ML15117A352
| ML15117A352 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 07/09/1996 |
| From: | Labarge D NRC (Affiliation Not Assigned) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-M86217, TAC-M86218, TAC-M86219, TAC-M93550, TAC-M96218, NUDOCS 9607100109 | |
| Download: ML15117A352 (13) | |
Text
7994 NOTE TO:
Docket Control Desk FROM:
David E. LaBarge, Senior Project Manae Project Directorate 11-2 Division of Reactor Projects -
I/II
SUBJECT:
CHART OF UNRESOLVED ITEMS RELATED TO OCONEE NUCLEAR STATION DRAFT ELECTRICAL REPORT WRITTEN BY NRR (TAC NOS. M86217, M96218, M86219, M93550)
Please insert the attached chart into the PUBLIC Docket File for the Oconee Nuclear Station.
Docket Nos. 50-269, 50-270, 50-287 9607100109 960709 PDR ADOCK 05000269 PDR
OCONEE EMERGENCY ELECTRICAL SYSTEMS
- CHART OF UNRESOLVED ITEMS1 AS DESCRIBED IN NRR DRAFT REPORT ITEM PAGE DESCRIPTION N
EVALUATION NO.
NO.
or D
1 ES-3 Review Duke commitment to modify permissives on emergency power path to delay loading of Keowee units until voltage and frequency are N
within approx. 90% of their nominal values. The staff will review the particulars of the modification when they are available.
4 ES-4 Testing performed has not block-loaded the emergency power sources utilizing actual emergency loads in an integrated fashion, to the levels that could be seen during an actual event. Therefore, analytical work D
performed by Duke must be relied upon to a larger degree to provide the level of assurance necessary that the safety loads will start and operate property.
5 ES-4 If the staff cannot establish to a reasonable degree of confidence from the analysis that the safety systems will perform property without motor tripping D
or thermal damage, then additional more fully integrated loading tests may need to be performed to obtain the necessary level of confidence.
6 ES-4 As a minimum, it appears that overfrequency protection on the underground and overhead paths, and undervoltage protection on the D
underground path should be installed to supplement protection that is already in place.
7 ES-4 The staff does not know what protective trips are available when a Lee gas turbine is powering Oconee electrical equipment to protect against a failure D
of the gas turbine voltage regulator or govemor that results in an out-of tolerance voltage or frequency.
8 ES-4 The staff is not aware of any failure analysis performed on the Lee gas turbine governor or generator voltage regulator that analyzes the potential D
for an out-of-tolerance voltage or frequency to occur.
9 ES-4 The staff believes that a system of voltage and frequency protection that does not rely on operator intervention is necessary to guard against Lee D
station voltage and frequency problems that may affect Oconee.
10 ES-5 The staff will determine whether more realistic loading tests should be performed on the Keowee and Lee gas turbine generators following its N
discussions with Duke on the CYME computer analyses.
11 ES-5 Duke plans to perform an integrated test of the SSF. The results could provide greater or lesser confidence in the ability of the SSF to perform its N
function, that in turn could affect the SBO CDF results. This issue may be revisited if the outcome of the SSF test is not satisfactory.
12 ES-5 The staff believes that the Keowee units should be tested on a monthly D
frequency by using an emergency start signal to initiate the monthly start test.
13 ES-5 A bounding test should be provided unless the acceptance criteria for the proposed degraded grid and switchyard isolation functional test or Keowee D
load rejection test will provide the needed assurance that the single load rejection limits would not be violated if those tests were passed.
ITEM PAGE DESCRIPTION N
EVALUATION NO.
NO.
or D
14 ES-5 Duke should ensure that procedures are in place in each Oconee unit to prevent paralleling of the Unit Auxiliary Transformer and the Unit Startup D
Transformer except for brief power transfer evolutions.
15 ES-6 The staff believes that recovery of the switchyard battery chargers should D
be included in the emergency recovery procedures.
16 ES-6 The licensee is currently in the process of developing an integrated test for the SSF makeup pumps. The staff has concerns that the planned flow testing will not be adequate to provide sufficient data to verify adequate D
seal cooling flow to each pump during actual SSF makeup pump injection.
The licensee should develop more detailed and meaningful acceptance criteria for these tests and submit the acceptance criteria for staff review.
17 ES-6 Because we have confidence that adequate seal cooling can be maintained (assuming acceptable integrated test results) if injection is restored within 10 minutes, the staff concluded that the licensee should D
place more emphasis on operator training and drills to assure this capability can be consistently and confidently maintained.
18 ES-6 Based on the staff's review of the Keowee PRA, the staff identified several actions that Duke should consider. The staff believes that implementation D
of these actions is needed to achieve the reported availability results in the Keowee PRA.
19 ES-7 Due to the importance of having a skilled technical specialist at the Keowee site during periods of severe weather and the unpredictable nature of traveling in these conditions, the staff believes that a Keowee technical D
specialist should be stationed at the site in advance, whenever severe weather is predicted to occur.
21 ES-7 The staff believes the modifier for scheduling maintenance for mild weather only is reasonable. provided that a program is referenced in the administrative controls section of the Oconee TS, and the program D
stipulates that pre-planned dual unit maintenance should be avoided and terminated (end equipment restored to operable status) when severe weather in imminent.
22 ES-7 The licensee should perform periodic testing of the air circuit breakers (particularly ACBs 3 and 4) and their new function and their associated logic, to ensure that these ACBs can achieve the reported high reliability D
values. Reliability goals should be established. ACB performance should be tracked and monitored against these goals under the maintenance rule.
23 ES-7 The licensee should perform periodic hot start tests.
D 24 ES-8 The licensee should evaluate potential mechanisms for a single common D
cause grid degradation failing both Keowee power paths when generating to the grid.
25 ES-8 Since the availability of the underground path from Keowee is risk significant, the staff recommends that Duke consider an additional TS to D
pre-align LEE during any CT4 maintenance activity.
26 ES-8 The staff recommends that Duke consider adding a TS to reduce the D
potential for dogging the Keowee generator cooling water strainers.
ITEM PAGE DESCRIPTION N
EVALUATION NO.
NO.
or D
27 ES-8 The staff recommends additional documentation and modeling for certain areas to provide robustness. For example, the staff believes that the D
modeling of CT5 power should be expanded from a 'black box" to explicitly account for all failure modes.
28 ES-9 The external events section of this report identifies key assumptions and conclusions from the licensee's IPEEE concerning the ability of Oconee's Electrical Power System and the SSF to withstand external events. These N
assumptions and conclusions stem directly from the licensee's IPEEE and have not been verified by the staff.
29 6
The December 12, 1995, Duke letter describes recent initiatives that have been taken, or are planning to be taken, in order to improve the reliability D
and operation of the Oconee ac electrical system.
30 10 It was found that there are, or will be, features in the Keowee voltage regulator and governor that could preclude certain failures in those units D
from producing an out-of-tolerance voltage or frequency outside a certain range.
31 10 A maximum volts-per-hertz trip will be moved to the emergency lockout D
circuit.
32 10 There will be an overfrequency permissive on Keowee output breaker D
closure set at 110%, separate from the govemor.
33 11 Alarms associated with the permissive will alarm on overfrequency D
condition during normal and emergency operation.
34 12 Duke committed in their January 31, 1996 letter, to implement D
modifications to monitor and alarm voltages and frequencies below the acceptable ranges.
35 12 It is believed that a system of voltage and frequency protection, D
permissives, and limiters that does not rely on operator intervention is necessary.
36 13 Overvoltage protection of the underground and overhead paths will be provided through the volts/hertz trip set at 110% that will be moved to the emergency lockout. Overfrequency protection on these lines will be provided only following a load rejection trip of the Keowee units for emergency generation purposes to Oconee. This will be implemented through overfrequency permissives set at 110% to be installed on the D
Keowee generator output breakers. Alarms will be initiated at 110%
overfrequency condition. Additional overfrequency protection will be provided during startup of the Keowee underground and overhead units for a particular governor failure by installation of a governor flyball motor monitoring circuit. The staff believes that this alarm should be supplemented with a protective trip that will separate the Oconee loads from the Keowee generators on an unacceptable overfrequency condition.
The trip should have suitable time delay, redundancy, and coincidence to ensure proper operation.
37 13 Duke has committed to modify permissives on the emergency power path to delay loading of the Keowee units until the voltage and frequency are D
within approximately 90% of their nominal values.
ITEM PAGE DESCRIPTION N
EVALUATION NO.
NO.
or D
38 14 It is not clear how the connected Oconee loads and Keowee unit would respond to the frequency overshoot resulting from failure of a Keowee gate limit feature to runback to its low limit setpoint following its initial run up to D
100%. The overfrequency protection should be designed to ensure satisfactory operation of equipment or separation of the equipment from the Keowee generator.
39 17 In their January 31, 1996 letter, Duke committed to modify permissives on the emergency power path to delay loading of the Keowee units until the voltage and frequency are within approximately 90% of their nominal D
values. This modification should resolve the issue. The staff will review the particulars of the modification when they are available.
41 17 The overspeed condition could result in the Oconee loads being energized at greater than their rated frequency or later than the Oconee accident D
analysis would allow. Duke Modification NSM ON-52966 will correct this problem by installing overfrequency permissives on the Keowee generator output breakers set at 110%.
42 21 This report addresses some of the TS changes that are pertinent to the purposes of this report. The full body of the changes, including those that N
are addressed in this report, will be addressed in detail during the staff's review of the proposed TS changes.
43 23 Licensee to amend TS to include proposed Keowee hydro unit load rejection test (corresponding to an EDG test to reject load equal to 90 to D
100 percent of its continuous rating...)
44 28 The annual test that includes differences in generator field flashing, use of auto synchronizer, and timing and application of gate limits in the govemor system that are tested annually, should be tested monthly by using an D
emergency start signal to initiate the monthly start test. The staff will pursue this issue with Duke. The staff will also determine and evaluate the acceptance criteria for the test at that time.
45 28 Because the Keowee units periodically supply commercial power to the grid they likely satisfy the monthly loading testing surveillance N
requirements. The staff will verify with Duke that this test is similar to the ISTS monthly test.
46 29 The existing Oconee TS tests in this area (trip coil surveillance and operability, overhead and underground paths, etc) appear to be generally appropriate to the Oconee design. The proposed changes from the N
existing specifications also appear appropriate; however, the staff will provide its final evaluation of these changes following completion of its review of the changes. The staff will also evaluate the acceptance criteria to these surveillances during the review.
47 30 The staff believes that the Keowee Monthly Start Test - SR 4.6.1.a - should be a monthly start and load test performed for the Keowee units. The staff D
will pursue this issue with Duke.
48 32 It may be that the testing criteria Duke has referred to is in these other tests, although they don't identify that criteria in their discussion of those N
tests. The staff will pursue this issue with Duke.
ITEM PAGE DESCRIPTION N
EVALUATION NO.
NO.
or D
49 32 A bounding test should be provided unless the acceptance criteria for the proposed degraded grid and switchyard isolation functional test or Keowee D
load rejection test will provide the needed assurance that the single load rejection limits would not be violated if those tests were passed.
50 33 The full load rejection test takes on added importance because the Keowee units are routinely paralleled to the grid for commercial generation purposes, the hydroelectric units undergo a large overfrequency excursion following a load rejection, and the Keowee generators are automatically N
connected to the Oconee loads following the load rejection. The staff will review the details and acceptance criteria for this test during its review of the proposed Oconee TS revision.
51 33 The Keowee black start test is intended to demonstrate Keowee's ability to emergency start with only DC power available to its auxiliaries. Duke has stated that this feature is also periodically verified during the EPSL D
functional test when it is performed on Oconee Unit 1. The test procedure did not substantiate the claim. The staff will be pursuing this with Duke.
52 34 The staff has not yet seen the data collected during the Keowee low power test that was performed in November 1995 to collect data on Keowee while the Keowee unit was loaded during its acceleration phase from a standby start. The EPSL logic will load the Keowee underground path unit with the Oconee unit accident loads during Keowee acceleration if a LOCA were to D
occur followed very quickly by a LOOP. If the overhead path were to fail, the Keowee underground path unit would also have to pick up the other two Oconee units' LOOP loads shortly after Keowee came up to full speed and voltage. Duke has provided a commitment to modify permissives on the emergency power path. The staff will review the particulars of the modification when they are available.
53 37 The staff will pursue its questions on the LOOP analysis regarding pump motor tripping with Duke in order to determine the accuracy of the results.
If the results are found to be highly accurate but there are still small margins to motor tripping, then the staff will need to pursue the accuracy and reliability of the motor overload protective devices. If the staff cannot N
establish to a reasonable degree of confidence from the analysis, that the safety systems will perform property without motor tripping or thermal damage, then additional more fully integrated loading tests will be needed to be performed to obtain the necessary level of confidence.
54 39 The staff believes a system of voltage and frequency protection that does not rely on operator intervention is necessary to fully guard against failures D
of the Lee gas turbine voltage regulator and govemor. The staff will pursue this issue with Duke.
55 41 The staff will pursue with Duke the status of the recommendations made in the analysis related to use of the Lee gas turbines and motor tripping. If the results are found to be highly accurate but there are still small margins to motor tripping, then the staff will need to pursue the accuracy and reliability of the motor overload protective devices. If the staff cannot N
establish to a reasonable degree of confidence from the analysis, that the safety systems will perform properly without motor tripping or thermal damage, then additional more fully integrated loading tests will be needed to be performed to obtain the necessary level of confidence.
EVALUATION NO.
NO.
or D
56 41 Loading a Lee gas turbine by picking up system grid loads does not demonstrate the ability of the unit to instantaneously energize a load block N
as would be required during an actual event. This issue will be further pursued during staff review of the proposed replacement Oconee Electrical TS.
57 43 In the case of an event that will automatically result in load shedding of the chargers and subsequent discharging of the batteries, the staff believes the recovery of the chargers should also be included in the emergency D
recovery procedures. The staff will verify with Duke that such recovery actions are included in the emergency procedures.
60 47 LER 287/80-03 stated that various means for assuring that the transformers are not used in parallel were under investigation. The staff D
could not determine if any follow-up corrective action had been implemented. The staff will pursue with Duke whether any action has been taken on this issue.
61 49 The lack of a Keowee degraded voltage/requency model in the Oconee PRA does not appear to be a significant effect provided that Duke installs D
the additional voltage and frequency protective features the staff has called for in this report.
62 49 Duke has committed to modify the permissives on the emergency power path to delay loading of the Keowee units until the voltage and frequency are within approximately 90 percent of their nominal values. This D
modification should resolve the early loading issue relative to the Keowee underground path. The staff will review that particulars of the modification when they are available.
63 49 The occurrence of certain ground faults on the switchyard side of the Keowee main step-up transformer, together with a subsequent single failure of a safety-related switchyard circuit breaker to trip that would result D
in lockout in both Keowee units, might increase the common cause actuation of Keowee generator lockout probability to a degree that generating both units to the grid would be found to be slightly less reliable, rather than more reliable.
64 50 The occurrence of certain events involving tripping of generator loss-of excitation relays might increase the common cause actuation of Keowee D
generator lockout probability to a degree that generating both units to the grid would be found to be slightly less reliable, rather than more reliable.
66 50 The staff does not have enough information on the CYME computer analyses performed for the Oconee emergency ac power systems to confirm at this time that they provide the level of assurance necessary that D
the safety loads will start and operate properly. The staff will further pursue its questions on these analyses with Duke.
67 50 The staff will determine whether more realistic loading tests are necessary on the Keowee and Lee gas turbine generators following its discussions N
with Duke on the CYME computer analyses performed with these units as power sources.
68 51 Duke plans to perform an integrated test of the SSF, the results of which could provide greater or lesser confidence in its ability to perform its D
function, that in turn could affect SBO results.
ITEM PAGE DESCRIPTION N
EVALUATION NO.
NO.
or D
70 51 As a minimum it appears that overfrequency protection on the underground and overhead paths, and undervoltage protection on the underground path D
should be installed to supplement protection that is already in place.
71 51 The volts/hertz limiter feature in the Keowee voltage regulator may be used together with an undervoltage trip to provide underfrequency protection if it D
can be shown that the comparable underfrequency setpoint will allow satisfactory operation of safety equipment.
72 51 A failure of the Lee gas turbine voltage regulator or govemor that results in an out-of-tolerance voltage or frequency, could expose the redundant safety equipment of the three Oconee units to that voltage and frequency, D
unless protective trips separate the Oconee equipment. The staff does not know what protection of this kind is available when a Lee gas turbine in powering Oconee electrical equipment.
73 51 The staff is not aware of any failure analyses performed on the Lee gas turbine governor or generator voltage regulator that analyzes the potential D
for an out-of-tolerance voltage or frequency to occur.
74 51 The staff believes a system of voltage and frequency protection that does not rely on operator intervention is necessary to fully guard against these D
failures. The staff will pursue this issue with Duke.
75 52 The staff believes the Keowee units should be tested on a monthly D
frequency by using an emergency start signal to initiate the monthly start test.
76 52 A bounding test should be provided unless the acceptance criteria for the proposed degraded grid and switchyard isolation functional test or Keowee D
load rejection test will provide the needed assurance that the single load rejection limits would not be violated if those tests were passed.
77 52 Duke should ensure that procedures are in place in each Oconee unit to prevent paralleling of the Unit Auxiliary Transformer and the Unit Startup D
Transformer except for brief power transfer evolutions.
78 52 In the case of an event that will automatically result in load shedding of the Oconee switchyard battery chargers and subsequent discharging of the D
switchyard batteries, the staff believes the recovery of the chargers should be included in the emergency recovery procedures.
80 57 It is our understanding that integrated testing from the spent fuel pool via the SSF makeup flow path is planned in order to verity the system flow models. However, in the interim we have no technical justification to conclude (based on no identified flaws in the flow models beyond D
verification by test) that the flow disparities would be significant enough to reduce the flow to any one pump to a degree that would jeopardize the RCP seal (i.e., result in a flow rate less than the leak-off rate).
81 60 The licensee has committed to provide remote makeup capability to allow D
refilling the spent fuel pool without entering to fuel pool area.
83 64 The only significant existing concems relative to the SSF are the SSF makeup pump's marginal capacity (which results in a required initiation of D
10 minutes) and the lack of integrated testing of the makeup pump's ability to supply balanced seal flow to all four reactor coolant pumps.
ITEM PAGE DESCRIPTION N
EVALUATION NO.
NO.
or D
84 64 The licensee is currently in the process of developing an integrated test program for the makeup pumps. The actual conduct of the test would not occur until at least July 1996. The test is intended to verity the flow models D
used in the analysis by demonstrating approximately equal flow to each of the four reactor coolant pumps.
85 64 Our understanding is that the present plans are to test flow up to the RCP injection point, this will verify the flows to each pump with the injection piping disconnected (does not include backpressure from pump and leakoff flow paths). Thus, their proposed integrated flow test will only test a D
portion of the entire flow path and will not include the RCPs. The staff is concerned that the planned flow test will not provide sufficient data to verify adequate seal cooling flow to each pump during actual SSF makeup injection.
86 64 Because of the marginal capacity of the makeup pumps, integrated testing that includes the seal return flow path should be performed to assure D
adequate seal cooling and to demonstrate adequate backpressure is maintained on the Number 1 seal during SSF events.
87 65 It would take only a small amount of seal degradation to result in excessive seal leakage during an SSF event. Therefore, adequate integrated testing D
should be performed.
88 65 The licensee should perform adequate integrated testing of the SSF makeup system and its capability to provide adequate seal cooling.
D Proposed acceptance criteria for these tests should be reviewed by the staff.
89 66 The licensee should put additional emphasis on operator training and drills associated with recognizing SSF events and the capability to initiate the D
SSF makeup system within 10 minutes from the loss of RCP seal cooling that accompanies all SSF events.
90 74 The staff believes that the Chi-Squared equation is not appropriate with respect to the number of degrees of freedom that it specifies for the Chi squared distribution. Using the equation may be misleading since it D
produces a probability estimate that is about a factor of 3 lower than the 50 percent confidence value.
91 79 Due to the importance of having a skilled technical specialist at the Keowee site during periods of severe weather, and the unpredictable D
nature of traveling in these conditions, the staff believes that a Keowee technical specialist should be stationed at the site in advance whenever severe weather is predicted to occur.
92 83 The staff believes that the unreliability assigned to CT5 power on a grid-D related LOOP is potentially underestimated.
93 84 The Lee station is under the management of Duke's Fossil Generation Department. Maintenance unavailability records are not kept with the D
Nuclear generation Department. Verification of any past and.future operational experience is therefore questionable.
ITEM PAGE DESCRIPTION N
EVALUATION NO.
NO.
or D
94 84 The staff believes that due to the importance of power from CT5 to the Oconee ac power system, either the modeling of CT5 power should be expanded from a 'black box" to explicitly account for all the failure modes D
to determine more accurately its reliability and availability, or a more robust screening value should be used in the 'black box* model.
95 84 Due to the importance in the emergency ac power system of all three Oconee units, the staff believes that the reliability of these components D
should be tracked under the maintenance rule implementation.
97 84 The second-most dominant cut set in the Oconee-Keowee ac power integrated model contains a modifier of 0.1 since Keowee maintenance is scheduled for mild weather periods. The staff believes this is reasonable modeling assumption, provided that weather considerations is referenced D
in the administrative controls section of the Oconee TS, and the program stipulates that pre-planned dual unit maintenance should be avoided and terminated (and equipment restored to operable status) when severe weather is imminent.
98 84 Because the staff believes that the unreliability of CT5 power is potentially underestimated, the validity of the assumption that the total Oconee D
emergency power system to two 100 percent EDGs is questionable.
99 84 When Duke integrated the Keowee PRA with the IPE, the COF at Oconee Unit 3 for loss of as power events was calculated to be 1 E-6/yr. Because D
the same concems with power from CT5 are carried through to this value, the staff believes that this value could be potentially underestimated.
100 85 In light of its importance, the staff believes that the SSF failure probabilities used for the IPE update (which is now being performed by Duke) should be examined thoroughly. In addition, since the validity of the data is D
dependent on the adequacy and scope of tests, any testing issues associated with the SSF should be resolved.
101 89 To ensure high reliability of automatic operation of ACBs is maintained, periodic testing (especially ACBs 3 and 4), their new functions, and the D
associated logic should be performed.
102 89 Periodic hot start testing of the Keowee units should be performed.
D Statistical failure probabilities should be determined from the test results data.
103 89 The sensitivity analysis assumed that dual Keowee unit generation occurs 3.4 percent of the time. Should this percentage increase, the risk impact of this common cause failure increases. Consequently, the staff feels that the licensee should determine how this event can occur and its likelihood. The D
staff needs this information to conclude there is no significant reduction in Keowee's reliability if both units are generating to the grid, particularly if the percentage of time that both Keowee units are generating to the grid is increased.
104 90 The licensee should consider taking opportunities to compare actual data for components that are tested/demanded infrequently but demanded on D
an emergency start with the data of similar components with more frequent test/demand intervals.
ITEM PAGE DESCRIPTION N
EVALUATION NO.
NO.
or D
105 97 Due to the importance of the strainers on the common intake header of the Keowee generator cooling water system, Duke should consider adding a D
TS item to assure periodic surveillance of these strainers.
106 97 The staff believes that a Keowee technical specialist should be stationed at D
the site in advance whenever severe weather is predicted to occur.
107 98 The staff suggests that use and interpretation of the results of the Keowee D
PRA should be applied with the generic data.
108 98 Most of the plant specific failure data are lower than their generic counterparts. A large amount of the plant specific data was obtained from the experience of Keowee during grid generation. Although it is reasonable to assume that the majority of this experience data would be D
applicable to emergency demand situations, there are some subtle differences in operation, such as the voltage adjust, for which grid generation experience applicability may be questionable. The Keowee PRA does not provide justification for the applicability of these cases.
109 98 Demand frequencies of components such as relays, for which plant specific data was calculated by combining all components of the same type into a type code, rang from daily to quarterly to every refueling outage.
Ideally, all components in the same group or type code should have the D
same or similar periodic testing frequencies. At Keowee, some components that are only challenged every refueling outage are applied the same failure probability as components that are demanded daily.
Therefore, the staff believes the results of the generic data sensitivity study are more robust that the base case.
110 98 Duke classified certain basic events as "undeveloped events." For these basic events, Duke could not find applicable generic data. Therefore, the "undeveloped event" failure rates were calculated using Keowee plant D
specific data only and remained at their plant specific values for the base case and the generic data sensitivity study. Because of this, the generic data result is not a completely generic data assessment.
111 99 The failure probabilities were not discussed in the text or the tables of the D
Keowee PRA.
112 99 For the integration with the IPE, Duke calculated the probability of losing all ac power for Oconee Unit 3 to be 6.35E-5/yr for internal events including D
severe weather. The staff believes that this probability could potentially be underestimated.
113 100 The Lee station is under the management of Duke's Fossil Generation Department. Maintenance unavailability records are not kept with the D
Nuclear Generation Department. Verification of any past and future operational experience is therefore questionable.
114 100 The staff believes that the unreliability assigned to CT5 power on a grid-D related LOOP is potentially underestimated.
115 100 Due to the importance of the Lee station in the emergency ac power system of all three Oconee units, the staff believes that the licensee should D
establish reliability goals for the CT5 power components, and performance should be tracked and monitored under the maintenance rule implementation.
ITEM PAGE DESCRIPTION N
EVALUATION NO.
NO.
or D
116 100 In a letter dated January 31, 1996, the licensee committed to include the Lee/Dentral Power system in the maintenance rule as a risk significant D
system. It is expected, therefore, that specific failure modes will be considered for reliability monitoring under that rule.
117 100 The probability of a Severe Weather LOOP with both Keowee units in maintenance was reduced by a factor of 10 in the Keowee PRA to account for maintenance being scheduled for mild weather periods. This D
assumption is reasonable, provided the TS stipujate that pre-planned dual unit maintenance should be avoided and also terminated (and equipment restored to operable status) when severe weather is imminent.
118 100 Because of the importance of CT4 (underground transformer), the staff recommends that Duke consider an additional TS to pre-align Lee during D
any CT4 maintenance activity, as is stipulated for dual Keowee maintenance activities.
119 101 A periodic hot start test should be performed to more accurately determine D
failure probabilities.
120 102 To ensure high reliability is maintained, periodic testing of ACBs (especially ACBs 3 and 4), their new functions and the associated logic, should be D
performed. Reliability goals should be established, and performance should be tracked and monitored against these goals under the maintenance rule.
121 102 Periodic hot start testing of the Keowee units should be performed.
Statistical failure probabilities should be determined from the test results data. Reliability goals should be established at the values used in the D
Keowee PRA and performance should be tracked and monitored against these goals under the maintenance rule.
122 102 The licensee should evaluate potential mechanisms for a single common D
cause grid degradation failing both Keowee power paths when generating to the grid.
123 103 The sensitivity of the results to changing the failure probability of infrequently tested components was somewhat significant, at 15 percent.
The licensee should consider the potential for differences in the failure probabilities of components with widely varying test/demand frequencies D
by taking opportunities to compare actual data for components that are tested/demanded infrequently but demanded on an emergency start with the data of similar components with more frequent test/demand intervals.
124 103 The Keowee PRA was performed under a less stringent framework than typical plant PRAs. For this reason, the staff and licensee should be D
sensitive to changes in any operating practices, test frequencies, time in configurations, etc., and their impacts should be addressed accordingly.
125 103 The IPEEE assumptions and conclusions presented in the report come N
directly from the licensee's IPEEE submittal and have not been verified by the staff.
126 107 The seismic fragility curves relating equipment failure probability versus ground acceleration will need to be reviewed further to assess the D
reasonableness of their current estimates.
127 107 The seismic cut set frequencies in Table 3-4 will need to be explored D
further; the cutsets appear to total 1.7E-04, not 3.6E-05.
-11i-
ITEM PAGE DESCRIPTION N
EVALUATION NO.
NO.
or D
129 110 Failure of equipment due to internal floods is dominated by submerged equipment. Examination of the internal fault trees indicates the potential for crediting the Keowee or Lee power sources through the link to the D
internal events electric power fault trees. It is assumed that these power supplies were included but unclear what, if any, impact they had on the results.
130 ES-8 The contribution of less significant but more likely external event scenarios D
may be misrepresented in the licensee's IPEEE-submittal.
131 51 The SBO results are also sensitive to the assumed availability and reliability of the LEE gas turbines. This issue, therefore, may be revisited if D
the outcome of the SSF test is not satisfactory.
132 94 Since the uncertainty analysis was performed with plant specific bayesian updated data, this analysis does not encompass the concerns the staff has with this data. The staff believes that interpretation of the Keowee PRA D
results should be based on generic data rather than plant specific bayesian-updated data.
133 94 The demand failure rate of components in similar groupings had varying testing frequencies. This grouping could bias the results of components D
that are tested infrequently.
134 94 Duke did not justify the applicability of using grid generation experience to calculate certain basic event probabilities that are specific to a Keowee D
emergency demand (i.e., the voltage adjust).
135 113 Since external event and severe weather event uncertainties can be large, the staff believes that there are uncertainties that should be taken into D
consideration when making decisions regarding the unavailability of the Oconee emergency AC power system.
136 ES-8 Since external event and severe weather event uncertainties can be large, the staff believes that these uncertainties should be taken into D
consideration when making decisions regarding the unavailability of the Oconee emergency AC power system.
137 ES-8 The staff intends to perform a thorough review of the Oconee IPEEE.
N
- 1. The items appearing in this table were taken from the NRC staff report on the Oconee Emergency Electrical Distribution System. Each is not necessarily met to stand alone, reference should be made to the Report itself for a more complete explanation. Duplicate items may appear in the chart if they are duplicated in the Report.