View source for PNO-V-87-047, on 870621,interruption in Power to Phase B of non-1E Uninterruptable Power Supply Caused Sharp Reduction in Feedwater Flow to Steam Generator 88 & Subsequent Reactor Trip.Caused by Loose Cable Plug Lug.Lugs Inspected

{{Adams
| number = ML20216F853
| issue date = 06/22/1987
| title = PNO-V-87-047:on 870621,interruption in Power to Phase B of non-1E Uninterruptable Power Supply Caused Sharp Reduction in Feedwater Flow to Steam Generator 88 & Subsequent Reactor Trip.Caused by Loose Cable Plug Lug.Lugs Inspected
| author name = Johnson P, Tatum J
| author affiliation = NRC OFFICE OF INSPECTION &amp; ENFORCEMENT (IE REGION V)
| addressee name = 
| addressee affiliation = 
| docket = 05000362
| license number = 
| contact person = 
| document report number = PNO-V-87-047, PNO-V-87-47, NUDOCS 8706300959
| document type = PRELIMINARY NOTIFICATION OF EVENT OR OCCURRENCE (PNO,, TEXT-INSPECTION &amp; AUDIT &amp; I&amp;E CIRCULARS
| page count = 2
}}
{{#Wiki_filter:!
  ''n                                                                 '                   '
l*
                                                                                  /
PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-V-87-47 Date: 06/22/87          i l
This preliminary notification-constitutes EARLY notice of events of POSSIBLE safety         {
or public interest significance. The information presented is as initially received          {
without verification or evaluation and is basically all that is known by Region V staff on this date.
FACILITY: Southern California Edison Company              Licensee Emergency Classification San Onofre Unit 3                                Notification of Unusual Event i l
DOCKET NO. 50-362                                Alert                         I Site Area Emergency           )
General Emergency              <
XX Not Applicable

==SUBJECT:==
REACTOR TRIP AND SAFETY INJECTION At 2:59 a.m. (PDT) on June 21, 1987, with the unit at 100% power, an interruption in power to phase B of the non-IE uninterruptible power supply (UPS) caused a sharp reduction in feedwater flow to. steam generator No. 88. One feedwater pump controller was also affected. Operators placed the feedwater control valve and feed pump controller in manual, but could not preclude a reactor trip on low steam generator level. A low level also occurred in steam generator No. 89 following the trip. The auxiliary feedwater (AFW) system actuated (all 3 AFW pumps). The UPS regained power following the trip, and the main feedwater pump and control valve which were still in manual caused overfeeding of steam generator No. 88 before operators terminated          j feedwater flow. The feedwater addition by the main and auxiliary feedwater pumps caused a reduction in reactor coolant system (RCS) temperature, accompanied by low pressurizer pressure which resulted in a safety injection actuation. Plant safety systems responded as designed, and the plant was stabilized in hot shutdown (Mode 3) shortly after the event.
Plant operators did not observe any injection of water into the RCS by the high pressure safety injection (HPSI) system, and an unusual event was therefore not declared.
However, the licensee's post-trip review subsequently determined that HPSI flow into the RCS had occurred for about 90 seconds at approximately 1250 psig. The minimum pressure reached was 1238 psig, with a total RCS cooldown of 62 F. The licensee has concluded that the pressurizer emptied but the surge line did not, since the minimum pressure reached exceeded the saturation pressure corresponding to RCS loop temperature. The minimum margin to saturation was 64 F.
Troubleshooting by the licensee has identified a loose cable lug on phase B on the UPS to be the cause of the temporary power interruption. This has been corrected and other lugs have been inspected for tightness. Inspection of the HPSI system by the licensee identified four failed snubbers; investigation and replacement of these is in progress.
87                                                   ~
PD        59 870$yy PNO ~y'67~04 7     pyg                                                   0

7,     ..
i 4
Water was introduced into one main steam line as a-result of the steam generator overfeeding; engineering evaluation by the licensee is in progress. The licensee is also taking advantage of the outage to perform scheduled maintenance not related to this   ,
event. Resident inspectors are still following up on the event and reviewing the
  . licensee's event assessment.
 ~ This information is current as of 1:00 p.m. (PDT) on June 22, 1987.
CONTACT:    P Johnson          J. Tatum FTS 463-3745       (714)492-2641 i
l DISTRIBUTION Phillips'b/W H St.                 MNBB                        Willste     Air Rights        Mail:
 . Chairman Zech         EDO     NRR         IE       NMSS                        ADM:DMB Comm. Roberts         PA                                                                      ,
Comm. Asselstine      MPA                 AE0D                                                i
'Comm. Bernthal          ELD                                                                   l Comm. Carr                     Regions:
SECY                           INP0T/O NSAC &So ACRS                            Licensee:   DJ'r CA                             (ReactorLicensees)                   REGION V: FORM 211 POR                            Resident Inspector $ Y'1         (Revised 3/14/83) k 9.9 W E*N Tiw e en n Q 9}}

{{PNO-Nav|region=V}}