ML20101H325
| ML20101H325 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 06/26/1992 |
| From: | William Cahill TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| CP-92-005, CP-92-5, TXX-92274, NUDOCS 9206290303 | |
| Download: ML20101H325 (4) | |
Text
.
e J
~*""
g L
Log
r File # 10110
&so,59(gy TUELECTRIC g,7, y
June 26, 1992 William J. Cahill, Jr.
3 o
Grc>up Yice Presidret U. S. Nuclear Regulatory Commission Attn:
Document Control Desk Washington, DC 20555 I
i
SUBJECT:
COMAi4CHE PEAK STEAM ELECTRIC STATION (CPSES)
DOCKET NOS. 50-445 AND 50-446 SAFETY CHILLCR CUNTROL CIRCUIT VOLTAGE DROP SDAR: CP-92-005 (FINAL REPORT)
REF:
.)
lelephone conversation between Mr. T. A. Hope, TU Electric, and Mr. L. A. Yandell of the NRC, Region IV, on June 11, 1992 Gentlemen:
On May 13, 1992, via facsimile, TV Electric notified the NRC of a deviation that may have prevented the Unit 2 safety chillers from starting in the event of a degraded voltage condition. TV Electric requested an extension to June 26, 1992, for submittal of the final report to allow for additional evaluation. Via Reference 1, the extension was granted by Mr. L. A. Yandell of NRC Region IV.
TV Electric has determined that this deviation is reportable pursuant to 10CFR50.55(e).
Attached is the written report which satisfies the reporting requirements of 10CFR50.55(e). The report has been formatted in a manner that corresponds to the specific information requested by subparts (i) through (viii) of paragraph 10CFR50.55(e)(8) of the regulation.
This is exclusive of that portion of subpart (viii) regarding the advice that has been or will be i
given to other facilities outside of TU Electric.
Such advice would be dependent on the facilities' specific use and operating / maintenance history of the subject-components.
Sincerely,
,f
[
William J.
hill, Jr.
RHS/tg c-Mr. R. D. Martin, Region IV Mr. L. A. Yandell, Region IV Mr. T. A. Bergman, NRR Mr. B. E. Holian, NRR Resident Inspectors, CPSES (2) 9206290303 920626 gy DR ADOCK 0500 5
doo N.otive sirect LB. si Daitas, Texas 75201
. Attachment to TXX-92274-Page 1 of 3 10CFR50.55(e) REPORTABLE CONDITICH INVOLVING SAFETY CHILLER CONTROL VOLTAGE DROP (i)
Information supplied by:
William J. Cahill, Jr.
TV Electric-400 North Olive Street, L. B.-81 Dallas, Texas 75201 (ii)
The basic component is the Unit 2 "A" Train safety centrifugal water i
{
chiller control circuit, j
(iii)
TV Electric has overall resronsibility for the construction,_ design and operation of the chiller control circuitry.
i (iv)
. Description i
i Starter circuits associated with-the safety chillers were not considered in the Unit 2 calculations.
In the event'of a degraded voltage condition, the voltage at the "A" Train safety chiller j
starter circuit would be considerably lower than required to operate
[
the chiller.
Site Soecific Summary j
To meet the Fire Safe Shutdown requirements of Appendix A, to Branch j
Technical Position APCSB 9.5-l', TU Electric evaluated cables for i
replacement with Rockbestos one hour fire rated cable. While-l evaluating Cable E0211269 it was discovered:that the."A" Train l
Safety Centrifugal Water-Chiller control l circuit was not enveloped by Engineering calculation 2-EE-0012, Rev. 0 (Voltage Drop on Class--
l 1E-Miscellaneous 120 V AC control Circuits)-or-2-EE-0007, Rev. 1-l (Class 1E 480V Motor. Control Centers Starter Coil Pickup Analysis).
Upon further investigation, it was determined that during.a degraded-voltage condition, the resulting voltage at the starter circuit-would be less than that required to-start the' chiller.
l Additionallyi-it was determined that.the existing cable (12 AWG)'was--
l not sufficient for the anticipated load.
This_ condition was caused by the lack of analysis for--a'somewhat unique control power circuit configuration.
This condition _'is-
. isolated to control circuits powered-at vendor-supplied. local-l panels. However, further review identified three additional control l
circuits not enveloped'by the Unit 2 Engineering calculations. The "B" Train Safety Centrifugal Water Chiller. control circui.ts' voltage
(--
drop was acceptable, but the existing cable size (12 AWG) is undersized for the anticipated load. _ Preliminary evaluations of=the i
l
Attachment to TXX-92274-Page 2 of 3 Unit 2 "A" and "B" Train Hydrogen Recombiner control circuits revealed that the voltage drop was unacceptable.
Using a LOCA voltage profile, the resulting voltages at the starter circuits were found to be less than required to start the Hydrogen Recombiners.
Site Specific Imolications The safety chillers are required to provide chilled water for the cooling coils to remove heat rejected by Engineered Safety Features (ESF) pump motors and electrical switchgear and to maintain ambient temperatures below design limits within specified rooms. The Fire Safe Shutdown Analysis (FSSA) requires that the safety chillers be available.
In the event of a fire in the control room, cable spread room or the mechanical equipment rooms, an alternate shutdown procedure is required. The alternate shutdown scenario requires isolation of control room cabling / circuitry for the Train "A" safety chiller via a control switch located on the shutdown transfer panel to preclude potential fire induced failure of the control circuit.
Starter circuits associated with the safety chillers were not considered in the Unit 2 calculations.
In the event of a degraded voltage condition, the voltage at the "A" Train safety chiller starter circuit would be considerably lower than that required to ensure operability of control components necessary to operate the chiller.
The excessive voltage drop in the starter circuit required to operate the "A" Train safety chiller would render the functionality of this circuit indeterminate. The "B" Train Chiller is considered unavailable due to the lack of control-circuit isolation from the control room.
During an alternate shutdown, if the "A" Train safety chiller did not operate, Unit 2 would be in an unanalyzed condition relative to the FSSA and could significantly affect the ability of-the plant to achieve and maintain a safe shutdown condition. Therefore, this deviation is reportable pursuant to 10CFR50.55(e).
(v)
I., formation about the defect was obtained by TV Electric evaluations and documented on TUE-92-4550,. Revision 1, dated April 8, 1992.
(vi)
Unit 2 has an "A" Train and "B" Train Safety Centrifugal Water Chiller and an "A" Train and "B" Train Hydrogen Recambiner.
(vii)
A Unit 2 non-conformance document was initiated to document the' hardware nonconformance for the Unit 2 "A" Train chiller. A design change for Unit 2 was-issued to upsize the subject. cables for the "A" and "B" Train Chiller control circuits and to rewire the,"A" Train circuit to shorten the total cable length and reduce the voltage drop to acceptable values.. TU Electric is currently evaluating the need to upsize the control power transformers for the
" A': and "B" Train hydrogen recombiners.
This-will reduce the impedance within the circuit and reduce the voltage drop to acceptable values.
1
4
{
Attachment to TXX-92274 Page 3 of 3 i
The lack of analysis which caused this condition was investigated and discussed with Engineering personnel during a-Quality Accountability meeting on April 7, 1992.
It was determined that the I
subject control circuits were unique in that they were fed directly from power feeders through a vendor supplied control transformer versus a distribution panel. The Unit 1 calculations used by Unit 2 assumed that all control power was fed from distribution panels.
(viii) The deviations discussed above are applicable to CPSES Unit 1.
A Unit I non-conformance document was initiated to document the undervoltage condition on the Unit 1 "A" Train chiller. A design modification was issued to correct the above condition and the f
undersized cable ondition on the Train "A" and "B" safety chillers, i
(
A periodic surveillance has been established to ensure that the j
voltage on the "A" Train bus does not drop below the appropriate i
limit until the design modification is implemented.
j As a result of a generic review of this issue a ONE Form has been issued to address the undersized co7 trol power transformers on the Unit 1 "A" and "B" Trains hydrogen recombiners.
j i
i
).
9 4
j j
I
+
.... - - -