ML20043D584
| ML20043D584 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 06/01/1990 |
| From: | Hopkins R, Plenienwicz R COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| BYRON-90-0497, BYRON-90-497, LER-90-006-05, LER-90-6-5, NUDOCS 9006080273 | |
| Download: ML20043D584 (6) | |
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7'x C i mmonwrith Edison Byron Nucl:ir Station
- __ J 4450 North G;rman Church Ror.d -
- - . , *'i{g --
7 Byron, Illinois 61010 i
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May 30,- 1990 Ltri. BYRON 90-0497 i
U. S. Nuclear Regulatory Commission- f
-Document Control Desk Washington, D.C. 20555 Dear Sir The enclosed Licensee Event Report from Byron Generating Station is being
' transmitted to you in accordance with the requirements of'10CFR50.73(a)(2)(iv).
i This report is number 90-006; Docket No. 50-454.
Sincerely, R. Plenlewicz Station Manager Byron Nuclear Power Station RP/jr Enclosure Licensee Event Report No.90-006 cci A. Bert Davis, NRC Region III Administrator
, . W. Kropp, NRC Senior Resident Inspector P INPO Record Center CECO Distribution List 9006080273 900601 PDR ADOCK 05000454 S PDC (0585R/0065R) l u
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3, LICENSEE EVENT REPORT (LER)
Fm W W ,
f b ty Name (1) Dicket Numb 3r (2) j'goe (3)
Bvron. Unit 1 01 51 01 01 01 41 51 4 1lof!0l5 i Titi s (4) Reactor Trip on Low-2 Steam Generator Level !
10?_. Unknown Reasons Durina Troubleshootina on the Turbine Dialtal Elaetro-Hydraulle Cgaggitr LER Number (6) Report Date (7) Other Facilities Involved (8) _
_f.vant Date (5). ]
honth Day Year Year fj/
//
f Sequential f/j/j/ Revision Month Day Year Facility Names Docket Number (s
/// Number /// Number )
NONE 01 51 01 01 01 l r
~~
Q_j 5 0 13 910 910
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01016 0l0 0l6 0 11 910 01 51 01 01 01 l l THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10CFR OPNW (Check on_e or more of the followina) (11) 1 20.402(b) _ 20.405(c) JL 50.73(a)(2)(iv) _ 73.71(b)
POWER _ 20.405(a)(1)(1) 50.36(c)(1) 50.73(a)(2)(v) _ 73.71(c)
LEVEL 20.405(a)(1)(ii) 50.36(c)(2) 50.73(a)(2)(vii) ,0ther (Specify l7 l9 _ __
(101 __. 20.405(a)(1)(iii) 50.73(a)(2)(1) _ 50.73(a)(2)(viii)(A) in Abstract
///////////,/,////,////////,// __ 20.405(a)(1)(lv) _ 50.73(a)(2)(ii) 50.73(a)(2)(vill)(B) below and in
//////////}/' ///}////////}///
/
j _._ 20.405(a)(1)(v) _,. 50.73(a)(2)(iii) _ 50.73(a)(2)(x) Text)
- LICiHSEE CONTACT FOR TH15 LER (12) i Name TELEPHONE NUteER AREA CODE R. Hooklas. Doeratina Enaineer Ext. 2216 8l 1 15 2 13 14 1 l 51 41 41 -
COMPLETE ONE LINE FOR EACH COMPONEN FAILURE DESCRIBED IN THIS REPORT (13) l CAUSE SYSTEM COMPONENT MANUFAC- REPORTABLE CAUSE SYSTEM COMPONENT. MANUFAC- REPORTABLE .
TURER TO NPRDS TURER TO NPRDS .
X Jl J X II lS I X 19 19 19 N X Jl J l IF IU W111210 N ;
X Jl J l IF IU W 11 12 10 N l l l l l l l I SUPPLE E NfAL REPORT EXPECTED (14) Expected tignth l Da_v l Year t SubelssIon lyes (If ves. comolate EXPECTED SUBMISSION DATE)
X l NO l l l ABSTRACT (Limit to 1400 spaces, i.e. approximately fif teen single-space typewritten lines) (16) j On 5/03/90, at 0300, with Unit 1 operating at 79% power, the Operating Department began surveillance 1805 l 3.4.2.a-1, " Turbine Throttle, Governor, Reheat, and Intercept Valve Monthly Surveillance." At 0359, the surveillance was held to accomodate troubleshooting on the turbine Digital Electro-Hydraulic Computer l (DEHC). Due to the repeated failure of a 2 ampere fuse on 1 of 4 loops on power supply card C1-H35, the j turbine runback pushbutton was removed to prevent a runback signal. As the surveillance continued, all j indication on ths DEHC panel was lost. The 5 ampere fuse on the same card was blown. As a replacement fuse was inserted, c 100 Megawatt power excursion occurred, followed by a complete load rejection. At 0631, a reactor trip occ e ed on Low-2 Steam Generator Level.
The 2 ampere fuse failed due to a short circuit in the pushbutton. The button was equipped with a grounded copper screen. When the button was moved inside the socket, the screen came in contact with the pushbutton light's power supply wt lch induced a short and blew the fuse. The root cause for the 5 ampere fuse failure and subsequent reactor trip remain indeterminate.
As corrective action, the screens in all the pushbuttons were removed. The lighting circuit was also rewired to be made separate from the runback circuitry so a loss of indication will not ef fect a runback signal.
This event is reportable per 10CFR50.73 (a)(2)(iv) for an event that resulted in an automatic actuation of an Engineered Safety Feature, including the Reactor Protection System.
(0585R/0065R)
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'5 LICENSEE EVENT REPORT fLER) TEXT CONT 218]AT10N Fern Rev 2.0
. ' FACI'LITY NA8E (1) DOCKET NUPSER (2) LER MufSER f 6) l Paae (3)
Year // Sequential /j/j/ Revistor j/j/
//
f Number /j// Number
. Byron. Unit 1 ~ 01510 l D l 0141514 9l0 - Ol0l6 - 0 l '1 0 12 0F 0 15 '
TEXT Energy Industry Identification System (EIIS) codes are identified in the text as (XX) .
A. PLANT C0teIT10NS PRIOR TO EVENT:
Event Date/ Time 5/03/90 f 0631 Unit 1 HDDE 1 - Power Goeration Rx Power 79% RCS (AB) Temperature / Pressure Normal Deeratina
- 8. DESCRIPTION OF EVENT:
On 05/03/90, at 0300, with Unit I at approximately 79 percent reactor power and 1000 Hegawatts (HWe), the Unit Nuclear Station Operator (NS0 licensed) started 180$ 3.4.2.a-1, " Turbine Throttle, Governor, Reheat.
and Intercept Valve Honthly Surveillance." During the previous two executions of the surveillance (on 4/29/90 and 4/30/90), the unit experienced a turbine runback while testing the turbine governor valves.
(In-house Deviation Investigation Report 6-1-90-073 documents these events). As a result, Operational Analysis Department. Technical Staff, and Westinghouse personnel were present during the test to troubleshoot the turbine Digital Electro-Hydraulic Computer (DEHC) (JJ) during valve testing. -
Troubleshooting and analysis of the last executions of the survelliance indicated the runback signal was being generated through one of the three runback inputs into the turbine DEHC. The signal was initiated due to a blown two ampere (amp) fuse on one loop of a 7300 series Quad Loop (NQP) power supply card in the DEHC computer location C1-H35. To prevent the unit from running back during the performance of the surveillance, the procedure had been temporarily changed to bias the stopping points for the turbine runback signal to higher values.
At 0359, while opening Governor Valve number 1, the fuse on the same DEHC power supply card blow. The DEHC l panel Open and Close pushbutton status lights went out and a turbine runback signal was received. With the l DEHC in Operator Auto, the unit ran back approximately 60 Hegawatts. The N$0 transferred the DEHC to l Hanual mode, stopping the runback. The plant was stabilized and the valve under test was reopened using the DEHC panel pushbuttons and the DEHC was returned to the Operator Auto mode.
To prevent any additional runback signals from being generated, the panel's turbine runback pushbutton was removed. The blown fuse was replaced and the surveillance was restarted. Again, while opening' Governor Valve number 1 the two amp fuse on the same power supply card blow. No runback signal was generated and the test continued without light indication for the DEHC Open and Close pushbutton status lights. Governor Valves I and 3 were then successfully tested.
To measure the current drawn by the circuit during the test, an ammeter was installed across the blown two amp fuse as Governor Valve number 2 was being closed. While opening the valve, the five amp fuse upstream of the blown two amp fuse which protects all four loops on card C1-H35, also blew and all light indication on the DEHC panel was lost.
At 0631, the 5 amp fuse was removed and a new fuse was inserted into the card. As the new fuse was installed, tha unit experienced a sudden 100 HWe load increase followed by a complete load rejection. The load rejection initiated a Steam Generator Low Low Level reactor trip.
l The operators entered emergency procedure 1BEP-0, " Reactor Trip or Safety Injection." All systems resp nded as designed. Aux 111ary Feedwater (AF) (BA) automatically started to maintain sttam generator levels. Stable conditions were achieved at 0700, as Auxiliary feedwater was secured and the Start Up
. Feedwater Pump was placed in service to maintain Steam Generator levels. The NRC Operations Center was l notified of the event at 0859 via the Emergency Notification System per 10CFR 50.72 (b)(2)(ll).
(0585R/0065R)
LIrrutrr EVENT REPORT (LER) TEXT CONTIIanTION Fore Rev 2_1
, FACILITY NAE (1) DOCKET NUPSER (2) LER lateER (6) Pane (3)
, Year fj/j/
/ Sequential /j/
j/
Revision ('
/// ""r / Neber Bvran tinit 1 0 l 5 l 0 l 0 1 0 1 41 El 4 910 - 010l6 - 0 10 0 13 0F 0 15 TEXT Energy Industry Identification System (EIIS) codes are identified in the text as (XXJ B. DESCRIPTION OF EVENT: (continued)
All actions taken by the operators were correct which minimited the severity of the event. There were no systems or components inoperable which contributed to the event. This report is being submitted pursuant to 10 CFR 50.73 (a)(2)H v) for any event or condition that resulted in an automatic actuation of an Engineered Safety Feature, including the Reactor Protection System.
C. cal'SE OF EVENT:
The initial runback was caused by a short circuit in the DEHC panel Open pushbutton which caused the two amp fuse on the NQP card to fail.
The Station installed a replacement DEHC panel during the recent refuelin) )utage (81R03). Some of the new panel's pushbuttons were equipped with a grounded copper screen designed to eliminate radio frequency interference. Ths Open pushbutton was equipped with this screen. When the pushbutten was moved inside the socket, the screen in the Open pushbutton came into contact with the pushbutton light's 26 volt positive power supply. This induced a short circuit which blew the two amp fuse for the pe'tton status light.
~
During a nomal valve test, the Open and Close pushbutton status lights lliuminate when the close signal for the valve under test has decreased enough to switch a comparator circuit. When the comparator switches, it brings in a ground on one side of the light to complete a circuit and turn the Open and Close lights on. When the valve is returned to its original position the comparator turns off, removes the ground, and the lights go off.
The turbine runback pushbutton was also installed as a modification during BIR03. When depressed, the
[
runback button would cause a transistor to switch sending a logic low signal to the DEHC computer. A l normal (no runback) signal was also provided to the cesputer through the pushbutton status lights. The power supply for the runback status light is the same as the Open and Close pushbuttons on the panel. When the valve test was in progress, the Open and Close lights had 26 volts on one side and ground on the
- other. As the fuse blew, the potential on both sides of the Open and Close pushbuttons and the potential at the runback pushbutton was pulled to ground through the valve test comparator circuit. The ground at the runback pushbutton generated a low at the computer which indicated a runback request.
In anticipation of receiving the runback signal during the surveillance, the stopping points for the runback with the DEHC in Automatic and Manual mode were biased higher. The stopping point for the DEHC in the Automatic mode was a sof tware adjustable value. The value was increased to 100 Megawatts above the I value at the time of the test. When the runback signal was initiated, the DEHC Impulse Pressure feedback loop'was rejected as expected. With no feedback in servire, the DEHC recalculated the expected Megawatt value based on valve position. The new reference value was approximately 80 Megawatts above the runback stopping point entered into the computer. As a result, the DEHC ran the unit back. As the value for the Manual mode had been raised to a point above the operational level the runback stopped when the Man d mode was selected.
The circuit in which the current was being measured had a second 2 amp fuse which was expected to blow if
! the current became excessive. For unknown reasons the 5 amp fuse which protects all four loops failed -
instead. Failure of the 5 amp fuse on the HQP card resulted in the loss of all DEHC panel indication.
The root cause of the blown 5 amp fuse and subsequent power excursion and load rejection remain i
indeterminant. The reactor subsequently tripped on low-2 steam generator level due to the shrink l experienced after the load rejection. It is speculated that the insertion of the fuse caused a spike on the 26 volt power supply that is cosunon to several 7300 series cards for DEHC. However, simulation of this event could not support this theory during subsequent troubleshooting.
(0585R/0065R)
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LICtN1EE EVENT REPORT f LER1 TEXT CONTnalaTIGN Fare Rev Q
.FAC} LIT,Y NADE (1) DOCKET NUISER (2) LER NLBSEE (6) Paan (3)
. Year //,j/ Sequential /// Revision f fff
/// "- " r
_ /// Number arren. unit i e I s 1 0 1 0 1 0 1 41 El 4 910 - 01016 - 0 l0 0 14 0F 0 15 TEXT Energy Industry Identification System (EIIS) codes are identified in the text as [XX)
D. SAFETY ANALYSIS:
This event did not endanger the health or safety of the plant or public. The plant functioned per design.
The reactor trip estabitshed a more conservative operating configuration. No safety systems were impaired..
J l
E. CORRECTIVE ACTIONS:
Corrective action taken to prevent recurrence of this problem include rewiring of the turbine runback l circuit and removal of the screens from the DEHC panel pushbuttons. The runback was rewired via minor change H6-1-90-649. The lighting circuit was made separate from the actual runback signal, so that loss of power to the lightbulbs would not cause a runback signal to be generated. The screens in all the pushbuttons on the panel were removed at the suggestion of the manufacturer.
With the unit off line, the DEHC simulator was connected to the DEHC and the conditions prior to the event were re-established. The 5 amp fuse was pulled, removing all power to the DEHC panel. The event was repeated many times and the response to reinstalling the fuse was varied. In some cases, the DEHC transferred to Hanual, and in some cases it stayed in Automatic. Based on the conditions dupilcated, it is suspected the DEHC transferred to Hanual mode during the event. In support of this theory, time was lost on the printout which indicates the computer did stop and DENC should have been in manual. Regardless, the signal to the turbine governor valves remained stable when the 5 amp fuse was replaced making the root cause for the load rejection indeterminate.
Due to past and recent troubles with DENC, the Station will pursue additional technical training for personnel involved with DEHC. Action Item Record 454-225-90-124 tracks completion of this item.
F. PREVIOUS OCCURRENCES:
Several problems with the DEHC system have occurred r'ecently. Problems with a failed fuse causing runbacks are documented in In-house Deviation Investigation Report 5-1-90-073. A historical event search identified a reactor trip that occurred during the same surveillance as documented in DVR 6-1-85-056 (LER 85-028).
However, the turbine was manually tripped with turbine power greater than 10%, so the root causes are not the same.
Station Trend 90-011 had been identified on 5/01/90 due to the recent transients caused by DEHC. Trend 88-08 has previously addressed DEHC problems involving failed servo valves.
SOER 84-6, " Reactor Trips Caused by Turbine Control and Protection System failures," and 04HR 3935, "Twn Consecutive Trips as a result of EHC Design Deficiency," are industry documents of similar nature as this event.
(0585R/3065R)
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.4; 9 LICENSEE EVENT REPORT (LER) TEXT CONTItRET10N Form tev 2.0
.. , 'FACfLIM NAM (1) DOCKET NUPSER (2) LER tEamr8 (El Pane (3)
/jj Year- /// Sequential // Revision
/j/jj/ f N&r /// "" r erren; unit i e I s I e I o I o 1 41 si 4 9Ie - oIeIa - eie o is or n is TEXT Energy Industry Identification System (E!!$) codes are identified in the text as (XX) l G. CONPONENT FAILURE DATA:
MANUFACTURER NDENCLATURE PSOEL NUPSER MFG PART ElPSER Electronic Technology pushbutton ---- 800-AICIE4-J3-L2N1(W)-12 i Systems Inc.
Westinghouse 2 ampere fuse ---- 669A699H05 Westinghouse 5 ampere fuse ---- 743A407221 RESULTS OF NPRD$ SEARCH:
The DEHC system is not reportable to Nuclear Plant Reliability Data $ystem (NPRO$).
(0585R/0065R)