxiliary power system via the Reserve Auxiliary Transformer (RAT), and the 138-kV circuit provides power to the CPS auxiliary power system via the Emergency Reserve Auxiliary Transformer (ERAT). This design for the offsite power sources meets the requirements of l 10CFR50 Appendix A, GDC 17. The NRC's review, evaluation and acceptance of the design for the electric power system at CPS was documented in the CPS Safety Evaluation Report (NUREG 0853). l The offsite power system for CPS, like those for other electric utilities, has more recently experienced greater voltage extremes relative to the voltage limits established for CPS (
Reference:
IEIN 98-07). These variations in voltage are primarily the result ofload growth without the addition of new generation capacity. The observed offsite voltages can be low during periods of peak demand and high when demand is low. As a result, o CPS has identified a number of plant modifications that will control voltages provided to the onsite emergency loads from the offsite power sources. These modifications include the installation of 480/120-volt regulating transformers (to replace selected non-regulating type transformers within the auxiliary power system), replacement of the ERAT (and later, the RAT) with a load tap changer (LTC) transformer, and the addition of static VAR' compensators (SVCs) on the 4.16-kV side of the RAT and ERAT. These modifications are intended to restore and maintain compliance with the licensing basis for the CPS auxiliary power system. Replacement of the ERAT with its LTC was recently moved ahead ofits original schedule when it was determined that the SVCs, which were intended to be in installed and service prior to this summer, would not be ready for service until late summer or early fall. Immediate replacement of the ERAT with its LTC is therefore necessary to provide voltage support for CPS in anticipation of high summer load demand and the associated low grid voltages expected during such conditions. Need for the Proposed License Amendment CPS is currently in an extended shutdown period, and will remain in a shutdown condition throughout this summer. In anticipation of the need for voltage support during this summer, installation of the ERAT LTC will ensure continued operability of the 138-kV 4 electrical power source for CPS, thus maintaining continued compliance with the plant i I Technical Specifications which require one of the two offsite electrical power sources to be operable during plant shutdown conditions.
h a Attachment 5
/-
to U-602983 LS-98-008 Page 2 of 3 The ERAT LTC modification (and associated changes to the CPS Updated Safety Analysis Report) was determined to involve an unreviewed safety question. As such, NRC approval in the form of a license amendment [per 10CFR50.90 and 10CFR50.59(c)] is required prior to implementation.
- Environmental 1moacts of the Proposed Change Although the probability and/or consequences of an accident comparable to a design-basis loss-of-coolant accident are greatly reduced during plant shutdown conditions, a minimum l required number of safety systems, including those needed to support or provide reactor core decay heat removal, are still required to be operable or available to prevent or mitigate certain events or accidents that could occur during plant shutdown, notwithstanding their low probability. Such events could conceivably still lead to a radiological release. Supporting proper voltage to CPS safety-related plant loads supports proper operation of such loads, thus reducing the probability of a radiological release.
As noted previously, use of the ERAT LTC to regulate voltage at CPS from the offsite 138-kV transmission will enable CPS to maintain compliance with the Operating License (Technical Specifications) with regard to requirements that apply to the single offsite power source required during plant shutdown conditions. Noncompliance with such requirements, the probability of which would be significantly increased without replacing the current fixed-tap ERAT with an LTC, requires action to be taken to restore the offsite source to an operable status. Such actions may include interruption of power to ! customers to support the transmission system voltage, which can itself have adverse environmental and public safety impacts. With regard to non-radiological impacts, the new ERAT LTC design may reduce the ! potential for an environmental impact or non-radiological release resulting from a transformer oil fire. A much-improved, larger-capacity structure for containing oil,
- combustion products, and deluge water from the transformer fire protection system, which g may be released in the event of a transformer fault or fire, will be constructed for the new l ERAT LTC. This will reduce the potential for such substances to flow into Clinton lake in such an event.
Alternative to the Proposed Action The proposed amendment involves replacement of an existing power transformer with one having a larger capacity and load-tap changing capability, However, with respect to
. environmental impact, there is no significant difference. Other alternatives include -
changes to the offsite transmission system or the installation of additional or temporary generating capacity to locally support voltage. These options, some of which would not l
- resolve the immediate need for voltage suppoit at CPS, would all likely involve more
- j. < sigmficant impact to the environment. Given that there are no significant environmental O
~
)
L ]
.} ..
Attachment 5 to U-602983 LS-98 008 Page 3 of 3, effects ass'ociated with the proposed amendment, any alternatives to the proposed amendment would have no greater, favorable impact. With respect to NRC approval of the requested amendment, the principal alternative
- would be to deny the requested amendment. This would require IP to seek another means -
(as noted above) to provide voltage support for CPS. It is unlikely that any alternative to simple replacement of the ERAT would have a more favorable environmental impact, in light of the immediate, net safety benefit to be gained from the replacement. Alternative Use of Resources The proposed amendment to support replacement of the current ERAT with an LTC
~ involves the use of resources already used for the facility or within the f acility area. With respect to natural resources and the environment, the proposed change involves no significant additional impact. As noted above, alternatives to the ERAT LTC modification would have no greater favorable environmental impact and would likely involve a more extensive use of resources (materials or fuel, for example).
1 o
--- _-_.-___.__m_ . _ _ _ _ _ _ _ __ _}}