ML17306B311

LER 93-001-00:on 930130,main Turbine Trip Occurred Which Initiated Manual Reactor Trip After Receiving High Pressurizer Pressure Pretrip Alarm.Caused by Failure of High Tank Level Controller.Failed Controller Replaced

ML17306B311
Person / Time
Site:	Palo Verde
Issue date:	02/24/1993
From:	Bradish T ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:
Shared Package
ML17306B312	List: ML17306B311 ML17306B313
References
LER-93-001-01, LER-93-1-1, NUDOCS 9303090204
Download: ML17306B311 (14)

Text

LICENSEE EVENT REPORT (LER)

FACILITYHAME (I) DOCKET NUMBER (2) PAGE 3 TITLE (4)

Palo Verde Unit 1 0 5.0 0 0 528 1OFO 7 Turbine Tri /Reactor Trip on IMoisture Se arator'eheater High. Level EVENT DATE (6) LER NUMBER (6) REPOR'1 DATE(7) OTHER FACILITIES INVOLVED (6)

MONTH DAY YEAR YEAR DAY YEAR FACILITYNAMES DOCKET NUMBER(S]

NUMBER O'UMBER N A 0 5 0 0 0 9 3 0 01 00 02 24 93 THIs REPoRT Is BUBMITTEDPIIRBUANTTo THE REDUIREMENTs oF to cFR (check one or more ol Ae Iclbwino) (I I) 0 '5 0' '0 OPERATING 6$

MODE (0) 20.402(b) 20.405(c) 50.73(a)(2)(Iv) 73.71(b)

POWER- 20.405(a)( I XI) 5026(c)($ ) 50.73(a)(2)(v) 73.7 $ (c)

LEVEL (to) 9 20.405(a)(t)(lip 5026(c)(2) 50.73(a)(2) (vli) OTHER (Specllyln Absc sct belovr anil In TexL NRC Form 20.405(a)($ )(IT) 50.73(a)(2)(I) 50.73(a)(2)(vIT)(A) 36M) 20.405(a)($ )(iv) 50.73(a)(2)(T) 50.73(a)(2)(vIT)(B) 20.405(a)(1)(v) 50. 73(a)(2)(vl) 50.73(aX2)(x)

LICENSEE CONTACT FOR THIS LER (12)

TELEPHONE NUMBER A 0 Thomas R. Bradish Nuclear Re ulatorv Affairs Mana er COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT(13) 60 2 393 -54 21 MANUFAC- MANVFAC CAUSE SYSTEM COMPONENT TURER CAUSE SYSTEM COMPONENT TUBER X S N MO 40 SUPPLEMENTAL REPORT EXPECTED (14) MONTH DAY YEAR EXPECTED SVBII6SSION DATE (16)

YES (Ilyes. ocmplele EXPECTED SUBMISSION DATE) NO ABsTRAGT (Um'I Io 1400 spaces. I e., spproxlms rely filleen slnolespsce rypevrn'nen fines) (16)

At approximately 0603 MST on, January 30, 1993, Palo Verde Unit 1 was in Mode 1 I (POWER OPERATION) operating at approximately 96 percent power when a Unit 1 Hain Turbine trip occurred. Control Room operators initiated reactor trip after receiving high pressurizer pressure pretrip alarms ainmanual anticipation of the Reactor Protection System high pressurizer pressure tri P ~

At approximately 0615 MST on January 30, 1993, Control operators

,stabilized the plant .in Mode'3 (HOT STANDBY). The ShiftRoom Supervisor classified the event as an uncomplicated reactor trip in accordance with Emergency Plan Implementing Procedures. No other safety system responses occurred and none were required.

APS Maintenance personnel have determined that the cause of the Main Turbine trip was due to the failure of Moisture, Separator Reheater D Drain Tank high level controller. This resulted in a high level condition in Moisture Separator Reheater D which actuated the Main .Turbine's electrical trip system.

No previous similar events have been reported pursuant to 10CFR50.73.

9303090204 930224 PDR ADOCK 05000528 S PDR

41 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITYNAME DOCKET NUMBER LER NUMBER PAGE

>>> SEOUENTIAL I(P REVISION YEAR NUMBER &<i NUMBER Palo Verde Unit 1 0 5 0 0,0 93 001 0 0 TEXT DESCRIPTION OF WHAT OCCURRED:

A. Initial Conditions:

At 0603 MST on January 30, 1993, Palo Verde Nuclear Generating Station (PVNGS) Unit 1 was in Mode 1 (POWER OPERATION) at approximately 96 percent power.

B. Reportable Event Description (Including Dates and Approximate Times of Major Occurrences):

Event Classification: An event that resulted in a manual actuation of the Reactor Protection System (RPS)(JC) ~

At approximately 0603 MST on January 30, 1993, a PVNGS Unit 1 Main Turbine (TA) trip occurred. Control Room operators (utility, licensed) initiated a manual reactor-(RCT)(AC) trip after receiving the high, pressurizer pressure pretrips on RPS channels A, B, and C in anticipation of a RPS high pressurizer (AB) pressure reactor trip. The manual trip functioned as designed by generating a trip signal that opened the Reactor Trip Switchgear Breakers (RTSGB)(AA) causing the Control Element Assemblies (CEA)(AA) to drop.

At approximately 0615.MST, on January 30, 1993; Control Room operators stabilized the plant in Mode 3 (HOT STANDBY). The Shift Supervisor (utility, licensed) classified the event as an uncomplicated reactor trip in accordance with Emergency Plan Implementing Procedures. No other safety system responses were required and none occurred.

Prior to the event, the 6A High Pressure Feedwater Heater (HPFWH)(HX)(SJ) level bridle (JB) was being modified in accordance with an approved Design Change Notice (DCN). This modification was made to permit the control of. the water level'n the shell side of the heat exchanger at a higher level. To support the. modification, Operations personnel (utility, nonlicensed) isolated the extraction steam and feedwater to the A HPFWH train. Part of the isolation procedure required the Moisture Separator Reheater (MSR)(SA) Drain

'Tank levels to be controlled by their respective high level controllers.

The MSR Drain Tanks are connected to the MSRs and have two level controllers (normal and high). The. normal level controller routes the condensate from the MSR Drain Tank, through the Heater Drain Tank and pump, and eventually to the suction of the Main Feedwater (SJ) pump. This flow path supplies a portion of the feedwater flow required at 100 percent power. The MSR Drain Tank high level

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LICENSEE EVENT REPORT, (LER) TEXT CONTINUATION DOCKET NUMBER LER NUMBER PAGE FACILITYNAME YEAR SEQUENTIAL I% REVISION NUMBER NUMBER Palo Verde Unit 1 52 8 93 001 0 0 0 QFO 7 controller routes the condensate from the MSR Drain Tank directly to the Main Condenser (COND)(SG) on a high level. The MSR Drain Tank high level controller prevents the MSR reheating steam tube bundles from becoming covered with condensate. Covering. these bundles reduces the MSR's efficiency and could cause an unacceptable amount of moisture to "carry-over" in the reheated steam, to. the Main Turbine. This "carry-over" could damage the turbine blades.- Each MSR 'drain system has level sensors that actuate the Main-Turbine's electrical trip system to prevent any "carry-over." This signal is set at 3 inches below the bottom of the MSR.

To isolate the MSR Drain Tank from the HPFWH train, the high level controller setpoint is:lowered below the normal level controller setpoint such that the control valve to the HPFWH train is closed and the dump valve to the Main Condenser is open. After completion of the modification to the 6A HPFWH, an Auxiliary Operator (utility, nonlicensed) was .transferring the level control for the D MSR Drain Tank back to normal. While raising the setpoint on the high level controller, a high level condition in MSR D occurred. The normal level controller, responded to the increasing level, but the normal level control valve. did not open. Also, the high level controller did not respond fast enough to the resulting high level and open the

.dump valve to the Main Condenser. This caused the level in the D MSR Drain Tank to increase above the Main Turbine trip setpoint for high MSR level, actuating a Main Turbine trip. This caused an increase in the primary plant pressure and the reactor was manually tripped by the Control Room operators.

At approximately 0615 MST, on January 30, 1993, Control Room operators stabilized the plant in Mode 3 (HOT STANDBY). The Shift Supervisor (utility, licensed) classified the event as an uncomplicated reactor trip in accordance with Emergency Plan Implementing Procedures. No other safety system resp'onses were required and none occurred.

C. Status of structures, systems, or components that were inoperable at the start of the event that contributed to the event:

Other than the isolated D MSR Drain Tank normal level'ontrol valve identified in Section I.I., no other structures; systems, or components were inoperable at the start of the event that contributed to the event.

D. Cause of. each component or system failure, if known During troubleshooting, the D MSR Drain Tank high level dump valve controller was determined to be defective. The controller did not operate smoothly and did not control the dump valve properly above

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LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITYNAME DOCKET NUMBER DER NUMBER PAGE yEAR '?Fc SEQUENTIAI % REVISION RN NUMBER Iz~ NUMBER Paio Verde Unit 1 TEXT

<<o<<5Z8 9 3 0 0 1 0 0 4 OF 40 percent open. The apparent cause of the failure was determined to be binding of the position carriage or the alignment of internal controller components. APS Engineering personnel are conducting an equipment root cause of failure analysis for the D MSR Drain Tank high level controller as identified in Sections I.I and III.B.

.E. Failure known:

mode; mechanism, and effect of each failed component,. if As described in Section I.B, failure of the D MSR Drain Tank level controller resulted in a high level in the D MSR. This high-resulted in actuation of the Main Turbine's electrical trip system on high MSR level resulting in a trip of the Unit l Main Turbine.

F. For failures of components with multiple functions, list of systems or secondary functions that were also affected:

Not applicable - no failures of components with multiple functions were involved.

G; For a failure that rendered a train of a safety system inoperable, estimated time elapsed from the discovery of the failure until the train was returned to service:

Not applicable - no failures that ren'dered a train of a safety system inoperable were involved.

H. Method of discovery of each component .or system failure or procedural error:

The failure of the D MSR Drain Tank high level control level controller was discovered during troubleshooting. valve high Procedural errors were not identified.

I. Cause of Event:

APS Maintenance personnel (utility, nonlicensed) have determined that the cause of the Main Turbine trip was the failure of the D MSR Drain Tank high level controller. This resulted in a high level condition in D MSR and actuation of the Main Turbine's electrical trip system resulting in a Main'urbine trip.

An investigation of this event was conducted in accordance with the APS Incident Investigation Program. An action plan was developed'o determine why the D MSR Drain Tank high level control valve did not prevent a high level in the D MSR. A functional test of the valve, performed by PVNGS Maintenance personnel, identified that the controller was defective. The initial testing determined that the

0 LlCENSEE EVENT REPORT (LER) TEXT CONTlNUATlON FACILITYNAME DOCKET NUMBER LER NUMBER PAOE YEAR SEQUENTIAL REVISION NUMBER NUMBER Palo Verde Unit 52 8 9 0 0 1 0 0 0 5 OF 0 7 controller did not control the dump valve smoothly above 40 percent open and evidence that pliers or vice grips may have been used to turn the setpoint adjustment on the controller because of a loose adjustment knob was found. The faulty controller was replaced (SALP Cause Code E: Component Failure).

APS Engineering personnel are conducting an equipment root cause of failure analysis for the D MSR Drain Tank high analysis results differ significantly from,the apparent cause, a If level controller.

supplement to this report will be submitted.

The Investigation Team also evaluated the failure of the D MSR Drain Tank normal le~el control valve to respond and control le~el.

Following the event, a walkdown of the system identified a closed unnumbered instrument air valve between the D MSR Drain Tank normal level controller and the associated control valve. This closed valve prevented the normal level control valve from functioning air correctly.

The procedures used to remove and restore the normal level controller and valve were reviewed. No reference to the unnumbered instrument air valve was found. No clearances were found that operated or used this unnumbered instrument air valve as a boundary for work or equipment isolation. Also, no work documents were found that would have operated this unnumbered instrument air Investigation Team is continuing to review the proceduresvalve. governing The these level controllers to deterTBine procedural adequacy and expectations of operator performance. These issues will be addressed within the Incident Investigation program.

If a procedural or personnel error is identified that change the readers perception of the cause of the would'ignificantly event, a supplement to this LER. will be submitted.

J. Safety Syst: em Response:

The reactor trip in this event was a manual action in anticipation of a RPS high pressurizer pressure tr'ip following the Main Turbine trip. No other safety system responses occurred and none were necessary.

Failed Component Information:

MAGNETROL Modulevel Pneumatic Proportional Level Controller Model 6450-P-6560BSW

0 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION DOCKET NUMBER LER NUMBER PACE FACIUIYNAME REVISION YEAR jg: SEOUENTIAL NUMBER NUMBER Palo Verde Unit 1 o so o o5 2 89 3 0 0 1 0 0 OF, 0 7 TEXT II. ASSESSMENT OF THE SAFETY CONSEQUENCES AND IMPLICATIONS OF THIS EVENT:

Nuclear Fuel Management (NFM) performed an assessment of the event and determined that the equipment and systems assumed in the UpdatedFinal Safety Analysis Report (UFSAR) Chapter 15 were functional and performed as required. Abnormal transients were not identified following the reactor trip. The scenarios .defined in UFSAR Chapter 6 concerning the Loss of Co'olant Accident (LOCA) were not challenged during this event.

A turbine trip, characterized as a decrease 'in heat removal, is normally evaluated- for peak pressures. The Reactor Coolant System (RCS) peak pressure of 2369 pounds per square inch absolute (psia) in this event is less than the 2742 psia peak RCS pressure for a Loss of Condenser Vacuum (LOCV) event. This is the UFSAR Chapter 15 limiting event in this category. The assessment concluded that this event did not result in a transient more severe than those already analyzed. The event did not cause any violation of Specified Acceptable Fuel Design Limits (SAFDL).

Safety system actuations did not occur and were.not required.

The, event did not result in any challenges to the fission product barriers or result in any releases of radioactive materials. Therefore, there'were no adverse safety consequences or implications as a result of this event. This trip did not adversely affect the safe operation of the plant or the health and safety of the public.

III. CORRECTIVE ACTION:

A. Immediate:

The failed high level controller was replaced and the new controller was tested and placed in service. The new controller functioned as designed.

Unit 1 Maintenance and Operations personnel functionally tested all of the normal and high level controllers for the High Pressure Feedwater Heaters (SJ), Low Pressure Feedwater Heaters (SJ), MSR Drain Tanks (SN)', and First and Second Stage MSR Drain Tanks (SN).

This consisted of manually raising and lowering the carriages on the controllers, watching the control valves stroke, and visually inspecting each pneumatic controller in the system. Only minor problems such as broken and sticking gauges, air regulator settings, air leaks, and worn gaskets were noted. These minor problems were corrected upon discovery.

A complete valve line-up for the Unit 1 Train A High Pressure Feedwater Heater and Extraction Steam was conducted and no other valves were found mispositioned.

41 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION DOCKET NUMBER LER NUMBER PAGE FACILITYNAME I5 SEQUENTIAL NUMBER

'?:I REVISION NUMBER Palo Verde Unit 1 0 5 0 0 0 OFO 7 TEXT A Night Order was issued to all three units. discussing the event and reminding Operations personnel of the need to maintain positive control of plant equipment.

B. Action to Prevent Recurrence:

As discussed in Section I..I, APS Engineering personnel are conducting an equipment root cause of failure analysis to determine the failure mechanism of the high level controller. If the analysis results differ significantly from the apparent cause, a supplement to this report will be submitted to describe the final root cause of failure. This analysis is expected to be completed by May 28, 1993.

Training personnel will evaluate -this event in accordance with approved procedures for inclusion into Industry Events Training for Operations, Maintenance, and Work Control personnel. ,This evaluation is expected 'to be completed by July 30, 1993'.

IV. PREVIOUS SIMILAR EVENTS There are no previous similar events reported pursuant to 10CFR50.73 where a Main Turbine trip, caused by MSR high level, resulted in a manual reactor trip.

V. ADDITIONAL INFORMATION The Plant Review Board, the Management Response Team, and the Plant Manager reviewed the Incident Investigation report and authorized a Unit restart according to approved procedures. Uni't 1 entered Mode 2 (STARTUP) at approximately 1220 MST'n January 31, 1993 and Mode 1 (POWER OPERATION) at approximately 1602 MST on January 31, 1993. Unit 1 was synchronized to the grid at approximately 0157 MST on February 1, 1993.

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