ML17305B599
| ML17305B599 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 05/28/1991 |
| From: | Conway W ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| To: | Martin J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| References | |
| 161-03974-WFC-M, 161-3974-WFC-M, NUDOCS 9106180306 | |
| Download: ML17305B599 (8) | |
Text
ACCELERATED DISTSJBUTION DEMONSTIRATION SYf)GM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
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NOTES:STANDARDIZED PLANT Standardized plant.
Standardized plant.
ACCESSION NBR:9106180306 DOC.DATE: 91/05/28 NOTARIZED: NO DOCKET FACIL:STN-50-528 Palo Verde Nuclear Station, Unit 1,,Arizona Publi 05000528 STN-50-529 Palo Verde Nuclear Station, Unit 2, Arizona Publi 05000529 STN-50-530 Palo Verde Nuclear Station, Unit 3, Arizona Publi 05000530 AUTH.NAME AUTHOR AFFILIATION CONWAY,W.F.
Arizona Public Service Co.
(formerly Arizona Nuclear Power RECIP.NAME RECIPIENT AFFILIATION MARTIN,J.B.
Region 5 (Post 820201)
SUBJECT:
Provides results of preliminary testing of power supplies DC distribution sys xn steam bypass control sys cab'.nets.
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TITLE: General (50 Dkt)-Insp Rept/Notice of Violation Response RECIPIENT ID CODE/NAME PD5 PD THOMPSON,M INTERNAL: ACRS AEOD/DEIIB DEDRO NRR SHANKMAN,S NRR/DOEA/OEAB NRR/DRIS/DIR NRR S/ILRB12 DIR REG FILE 02 EXTERNAL: EG&G/BRYCE,J.H.
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D NOTE TO ALL"RIDS" RECIPIENTS:
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WILLIAMF. CONWAY EXECUTIVEVICEPRESIDENT NUCLEAR t
RECEIVEO NRC REGIOtl V Arizona Public Service Company P.O. BOX 53999
~
PHOENIX. ARIZONA8)0@3@.'f P g g'I 9e ps 161-03974-WFC/MEP May 28, 1991 Docket Nos.
STN 50-528/529/530 Mr. John B. Martin Regional Administrator, Region V U.
S. Nuclear Regulatory Commission 1450 Maria Lane, Suite 210 Walnut Creek, California 94596-5368
References:
1)
Letter from W.
F.
- Conway, APS, to J.
B. Martin, USNRC (161-03569-WFC/MEP/RAB), dated November 1,
1990
Subject:
Justification for Continued Operation
- Potential for a Single Failure Causing the Opening of All Steam Bypass Control Valves 2)
Letter from W.
F.
- Conway, APS, to J.
B. Martin, USNRC (161-03678-WFC/JST),
dated December 31, 1990
Subject:
Results of Analysis Supporting Justification for Continued Operation
- Potential for a Single Failure Causing the Opening of All Steam Bypass Control Valves 3)
Letter from W. F.
- Conway, APS, to J.
B. Martin, USNRC (161-03893-WFC/JST),
dated April 23, 1991
Subject:
Results of Engineering Review of Steam Bypass Control Valves
Dear Mr. Martin:
Subj ect:
Palo Verde Nuclear Generating Station (PVNGS)
Units 1, 2, and 3
Results of Preliminary Testing of Power Supplies and DC Distribution System in the Steam Bypass Control System Cabinets File: 91-056-026 This letter provides the results of the preliminary testing of the power supplies and the DC distribution system in the steam bypass control system (SBCS) cabinets.
The commitment to perform the testing and a discussion of a proposed voltage monitoring scheme were included in Reference 3.
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61-03974-WFC/MEP May 28, 1991
. Mr. John B. Martin U.
S. Nuclear Regulatory Commission Page 2
Arizona Public Service Company (APS) has evaluated the effects of installing a voltage monitoring system in the SBCS cabinets.
The
- system, as originally envisioned, would have provided a trip of the SBCS to the "Emergency Off" mode of operation whenever DC power supply voltage was out of specification for the Foxboro modules in the cabinets.
The evaluation has determined that such a
voltage monitoring scheme was not desirable since an active device would be placed across the SBCS power supply.
This de~ice would have its own failure
- modes, which could affect the SBCS in the same manner as the original Foxboro power distribution module failure on October 20, 1990.
Hardware to perform the task is not readily available.
- Also, the addition of new hardware could negatively impact the reliability of SBCS.
After reaching the conclusions that a
voltage monitoring system was not desirable, APS tested a mock-up of the critical portions of the SBCS, and created faults essentially identical to the one experienced in Unit 3 last year.
The obj ective of the testing was to determine if 1) voltage monitoring was unnecessary because the power transient was short and the cards would be unaffected or, 2) another method of providing protection against the transient could be used which would have less impact on the SBCS.
The testing was performed in the PVNGS Root Cause of Failure Lab.
The output of the controllers was observed during and after an induced power transient to quantify the effect of a short in the SBCS power supply power distribution.
During the faulted condition the power supply'output voltage dropped to approximately 4Vdc for up to 4 seconds as the fuse burned.
After the fuse isolated the faulted module, the system returned to the +15Vdc.
Upon isolation of the fault and consequent restoration of power, the SBCS provided simultaneous demand and permissive signals of up to 100%
demand lasting several minutes.
This would cause the inadvertent opening of all the SBCS valves.
In order to scope the sensitivity of the system to transients, fuses of different sizes were tested in the mock-up.
These test results suggested that smaller
- fuses, than those currently supplied in the Foxboro Nest Power Distribution Modules, burned fast enough to eliminate or greatly alleviate the problem.
APS contacted ABB Combustion Engineering (CE) regarding the results of the testing.
CE acknowledged the problem and proposed additional testing with their personnel in attendance, in order to further quantify the problem.
On May 15 and 16,
- 1991, CE was on site to assist and observe additional testing.
Based on that testing, even smaller fuses (1.5 Amp in lieu of the standard 3
Amp) could not be relied upon to burn sufficiently fast to prevent a future occurrence of the same problem as that experienced by Unit 3.
Another solution, in the form of removing the permissive and main channel signal mixing was proposed.
This was
- modeled, and the results demonstrated that such a
scheme would prevent inadvertent opening of more than one SBCS valve for a single power system transient.
With the channels fully separated, no single power failure could effect the other channel.
f tp 1
(
161-03974-MFC/MEP May 28,
1 99 1 Mr. John B. Martin U.
S. Nuclear Regulatory Commission Page 3
Additionally, CE has provided an alternate design modification and will provide the results of computer modeling of the modified system (i.e.,
main and permissive channel cross connects deleted) to APS by June 15, 1991.
These test'nd modeling results will be used as the basis for a design modification to bring the SBCS back into its original design basis.
The schedule for the Design Change Package to be issued, based on using one of the current potential solutions, is September 1,
1991.
This schedule supports the existing JCO for SBCS at PVNGS.
Based upon this schedule, APS will forward a description of the final design change by October 1,
1991.
In addition to the
- above, APS also requested CE to assess the impact of an inadvertent opening of all eight SBCV on the Unit 3 Cycle 3 reload analysis of record.
The operating characteristics of the SBCS required that five Unit 3 reload design analyses be reanalyzed.
The reanalyses covered the following events:
Excess Load Event; Delayed Trip CEA Ejection; Reactor Power Cutback Activation with SBCS failure; Part Length CEA Drop; and Single CEA Withdrawal Within the CPC Deadband.
CE concluded that by providing adequate analysis margin these events are bounded, and therefore require no additional COLSS penalties.
If you have any questions on this issue, please contact Michael E. Powell of my staff at (602) 340-4981.
Sincerely, WFC/MEP/pmm cc:
Document Control Desk D. H.
Coe A. C.
Gehr A. ii~ Gutterman
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