ML20092J239

Investigation of Unit 2 Power Transient of 840528. Related Info Encl

ML20092J239
Person / Time
Site:	Susquehanna
Issue date:	06/06/1984
From:	Willenberger J PENNSYLVANIA POWER & LIGHT CO.
To:
Shared Package
ML20090A536	List: ML20092J232 ML20092J239
References
7-84, NUDOCS 8406260401
Download: ML20092J239 (25)

Text

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N EENMM P.00 9 .

Wuelear Safety Assessment

. Croup Project Report No. 7-84 Investigation of Unit Two Fover Tranatest of May 28, 1984 .

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I 1.0 h At about 0100 en 3/24/44 Unit Two reaeter power intressed to a level of about S.95. This esseeded the liessee limit of 3.02. The power escursion lasted for less than three minutes. It wee apparently caused by a maliunation of the humber One Turbine Bypase Valve. h trenaient oesurred while the operators were establishing plant conditione for en i approved test. Operater actions were prompt and ef fective. N reaeter i did met SCRAM. We emergency care seeling systems were actuated. No 1 .

analear esfety hasard esisted.  :

2.0 Descristies of tesident 1

At the time of the insident power use being incrused by withdrawing ,

l sentrol rede. The objective was to ashieve about 605 opentas of the No.

1 Turkise typese Valve (TST). which esaura at a power level f.i about 45. r This acties womid provide sufficient seems flow to permit tuting of t,he -

RCIC' system without perturbating plast pressure.  !

, At a reaeter power et about 3.88 a Lev Dilutten Flow slarm was resetved

for the Off Gao Rosembiner sysses. The operators observed that reaeter a power was 1seressing and reseter water level wee fluetuating. They i Laserted eestrel rede, seek seenal sentrol of the feed water system and ,

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the.1 seek the Unit Two Off Gas tesembiner System out of servies. These I

! actions termiasted the tranalest. Power rose to a level of 5.95 em the i highest indiesties (APRN 5) and then returned to less thes 48.

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I h Duty Manager woe infetuod. At 0139 the WRC wee informed that a power J -

esaursten beyeed the liessee limit had escurred.

After the tramotest had settled out the Duty Manager made the desisten te  !

. eentinue testing. N RCIC tests were sempleted as scheduled. At 0530 a L

! senest shutdeva begaa. At 0600 it was discovered that No. 1 TSV would ,

not eleoe. It hung up at ebest its open. h Duty Manager use informed  !

and trouble sheeting of the T3V wee seamenced. The reester was shutdown

• at 1330.

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h insident securred dhing the sentee of establishing plant tenditiene i' for planned tests of the RC1C system. power was well within the eyesified limite when the transiese bogen. The traseiset was caused by, equipeest malfusation. < Since plant Staif was lavestigating the seekaical l i .

aspects of the transiest ta detail, the Neelear safety Assessment Group- i

, esseentrated upes the prestemmette taeves. Wade attempted to determine

.. whether the plaat wee being operated prudently.

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i MILEM DCPT (t LENT 06#4 40 P.10

{ 3.1 Power Honitorina was correct Power wee being monitored using the ein Average Fewer Range Monitore  !

(APRM's), which were displayed on a CRT on panel 2C631. The seine i of the APAN's had been adjusted to the highest possible values in order an lower the actual SC&AN set pointe for intatal testing aed L to improve the indicaties at the low end of the seale. Gain

settings ranged from 1.85 to 2.37. The APRM displays showed the setual power multiplied by the gain setting. The manimum reading l

! ebeerved during the transient wee lit read on APRM "B". The setual power, these was 112 divided by the gata of 1.85 or 5.95.

The Techatsal $pecifisations require that during startup the APRM .

SCRAN be set at a maaimum of 155 and the red bleek he set at a manimum of 121 (Tables 2.2.1-L sed 3.3.4-2). The values actually

, set were SCRAN'at 145 and red bleek at 113. When one correcte for instroomt gata.. the SCRAN values would range between 7.$72 and l

3.915 and the red bleeke between 5.932 and 4.64X.

During the tranetes't a red hisek eseurred but as SCAAN signale same in. This fisse the actual power between 4.64X and 5.913 (minimum

{ red bleek settias and staissa SCRAM setting).

l l .The Intermediate Range Nemiters (IBM's) were displayed en recordere i

en the Standby tefossetion Fanel. It is supossible to fin an

} eesurate serrelaties between the IBM readings and eere thermal .

,; power.

II The APRN's were salibrated on 1/13/84. The IEN's were salibrated on 4/27/44 (Beth are semi-seauel requiremente. Teek Spose Table j

4.3.1.1=1). The Weekly Cheesel Fumettensi Tests were done en

• 3/21/84 (AFSM) and on 3/22/84 (IEN). The mest teste were deae 3/29/84 and $/30/84 roepeatively. There la ev*:y resses to believe that the APRM and the IBM $CRANs would have feastioned if required.

j The operstere had been speettitally directed to monitor power en the

! APRM's. A night order entry dated S/21/84 reade.

" Unit 1 APRM's used to determine SI power limit. (Rated Temp .

end Press 733 1 bypsee.)" '

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The ender is somewhat vague in that it dess set specify that the power limit is setual power met indicated power. That is, it does .

not sleetly state that the limit is the APRM reedias divided by the,

$. tastrument gais. Bewever, this was understeed. The lastrument seine were posted en panel 2C431. The operater, and the startup '

engineer referessed the sais settings in their les estries. There

• wee as seatusion en the part of the operating erew. Wenitertag

• power was set es issue la the insident. '

'.' At the time of the insident veneter power wee being ineressed in preparation for testing the RCIC system. The test precedures called for power level greater them.25 with sufficient steem flow to, , i

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~ NJCLEAR DEPT ALLENTOLN GO P.11 l

prevent reactor pressure decay during RCIC operation. The Unit,

. Supervisor's goal was 60% opening on No. 1 TBV which corresponds to about 4% actual power. (APRM reading corrected for gain.) When the transient occurred APRM "5" reading was about 7% and No. 1 TBV was l about 55% open. A 7% reading equates to 3.8% actual power. The 1 plant was being operated conservatively. Three-poine-eight percent l i

, is comfortably below the limit of 5%.  !

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o The instruments were set in a conservative manner.

, o The instruments were in calibration and the required functional tests had been done.

o SCRAM protectica existed from the APRM's and the IRM's.

. 1 s Tha operators vara monitsring ptirar in acesrdan=t trich l management's instructions.- i

.i e The plant was operating at a conservative power level. l 3.2' The Dvoasa Sveten had been Proserly Tested

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4 The following tests were performed prior to the incident. They required proper response by the pressure reguistor

,' , . Pressure Test Description 135# '

57-293-030 Verify proper response of BPV's to -

.. pressure regulator setpoint changes.

.'" 150# 80-250-003 BCIC Full Flow Test

, Steam flow to RCIC requires Pressure.

Regulator (P.R.) to close BPV slightly to maintain pressure.

Initially No. 1 BPV about 0.5 open. '

150# S0-252-003 IPCI Pull Flow Test

' Steam flow to EPCI requires P.R. to close

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SPV by '502 to maintain pressure. * ,

Initially, #1 BPV-3/4 open. j l

150# ST26.1 SRV Inw Pressure Test s i

, Steam flow to S/RV requires P.R. to I i 'close *1 BPV to maintain pressure.

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C , Initially, *2 SPV's open. '

920# IF-250-010' RCIC Punctional checks -

i ST14.1 RCIC CST to CST 30-250-002 RCIC Ful'. Fler Test ,

. Steam Flow to RCIC requires P.R. to elese '

'5% of one BPV to maintain pressure.

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NUCLEAR DEPT ALLENT 0844 Go P.12 i 920# $0-252-002 HPCI Full Flow Test Steam flow to HPCI requires P.R. to close

'50% of one BPV to maintain pressure.

t l 128-250# CRD Movement Movement of CRD's to increase power to 920-950# perform above test requires P.R. to open BPV's to maintain preneure.

In each of the abave tests the performance of the system was monitored using the GETARS. The turbine bypass valves responded properly in every one of these teste.

On the night of 5/28/84 there was no reason to expect problems with the pressure control system or the bypass valves.

l 3.3' ,Inc,1de,nt e h sed by Equipmenti Malfunction

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At about 0100:30 the TBV's began to oscillate. At 0101 a Low Dilution Flow alarm was received on the Off Gas Recombiner Panel.

The nazimum power occurred at about 0101:45, and the transient was over by 0104.

Over the course of the previous twenty-fwur hours several flow ,

oscillations had occurred in the off Gas Recombiner System. It

, annaared at the time that the oscillations in the TBV's had been caused by the perturbation on the off Gas system. The Off Gas l System was taken out of service and vacuum was maintained by the. l mechanical vacuna pump. No further oscillations were observed.

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, Eowever, during the subsequent reactor shut down TSV No. I could not' )

', be closed fully. Subsequent trouble shooting indicated that at least one T3Y was operating sluggishly. Debris was found in the .

number one bypass valve.

j NSAG did not attempt to determine the cause of the equipment i aalfunction. That is being done by the plant staff Technical Section. We are satisfied, however, that the transient was not

, caused by operator error. Clearly there was a salfunction of some .

kind which caused reactor pressure and feed water flaw transients that resulted in minor power excursions.

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. 3.4' operator Ressonse was Frompt end. Effective The first indication of a problem was the Low Dilution Flow stars which occurred at 0101. At this time APRN "3" indicated that *

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reactor power was about 73 (3.83 corrected for gain). NgAG could not determine precisely whether or not a control rod ute,being moved

• at the time the alars appeared. At any rate, the oport. core observed-that power was increasing, that the T37's were oscilla.:ing and thac .

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reactor water level was fluctuating. The operatore ir.serted control.

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rods into the core and took manual control of feed water flow. -

,  ; Fower increased to 11% on APRM B. Power turned at about 0101:45 and g , -4=

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NJCLEAR DEPT (LLCNTCW GO P.13 the TSV oscillation died out by 0104. The operators then isolated the Off Gas Recombiner System and started the mechanical vacuum pump.

Within a period of less than four minutes the transient was over. )

The operators then proceeded to correct the apparent cause of the '

problem by securing steam to the air ejector system. There were no ,

further symptoms until about 0600 when T3V No. I would not close , j during the plant shut down. i l

The operators recognised that a limit may have been exceeded. After I conditions had stabilised they notified the Duty Manager and

, subsequently notified the NRC.

In the opinion of NSAG, the operators responded effectively. They recognised the probles, took steps to terminate the transtant, corrected what they believed to be the cause, and informed the proper; authorities.

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3.3 Evolutions were Auihorised

• Tests IF-230-010, RCIC Turbine Control System Tune g and ST14.2, .

Reactor Vessel *In_1ection were scheduled on the T rtup and Test

• Three-Day Schedule dated 5/25/84 and signed by the Day shift' =-

Supervisor. The cover sheet indiedting that t'ne schedule applied ~ ~ ~

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from 1600 5/25/84 through 1600 5/29/84 was aigned by the Unit '

Coordinator. The test procedures had been approved by the PORC and -

had been signed by the Plant Superintendent. The initial conditions l

' were in accordance with the procedures and had been successfully achieved on several previous occasions. After conditions had -

., stabilised the Duty Manager was informed. He concurred in the decision to notify the NRC and he granted permission to complete the scheduled testing.

.' The evolutions were prop'erly authorized by cognisant line management. There was no improvisation by the operating crew.

• 3.6 One Hour Report was Ruuired There has been some discussion as to whether the event should have been reported to the NRC at all. The reactor was being operated l .

within the limits of the license and a brief transient was caused by; an equipment asifunction. No safety limits were violated. In the

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6 pinion of NSAG, the situation is analogous to operating at 100%

• power and experiencing a casualty which causes an excursion above .

the steady state limit but below the SCRAM setting.

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The 1002 power level escursion is covered by Ntc memorandum SSINS '

0200 E. L. Jordan to Distribution, " Discussion of Licensing Power Level (AITS F1458082)". August 22, 1980. The basic guidance is that average power over an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> interval may not exceed the licensa limit and that the instantaneous power may not exceed 102% of the license limit.

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NJCLEPR DEPT N0144 GO P.14 102% of SE is 5.12. An excursion of 5.9% violates the 102%

1 guideline for instantaneous power. l l Fa'ragraph 6.6 of the Technical Specifications defines Reportable Event Action. It states, l

"a) The commission shall be notified and a report subnitted pursuant to the requirements of Section 50.73 to -

10CTR50,..."

Specific instructions to the operators are found in Administrative Procedure AD-QA-424, 51anificant Operatina Occurrence Reports. Rev. 1 4 effective 1/1/84. Table A of Attachment C Operational Events One

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Hour ENS Not_ification lists item 8. " Violations of Operating License." Page 27 of 53 discusses item 8 and specifically states "Any violation of License Conditions 2C(1) . . .". Condition 2C(1) of the Unit Two operating license states "... Fending Commission approval, this license is restricted to power limits not to exceed five percent of full power (164.6 megawatts thermal) ."

It is clear that th's decision to make a oco-hour report to the NRC

', was consistent with the Technical Specifications, the NRC ..

interpretation of the power limits, and the station _ instructions.

. 3.7 No Essard Raisted .

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' "The Nuclear Plant Engineering Engineering Analysis Group analysed

, the transient and determined that.it is within the bounds of -"

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transients analysed in the FSAR.

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i A copy of the NFE Evaluation (File 247-01 of 5/30/84) is attached. * '

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R. 4.0 Conclusions

1. The license power limit of 52 was exceeded for less than 3 sinutes.'

Maxinus power was 5.92 per AFRM "B" after gain adjustaant.

2. No nuclear safety hasard existed to the plant or to the public.

3. The transient was caused by an equipment malfunction.

, 4. Operator actions to control the casusity were prompt and effective.

c -5._ All evolutions were authorised by responsible line usanagement. i l

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. - . ---.. 4 3 4 , l M._ ml MEMORANDUM PAGE 1 0F 1 TO: nick Nobles OATE: May ao, 1984 d

FRON: ,a. J. soecioli .

T. M. Crimmins, A4-2 J08: sa too4so NUMBER: sa-o96 COPIES TO:: c. a. miller, A2-s

. J. s. stefanko, A2-5 Fil.E: 247-01 - " ****** * * **

R.EPl.Y No SENS IAtter File,'A6-2

SUBJECT:

svAmATzow or mar 2s, iss4 ssas ouzT 2 Tmamarzur svzwr -

! During the S/28/84 8838 plant event, the bypass valvers closed as demanded by the pressure regulation controller. The bypass valves remained closed until

. pressure and power exceeded their initial values cf the transient. As a - -

result power increased above the 54 licensed power level before the bypas's

. valves reopened to control pressure and, mitigate the power rise.

This event is less limiting than the Turbine Trip without Bypass transient from 4 3ot power which is discussed in section 15.2.3 of the SSES FSAR. The turbine trip event results in a faster reduction in steam flow and a higher initial power level. The higher initial power level results in a larger void.

collapse in the. core causing"a higher power spike.' section 15.2.3.3.3.3 a states that the turbine trip without typass event results in a high vesset ,

pressure scram. Therefore, the-simulated thermal power upscale'trip peak powerand setpoint remainethe MCPR belowremains the flowwell biased above the GETAB safety limit. ,

Since the initial power is lower, the steam flow reduction and subsequent

• pressurization is slower, the magnitude of the pressurization is mitigated by reopening of the bypass valves, and the void collapse is less severe due to ,

the lower initial power, the event'that occurred at sans on 5/28/84 is much

?, less severe than the Turbine Trip without bypass event from low power which is analyzed in section 15.2.3 of the tsar.

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