ML20212B611
| ML20212B611 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 08/01/1986 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | Youngblood B Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20212B615 | List: |
| References | |
| NUDOCS 8608070177 | |
| Download: ML20212B611 (6) | |
Text
m-SN 157B Lookout Place AUG 1 HN3S Director of Nuclear Reactor Regulation Attention:
Mr. B. Youngblood, Project Director PWR Project Directorate No. 4 Division of Pressurized Water Reactors (PWR)
Licensing A U.S. Nuclear Regulatory Commission Washington, D.C.
20555
Dear Mr. Youngblood:
In the Matter of
)
Docket Nos. 50-327 Tennessee Valley Authority
)
50-328 In my letter to you dated February 27, 1986, my response identified that the electrical restart calculations program had determined problems in the following systems (TVA Significant Condition Report (SCR) number is in parenthesis):
1.
Auxiliary Power System - Voltage Calculations (SQNEEB8607) 2.
Control Power System - 120V ac Voltage Calculations (SQNEEB8532) 3.
Control Power System - 125V de Voltage Calculations (SQNEEB8605)
A review of each of these problems has been completed and corrective action where required has been determined.
The corrective action is as follows:
1.
SONEEB8607 - This problem concluded that deficiencies exist with respect to individual components voltage in the Class IE auxiliary power system (480V AC) for operation at the degraded voltage setpoints. The corrective action for this item involves two modifications. An existing time delay relay in the control circuit of the 480V ac component cooling system pump motors will be used to delay the motors starting for 20 seconds upon receipt of a safety injection signal.
This time delay is consistent with the plant design basis for this system.
In addition, it has been determined that the 480V ac supply to the main feedwater isolation valves must be modified such that the electrically operated brakes are wired independent of the valve's motor operator. This will ensure adequate voltage for the brakes to operate properly during a degraded voltage condition. This involves the installation of eight new cables in addition to eight new 80 percent voltage solenoid valves which were added to the main feedwater isolation valves during the environmental qualification process. These corrective actions will be completed before restart of Sequoyah Nuclear Plant (SQN) and will resolve this deficiency.
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SONEEB8532 - This problem concluded that deficiencies exist with respect to individual components' voltage in the 120V ac vital instrument power system for operation at the minimum system voltage. The systems affected are the radiation monitoring, postaccident sampling, and reactor vessel level. instrumentation systems. The corrective action for this deficiency involved:
(a) pulling larger size cable to reduce cable impedance, and (b) paralleling supply cables to reduce the current through various portions of the affected circuits. A total of 15 cables will be pulled. This corrective action will be completed before restart of SQN and will resolve this deficiency.
3.
SONEEB8605 - This problem area involved the unit 1, 120V ac vital inverters with respect to an inadequate minimum de input voltage.
Original manufacturer minimum input voltage was 105V dc.
Subsequently, the inverter vendor has performed a recertification test for the same type inverter at TVA's Watts Bar Nuclear Plant and confirmed that the SQN unit 1 inverters will operate properly at 100V de minimum, which is acceptable.
In addition, this SCR identified a problem with inadequate de input voltage for 24 solenoid valves during a minimum vital de system voltage condition (150V de) and excessive voltage drop for two flow-modulated solenoid valves between the modulator and the valve during any de system voltage, based on original manufacturer's data.
Further TVA review has concluded that operation of these 24 valves is not required at the minimum de system voltage-(i.e., these valves are not required to perform a safety function during battery discharge).
In addition, further review by the manufacturer has concluded that adequate voltage is available for the flow-modulated solenoid valves.
Two additional SCRs (SQNEEB8629 and SQNEEB8646) have been written from the reevaluation of the diesel generator load analysis. A copy of this reanalysis is included in enclosure 1.
This reevaluation was discussed in the referenced-February 27, 1986 submittal; however, this reevaluation has identified a problem with the diesel generator's (DG) capability to meet the voltage and frequency requirements of Regulatory Guide 1.9, Rev. O.
These requirements may not be met should the identified random process loads be running or started concurrent with the sequenced load (containment spray pump motor) at the t=30 second step. The corrective action for this problem area involves the intentional time delay of eight 480V ac loads.
These loads include four supplies to the 480V ac electric board room air handling units, compressors, and condensers, and four supplies to 480V ac vital transfer switches I, II, III, and IV.
(Each transfer switch supplies one channelized 125V de vital battery charger, two channelized 120V ac vital inverters, and one non-Class 1E instrument power transformer.)
. Director of Nuclear Reactor Regulation AUG 1 t)B6 This modification will be completed before restart of SQN and will correct this deficiency.
In addition, when the t=0 loads are applied, the transient voltage will fall below the 75 percent minimum allowed by R.G. 1.9 and will not recover within the specified time interval. This is due to the 6.9kV shutdown board DG supply breaker closing at 80 percent of nominal voltage (permission to close breaker is established by a voltage relay that picks up at this voltage). However, there are two permissives required for breaker closure: voltage and RPM.
A review of the DG peroperational test results and the surveillance instruction results has concluded that DG voltage is actually above nominal before receiving the RPM permissive; therefore, no corrective action is required and this item is resolved.
TVA's February 27, 1986 letter also discussed a review of the overall electrical calculations program for SQN being performed by Sargent & Lundy (S&L). This review is complete and a final report was issued to TVA on April 8, 1986 (enclosure 2).
Overall, this review concluded that SQN was equivalent with other nuclear plants of its vintage with respect to electrical calculations. However, based on this review, TVA has concluded that revisions to existing calculations and/or formal documentation for some electrical systems are necessary before restart of SQN. This work will be performed in the following systems:
1.
Auxilary Power 2.
Control Power 3.
Instrumentation and Control (I&C) 4.
Raceway 5.
Station Grounding The majority of this effort represents revisions to existing calculations, with the control power, station grounding, and I&C systems requiring additional formal documentation for the existing system's configuration.
In addition, new calculations for I&C mild environment instrument accuracies are required. This effort is presently underway at TVA and will be complete before restart of SQN.
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Director of Nuclear Reactor Regulation AUG 1 1335 Completion of these efforts will conclude phase one of the electrical calculations program. Phases two is an ongoing review effort for new complete before restart.
Phase two is an ongoing review effort for new modifications and will remain in this status until phase three, the long-term portion of this program is complete. Phase three will be established and scheduled before restart of SQN. The objectives of phase three will be:
o To obtain established standards, procedures, and computer programs for the performance of electrical calculations.
o To train TVA design personnel in the performance of electrical calculations.
o To perform all future electrical calculations required to ensure that:
(1) the plant safety-related electrical design bases are met, and (2) the plant electrical systems support the nuclear program's reliability and availability goals.
o To develop an efficient, verifiable method for maintaining issued electrical calculations.
Upon the completion of phase one, including a secondary review by S&L of those restart calculations requiring revision or initial preparation and of corrective actions identified as a result of the calculations effort, the SQN electrical restart calculations program will be complete. Should further corrective actions be identified during the secondary S&L review, a licensing submittal will be prepared to address each. Should the review find the calculation program complete and satisfactory, no further submittal will be forthcoming.
Very truly yours, TENNESSEE VALLEY AUTHORITY R. Gridley, Director Nuclear Safety and Licensing Enclosures cc: See page 5 i
. AUG 1 1936 Director of Nuclear Reactor Regulation cc:
U.S. Nuclear Regulatory Commission Region II Attn:
Dr. J. Nelson Grace, Regional Administrator 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Mr. Carl Stahle Sequoyah Project Manager U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue Bethesda, Maryland 20814 l
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