ML20118B681
| ML20118B681 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 09/29/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20118B680 | List: |
| References | |
| NUDOCS 9210060428 | |
| Download: ML20118B681 (6) | |
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t, e... + f SAFETY EVALUATION BY THE OFFIIE.0E. WCLEAR REACTOR REfUL ATION MLAl[Q_.lg AMENDMENT NO. 64 TO FAClllTY OPERATING LICENSE NO. NPF-47 GULF STATES UTILITIES COMPANY MyER BEND STATION. " NIT 1 DQGKET NO. 50-458 1.0.1ERODRCll0B The reliability of diesel generators (DGs) to start and load safety-related equipment following an accident has been a long-term concern to the staff.
The reliability of DGs during normal plant operation is demonstrated by surveillance testing required by the plant's te.hnical specifications. The frequency of such testing is based on past performance with increased testing required to demonstrate continued reliability when test failures occur.
In addition to these normal surveillance tests, technical specifications also require testing DGs whenever an offsite power source is lost or if a DG is declared inoperable for a reador other than preplanned preventive maintenance.
The purpose of the latter testing is to verify that there is no common mode problem that could affect the remaining DGs and to provide additional assurance that the DCs are, in f act, operable during those conditions when they might be called upon.
While the additional testing described above provides assurance that the DGs are operable, the demands of testing causes additional wear on the diesel l
components. Operational experience has shown that technical specifications have required DGs to be tested when there was clearly no reason to believe that common mode failure was a possibility.
Such testing that does not contribute to improved DG reliability is considered excessive.
Excessive testing is detrimental to the mechanical coinponents in that it could contribute to an overall reduction in the reliability of the diesel to start and perform its intended function.
Past efforts have been taken to reduce or eliminate unnecessary DG testing, in July 1984, the staff issued Generic Letter 84-15. " Proposed Staff Actions to Improve and Haintain Diesel Generator Reliability," in order to improve and maintain DG reliability. One of the principal obje:tives of this generic letter was to reduce the number of DG " fast starts" which the staff had determined results in premature diesel engine degradation. Other DG start tests were also targeted for reduction on the basis that excessive testing results in degradation of diesel engines.
The recommendations of Generic letter 84-15 regarding testing of the DGs have previously been incorporated into the River Bend Technical Specifications.
By letter dated May 2, 1989, Gulf States Utilities Company (GSU), requested an amendment to Facility Operating License No. NPF-47 for the River Bend Station, Unit 1.
The proposed amendment inclutied revisions to the action statements for Specification 9210060420 920929
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r 3/4.8.1, "AC SOURCES - OPERATING." The net result of these proposed changes l
would be a reduction in the amount of DC testing and the elimination of unnecessary plant shutdowns.
Specifically, the proposed changes are as follows:
1)
Current technical specifications require that if a DG is inoperable due to any cause other than preplanned oreventive maintenance, the remaining DG must be started and loaded to demonstrate operability.
In lieu of starting and loading the remaining DG, GSU has proposed adding a provi ion to 3110w verification that the cause of the DG being inoperable does not impact the operability of the remaining DG. Thus, the licensee will be demonstrating that-the potential for a common mode failure does not exist.
2)
As discussed above, declaring a DG inoperable due to " preplanned preventive maintenance" does not require an operability test of the remaining DG.
GSU has proposed deletty the word " preventive" in order to permit corrective maintenance on a DG without needing to demonstrate operability on the remaining DG.
3)
Current technical specifications require starting and loading the DGs if one or both of the required offsite power supplies become inoperable.
GSU has proposed deleting this requirement.
4)
Current techni al specifications require that if a DG becomes inoperable, all equipment that is povered by the remaining DG must be verified as operable within two hours or plant shutdown must commence.
GSU has identified co' ditions wnere the individual equipment technical n
specification is not as conservative and may allow continued plant operation with both trains of equipment inoperable.
Therefore, the licensee has proposed an option of declaring both trains of equipment inoperable and following the associated action statement of the individual component.
2.0 EVALUATION item 1 - Demonstrating the Absence of Common Mode failures
- Specification 3.8.
.1, Actions b, c, d and g The current River Bend Station Tecnnical Specifications require all operable l
DGs to be started and loaded to cffsite power to demonstrate their operability in the event a DG becomes inoperable due to any cause other than preplanned preventive maintenance or testing. The intent of this additional testing is, in part, to determine if a common mode failure exists and, in part, to provide l
added assurance that the remaining operable DGs are capable of supplying i
emergency power.
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GSU has proposed a change to allow for verification that the cause of the DG being inoperable does not impact the operability of the remaining DGs.
This would determine the potential for common mode failure without causing unnecessary testing of the operable DGs.
The normal technical specification surveillance testing schedule demonstrates acceptable reliability and assures that the DGs are capable of performing their intended safety function.
The staff agrees that, once the potential for common mode failure has been examined and dismissed, testing beyond the normal surveillance schedule described above is excessive and does not contribute to improved DG reliability. Therefore, since the proposed change will allow for verification that the cause of the DG being inoperable does not impact the operability of the remaining DGs and will result in the elimination of cnnecessary testing, the staff finds this proposed change acceptable.
For those situations when a DG is declared inoperable and a common mode failure cannot be ruled out, GSU has proposed that the remaining DGs be started but not loaded.
This is a change to the current River Bend Station technical specifications which require running the DGs fully loaded for a period of not less than 60 minutes. While the successful start of a DG does not ensure successful loading, IE Information Notice 84M and Supplement 1,
" Operation of Emergency Diesel Generators," alerted lic osees that when a DG is operated connected to offsite or nonvital loads, the emergency power is not independent of disturbances on the nonvital and offsite power systems that can adversely affect emergency power availability. At a time when at least one DG is inoperible, the action statements increase the potential for a station bla-kout condition.
In a letter to GSU dated January 14, 1988, the staff recommended that the loading requirements of Specification 3.8.1.1, Actions b, c, d and g be eliminatad. Therefore, based on the staff's Information Notice and previous recommendation, this change is found acceptable.
The staff notes that in GSU's letter of May 2, 1989, they indicated that although the revised action statements will eliminate the requirement for DG loading in the technical specifications, GSU will continue to maintain a requirement to load the DGs whenever they are started, for a period of time s
(less than 60 minwtesi adequate to precluoc buildup of carbon deposits. The rationale that they pn, vide for voluntarily #ntaining this requirement outside technical specifications is that th y b lieve it is undesirable to start and not load the DGs as this can cause A formation of carbon deposits in the cylinders.
This is also in agreement with the DG manufacturer's recommendations.
The staff finds these provisions acceptable because, by not having a technical specification action statement to always load the DGs, an operator will have more flexibility to determine whether or not to load the DGs based on existing conditions and ultimate plant safety. For example, if the remaining onsite power sourcu are available and there are no conditions expected that would cause perturbations or jeopardize the availability of the offsite sources, the operator may choose to load the DG that is required to be started in order to p aclude the buildup of carbon deposits and maintain a high level of DG reliability. On the other hand, if the remaining onsite power sources are not available and there are conditions that might cause grid perturbations or jeopardize the availability of the offsite sources, the
operator could choose not to load a DG that is required to be started but rather choose to load it at a later time to burn off carbon deposits when the onsite power source availability at;d grid situation improves.
Item 2 - Deletion of " preventive" from " preplanned preventive maintenance" Specification 3.8.1.1., Actions b, c and d The current technical specifications require all operable DGs to be started and loaded to offsite power to demonstrate their operability in the event any DG becomes inoparable due to any cause other than preplanneo preventive maintenance.
The intent of this exclusion is to require additional testing only in those cases where a potential for a common mode failure exists or the reliability of the onsite AC sources is reduced.
GSU has proposed deleting the word " preventive" from the phrase " preplanned preventive saintenance.".GSU has taken the position that the specification, as currently worded, requires testing of the remaining DGs whenever
" corrective" maintenance is being performed.
Corrective maintenance is considered to be work that can be delayed witho'it the DG being declared inoperable and that the condition requiring corrective maintenance has not prevented the DG from performing its intended function.
The staff notes that the revised wording of Actions b, c and d, as discussed in item 1 above, requires that verification be made that the cause of a DG being inoperable does not impact the operability of the remaining DGs.
This eliminates the staff's concerns of corrective maintenance masking any potential :ommon mode failures.
In addition, the staff notes GSU's commitn.ent which states that, if during the performance of preplanned maintenance it is discovered that the DG is in fact inoperable and requires corrective maintenance to restore it to operable status, the operability of the remaining DGs would then be required to be demonstrated. With these assurances, the staff finds the proposed change acceptable.
1 Item 3 - Deletion of DG testing following an inoperable offsite AC source
- Specification 3.8.1.1, Actions a and f l
The current technical specificationt require operable DGs to be started and loaded to offsite power to demonstrate their operability in the event that one or both offsite.AC sources become inoperable.
The intent of this additional 19 sting is to provide added assurance that the operable DGs are capable of t,upplying emergency power when the offsite AC souices are abnormally degraded.
At the River Bend Station, loss of an offsite AC power source will l
automatically start the associated DG, As previously discussed, IE Information Notice 84-69 alerted licensees against loading a DG to a potentially unstable offsite grid. To require the remaining DGs to be started and loaded to offsite powar increases the risk of losing all AC power to their safety buses causing station blackout. Therefore, DG availability is potentially lessened by a demonstration requiring connection of the DGs to offsite sources when the offsite sources are abnormally degraded.
GSU has proposed to delete the requirement to start and load DGs when an offsite AC source becomes inoperable. As previously discussed, the staff considers the normal technical specification surveillance testing sufficient to demonstrate acceptable reliability and assurance that the DGs are capable of performing their intended function. Therefore, this testing is considered excessive and should be eliminated.
The staff agrees that loss of an offsite
.AC power supply does not imply any loss of DG reliability or common mode failure.
Based on the above, the staff finds the licensee's propost) to eliminate this testing acceptable.
See item 1 for the staff's evaluation of GSU's voluntary requirement to load the DGs whenever they are started.
Item 4 - Verification of operability of required equipment
- Specification 3.8.1.1, Action e The current technical specifications require that, within two hours of the Division I or 11 DG becoming inoperable, all required systems, subsystems, trains, components and devices that depend on the remaining DG as a source of emergency power be verified operable.
If this condition cannot be met, actions must be taken to begin plant shutdown.
The intent of this item is to provide assurance that a loss of offsite power, concurrent with the loss of a DG, will not result in a complete loss of safety function of essential systems.
eSU has identified a number of non-safety related and non-redundant systems / components that are powered by emergency DGs but do not represent essential safety functions. Additionally, there are systems / components that are supplied amergency power by the DGs that do not have technical specification operability requirements and are not necessary for safe shutdown of the facility.
However, at the River Bend Station, if such a system / component was inoperable concurrent with the opposite train DG, a plant shutdown would be required.
The relative significance of the inoperability of the systems / components can be judged from the associated action statement when both trains of equipment are inoperable.
GSU has identified action statements that permit contir.ued plant operation with both trains of equipment inoperable. An example being the fuel building radiation monitors.
If both monitors are inoperable, the action statement for the individual specification allows for continued plant operation contingent on grab samples being taken.
However, under these same conditions, Action e of Specification 3.8.1.1 would require an unnecessary plant shutdown.
GSU has proposed that Action e be modified such that the option is available to declare inoperable the redundant systems / components served by the l
inoperable DG and take the action required by the associated specification.
This will only apply when the action statement permits continued plant i
operation for greater than 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> but not more than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> as this is the maximum time permitted to operate with an inoperable DG, GSU is also addinc the word " redundant" to those systems / components served by a C9-to avoid tb se j
situations when a non-essential system / component is powered by a DG.
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l The staff notes that the proposed revisions to Action e will provide the same degree of safety for those significant critical systems while allowing the operational flexibility intended for less cri+.ical emergency powered systems / components.
The staff also agrees that the current action requirements for the affected equipment should determine if an immediate plant shutdown should be initiated since they hav: been established to support safe operation based upon the effect of the less of the equipment's safety function.
In addition, if the action requirement for both redundant systems / components inoperable is 1, ; than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, the licensee has comitted to follow the requirements of Action e or the action requirements for both redundant systems / components.
The staff finds the proposed actions to be consistent with the intended level of safety as described in the-technical specificatior-for the affected equipment and, therefore, acceptable.
3.0 STATE CONSULTAT103 In accordance with the Commission's regulations, the Louisiana State official was notified of the proposed issuance of the amendment.
The state official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR 20 and changes surveillance requirements.
The NRC staff has determined that the amendment involves no significant increase in the amoLnts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (57 FR 37568).
Accordingly, the amendment meets the eligibility criteria fer categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant ta 10 CFR 51.22(b) ro environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
5.0 CONCLUSION
t The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonabic assurance that the health and-safety of the public will not be endangered by operation in tha oroposed manner, (2) such activities will be conducted in compliance with tb, Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: Douglas V. Pickett, PDIV-2, NRR Date:
September 29, 1992 T
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