ML20043H174

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AEOD Technical Review Rept AEOD/T90-08, Turbine Bypass Malfunctions
ML20043H174
Person / Time
Issue date: 06/14/1990
From: Kaufer B
NRC
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ML20043H173 List:
References
TASK-AE, TASK-T90-08, TASK-T90-8 AEOD-T90-08, AEOD-T90-8, NUDOCS 9006220129
Download: ML20043H174 (36)
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{{#Wiki_filter:* ? i AEOD TECHNICAL REVIEW REPORT UNIT: Various TR REPORT NO.: AE0D/T90-08 DOCKET NO.: Various DATE: June 14, 1990 LICENSEE: Various EVALUATOR / CONTACT: B. Kaufer NSSS/AE: Various

SUBJECT:

TURBINE BYPASS MALFUNCTIONS EVENT DATE: January 1980 through December 1989

SUMMARY

Thistechnicalreviewdocumentsoccurrencesofturbinebypass(steamdump) malfunctions, inadvertent opening or closing of turbine bypass valves, and the resultant effect on plant startup, operation, and shutdown. Searches of the Nuclear Documents Systems (NUDOCS) and Sequence Coding and Search Systems (SCSS) data bases found 140 domestic events reporting these types of malfunc-tions since 1980. Most of these events have led to a plant transient (usually primary system pressure or level) and 61% of the events have ended in a reactor trip. 1 The failure mode cannot be attributed to a dominant single fact; events varied both as to root cause and plant status. While a significant fraction of these events can be attributed to personnel error (approximately 24%), the largest category was steam bypass control system malfunctions (approximately 50%). This review identified that the major cause of these events was not the malfunction or failure of the bypass valve itself (less than 15%), but failures of supporting components or systems. Theseinturnledtovalve(s) malfunctions and subsequent plant transients. Based on this review, the following conclusions have been reached: 1. Actual malfunctions of turbine bypass valve (s), where the root cause was directlyattributablevalvefailure,werefew(15%)comparedwithother Causes. 2. The direct cause of most events, was failure of the steam bypass control system or other supporting components associated with these valves. 3. Based upon the events reviewed, turbine bypass malfunctions create a condition which challenged a safety system in almost every case. 4 The risk of potential core damage as evaluated by(Ref.1-6) was " Precursors to Potential Severe Core Damage Accidents" studies detremined to be very small. 5. Continuing occurrences of these types of events in the future, may warrant further study into the root causes which precipitated the turbine bypass malfunctions and their associated controls. 9e os pt 2 o t u ? 9ocuY = POR CAG NEXb fpc

E ,o 2 l INTRODUCTION Turbine bypass valves are a non-safety related part of the main steam system. They are used to bypass a portion of the steam flow to the condenser as a heat sink during plant startup, shutdown, and some transients. Bypass system malfunctions lead to plant transient conditions involving feedwater/ steam flow, reactor or steam generator water level or pressure. 3 DISCUSSION In most of the events reviewed, an ESF actuation resulted from a bypass valve malfunction. Depending on plant conditions, operator responses are seldom quick enough to prevent safety system actuations. Based u)on the events reviewed, turtine bypass malfunctions create a condition w11ch challenged a safety system in almost every case. In almost every instance a power transient or a scram has occurred. We attempted to judge the significance of these events for safe operation and l shutdown of the plant. A cross check was done of these events against those i events studied between 1980 and 1987 as

  • Precursors to Potential Severe Core Damage Accidents" (Ref. 1-6).

They are considered to be accident sequences l that, if completed, would have resulted in inadequate core cooling. Of the two hundred and eighty-three events included in the precursor studies during this period, ten were bypass system malfunctions identified in this report (AttachmentC). The CPCD in the ten events ranged from 1.0E-04 to i 6.9E-07, and eight of the events had a conditional probability of core damage (CPCD) of greater than 1.0 x 10 E-6. A comparison of the percentage of risk associated with the bypass system events and the entire precursor data base revealed that the contribution to CPCD from the eight events was less than 1%. Except for two years, 1984 (4.8%) and 1986 (2.4%), the results on a yearly basis verified these low values. Although the 1984 percentage is significant in comparison to the other years, taken in context of the overall data, it still represents only a small risk. In sumary, the events studied present a case in which the failure mechanism 4 most often leads to a plant transient involving actuation of engineered i safety features systems but only a small contribution to risk associated with potential severe core damage probability. ANALYSIS OF EVENTS The inadvertent opening or closing of a bypass valve creates a condition in which steam flow changes cause pressure and level variations in the reactor pressure vessel or steam generators. The characteristics of the transient are dependent on initial plant conditions, time sequence of valve operation, control system responses, and operator response.

.. : l ' p

  • 1.NALYSIS OF EVENTS (cont'd)

We reviewed bypass system failure events occurring s'.nce 1986. Of the 72 opening (ported, the most common valve malfunction was that of an inadvertent events re 31 events). In BWRs, as would be expected, this usually precipitated a reactor low level transient and the associated safety system actuations. Responses to this condition on PWRs varied significantly. As expected steam flow and pressure changes along with resultant RCS temperature fluctuations were experienced which in turn led to safety system actuations. The second highest category (22 events) involved malfunctions in which the valve either failed to operate at all or valve response was to slow. The majority of these events occurred in PWRs, and resulted in varying system responses depending upon plant conditions at the time. The remaining malfunctions involved events where valves either inadvertently closed or cycled open and closed. A closing bypass valve resulted in either i a high reactor, pressurizer, or steam line pressures and the subsequent safety system actuations. Plant responses to the effects of valve position changes were as would be expected. System actuations were consistent with the plant conditions. Several events which were the result of inappropriate operator actions were i-identified. SYSTEMATIC TF. ENDS l Review of the entire data base of events was performed to determine if any systematic trends could be related to these failures. As discussed in the following no specific trend could be identified. - PLANT TYPE: Of the total events; 56 (40%) occurred at BWRs and 84 (60%)atPWRs. The significant difference between the two types of plants was the scram ratio. Of the 56 events in BWRs, 46 (82%) caused or led to a subsequent scram while only 40 of 84 (48%) PWR events resulted in. trips. - EVENT DATES: A review of the event dates did not distinguish any ? increasing or decreasing trends. From 1980 to 1983 only 14 events werc recorded. Since 1984, roughly 21 events per year have occurred. The increased amounts since 1984 i can be attributed to changes made in reporting require-ments and an increase in the number of reactors in service. - PLANT STATUS: Again no positive trend could be established. Events were equally distributed between the different plant modes of operation and shutdown.

i

  • SYSTEMATIC TRENDS (cent'd)

- ROOT CAUSES: As stated previously most of events occurred because of 4 failures of support components associated with the l turbine bypass valves control systems. Most of the operator errors involved events which occurred during plant startup. Additionally, several events were due to procedure deficiencies, which in turn led to operator errors. CONCLUSIONS This review was initiated to eva unte the effects of main turbine bypass (steam dump) valve malfunctions during the various stages of operation and shutdown. In this regard, many events were documented involving these failures. The results of this review found that the direct cause of most i events, was failures involving tie steam bypass control systems associated with these valves. Failure or malfunction of a bypast valve due to the mechanics or operation of the valve itself occurred in only a small percentage of the events. Most of 1 these failures can be related to problems associated with the types of valves I involved and have been covered in other NRC studies (such as studies on operating (SOVs).)(Ref.7-8-9). problems of motor operated valves (MOVs) and solen problems The safety significance of bypass system failure is similar in nature to that of failures of non-safety related systems which lead to a plant shutdown. These events almost always result in a primary system transient and subsecuent reactor trip or ESF system actuation. However, the )otential risk of core damage is low. Ther:: fore, No further AEOD action on tais issue is recommended at this time. l i l l i l i i

"' 4 REFERENCES 1. NUREG/CR-3591 Volume 1 " Precursors to Potential Severe Core Damage Accidents: 1980-1981". 2. flVREG/CR-4674 Volume 3. " Precursors to Potential Severe Core Damage Accidents: 1984". 3. NUREG/CR-4674 Volume 1, " Precursors to Potential Severe Core Damage Accidents: 1985". 4 NUREG/CR-4674 Volume 5, " Precursors to Potential Severe Core Damage Accidents: 1986". L 5. NUREG/CR-4674 Volume 7, " Precursors to Potential Severe Core Damage l Accidents: 1987". 6. NUREG/CR-4674 Volume 9 " Precursors to Potential Severe Core Damage Accidents: 1988". 7. Case Study AE0D/C603, "A Review of Motor-Operated Valve Performance," December, 1986. 8. Spect'1 Study AE0D/S503, " Evaluation of Recent Valve Operator Motor Burnout Events," September, 1985. 9. braft Case Study " Solenoid Valve Problems," to be issued in 1990. I i l

} l 1 ATTACMENT A BWR TURBINE BYPASS fSTEAN DLMP) NALRMCTIONS NOTE: Details of each event are presented following the general listing below. 1. COOPER (298) LER 80-031 08/04/80 2. PEACH BOTTOM 2 (277) LER 80-027 11/06/80 3. COOPER (298) LER 80-044 11/15/80 4. LA SALLE 1 (373) LER 83-085 07/18/83 5. LA SALLE 1 (373) LER 83-087 07/18/83 6. 8RUNSWICK 1 (325) LER 84-002 02/03/84 7. WPPS$ 2 (397) LER 84-044 05/13/84 8. WPPSS 2 (397) LER 84-045 05/18/84 9. SUSQUEHANNA 2 (388 LER 84-008 05/27/84 10. WPPSS 2 (397 LER 84-056 06/01/84 11. FITZPATRICK (333 LER 84-013 06/25/84 12. LA SALLE 2 (374) LER 84-035 07/09/84 13. DRESDEN 3 (249) LER 84-007 07/22/84 14. 8IG ROCK P0 INT (155) LER 84-009 07/26/84 15. BIG ROCK POINT (155) LER 84-012 08/03/84 16. LA SALLE 2 (374) LER 84-050 00/10/84 17. QUAD CITIES 1 (254) LER 84-015 08/25/84 18. GRAND GULF 1 (416) LER 84-040 09/05/84 19. LA SALLE 2 (374) LER 84-069 09/12/84 20. WPPS$ 2 (397) LER 84-104 10/04/84 21. WPPS$ 2 (397) LER 84-109 10/13/84 I 22. WPPSS 2 (397) LER 84-112 10/20/84 i 23. WPPSS 2 (397) LER 84-113 10/21/84 24. DRESDEN 3 (249) LER 84-020 10/26/84 25. LA SALLE 2 (374) LER 84-076 11/20/84 26. WPPS$ 2 (397) LER 85-014 02/14/85 27. PILGRIM 1 (293) LER 85-014 06/15/85 28. FERMI 2 (341) LER 85-033 07/05/85 l 29. FERMI 2 (341) LER 85-066 09/27/85 30. FERMI 2 (341) LER 85-068 10/01/85 31. NINE MILE POINT 1 (220) LER 85-022 11/07/85 32. NINE MILE POINT 1 (220) LER 85-023 11/08/85 33. SUSQUEHANNA 2 (388) LER 86-001 01/21/86 34. HOPE CREEK 1 (354) LER 86-044 07/25/86 35. HOPE CREEK 1 (354) LER N -048 07/30/86 36. FERMI 2 (341) LER e6-031 08/29/86 37. PERRY 1 (440) LER 86-055 09/02/86 38. QUAD CITIES 1 (254) LER 86-030 10/16/86 39. BRUNSWICK 1 (325) LER 86-029 11/16/86 1 40. 0YSTER CREEK 1 (219) LER 86-032 12/24/86

l 2 l 41. 0YSTER CREEK 1 (219) LER 87-005 01/16/87 42. FERMI 2 (341) LER 87-008 03/01/87 43. PEACH 80TTOM 3 (278) LER 87-002 03/25/87 44. CLINTON 1 (461) LER 87-020 03/30/87 45. LA SALLE 1 (373) LER 87-022 05/28/87 46. NINE MILE POINT 2 (410) LER 87-043 07/11/87 47. VERMONT YANKEE (271) LER 87-005 08/07/87 48. GRAND GULF 1 (416) LER 88-005 01/11/88 49. PERRY 1 (440) LER 88-015 04/30/88 50. VERMONT Yt.NKEE (271) LER 88-009 07/03/88 51. PILGRIM 1 (293) LER 89-011 03/04/89 l 52. QUAD CITIES 1 (254) LER 89-003 04/12/89 i 53. NINE MILE POINT 2 (410) LER 89-009 04/22/89 54. PEACH 80TTOM 2 (277) LER 89-023 10/05/89 55. SIG ROCK POINT (155) LER 89-009 10/27/89 56. FITZPATRICK (333) LER 89-020 11/05/89 l ,,--.-,-n.e.,,.,,,,,. -- e.

3 BWR TURRIME BYPASS fSTEAM DWPLMALFUNCTIONS 1. COOPER (298) LER 80-03) 08/04/80 Event: Voltage transients due to line fault caused false signals to i be induced into Turbine Generator DEH computer, which resulted in TBVs opening. This in turn caused Group I (MSIV) i isolation and Rx SCRAM. 2. PEACH BOTTOM 2 (277) LER 80-027 11/06/80 EVENT:

  1. 3 Bypass valve exhibited erratic operation due to a lug I

connector which was found to be broken. Power was reduced I and valve was failed closed to repair. 3. COOPER (298) LER 80-044 11/15/80 l EVENT: Following Rx scram normal cooldown rate (100F/hr) was exceeded due to a failed card in the Turbine Control System which caused the (?) steam bypass valves to remain open. Cooldown rate was exceeded. 4. LA SALLE 1 (373) LER 83-085 07/18/83 l EVENT: During EHC troubleshootini) a bypass valve transient occurred causin!1 a Rx SCRAM. Addit <onally, cooldown rate was exceeded follow' ng scram due to rapid depressurization, full core scram and HPCS and RCIC injection. l 5. LA SALLE 1 (373) LER 83-087 07/18/83 i EVENT: All 5 TBVs went open due to work being done on EHC system. RFP tripped on high level and Rx level dropped to -40". T8V that had closed went open due to EHC card movement, Rx level -50". Primary Containment Isolations, HPCS & RCIC initiated and a i Rx SCRAM. t 6. BRUNSWICK 1 (325) LER 84-002 02/03/84 L EVENT: While preparing to roll & place the turbine into service a Rx L scram occurred due to High Rx pressure (1049 psig). Caused L by a loss of EHC system fluid actuation supply (FAS) pressure, L which resulted in the TBVs closing. Loss of FAS due to 2 through-wall cracks in header attributed to cyclic loading fatigue. l' l 7. WPPSS 2 (397) LER 84-044 05/13/84 l EVENT: During power ascension test program, turbine being rolled to synchronous speed, as turbine speed approached 1650 rpm, the l DEH system emergency trip header allowed leakage of DEH fluid l past the closed seat of the bypass reset solenoid which caused .. ~

4 7. WPPSS 2 ~(Cont'd) MSBV to open and remaining three compensated and went closed resulting in a Rx high pressure SCRAM. 8. WPPSS 2 (397) LER 84-045 05/18/84 EVENT: Rx high pressure trip as a result of MS bypass valves closing due to low DEH fluid pressure which resulted when main turbine was manually tripped. 9. SUSQUEHANNA 2 (388) LER 84-008 05/27/84 PRECURSOR: PROBABILITY 0F CONSITIONAL CORE DAMAGE = 3.3E-6 EVENT: During plant shutdown (due to LPCI 'B' loop inop.) which was being accomplished by inserting CRs the #1 TBV would not close below the 18% open position. Shutdown was stopped and CRs were positioned to control and maintain Rx pressure. Rx was then manually scrammed. RFP was manually tripped and the inboard MSIVs were manually closed. 10. WPPSS 2 (397) LER 84-056 06/01/84 EVENT: During power ascension testing program all TBVs went closed due to a failure in the DEH (defective electronic circuit card) system. RX pressure increased and operators attempted to force them open by withdrawing a CR and other system actions. TBVs did not respond and h' gh RX pressure (1038 psig) SCRAM resulted. t 11. FITZPATRICK (333) LER 84-013 06/25/84 EVENT: Rx scram occurred due to high Rx pressure (1060 psig) resulting from TBVs failing closed. Cause was plugging of I hydraulic fluid filters on the servoactuators for 2 of the bypass valves. 12. LA SALLE 2 (374) LER 84-035 07/09/84 EVENT: During Startup test program, while troubleshooting on EHC system, a probe slipped causing a momentary loss of 30 volt power supply to EHC system, which resulted in cycling of TBV, control and intermediate valves and subsequently a Rx scram on high pressure. 13. DRESDEN 3 (249) LER 84-007 07/22/84 EVENT: During startup of unit, the #1 TBV operated erratically, causing a Group I isolation on MS low pressure while in run. Caused by failure of servovalve mechanism for opening / closing valve due to sediment deposits which had accumulated.

5 14. BIG ROCK POINT (155) LER 84-009 07/26/84 l EVENT: Turbine load had been tripped as part of a routine overspeed test. TBV failed close (2 minutes after test completed) in automatic mode causing a Rx high pressure scram. Failure due to low amplitude /high frequency oscillation initiated by test. i 15. BIG ROCK POINT (155) LER 84-012 08/03/84-EVENT: Rx scram with turbine generator off-line and isolated. TBV in automatic control at a partial opening went full open. Following a slight drop in pressure TBV closed causing high neutron flux and low steam drum level (similar to LER 84-009). 16. LA SALLE 2 (374) LER 84-050 08/10/84 EVENT: During performance of Control valve surveillance startup test, the maximum combined flow limiter (MCFL) of the EHC system limited opening of the #1 TBV to compensate for l increased pressure when the #1 control valve was closed. Rx scram occurred due to high pressure (>1043 psig), also half isolation signal was received on level drop (approx. -50") as well as RCIC initiation and recire, pump trip (ATWS signal), 17. QUAD CITIES 1 (254) LER 84-015 08/25/84 EVENT: Unstable voltage output due to dirty contacts on the back-up speed control circuit board caused TBVs to suddenly cycle open/close which resulted in pressure spike and subsequent Rx scram on hi-hi APRM signal, 18. GRAND GULF 1 (416) LER 84-040 09/05/84 EVENT: Following a Rx scram the pressure reference setpoint was lowered to a point which caused TBVs to fully open. Rx water level decreased to scram setpoint. l 19. LA SALLE 2 (374) LER 84-069 09/12/84 EVENT: Bad lug on EHC control unit #2 bypass valve limit switch terminal board was not crimped correctly causing spurious opening of 3 BVs resulting in Group I isolation (signal closed the main steam drains, MSIVs were already closed). 20. WPPSS 2 (397) LER 84-104 10/04/84 EVENT: During startbp vendor rep, removed an electronic power supply printed circuit card from the DEH control cabinet resulting in all 4 TBVs going full open. He then replaced

.l ~ l l l 20. WPPSS 2 (Cont'd) I 1 card causing them to go closed. Resulting pressure and i level trans' ent caused a Rx low water level SCRAM. l 21. WPPSS 2 (397) LER 84-109 10/13/84 1 1 EVENT: While investigating a DEH (high fluid temp.) problem on the l l: main turbine the turbine generator (TG) and TBVs were observed to be oscillating. A power reduction was commenced l to reduce fluid temps, and the TBVs were noticed to be l oscillating between open/close. As cycling increased the Rx was manually scrammed. Oscillation was due to radio fre-quency interference. 22. WPPSS 2 (397) LER 84-112 10/20/84 EVENT: During performance of power ascension test, operator l initiated a setpoint change. The DEH control console did not accept digit (4) and new setpoint became 95 instead of 945. l This unnoticed and test was initiated, which caused TBVs to fully open. Rx pratture was then reduced to <831 with the resultant cle:ure of MSIVs and Rx scram. 23. WPPSS 2 (397) LER 84-113 10/21/84-i EVENT: Operators were using BVs to remove decay heat following a Rx l scram from 75% power. Cooldown rate was determined to be l. more than desired, operators therefore closed down on BVs to reduce steam flow. This action caused sudden decrease in Rx i water level <1evel 3 setpoint) resulting in a RPS actuation. l 24. ORESDEN 3 (249) LER 84-020 10/26/84 EVENT: During planned unit shutdown, Rx scramed on MSIV not full open caused by Group I isolation (on < 850 psig with mode switch in run) when turbine was manually tripped. Group I ~ isolation was caused by TBVs opening all at once due to a faulty voltage comparator and lower than normal Rx pressure (due to computer ind, reading 10 psig to high). 4 25. LA SALLE 2 (374) LER 84-076 11/20/84 EVENT: The TB system was declared inoperable when the fast acting solenoid on #5 TBV showed infinite resistance (open coil). Electrical junction box was found full of water and j subsequently Rx power was reduced to <25% per T/S.

-- ~ i l i 7 I 26. WPPS$ 2 (397) LER 85-014 02/14/85 EVENT: While investigating a failure of the main turbine to latch, additional problems were found. Tech staff direction was l given to open vacuum trip test valve (even though OP I discussed this situation, it was not recognized that this would result in automatically switching TBV control to manual mode). A Rx scram occurred due to pressure spike from TBVs closing. 27. PILGRIM 1 (293) LER 86-014 06/15/85 EVENT: Operator cracked open TBV and Rx water level was slightly high. The resulting (expected) level swell associated with i opening the bypass valve and fluctuating water level resulted in a high level MSIV isolation, Rx pressure > 600 l psig and therefore a RX SCRAM. 28. FERMI 2 (341) LER 85-033 07/05/85 EVENT: RX scram resulting from a water level transient [ level 3) occurred when TBV controllers malfunctioned caus'ng the TBVs to close. l 29. FERMI 2 (341) LER 85-066 09/27/85 1 EVENT: One TBV went closed during main turbine run-up testing. Closure caused Rx pressure to increase and led to RPS trip on high pressure (1068 psig). It was determined that at the gain setting used in testing, the noise picked up by the turbine speed pickup was amplified and seen by the run-up l module as part of the speed pick-up. This caused a rapid control action on the TBV, which in turn caused a large j valve position error signal leading to a closure of the TBV. l 30. FERMI 2 (341) LER 85-068 10/01/85 EVENT: While increasing Rx pressure for performance of a startup test both TBVs went full open. Resulting pressure drop caused Rx water level to swell above level 8 setpoint, automatically tripping Rx feed pump. Operators then closed TBVs causing Rx water level to decrease to level 3 resulting in an automatic Rx SCRAM. The initiatinq cause was traced to a discontinuity in the motorized potent <ometer which derives the Rx pressure setpoint signal. 31. NINE MILE POINT 1 (220) LER 85-022 11/07/85 EVENT: Twice during plant startup, TBV inadvertently closed resulting in a decrease in Rx water level and subsequent scram, and initiation of HPCI. The problem with the TBV was attributed to sticking at elevated temperatures. ---w ,e a ,--n-- r,,- - - -~ e, ,,-,-----,ev.,- ,w., wwn---

I ^ y 8 32. NINE MILE P0 INT 1 (220) LER 85-023 11/08/85. EVENT: While preparing for main turbine startup, high temperature in the main turbine exhaust hood caused a turbine trip and actuated HPCI mode of FW. The condition was a result of i multiple T8Vs open for electromatic relief valve surveillance testing, prewarning of 2nd stage reheaters, and manual control of the exhaust hood desuperheating sprays. 33. SUSQUEHANNA 2 (388) LER 86-001 01/21/86 EVENT: Operator failed to notice that 2 T8Vs opened while he was withdrawing control rods during startup. This resulted in a l decrease of reactor water level to +13" (low level) and Rx SCRAM. i 34. HOPE CREEK 1 (354) LER 86-044 07/25/86 EVENT: While testing was being performed on main turbine stop valves, operator was preparing for shell warming and selected "all valves closed" on EHC panel. All T8Vs went open, Rx level increased (level 8) and Rx feed pumps tripped, operating secondary condensate pump tripped, Rx { 1evel decreased (level 3) and Rx SCRAM. RCIC used to reestablish level i 35. HOPE CREEK 1 (354) LER 86-048 07/30/86 EVENT: A power failure of the EHC occurred, during main turbine j ro1111g in preparation for generator synchronization, resulting in the T8Vs cycling open/ closed in conjunction with the inability of operator to maintain level, low level (3) Rx scram. Cycling of T8Vs caused Rx water level to swell to high level (8) first, tripping Rx feea pump Level was regained using other RFP and RCIC. 36. FERMI 2 (341) LER 86-031 08/2g/86 EVENT: While heat removal was being performed with the main turbine off-line, following an inadvertent loss of condensate heater feed pump flow, steam bypass to the conder.ser was isolated, resulting in a high Rx pressure and an automatic actuation of the RPS and a Rx SCRAM. 37. PERRY 1 (440) LER 86-055 09/02/86 EVENT: During startup, a sudden increase in sensed steam pressure caused TBVs to fully open resulting in a Rx pressure decrease. Subsequent operator action to reclose the valves in combination with an isolated press, transmitter caused valves to shut more rapidly than expected resulting in a void collapse and neutron flux spike, and therefore an

(.,'- . v r e 9 37. . PERRY 1 (Cont'd) .u!olationvalveswerefoundshut. scale Rx SCRAM on IRMs. The MS pre i 38. QUAD CITIES 1 (254) LER 86-030 10/16/86 EVENT: While tt oubleshooting EHC probles (making adjustments to pressure regulators), the TBVs opened causing a MS line low I pressure, MSIVs isolated and Rx SCRAM (from MSIV not full e open). 39. BRUNSWICK 1 (325) LER 86-02g 11/16/86 t ~ EVENT: During a runback of the main generator TBV bypass capacity = was exceeded, resulting in RX pressure increasing (1065 j psig) and subsequent Rx SCRAM. 40. 0YSTER CREEK 1 (21g)- LER 86-032 12/24/86-EVENT: M iowing a Rx t< p, dile operators were in the process of controlling systens, problem with the TBV position indicator occurred which cs. Min considerable concern in that operators were partially mislead / distracted by. false indication. m { 41.. 0YSTER CREEK 1 (21g) LER 87-005 01/16/87 EVENT: Following a APRM high flux scram, second scram occurred due to slow response of mech. press. reg. which was being used to control Rx pressure. Slow. response was due to cal' bration error, since MPR had been set with the turbine cold. As r operating temp. increased response rate decreased resulting in excessive opening of T8Vs, when valves were closed, low y water level Rx SCRAM occurred. 42. FERMI 2 .(341) LER 87-008 03/01/87 EVENT: While resetting the ciectrical governor trouble alarm, during startup, power to parts of turbine control circuitry was lost which caused TBVs to fully close, resulting in Rx press. increase and level decrease, valve isolations and RX 3 SCRAM. 43. PEACH BOTTOM 3 (278) LER 87-002 03/25/87 i EVENT: While troubleshooting EHC system a lead was lifted, all 9 y TBVs went open (Rx power <1%). As Rx pressure decreased, water level increased and per design Rx feed pump tripped on high level (+45"). Rx level then decreased to low level (+4") causing Rx to scram. NOTE: Minimum level reached was - 30". ig

4 l I i 10 44 CLINTON-1 (461) LER 87-020' 03/30/87 .{ EVENT: Operator believing that he had equalized pressure around one MSIV, opened valve, which caused TBVs to open compounding the pressure transient and Rx water level to swell high (off 4 scale). MSIV was shut and water dec' eased. At the same time RWCU pump tripped on low flow causing RWCU isolation. 85. LA SALLE 1 (373) LER 87-022 05/28/87 EVENT: Operator was cycling #1 TBV as per. surveillance test. When valve was ramping closed, Rx feed pump discharge flow-decreased, which decreased Rx water level. Operators were not able to gain control of RFP prior to scramming on low level-(3). 46. NINE MILE POINT 2 (410) LF.R 87-043 07/11/87 1 EVENT: Turbine tripped on low EHC system fluid pressure (due to a tube rupture) which resulted in the open TBV drifting close and therefore Ry pressure began increasing. Rx scrammed on high steam dome pressure (1027 psig) before operator could manually scram the unit. Tube failure was due to excessive vibration due to speed signal noise. 47. VERMONT YANKEE (271) LER 87-005 08/07/87 EVENT: During shutdown (for refueling), with main generator off-line and turbine in coast-down malfunction of turbine ep. trol system caused TBVs to close resulting in a pressure transient and Rx Scram. Due to inability of mech, press. l reg. (control had just been switched from elect. press, reg.) to control pressure because of a clogged sensing line valve. 48. GRAND GULF 1 (416) LER 88-005 01/11/88 i PRECURSOR: PROBABILITY OF CONDITIONAL CORE DAMAGE = 6.9E-6 EVENT: While in hot shutdown operators observed increase in Rx water level which was caused by pressure controller setpoint opening TBVs to reduce Rx pressure. Setpoint was raised which closed TBVs, and Rx water level decreased below low level scram setpoint (reached +9") causing an RPS actuation at low level SCRAM setpoint. 49. PERRY 1 (440) LER 88-015 04/30/88 EVENf: During startup TBVs opened unexpectedly upon opening of the 8 MSIVs resultir.g in a low level transient (level 3) and Rx SCRAM.

C ) 11 50. VERMONT YANKEE (271) LER 88-009 07/03/88 y EVENT:- During.a shutdown after main turbine was taken off-line, operators observed Rx pressure decrease. Various modes of the mechanical hydraulic control (MHC) were tried to control pressure, but system was found to operate erratically.' Attempts to control using BVs resulted in large valve i movements and subsequent Rx pressure / water level oscillations which caused a Rx feed pump to trip. Standby RFP was started introducing relatively cold water into Rx, which then caused a rapid neutron flux / power increase and Rx SCRAM. 51. PILGRIM 1 (293) LER 89-011 03/04/89 f EVENT: A pressure decrease due to automatic closing and reopening of TBVs, which occurred because of a bypass valves vacuum trip and unexplained reset of the trip, resulted in a primary containment isolation control (PCIS) & RPS actuation since MS/Rx low pressure trip setpoint was reached with mode switch in RUN. The PCIS isolation included automatic closing of MSIVs and subsequently a Rx scram occurred.

52.. -QUAD CITIES 1 (254)

LER 89-003 04/12/89 L EVENT: All 9 TBVs opened in sequence (1 had oscillated opened l earlier).due to a circuit board within the combined maximum flow limit (CMFL) circuit which had a decreasing output. The board limits the opening of the TCVs, and as a result caused them to close, resulting in the TBVs opening (as designed) to control Rx pressure. A Manual Rx SCRAM was initiated due to TBVs opening. 53. NINE MILE POINT 2 (410) LER 89-009 04/22/89 EVENT: While preparing to perform weekly turbine backup overspeed trip test, an operator keyed a radio in the vicinity of the EHC cabinet causing disturbances resulting in inadvertent movements of the TCVs and TBVs. This malfunction caused a pressure spike which caused all 6 APRMs to exceed their upscale trip setpoint and a Rx SCRAM. 4 54. PEACH BOTTOM 2 (277) LER 89-023 10/05/89 EVENT: Following a Rx trip from 99% power all TBVs went full open and remained open, due to problems with the "A" EHC pressure transducer, causing Rx water level to decrease to +8" and then increase to +70" following RFP trip (RWCU isolation occurred). EHC pumps were stopped in order to close the valves.

.f.%' .= 12 55. BIG ROCK POINT.- (155) LER 89-009 10/27/89 EVENT: - While attempting to control steam flow / reactor pressure during power escalation, operators could not open a TBV remotely. Subsequently, it was determined that the " packing" was severely hardened and bound to the valve-stem. Plant was shutdown (several days later) following an investigation that showed other valves with similar packing. 56. FITZPATRICK-(333) LER 89-020 11/05/89 EVENT: Failure of an electronic control card (suspected ~to be from an electronic noise generated turbine overspeed signal in-the EHC system for the main turbine) caused TBVs to open and subsequently a pressure transient occurred resulting in a Rx ~ high flux SCRAM. HPCI was inoperable prior to the scram, c RCIC actuated automatically to restore water level. 1 L r l

1 i 1 KiTACHMENT B PWR TURBINE BYPASS fSTEAR DNP) RALFMCTIONS (NOTE: Details of each event are presented following the general listing below. ) 1. ARKANSAS NUCLEAR ONE 2 (368) LER 80-015 01/29/80 2. ST LUCIE 1 (335)- LER 80-069 12/16/80 3. NORTH ANNA 2 (339) LER 81-001 01/01/81 4.- NORTH ANNA 2 (339) LER 81-076 10/03/81 5. CALVERT CLIFFS 2 (318) LER 83-030 05/16/83. 6. PALISADES (255) LER 83-077 08/12/83 7 SUMMER-1 (395) LER 83-110 09/12/83 8. FARLEY 2 (364) LER 83-050 10/24/83 9. SALEM 1 (272)' LER 83-056 11/11/83 10. SEQUOYAH 1 (327) LER 84-006 01/10/84 11. CRYSTAL RIVER 3 (302) LER 84-010 04/26/84 12. SUMMER 1 (395) LER 84-026 05/05/84 13. DIABLO CANYON 1 (275) LER 84-015 05/08/84

14. -

SEQUOYAH 1 (327) LER 84-033 05/11/84 15. ST. LUCIE 1 (335) LER 84-006 07/26/84

16. -

CALLAWAY 1 (483) LER 84-051 10/14/84-17. CALLAWAY 1 (483) LER 84-056 10lt2/84 18. CALLAWAY 1 (483) LER 84-058 10/30/84 19. DIABLO: CANYON 1 (275) LER 84-030 11/24/84 20. .D.C.C00K 2 (316) LER 85-002 01/12/85 21. SURRY 1 (280) LER 85-004 01/27/85 22. BEAVER VALLEY 1 (334) LER 85-006 02/21/85 L_ 23. SAN ONOFRE 3 (362) LER 85-006 03/13/85 24.- CALLAWAY 1 (483) LER 85-019 03/30/85 25. WATERFORD 3 (382) LER 85-022 05/24/85 - 26. BYRON 1 (454) LER 85-062 06/27/85 27. BEAVER VALLEY 1 (334) LER 85-013 07/06/85 28. SALEM 2 (311) LER 85-012 07/08/85 29. BYRON 1 (454) LER 85-066 07/12/85 30. CRYSTAL RIVER 3 (302) LER 85-014 08/16/85 31. ARKANSAS NUCLEAR ONE 2 (368) LER 85-018 08/16/85 32. CALLAWAY I (483) LER 85-044 10/03/85 g

33..

DIABLO CANYON 2 (323) LER 85-016 11/26/85 PALO VERDE 1 (528) LER 85-071 10/24/85 34. 35. DIABLO CANYON 2 (323) LER 85-024 12/25/85 i L 36. RANCHO SECO (312) LER 85-025 12/26/85 L 1

a ;.. L 2 L 37.- _NILLSTONE,3 (423) LER 86-001 01/16/86 38.. MILLSTONE 3 (423) LER 86-012 02/06/86 .39. DIABLO CANYON 1 (275) LER 86-004 03/14/86 40.- DIABLO CANYON 2 (323) LER 86-011 03/30/86 41. INDIAN POINT 2 (247) LER 86-017 05/28/86 42. PAL 0 VERDE 2 (529) LER 86-027 05/31/86 43. INDIAN P0 INT 2 (247) LER 86-019 06/09/86 44.. FORT CALH0UN 1 (285) LER 86-001 07/02/86 4 45.. PALO VERDE 1 (528) LER 86-045 08/15/86 46. PAL 0 VERDE 1 (528) LER 86-053 09/11/86 47. WATERFORD 3 (382) LER 86-025 10/22/86 i 48. POINT BEACH (301) LER 86-008 11/28/86 49. SAN ON0FRE 2 (361) LER 86-029 12/10/86~ 50. DIABLO CANYON 1 (275) LER 86-020 12/28/86 51. TURKEY POINT 3 (250) LER'87-003 01/12/87 L 52. WATERFORD 3 (382) LER 87-007 03/07/87 l 53. V0GTLE 1 (424) LER 87-015 04/13/87 54. DIABLO CANYON 2 (323) LER 87-015 07/14/87

55. -

BEAVER VALLEY 2 (412) LER 87-009 07/22/87 56. BYRON 2 (455) LER 87-011 07/25/87 57. BEAVER VALLEY 2 (412) LER 87-014 08/15/87 58. BEAVER VALLEY 2 (412) LER 87-017 08/16/87 59. DAVIS-BESSE 1 (346) LER 87-011 09/06/87 i 60. ARKANSAS NUCLEAR ONE 2 (368) LER 87-007 09/09/87-61. BEAVER VALLEY 2 (412) LER 87-032 10/24/87 62. SUMMER 1 (395) LER 87-027 10/29/87 63. SHEAR 0N HARRIS 1 (400) LER 87-062 11/07/87 64. CALLAWAY 1 (483) LER 87-032 11/08/87 65. DIABLO CANYON 1 (275) LER 87-025 12/17/87 66. SHEARON HARRIS 1 (400) LER 88-003 01/21/88' 67. PALISADES (255) LER 88-007 04/29/88 68. PALO VERDE 1 (528) LER 88-021 08/21/88 69. BEAVER VALLEY 2 (412) LER 88-011 08/23/88 70 WATERFORD 3 (382) LER 88-033 12/08/88 71. DAVIS BESSE 1 (346) LER 88-028 12/17/88 l 72. RANCHO SECO (312) LER 89-001 01/31/89 L 73. CATAWBA 1 (413) LER 89-003 02/06/89 74. CATAWBA 2 (414) LER 89-004 02/21/89 i 75. ROBINSON 2 (261) LER 89-004 02/27/89 76. PALO VERDE 3 (530) LER 89-001 03/03/89 77. V0GTLE 2 (425) LER 89-014 04/03/89 '78. TROJAN (344) LER 89-006 04/06/89 79.- DIABLO CANYON 2 (323) LER 89-005 04/16/89

80..

BEAVER VALLEY 1 (334) LER 89-007 05/18/89 81. V C SUMMER (395) LER 89-011 05/28/89 82. SEABROOK (443) LER 89-008 06/22/89 83. PALO VERDE 2 (529) LER 89-009 07/12/89 84. SAINT LUCIE 2 (389) LER 89-007 09/23/89

,7 3 PldR TURBINE BYPASS fSTEAN DLBIP) RALRBICTIGHS i 1.- . ARKANSAS NUCLEAR ONE 2 (368) LER 80-015 01/2g/80 EVENT: During recovery from planned unit transient per power escalation 100% turbine trip test RCS depressurized to 1350 psia (min.), due to pressurizer spray valve and steam dump & bypass valve not fully reclosing on demand (following turbine trip). ECCS safety injection actuation signal occurred at 1740 psia setpoint. 2. ST. LUCIE 1 (335) LER 80-06g 12/16/80 EVENT: A 10% steam dump bypass valve failed open due to a failure in the steam bypass controller cabinet, resulting in a Rx power increase. Turbine load was decreased and valve was manually closed (by failing the positioner) which then caused Tc to momentarily rise to 542F (> T/S limit of 542F). 3. NORTH ANNA 2 (339) LER 81-001 01/01/81 -EVENT: The average RCS temperature was less than 541F as a result of over-cooling the primary using the SDVs. Temperature was restored (within 15 min.) by securing SG blowdown, withdrawing control rods and diluting the RCS. 4. NORTH ANNA 2 (339) LER 81-076 10/03/81 PRECURSOR: PROBABILITY OF CONDITIONAL CORE DAMAGE = 8.4E-6 EVENT: During startup a safety injection and Rx trip occurred, due to high steam flow (40% > setpoint and lo-lo Tavg (543F) as a result of high signal to steam header pressure controller as operator selected auto after shifting from Tavg to steam press, mode of-steam dump control. All 8 SDVs inadvertently opened.- 5. CALVERT CLIFFS 2 (318) LER 83-030 05/16/83 EVENT: Hydraulic damper bypass valves (HDBV) on TBCVS were closed which apparently provided an excess damping effect TBCVs were sluggish to respond. Pressurizer pressure and level decreased. After being returned to normal pressurizer level again decreased (112") when main turbine generator was paralleled and later returned to normal. 6. PALISADES (255) LER 83-077 08/12/83 EVENT: During a routine shutdown the reactor entered an undefined condition (requirements of hot standby, hot shutdown, or cold shutdown not satisfied-Tavg fell below 525 F to approx. 512 F), due to problems associated with the bypass valve.

' ' jf l 4 7. SUMMER 1 (395) LER 83-110 09/12/83 EVENT: Reactor Coolant System (RCS) Tavg' exceeded T/S limits by 2 L 1/2 degrees due to failure of permanent magnet generator (22 s volt power supply) resulting in failure of 2 CDVs and 3 l ADVs.

8..

FARLEY 2 (364) LER 83-050 10/24/83 EVENT:- During routine startup RCS Tavg dropped to 540F (T/S requires it to be >or equal to 541F) when an operator placed t the steam dump controller in auto control without first checking the controller setpoint (which was low) causing the $9Vs to fully open, t 9. SALEM 1 (272) LER 83-056 11/11/83 EVENT: During a shutdown, the steam dump pressure controller signal l went full scale (low) causing the SDVs to fully open and.RCS l. pressure to decrease below T/S DNB limit (restored within ? the allowable band of time specified by an LCO). The servo-driven setpoint station output was found to be unstable, i L 10. SEQU0YAH 1 (327) LER 84-006 01/10/84 l EVENT: During startup RCS pressure began to decrease, in order to compensate, the c arator slightly increased Rx power. ' Power increase caused tae SDVs (which were in pressure control) to momentarily open, resulting in a swelling of SG 1evels. ( .This in turn resulted in a high-high level in #4 SG which l caused a turbine trip and main FW isolation to all 4.SGs, which led to shrink in SG 1evels and subsequent Rx trip on l' low-low level in #2 SG.. Decrease in RCS pressure was due to failure of one bank of pressurizer backup heaters, which had a failed to energize due to burned contacts. Cause of the burned contacts an earlier failure of the heater bkr linkage t which caused the trip coil to short out-(BKR had been i replaced prior to startup but damage was missed). n 11. CRYSTAL RIVER 3 (302) LER 84-010 04/26/84 EVENT: Following a Rx scram one ADV and several MSSVs failed to reseat.-'The ADV was manually isolated and the MSSVs reseated when S3 pressure was reduced slightly. 12. SUMMER 1 (395) LER 84-026 05/05/84 EVENT: While in Hot Standby, the high steam bistables had been tripped for maintenance work, simultaneously work was being performed on the master steam dump controller when a main steam isolation occurred during installation of an electronic card into the controller.

y .;.y :.. 5 i -13. DIABLO CANYON 1 (275) LER 84-015 05/08/84 [ EVENT: During startup a failed pressure control module caused a malfunction in the. steam dump control system resulting in the several 40% SDys opening. This initiated a high steam-L flow coincident with low-low Tavg Rx trip and safety injection. 14. SEQU0YAH 1 (327) LER 84-033 05/11/84 g L PRECURS0R:- PROBABILITY OF CONDITIONAL CORE DAMAGE = 4.8E-6 l-EVENT: One SOV spuriously opened resulting in SG 1evel swells and j subsequently a high-high level in #3 SG. This caused a turbine trip and main FW isolation to all 4 SGs, which -resulted in a shrink of SG 1evels causing a reactor trip on low-low level in #2 SG. A broken repositioning linkage on the SDV was'found. i 15. ST LUCIE I (335) LER 84-006 07/26/84 i EVENT: Following a Rx trip the steam bypass and control system did not fully actuate causing 5 SG safety relief valves to lift momentarily. A failed pressure transmitter was found which. provides header pressure input to. the quick open logic L circuit of the SBCS. Without this logic the system I therefore was unable'to react fast enough to prevent opening .of the SG safety reliefs. 16. CALLAWAY 1 (483) LER 84-051 10/14/84 EVENf: During startup the SDVs were in manual mode being.used for g plant restoration following natural circulation testing of the RCS, when during manipulation the SDVs went unexpectedly from 20% to 40% open.'The change in steam demand caused SG levels to swell to the high-high setpoint resulting in a FW isolation signal. 17. CALLAWAY 1 (483) LER 84-056 10/22/84 ] P EVENT: SG 1evel oscillations caused by-SDVs cycling during the main l turbine roll-to speed caused a FW isolation signal, aux. FW actuation, SG blowdown isolation and subsequently a low SG 1evel resulting in a Rx trip. 18. CALLAWAY 1 (483) LER 84-058 10/30/84 EVENT: Following a turbine trip on a spurious high vibration sigaal the SDVs failed to operate properly in the Tavg mode causiag the SG atmospheric reliefs to open. The oscillations between the ARs and the SDVs caused SG 1evel oscillations which reached the high level setpoint on "B" SG resulting il

.,.,e 1,;. i ',i

  • t

,t 1 6 y-18. CALLAWAY l' (Cont'd)- a FW isolation signal, Aux. FW actuation, and SG blowdown i isolation. ) 19. DIABLO CANYON 1 (275) LER 84-030 11/24/84 EVENT: The turbine control system malfunctioned due to a loose l wire. The turbine and Rx tripped when-the 40% SDVs failed to. open as a result of installing the control wiring to an incorrect drawing. Safety injection was caused by the failure of an operator to reset the SDV pressure controller for normal operation after the turbine was placed'on line. g - 20. D.C. COOK 2 (316) LER 85-002 01/12/85 i EVENT: A low-low in SG 22 occurred as a result of an unexpected i l increase in steam flow experienced while returning an - -isolated SDV to service. This caused an automatic ESF actuation resulting in a Rx trip. 21. SURRY 1 (280) LER 85-004 01/27/85-EVENT: Following a Rx trip with the plant stable (5%) and SDVs isolated due to known (but unidentified) leakage, operators began to unisolate the SDVs resulting in leakage which led to a primary system temperature decrease and Rx power increase. Near.10% power it was decided to latch the turbine to avoid a trip. Two minutes following latching all 4 turbine stop valves'went closed resulting in Rx trip. 22. BEAVER VALLEY 1 (334) LER 85-006 02/21/85 EVENT: Operator actions (during startup) on mde FW regulating valves, combined with sluggish response of bypass FW regulating valves and concurrent SDV operation led to SG l swells resulting in a turbine trip and subsequent Rx trip. 23. SAN ONOFRE 3 (362) LER 85-006 03/13/85 EVENT: During cooldown and depressurization a safety injection l signal automatically actuated (SIAS). Analysis showed that a sudden increase in cooldown rate occurred when SBCV l improperly opened due to a sticky operator. This caused RCS pressure to be reduced below SIAS setpoint sooner than I-expected (when operator would have bypassed it). 24. CALLAWAY 1 (483) LER 85-019 03/30/85 EVENT: The ASDVs were being controlled in automatic with manual adjustments to the steam pressure setpoints in order to I sustain the desired primary cooldown rate. Operator 1' l-l . ~

y *,1 4; i 7' 24. CALLAWAY 1 (Cont'd) adjusted the SDVs and steam pressure decreased 10 to 15' psi. This signal fed into the ESF logic is rate sensitive and amplified by a factor of 10, therefore steam pressure decrease appeared to be 100 to 150 psi resulting in a safety injection actuation due to low steam line pressure. 25. WATERFORD 3 (382) LER 85-022 05/24/85 f EVENT: Operators were in the process of warming up main turbine when 1 TBV suddenly opened (instead of modulaing) which precipitated a' swell in SG 1evels causing a Rx trip._ j 26. BYRON 1 (454) LER 85-062 06/27/85 EVENT: An automatic Rx trip occurred due to over temperature differential temperature (OTDT) on the loss of 2 circulation water pumps-(CWP), because of overheated exciter ccotrol circuits. The loss of cps prevented the operation of SDVs to mitigate RCS pressure & temperature transient. t 27. BEAVER VALLEY 1 (334) LER 85-013 07/06/85 EVENT:- During a controlled shutdown following removal of the turbine from service the SDVs were placed in steam pressure mode. A fault in the steam dump control circuitry caused the SDVs to open to 20%. Operators were able to control SG 1evel temporarily at 11% power. RCS temperature decreased to low-low Tavg, which blocked.the SDVs and caused steam i pressure to increase, resulting in rapid shrink of SG level j (low-low setpoint)-and Rx trip. 28. SALEM 2 (311) LER 85-012 07/08/85 EVENT: During main steam warmup operations, SDVs opened rapidly upon increasing steam pressure, resulting in SG level swings and a lowering RCS Tavg. One operator attempted to compensate by pulling CRs, while another tried to stabilize using Aux FW. This caused power level to be raised to a point that exceeded capacity of AFW and resulted in Rx trip on low-low SG 1evel. 29. BYRON 1 (454) LER 85-066 07/12/85 EVENT: During 50% load rejection test at 100% power the plant I exceeded the OTDT trip setpoint resulting in a turbine trip and Rx trip, caused by response times of the SDVs. l

.,o 8 30.- CRYSTAL RIVER.3 (302) LER 85-014 - 08/16/85 EVENT: TBVs were isolated to prevent valve leakage and conserve RCS heat during turbine testing, operators were in the process of adjusting Tavg. FW control valves and main FWP were in L manual. with pressure set below normal. After turbine ~ testing operators realized T8Vs were still isolated and i opened them, failing to recognize FWP was in manual. SG 1evels boiled down to 19" and EFIC actuated'to restore 3 level. After reset, SG 1evel again decreased to 11" :nd EFIC actuated again, t

31. e ARKANSAS NUCLEAR ONE 2 (368) LER 85-018 08/16/85 PERCUSSOR:

PROBABILITY 0F CONDITIONAL CORE DAMAGE = 6.9E-7 EVENT: Following Rx trip 1 SDV did not close when steam pressure was reduced due to broken feedback arm on valve positioner. 32. CALLAWAY 1 (483) LER 85-044 10/03/85 EVENT: Three events in which FW isolation, Aux FW actuations, and SG blowdown isolations occurred as a result of SG 1evels being above high-high trip setpoint during either startup or shutdown. Abnormal operations of.SDVs along with inappropriate operator actions. 33. PALO VERDE 1 (528) LER 85-071 10/24/85 EVENT: Following a RX trip during cooldown and depressurization a i safety injection actuation signal was received due to the steam bypass control ystem not operating as designed. 34. DIABLO CANYON 2 (323) LER 85-016 11/26/85 EVENT: During 50% load rejection testing from 75% power, 2 Rx trips occurred, one with safety injection. One due to-high steam flow with low steam line pressee resulting from SDVs responding inappropriately. Secona was a problem with FW control system. 35. DIABLO CANYON 2 (323) LER 85-024 12/25/85 EVENT: Following a full load rejection test at 100% power, the slow respons9 of the steam dump control system resulted in an increase in SG pressure which caused a reduction in SG 1evel (low-low) and subsequently a turbine trip and Rx trip.

9

..[,,

4: col 9 36. RANCH 0 SEC0 (312) LER 85-025 12/26/85 PERCUS$0R: PROBABILITY 0F CONDITIONAL' CORE DAMAGE = 1.6E-5 EVENT:1 A loss of power to the ICS resulted in all ICS demand signals assuming mid-scale values (0 volts) which caused main FW valves to close to mid-position, MFWP speed to decrease to idle, and the Aux. FW and TBV valves to open to-mid-position. This caused reduced-flow through the'SGs and-increasing RCS pressure and temperature, leading to a high RCS pressure Rx trip. In addition, due to the position of the ADV and TBV valves along with AFW initiated, rapid RCS cooldown occurred which exceeded T/S limits and SFAS-actuated including CR/TSC essential HVAC on low RCS pressure. 37. MILLSTCNE 3 (423) LER 86-001 01/16/86 -EVENT:- While k. not standby a safety injection signal from the rate compensated steam line low pressure (SG A) resulted when an ASDV was opened to quickly. 38. PiLLSTONE 3 (423) LER 86-012 02/06/86 EVENT:; The main steam supply header (MSSH) pressure signal momentarily shorted out which caused it to momentarily fail to O psig which in turn caused the TSVs to modulate closed. The resulting main steam /feedwater transient caused a high-high SG 1evel which initiated a feedwater isolation. 39. DIABLO CANYON 1 (275) LER 86-004 03/14/86 EVENT: While at power, a high steam flow / low steam line pressure safety injection '..ith a subsequent Rx trip occurred when all SDVs fully oper.ed ( SDVs went closed when main turbine tripped), L e to a failed control moduie in the steam dump control system. Following the trip a high steam flow and low-low Tavg injection occurred. -The high steam flow was caused by the SDVs opening momentarily. 40. DIABLO CANYON 2 (323) LER 86-011 03/30/86 EVENT: Following a manual unit trip, an automatic safety injection occurred (on high steam flow / low-low Tavg) when a SDV malfunctioned due to a mechanical problem that bent the positioner linkage on the valve causing a pressure transient and subsequent high steam flow condition.

e .t 1.,.... -j 4 10 41. INDIAN POINT 2 (247) LER 86-017 '05/28/86 PERCUSSOR: PROBABILITY OF CONDITIONAL CORE DAMAGE = 1.0E-4 EVENT: During plant operation SDVs opened creating a high steam flow condition with a low RCS Tavg resulting in a safety injection actuation and Rx trip. 42. PALO. VERDE 2 (529) LER 86-027 05/31/86 L j b EVENT: During plant operation an RPS actuation initiated an L automatic Rx trip following an unanticipated turbine trip. s l-Operators'were not instructed (by procedure) to place master controller for. the steam bypass control system in the E remote-auto position after placing TG on line during power ascension. 43. INDIAN POINT 2 (247) LER 86-01g 06/09/86 EVENT: Following a Rx trip, safety injection system was actuated on a high steam flow / low Tavg (no water was injected) caused by i inadvertent opening of several SDVs due to failed bistable. i 44. FORT CALHOUN 1 (285) LER 86-001 07/02/86 PIRCUSSbR: PROBABILITY OF CONDITIONAL CORE DAMAGE = 4.1E-5 l i EVENi; A loss of 120 VAC instrument power to EHC resulted in TCVs closing (and subsequent turbine /Rx trip, inopped SDVs, l . bypass valves and FW valve rampdown circuitry. These-additional failures combined to cause an abnormal post-trip 1 pressure transient in the RCS. - 4 5. PALO VERDE 1 (528) LER 86-045 08/15/86 EVENT: A manual trip of the main generator. (MG), resulted in a turbine trip which in turn caused a loss of secondary heat removal. This along with the malfunction of the steam-bypass, control system (SBCS) caused RCS pressure to increase to high pressurizer pressure setpoint and subsequently a Rx trip. 46. PALO VERDE 1 (528) LER 86-053 09/11/86 EVENT: During plant operation a loss of the main steam (MS) flow signals to the steam bypass control system (SBCS) caused by a circuit card extender board which produced a short circuit ( while a computer technician was performing maintenance) from a plus signal to the minus signal at the emergency response facilities data acquisition and display system. A Rx power cutback occurred which caused all 8 SBCSVs to open and as a result the Rx tripped on low steam generator pressure and an automatic MSIV isolation signal occurred.

.Y x-11 47. WATERFORD 3-(382) LER 86-025 10/22/86_ [ EVENT: While power was being held in a low range (approx.7%) a 1-steam bypass control system (SBCS) transient raised Rx power above this threshold (due to post-trip xenon distribution being such that the axial shape index was out of allowable range), resulting in a Rx trip. The SBCS valve positioner i was suspected of being the cause. 48. POINT BEACH (301)- LER 86-008 11/28/86 EVENT: The water level in SG "A" decreased below Rx trip setpoint when power was increased to rapidly for effective operator control when constrained by the fact that the ASDV would not i open from the control room (air supply pressure was found to E be to low), resulting in a Rx trip. 49. SAN ONOFRE 2 (361) LER 86-02g 12/10/86 EVENT: Following a Rx trip, the SBCS did not ini ially actuate and t a main steam sifety valve briefly actuated. 50. DIABLO CANYON 1 (275) LER 86-020 12/28/86 EVENT: A Rx trip occu" red from a momentary steam flow /feedwater flow mismatch signal (caused by a momentary steam line pressure tran',ient resulting from the opening of the 10% SDVs) coinciaent with a low SG 1evel caused by closure of the TG govcrnor valves when removing unit from service. l 51. TURKEY POINT 3 (250) LER 87-003 01/12/87 EVENT: During a plant shutdown rapid load reduction caused Tavg to increase resulting in 2 SG safety valves to lift and reseat, while at the same time the 2 SDVs armed but failed to open and one other did operate correctly. This created a large difference in Tavg and Tref. During rapid load reduction alarm for extra low rod insertion limit was received and operator initiated emergency boration (per procedure), which decreased RCS pressure until the Rx trip setpoint occurred. L 52. WATERFORD 3 (382). LER 87-007 03/07/87 EVENT: Hydraulic fluid was unisolated (normally closed at high. o power'1evels to prevent wear due to vibration) to #4 main turbine governor valve for valve testing.. High pressure and emergency trip lines were reversed (inadvertently) therefore L vhen emergency trip pressure was bled off it resulted in raid closure of all turbine governor and intercept valves. With one SBCS valve out of service, response of SBCS was insufficient to limit RCS pressure transient and Rx trip on L high RCS pressure. .~..

4 _ t*' 12' '53. V0GTLE 1 (424) LER 87-015 04/13/87 EVENT: While connecting test equipment.-a steam header pressure transmitter momentarily failed high causing SDVs to open. SG levels swelled to the high-high level setpoint-resulting in a main FW isolation,-turbine trip and aux FW actuation. RCS temperature dropped to 550F resulting in low-low Tavg. interlock causing SOVs to close. 54. DIABLO CANYON 2 (323) LER 87-015-07/14/87 EVENT: During plaat startup turbine trip, main FWP trip and FW isolation v:1ve closure occurred due to high SG level caused-by FW control problems which were the result of mechanical o problsens with 2 SDVs and operating with a positive moderator temperature coefficient. 55. BEAVER VALLEY 2 (412) LER 87-009 07/22/87 L EVENT: SG "C" pressure had increased to 1040 psig, although SDVs I were set to control pressure at _1005 psig they were blocked (done during plant heatup and not restored as they should have been). Operator reset SOC circuitry causing 9 SDVs to open (as per design). NOTE: 3 of g were found to be out of adjustment and popped open instead of modulating open. SG pressure decreased rapidly which caused SG levels to swell to high-high setpoint resulting in a FW isolation signal. 56. BYRON 2 (455) LER 87-011 07/25/87 EVENT: Following a 30% load rejection test, a Rx trip occurred partially due to the digital electro-hydraulic (DEH) ~ controller being in sequential valve mode program which caused the governor control valves to be most efficient during power operation, but during runback caused the valves to be in varying positions causing Tref to widely vary. Additionally, the SDVs did not stroke fully open_resulting in decreased secondary side heat removal. 57. BEAVER VALLEY 2 (412) LER 87-014 08/15/87-EVENT: The steam dump system (which was being used to compensate for Rx power changes) did not appear to respond properly in automatic mode and operator subsequently placed it in manuti mode, input a 3% demand and replaced the system in automatic s control. Demand increased to 16% due to upward rod motion, i ending RCS temperature rise. SG 1evels swelled in response to increased steam demand then rapidly dropped, with FW being controlled in manual, it could not respond to increased demand. Operator attempted actions to increase FW flow but levels continued to drop until a low-low SG 1evel occurred causing a Rx trip.

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13 58; BEAVER VALLEY 2-(412) _ LER 87-017-- 08/16/87-EVFNT:- Following a test on the steam dump system, the analog signal l (which had been input for the test) was removed prior to placing the system in the steam pressure: mode. This i resulted in a large enough temperature error to open all i SDVs and the SGs swelled to the high level setpoint resulting in a turbine trip and FW isolation signal. 59. DAVIS-BESSE 1 (346) LER 87-011 09/06/87 ] PERCUSSOR: PROBABILITY OF CONDITIONAL CORE DAMAGE = 5.8E-6 i EVENT: Following a Rx trip, a TBV failed open due to an improper valve travel stop adjustment causing a steam /feedwater rupture control system actuation. 60. ARKANSAS NUCLEAR ONE 2 (368) LER 87-007 09/09/87 PERCUSSOR: PROBABILITY OF CONDITIONAL CORE DAMAGE = 2.0E-7 EVENT: During a Rx trip 2 TBVs failed to respond properly due to failure of positioners associated with their actuators, g 61. BEAVER VALLEY 2 (412) LER 87-032 10/24/87 EVENT; During 100% load rejection test when operators manually opened the main output breakers (as per. procedure) the SDVs automatically opened in response to loss of load. The resultant steam flow transient caused all 3 SG 1evels to drop and subsequently a Rx trip occurred on low-low level. 62. SUMMER 1 (395) LER 87-027 10/29/87 EVENT: During plant operation both the primary and backup power supplies to one of system process rack panels. failed, which was subsequently attributed to a failed capacitor on a steam dump control (SDC) signal converter card in one of the panels. This power failure resulted in a loss of FW controls, pressurizer pressure and level controls, and SDC. Manual. control of the FW system was attempted but recovery was not possible, and a Rx trip occurred on low SG 1ev91 and steam flow / feed flow mismatch. The PORVs lifted and notor and turbine driven emergency FWPs started. 63. SHEARON HARRIS 1 (400) LER 87-062 1)/07/87 EVENT: Several actuations occurred due to excessive, apid, automatic cycling of the SDVs after the 'A' MSIV was opened as a result of incorrect settings on the steam header controller. The safety injection system and main steam isolation and a Rx trip on low steam line pressure occurred.

(j. e ag oy. 14 64. CALLAWAY 1 (483) LER 87-032 11/08/87 EVENT: Following a retest of leaking MSIV, operators failed to follow procedure (re additionally the "B" quired plant to be in mode 3);and-SDV group was cycling due to a low control band. This magnif' ed the perturbation of the test on. the plant and operators were unable to control RCS pressure oscillations and the Rx tripped. Also, a FW isolation and aux. FW actuation occurred. 65. DIABLO CANYON 1 (275). LER 87-025 12/17/87 EVENT: Operators were increasing the power level when SG(s) high ~ level setpoint was exceeded resulting in a turbine trip and FW isolation. The combination of SG 1evel control in manuel and perturbations caused by rapid changes in steam dump demand (while switching from manual to automatic control) resulted in the high SG level. 66. SHEARON HARRIS 1 '_ (400) LER 88-003 01/21/88 EVENT: During a loop calibration of the turbine 1st stage pressure channel 5 of 6 SDVs opened and caused steam flow to increase and Rx power to ramp up (103% was reached). Operator action was taken to close SDVs and take manual ~ control of FW regulating valves to control SG 1evel. The cause was found to be a jumper wire installed in Train "A" of solid state protection system cabinet which was around the output contacts providing turbine trip indication to SD logic. Wire was installed at time of manufacture and effectively allowed SD logic to operate in Tavg and steam pressure mode was selected. 67. PALISADES (255) LER 88-007: 04/29/88 3 EVENT: Inadvertent opening of ADVs causing a temporary low SG' level (secondary side water) and actuation of auxiliary feedwater, occurred'during Hot Shutdown. ADVs opened as designed after receiving a simulated Tavg signal from the reactor regulator in excess of their setpoint. 68. PALO VERDE 1 (528) LER 88-021 08/21/88 , EVENT: A turbine trip occurred due to the failure of a microswitch in the stator coolant flow trip circuit. This was immediately followed by a Rx trip on high pressurizer pressure due to 2 steam bypass control valves closing faster than expected and one that malfunctioned. I

. - - ~ -. - - ,..*:.c 0: 15 69. BEAVER VALLEY 2 (412) LER 88-011 08/23/88 EVENT: While performing turbine trip test operators were controlling steam pressure by th cttling SDVs in manual. MS E pressure increased after completi(n of test until "B" SG L ASDV lifted causing a steam flow r, pike that resulted.in SG 1evel increase _to hinh-high setpoint and subsequently a FW -isolation signal, wh'ch in turn tripped the MFWP and L initiated Aux. FW injection. L 70. WATERFORD 3 (382) LER 88-033 12/08/88 EVENT: Transient was induced by cycling of power distribution panel (PDP) bkrs which caused Rx trip on low departure from nucleate boiling (DNBR) ratio. PDP cover slipped while being removed (for maintenance) causing 1/2 of bkrs to open. Bkrs were then closed causing pressurazer pressure instr. control i loops to reenergize, wh'ch appeared to the SBCS and Rx power cutback (RPC) as a large load rejection. SBCVs quick opened and RPC actuated. Due to loss of MT control circuits, MT was-1 -not setback by RPC and with resulting steam demand greater than Rx power RCS pressure decreased and core protection calculators tripped Rx on anticipated low DNBR, 71. DAVIS BESSE 1. (346) LER 88-028 12/17/88 EVENT: Following a high flux trip, TBV failed open (due to water accumulation) and increased cooldown rate. 72. RANCHO SECO-(312) LER 89-001 01/31/89 EVENT: Immediately following a manual Rx trip operators noted an abnormal rate of decrease in "A" SG. This was due to a failed open TBV, caused by a mechanical failure of the positioner. 73. CATAWBA 1 (413) LER 89-003 02/06/89 EVENT: While placing TG on line, high vibration was experienced on a low pressure turbine B and subsequently operators tripped TG, broke condenser vacuum and-reduced Rx power. High vibration was caused by a packing rub within the LP turbine B, possibly as a result of an uneven temperature differential across the 3 LP turbines. This is directly-related to the operation of SDVs and the ability of each condenser to handle the steam. 74. CATAWBA 2 (414) LER 89-004 02/21/89 EVENT: Following entrance into T/S 3.0.3, operator opened SDVs to obtain T/S requirement, subsequently 3 of 4 FW regulating control valves automatically opened. These actions i

k.* 4' t Y - s 16 74. CATAWBA 2 (Cont'd) i decreased steam pressure resulting in a safety injection on rate compensated low steam line pressure, 75. ROBINSON 2 (261) LER 89-004 02/27/89 EVENT: While investigating a turbine control system (TCS) problem, technician caused a short circuit which resulted in the turbine governor valves going closed and the SDV responded. When corrected the TGVs reopened, but the SOVs had not L modulated closed (as a result of saturation of the SD signal L summator) and a safety injection signal was initiated on high steam. flow with low steam line pressure and low RCS Tavg, subsequently leading to a Rx trip. 76. PALO VERDE 3 (530) LER 89-001 03/03/89 EVENT: An electrical grid disturbance resulted in the main generator output bkrs opening and subsequently a Rx power cutback (RPC) and~ SBCS actuation. An SBCS malfunction resulted in SG "2" low pressure Rx trip, turbine trip, MS isolation signal and containment isolation signal, followed by a safety injection actuation signal due to low pressurizer pressure. While attempting to remove decay heat and control SG pressure operators could not remotely operate ASDVs. h I 77.. V0GTLE 2 (425) LER 89-014 04/03/89 EVENT: An incorrect test signal was input to the steam dump control circuit causing SDVs to fully open instead of opening 10-15% as expected, which led to a SG 1evel swell and a FW isolation at high-high level. '78. TROJAN (344) LER 89-006 04/06/89 INITIATING EVENT FOR THIS REPORT EVENT: During a planned shutdown with the SDVs partially opened (as per design) one of the valves went to full open rather than modulating flow. Shortly after the same valve went full closed due to loss of instrument air (IA) when the air line ruptured. This led to a increase in SG 1evel which eventually reached high-high setpoint resulting in a FW isolation, Aux FW pump start, and SG blowdown isolation. Erratic operation of the SDV was caused by a shorted solenoid caused by a broken wire. Additionally, there was an inability to manually drive bank A shutdown control rods due to a blown fuse.

.,* f '. ) 1 s 1 i 17 79. DIABLO CANYON 2 (323) LER 89-005 04/16/89 + EVENT: Actuation of the generator backup protective relay caused the main generator trip. Coincident with the generator bkrs opening, all vital buses transferred.to standby power and a. circulating water pump (CWP) failed to restart on this-transfer which prevented actuation of.the SDVs. SG pressure increased causing level to shrink to the low-low setpoint and subsequently a Rx trip. - 80. BEAVER VALLEY l' (334) LER 89-007 05/18/89 L EVENT: During a breaker verification evolution the electrical L supply bkr to the ATWS mitigating system actuation circuitry t 0 panel was accidently opened resulting in a loss of turbine l-impulse pressure signal to the SDCS, opening SDVs and 'q lowering steam line pressure. This caused a low steam line rate compensated safety injection signal and a Rx trip. 81. .V C JUMMER. (395) LER 89-011 05/28/89-EVENT: Following a failure of a Pressurizer safety valve, which became unseated and caused a rapid depressurization of RCS a 1 manual Rx trip was initiated. SDV failed to close (current / pressure converter being out of adjustment) and an operator had to fail the air to the valve for closure. 82. -SEABROOK (443) LER-89-008 06/22/89 EVENT: Shortly after tripping the reactor coolant pumps (in l. accordance with the " Natural Circulation Test procedure") one of the SDVs being used to control temperature failed to L the full open position (due to the positioner' feedback I linkage becoming disconnected) which caused an increased =-, ' steam demand which in turn initiated an unplanned plant cooldown. This cooldown caused pressurizer level to decrease below 17% manual trip criteria, but due to misinterpretation the plant was not manually tripped. When the SDV was closed pressurizer level and pressure began increasing until pressurizer pressure began approaching (2310 psig) manual trip' criteria at 2340 psig and at this L. time the unit was manually tripped. 83. PALO VERDE 2 (529) LER 89-009 07/12/89 EVENT: Following a Rx trip, Safety Injection and Containment Isolation actuation occurred on low RCS pressure, which resulted from improper steam bypass control system response and excessive leakage past the pressurizer spray valves. l The SBCS response was due to calibration error in the proportional integral controller. L r--*

,,,,.7_,. L z 18. 84. . SAINT.LUCIE 2 (389) LER 89-007L 09/23/89 EVENT: Following a Rx trip, operators had to take manual control of. 10% S8V which did not automatically open. No cause was found for this valve failure.- 1 l -{ t l+ i 4 'f o, i ,3 I i ) i i } a

( .> a : 1 ATTAGMENT C PERCURSERS f CONDITIONAL PERCENTAGE PR08 ABILITY OF RISK PLANT LER NUMBER 0F CORE DAMAGE CPCD - YEARLY NORTH ANNA 2 81-076 8.4E -06 0.03% (1980 -81) l l l SEQUOYAH 1 84-033 4.8E -06 1 SUSQUEHANNA 2 84-008 3.3E -04 ANO 2 85-018 6.9E.-07 -) 0.09% (1985) RANCHO SECO 85-025. 1.6E -05 i i INDIAN POINT 2 86-017 1.0E -04 2.42% (1986) { l FORT.CALHOUN 86-001 4.1E -05 i DAVIS BESSE 1 87-011 5.8E -06 l-0.14% (1987) l ANO 2 87-007 2.0E -07 . GRAND GULF 1 88-005 6.9E -06 0.29% (1988) i 1 .\\ PERCENTAGE OF RISK ASSOCIATED WITH BYPASS SYSTEN MALFUNCTIONS AS CONPARED TO i ALL PRECURSOR EVENTS STUDIED: 0.82% THESE EVENTS NOT INCLUDED IN PERCENTAGE CALCULATIONS i ....}}

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