ML20206E090

Analysis of TMI Accident

ML20206E090
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Site:	Three Mile Island, 05000000
Issue date:	01/29/1980
From:	Cale Young AFFILIATION NOT ASSIGNED
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NUDOCS 8811170394
Download: ML20206E090 (28)

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Analysis of Three Mile Island Accident _

A Study by Charles Young January 29, 1980 Summary Reason for Damage to the Reactor Core -

Summary Plant Conditions and Operations Leading to the Accident ,

Reason for Damage to the Reactor Core The Accident Operatin6 License / Technical Specifications .

1 Primary Plant Operater and the High Pres ure Injection System  :

Operators and other Evolutions 4

Operator's Capabilities Reascn for Core Damage ,

Correctivo Action Plar.t Conditions and Operations Imading to the Accident Condition of the Reactor Coolant System Control Room Indicators and Instruments Working on Condensate System Corrective Action ,

Lesign Defect Re ferences :

Report Of The President's Commission On The Accident At f Three Mile Island. j Investigation Into The March 28, 1979, Three Mile Island  !

Accident By Office Of Inspection And Enforcement (USHRC Report HUREG - 0600).

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t Analysis of Three Mile Island Accident Reason for Damage to the Reactor Core Summary The Three Mile Island Unit 2 reactor core was damaged following the turbine trip and reactor scram at 040C March 28,

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1979, because the Control Room Primary Plant Operato?, at time 0403 and 13 seconds, turned off high pressure inject:en. The Primary Plant Operator turned off high pressure injection because the Three Mile Island training staff had instructed Operators to turn off high pressura injection ai'ter the system had been i

initiated following a reactor scram, and all Operators were

conditioned to do this. High pressure injection when initiated autcmatically following a reactor scram on March 29, 1978, was turned off by the Operetor.

I The Three Mile Island Unit 2 Operating License / Technical Specifications, which stipulates rules for operating the nuclear plant to pre *!ent damage to tha reactor coro, requires high pressure injection to function after automat; initiation if reactor coolant pressure is below 1600 psig, the initiation setpoint. If high

! pressura injection had continued to function as required by the l Operating License / Technical Specifications after initiation at 0402 on 2 March 28 (reactor coolant pressure remained below 1600 psig Lfter

this tim,e), voids would not have formed in t he reactor coolant system and the reactor core would not have been damaged.

I Operators on shift at Three Mile Island Unit 2 at 0400 j March 28, 1979, followed operating orders in handling the loss of feedwater emergency, turbine trip and reactor scram.

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The Primary Plant Operator was following operating orders when he turned off high pressure injection promptly af ter the system was initiated automatically. He would have allowed high pressure injection to continue to function if his orders had so directed.

The Primary Plant Operator turned off high pressure injection to shorten plant down time, i To prevent damage to the reactor core following reactor scrams at Three Mile Island, Operators should be directed by 3

Metropolitan Edison Corporate Management to follow the require-ments of the Plant's Operating License / Technical Specifications.

Operators chould be directed by Metropolitan Edison Corporate Management to follow the requirements of the Plant's Operating License / Technical Specifications during all reactor i plant operations and under all reactor plant conditions.

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- Analysis of Three Mile Island Accident Plant Conditions and Operations _teading to the Accident Summary Three Mile Island Unit 2 sustained a luss of coolant accident and reactor core damage following the turbine trip and reactor scram at 0400 March 28,1979, because Control Rocm Opera tors did not close the electromagnetic relief valve's block valve when required.

Station Emergency Procedure 2202-1 5 requires the block valve for the electromagnetic relief valve to be closed if the

- temperature of the relief valve's discharge pipe exceeds 130 0F, The temperature of the relief valve's discharge pipe was 1800F before 0400 March 28, 1979, but Operators had not closed the block valve.

' If the block valve had been closed, the electromagnetic relief valve would not have opened and stuck open during the pressure transient in the reactor coolant system following the 0400 ree otor scram, and there would have been no lose of coolant accident and nc core damage.

i The Three Mile Island Operating License / Technical Specifications requires that Operators follow Plant Procedures in operating the reactor plant.

To prevent loss of coolant accidents at Three Mile Island, l Operators should be directed by Metropolitan Edison Corporate l

Management to follow the requirements of the Plant Operating License /

l l Technical Spec,1fications and Procedures when cperating the nuclear plant.

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Several hours before the March 28 accident, the Station ,

attributed approximately 6 gallons per minute leakage from the Unit 2 reactor coolant system to one or more of three valves:

2 safety valves and the electromagnetic relief valve. The safety valy's cannot be isolated from the reactor coolant system. The electro-Mgne'ic relief valve is isolated from the reactor coolant system t:r i Fi n valve. According to Three Mile Island Operators, this block  ;

vw ' '.'e ri ght stick open or shut. Plainly, the electromagnetic relief val, ould not be isolated from the reactor coolant system with e or' .tnty.

A reactor coolant system pressure boundary leaking 6 gallons per minute through one or more of 3 valves is seriously degraded if the 3 valves cannot be isolated from the system with certainty.

1 Three Mile Island Unit 2 was operated with the reactor coolant system pressure bcundstry seriously degraded March 28, j 1979, before the accident which damaged the core. If Operators had reacted to the degraded condition of the reactor coolant system, the scoident could have been prevented.

A Shift Foreman and Auxiliary Operator were attemptir.g  !

I to transfer resin from a condensate polisher tank at Three Mile Island Unit 2 March 28, 3979.

Operators had been trying to do this for 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br />. At 0400 they were using demineralized water at 160 psig and service air F

! at 100 psic together in the tank. -

The service air system was cross connected with the instrument air system.

Operators thought that water in the instrument air system at the condensato polishin: system would cause condensate polisher air operated outlet valves to close.

On October 19, 1977, and May 12, 1978, the station had problems with water in the condensate polisher air system.

On !!ovember 23, 1978, opening a control power breaker by mistake caused condensate polisher outlet valves to close, Joss of condensate flow, a turbine trip and reactor scram. The Plent was at 905 power when this happened.

Three Mile Island Unit 2 was at 975 power during the period that Operators were attempting to transfer resin from the condensate polisher tank on March 27 and 28.

At the time that "turbine trip / reactor trip" was announced on the Station page system, the Operator at the condensate pelisher station saw the condensate oo11 sher panel indicate "condensate polisher isolation" and therefore no condensate flow.

3 Operators working to transfer resin from a condensate polisher tank at Three Mile Island March 27 and 28,1979, were risking a turbine trip and reactor scram. At 0400 March 28, a turbine trip and reactor scram occurred leading to a loss of I

3 coolant accident and reactor core damage.

Despite the fact that the seccadary plant at Three Mile Island was cperated precariously Marer 27 and 26, causing a turbine trip and reactor scram, there would have been no loss of i coolant accicent and no reactor core damaged if the reactor plant had been operated in accordance tr e Operating License / Technical Specifications and Operators had closed the block valve.

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-4 The design defect in the reactor coolant system (the electromagnetic relief valve opens regularly on reactor scrams from high power) may or may not have been a factor in the Three Mile Island accident.

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. 1 Analysis of Three Mile Irland Accident Reason for Damage to the Reactor Core The Accident The accident at Three Mile Island Unit 2 on March 28, 1979, started at Oh00 with a loss of feedwater and turbine trip. A reactor acram followed 8 seccnds later.

The reactor scram was caused by high pressure in the reactor coolant rystem (2355 psig). The reactor coolant system electromagnetic relief valve opened at 2255 psis just before the reactor scram, but failed to close as system pressure decreased te the valva's closure setpoint of 2205 psig abcut eight seconds after the valve opened.

Pressurizer level was increasing at the time of the reactor scram and continued to increase for several seconds, reachin6 a maximum level of 255 inches. Reacter coo) ant system pressure snd pressurizer level then decreased to6 ether. At time SS seconds, a low level pressurizer alarm uns received (at 185 inches). At time 60 seconds, the reactor ecolnnt systen pressure was 1800 psig.

d ec reas ing .

At time 2 minutes 2 seconds, that is 2 minutes 2 seccnds after the accident started, the Emergency Safeguards Signal was actua'.ed as reactor coolant system pressure reached 1600 psig, decreasing. On this signal Emergency Core Cooling was initiate'd:

l 2 high pressure injecticn pumps with a combined capacity of 1000 l

l gallens per minute, started to deliver Seavily borated water te f the reactor coolant system througn four paths, i

y Three Mile Island Unit 2 Procedure 2202-1,3 Loss of Reactor Coolant / Reactor Coolant System Pressure, applies upon initiation of Emergency Core Cooling due to low reactor coolant system pressure. This Procedure requires the primary plant Operator to verify:

1. High pressure injection operating properly as evidence by injection flow to all four reactor coolant legs and

2. Safety injecticn equipment in the emergency positien.

i Operators were trained differently by the Three Mile Island training staff, however. Three Mile Island Operators were trcined to reset the Emergency Safeguards Signal promptly after actuatien and then to throttle the high pressure in.iection purps .

i Accordingly, 1 minute 11 seconds after Emergency Core I Cooling System ir.itiation, Edward Frederick, the primary plant Centrol Room Operator for Three Mile Island Unit 2 at the time of the reactor scram and Emergency Core Cooling initiation:

. Bess t (bypassed) the Emergency Safeguards Signal thus enabling manual centrol of the high pressure injection system.

P. Throttled and closed valves from the high pretsure injection system to the reactor coolant system thus limiting flow of high pressure injection water to 100 gallons per minute.

One minute 25 seconds later, Frederick tripped high pressure injection pump 30, leaving one high pressure injection pump running.

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• Three Mile Island Operators had operated beforo like 1 this. On March 29, 1978, following a reactor scram, the electro-magnetic relief valve opened but did not cloce causing reactor coolant system pressure to decrease. At 1600 pJig, the Emergency Safeguards Signal was actuated, and high pressure in,iection was initiated. Operators then bypassed and manually shut off the l high pressure injecticn system, f f

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' h Operating License / Technical Specifications A nuclear Plant's Operating License / Technical Specifications defines limits, called safety limits, en reactor coolant presture, temperature, flow and reactor power to in.ure integrity of the reactor coolant system and the nuclear fuel rods thereby preventing release of radicactivity and potential injury to personnel. The Operating License / Technical Specifications also lists safety systems designed to functicn autcratically to prevent cafety limits frem being exceeded, and stipulates rules for operating these systems.

Technien1 Specificatiens are a part of a nuclear plant 's Operating License and are develeped frcm the plant's Safety Analysis Report. Safety Analysis Reports, wnich describe the 1

i performance required of the plant's structures, systems and com-ponents to prevent release of radioactivity and injury to persennel l while generating electricity with nuclear power, are develeped l

l b :, engineers while the plant is being designed and censtructed.

Safety Analysis Reports are reviewed by Nuclear Regulatorv Ccmmis s ien enginee rs .

Three Mile Island Technical Specification 3 7. 2 Engineered Safety Feature Actuaticn System Instrumentatien, requires that engineered safety features actuation system instrument channels be operable when the reactor plant is being operated.

Technica3 Spacificatien ?.5.2 Ssfet v Features Actuat ien Systeg requires cperability of the safety features actuatien system during plant operatient.

Technien1 Specificaticns stipulate that Operators shall fellcw Station Frocedures in operating the reactor plant.

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g Station Procedure P105-1.3 Safe 2v Features AcQuation System, requires operab:,11ty of the Emergency Core Cooling System during plant operations.

I Station procedure PPOP-1.3 Loss of Peactor Coolant /Peactor Coolant System Pressure requires the Operator to check the high f pressure injection sys tem for proper operation when baitiated and [

requires the system to operate as long as reactor coolant system pressure is below the initiation setpoint. j l

The Three Mile Island high pressure injection system is j i

designed to prevent reactor fuel cladding failure due to a loss  ;

r of coolant accident by injecting water into the reactor coolant  !

i syst?t to keep the core covered. If the high pressure injection  !

3 systen nad been allowed to centinue to functien, after initiation i at 0402, March 28, at Three Mile Island as required by the cited l l

Technical Specificatiens and Station Procedures, the formation of  !

4 voids in the reactor coolant system during the first few minutes j of the accident would not have occurred and subsequent dattge to l i

the core would have been pre 'nted.

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6 Primary Plant Operator and the High Pressure Injection System The Three Mile Island Procedure for loss of reactor coolant and loss of reactor coolant system pressure, Procedure r

2202-1.3, cited above, requires the Operator te check the high pressure injection system for proper operatien when initiated and requires the system to operate as lcng as reactor coolant system pressure is below the 1640 psig initiation setpoint. 1 High pressure injection was initiated 2 minutes 2 seconds after the turbine trip when the reactor coolant system l pressure reached 1600 psig, decreasing, the morning of the Three l Mile Island accident.

Fredrick, the primary plant Operator, started turning  :

I off this system 1 minute 11 seconds later by resetting the i

Emergency Safeguards Signal.

i He completed shutting down the system 2 minutes 36 seconds after the system was initiated by turning off a pump having also l throttled the injection valves. Reactor coolant system pressure was IL53 psig at this time .

During the time that Fredrick was turning off the high i L i pressure injecticn system, reactor coolant system pressure was t j decreasing from 1600 psig to lh50 psig and pressuri:er level was  ;

E increasing through the normal range and the high level alarm setpoint. Tne high level alarm setpoint is 134 inches below the ,

t maximum indicated level of 400 inches. [

Fredrick did not follow the Three M13e Island Procedure }

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for loss of reactor coolant and loss of reacte.r coolent system prer- l I

sure after Emergency Core Cooling initiation with reactor coolant [

i pressure belcu the initiation setpoint. Instead of verifying t I

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high pressure injection flow to the reactor coolant system and verifying safety injection equipment in the emergency position, he shut down the system.

When he reset the Emergency Streguards Signal and shut down the high pressure injection system promptly after actuation, Fredrick was following training given him by the Three Mile Island training staff, performing as Three Mile Island Operators were conditiened to perform and handling the high pressure injection system as had been done in the past.

The reason given by the Tnree Mile Island training staff for training Operators to bypass the Emergency Safeguards signal and throttle the high pressure injecticn system thereby shutting off hign pressure injection after Emergency Core Cooling initiation, was to prevent injecticn of sedium hydroxide into the reactor and an extended plant outage. The training staff stated that this philosophy of operatien had been developed follcwing the admissien of sodium hydroxide into the reactor coolant system twice following Unit trips uith Emergency Safeguards initiation. The consideration was the time and effort required to clean up and deborate the reactor coolant system after additien of substantial amounts of sodium hydroxide and borated water (2300 ppm) into the system folivwing Emergency Safeguards initiations.

Fredrick, in stopping high pressure injection, prevented injection of heavily borated water into the reactor coolant systen at 1000 gallens per minute. If high pressure injection had been allowed to centinue and had there been no accident, it would have been necessary to put the plant in hot shutdewn and deborate the reactor coolant system before returning, to power. This process would have required a shut down of about 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

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. If high pressure injection had been allowed to continue

• and if sodium hydroxide had been introduced into the reactor coolant ,

system as had happened in the past, it would have been necessary '

to go to cold shut down to clean up the reactor coolant tyrtem.

Tnis process would have required a shut dovm of several days. l

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. 9 Operators and 0,ther Evolutions Three Station Procedures were applicable at Three Mile Island before the loss of reactor c^olant Procedure. These Procedures were:

(1) Procedure 2202-2.2, Loss of S/G Feed; Procedure 2203-2.2, Turbine Trip and  !

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(3) Procedure 2202-1.1, fenctor Trip. l Craig Faust, the Unit 2 secondary plant Operator, handled the loss of feedwater and turbine trip. He prompt?.y verified the '

turbine tripped and stop valves closed. He verified 3 emergency j feedwater centrol valves in automatic and started to menitor steam generator level. He verified generator and field breakers  !

t cpen; seal oil backup pump, turbine gear oil pump and tearing lift pumps started and extracter steam valves c1csed. He noted ene turbine stop valve which did not indicate closea but noted the r centrol valve closed. The main steam safety valves lifted and Faust noted that the main steam bypass valves were maintaining ,

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steam header pressure.

3 Frederick handled the reactor scram. Immediately after i o

the scram, he returned the pressurizer heaters and spray to Automatic; verified centrol rods bottomed; started a second make up pump; opened the suction valve frc the Borated Water Storage  !

i Tank; and opened a make up pump valve to increase flew to the loeps. -

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Frederick was assisted by Faust in handling the reactor Faust also verified centrol rods bottomed; closed the let l scram.

down icolation valve; and verified electrical systems normal. l l

William Zewe , the Tnree Mile Island Shift Supervisor, also participated in handling the reacter scram. He anncunced "turbine trip reactor trip" on the page system; verified reactor shut dcwn

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10 margin; called the Shift Foreman to the control room; and had the Statien Manager and Supervisor of Technical Support called and b3 formed of the turbine trip and reactor scram.

The loss of feedwater casuality which started the Three Mile Island accident, and the turbine trip and reactor scram which followed, were handled competently and efficiently by the Operators. Fredrick and Faust, the Control Room Operators, accomplished actions required by Station Procedures in a timely manner under the cognisance of the Shif t Su erviser, 2 ewe.

After the turbine trip and reactor scram at Tnree Mile Island Unit 2 en March 25, 1979, Operators shewed by their actiens that their first priority was to Eet the Unit back on line.

Fredrick, the primary plant Operator acted so as to shorten Unit dcwn time by preventing injection of borated water into the reactor coolant system. Faust, the secondary plant Operator acted at oh05 to restore tne condensate system to normal operations. Zewe, the Shift Supervisor, worked en the cendensate system away from the Centrol Roem in the Turbine Building from 0415 to 0500.

In crder to shorten down time and start the Unit up 9*

again as soon as th: secondary plant was made ready to do, the primary plant Operator turned off the high pressure injection system.

This was done en the assumption that there were no problems in the primary plant after the scram-there had been no serious problems following previous reactor scrats. On March 23, however, there was a problem in the reacter coolant system-the electromatic relief valve had stuck open.

A reactor scram is the proper way to move a reactor plant toward a safe condition when a problem cecurs in either I

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the reactor plant or the secondary plant, howQver scrams are not free from risk because a scram sets up conditiens and pertubations '

in plant systems and components which can ler.d to serious problems.

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Every reactor scram should therefore be treated as an emergency and t l

safety systems should remain lined up and functioning in accordance  !

with design requirements as stipulated in Plant Technical i

i Specifications.

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. 12 Operator's capabilities Zewe, Fredrick, and Faust, the Operators at Three Mile when the accident began, were experienced nuclear plant operators,  !

having completed the Nav.y's nuclear power program, operated Navy nuclear plants, been licensed by the Nuclear Regulating Commissien, t

and operated at Three Mile Island for at least 5 years. Tnese een  !

I demenstrated in handling the loss of feedwater casualty, and the l turbine trip and reactor scram that they were proficient operators who follow operating orders, j Fredrick, the primary plant Operator, was folicwing operating orders when he turned off the high pressure injecticn i I

sys tem promptly af ter the system was initiated. He would have 1 allowed the high pressure injection system to centinue to functicn, l

if his operating orders had so directed.

Reason for Fore Damsce The serious damage te the core during the Three Mile Island accident on March 28, resulted because Metropolitan Edisen Company, Three Mile Island Unit 2 licenree, did not require that Operators operate the reactor plant in accordance with the Facility Operating License / Technical Specificaticns. Instead Metropolitan Edisen hud Operators follow a practice of turning off an Emergency Core ^ooling System after the system had been initiated follcwing a reacter scram ba order to shorten plant down time.

Cerrective Action To prevent damace to the reactor core during reactor plant emergencies at inree Mile Island, Operators should be directed by Metropolitan Edison Corporate Management to follow the requirements of the plant's Operating License / Technical Specificatiens.

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. Operators should be directed by Metropolitan Edison  !

L Corporate Management to follow the require.T.ents of the Plant's

.i Operating License / Technical Specifications during all reactor l plant operations and conditions, c I

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Annlysis of Three Milo Island Accident Plant Cenditicnet and OperC.icns lendinc to the Accident Condition of the Reactor Ccolant System Three Mile Island ratt 2 wan cperating at 975 power (878 MW) at 0400 March 28 1979 and had been operating at this power level for three weeks.

The reactor coolant system was leaking; the system had been leaking since the Fall of 197c.

3 During the first k'1/2 hours of the shift en which the accider.t occurred, more leakage water was transferred from the reactor coolant drain tank than earlier, suggesting a substantial increase in the reacter ecolant system leak rate.

Three Miie Island Operators knew that the reacter ecolant system was leaking because they were operating the plant abncrmally:

1. Pressuriter heaters were eaercized and the spray valve was open te ecunteract the boren increase in the pressurizer caused by steam leakage from the pressurizer.

2. Leakage water was being transferred frcm the reacter coclant drain tar's thrcugh a cooler centinuously to Icwer the temperature er the leakage water to amtient, i

3 Make up ficw to the reac*.cr ecolant system wa s above ncrmal.

Three Mile Island Unit 2 Operating License / Technical Specifiesticna stipulates that Operators shall fc1'acw Statien Procedures in cperatinc tne reactor plant.

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Three Mile Island Unit 2 Emercency Precedure 2202-1 5, i

Pressurizer Systen Failure, requires the bicek valve for the electre-r.agnetic relief valve t o be closed when the temperature of the l.

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- relief valve discharge line exceeds 130 F.

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discharge line was approximately 180 F at Three Mile Island Unit 2  :

at 0400 March 26, 1979 l The block valve was open.

1 Following the turbine trip and reactor scram at 0400  :

March 28, 1979, the electrcmagnetic relief valve opened to relieve f

the high pressure in the reactor ecolant system which resulted frem the transient. The relief valve failed to close when system pressure decreased to the valve's closing setpcint but stuck cpen causing the loss of coolant accident which damaged the reactor core.

l If Three Mile Island Operaters had followed Station Emerrency Procedure 2202-1.5 as required by the Plant's f

Operating Licende/ Technical Specifiertions, they would have shut the block valve for th. ele:tromagnetic relief valve before l

0400 March 25.

Had this been dcne,the reactor ecolant system i

leak caused by the stuck vpen electrcmagnetic relief valve weald net have cecurred and the reactor core would not have been I damaged.

Three Mile Island Unit 2 Operating License / Technical Spec-l

' ificatiens (Technical Spe:1rication 3.4.6.2), requires that the plant i be shutdcwn if the reacter ecolant system leak rate exceeds 1 l identified.

Eallon per minute frcm sources that are ene not (

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3-Station calculations for gross leak rate from the reactor coolant system were March 22 6.73 spm; March 24 6 55 spm; March 25 6.60 spm; and March 28 6.94 spm, Station calculatiens for reactor coolant system leak rate v

l from scueces that were not identified was less than 1 gallon per i

minute on these dates and the plant was not shutdown.

The Station identified the source of approximately 6 Fallon, per minute leakage frcm the reactor coolant sy. tem cn March 26. se one er mere of the pressurizer relief valves (1 1

l electremagnetic relief valve and 2 code safety valves). This measurement was performed frcm 0134 hours0.00155 days <br />0.0372 hours <br />2.215608e-4 weeks <br />5.0987e-5 months <br /> to 0234 hours0.00271 days <br />0.065 hours <br />3.869048e-4 weeks <br />8.9037e-5 months <br /> March 2o.

The 2 cede safety valves cannot be isolated from the reacter ecolant system.

The one electrcmagnetic relief valve can be isolated fnom s

the reacter ecolant system by the block viilve.

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The block valve had work performed en it en September 14, 1977. The moter operator was remcVed to allen repacking the valve.

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i The valve wa s cycled. Station persennel indicated concern that the i block valve could stick shut er cren if used tco often. Operaters using the block valve later during ute accident showed concern for failure of the valve in the open position.

The tempersture of the discharge line of the electro-magnetic relief valve was 1800 F at the time of the accident indicating - noter coolant leakage through this valve.

The leakage from the reactor ecolant system of apprcximately 6 gallene per minute calculsted for the peried 0134 to 0234 March ES, 1

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1979, was thrrught (1) 2 valves which cannot be isolated from the #

l reactor coolant system; or (2) 1 valve of questionable i isolability; or (3) a combination of these valves. l Thia leakage indicates serious degradation in tne >

reactor coolant pressure coundary. ,

f If Operators had reacted properly to this indication  ;

of derradation in the reactor coolant predsure boundary, the  ;

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e a c e '. dent could have been prevented.

l Cent"el Pec- Indic9 teas nnd Instrurents In the Control Room before the accident, numerous alsr l lights were illuminated; numerous out of service cards were pcsitioned on instrument panels; and numerous instruments were l r

cut of es11bration.

The temperature of the electromagnetic relief valve dis- l charge pipe indicates the pcsition of the valve. The temperature of this pipe was 160 F (instead of 130 F) on March 26 indicating an ,

i open valve. Therefore Operators were cperating with the valve f i

showing open and ignoring the indication en March 26. Operators j l

l had teen operating with the valve showing cren for seversi months and icncrinc the indication.

The primary plant Operater centinued to icnore the valve's position indication after the eccident started. Approxir.ately 37 minuten after the electremacnetic relier valve opened at the start of the accident. the tetc.pera ture of the valve 's discharce j line was creater than 280 F, showinr the valve to be open. The i

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temperature of the valve's 34,scharge line was a good indication [

of the valve's pocition at thic time.

s Two hours and 18 minutes after the accident started, f the Operator checked the temperature of the electromagnetic j i

rolief valve's discharge pipe; learned the temperature was [

229 F, and shJt the block valve stopping the reactor coolant f

I rystem le3k.

If the Operator had used the position indicatien of f s

j t..e relief valve, he could have discerned pcsitively 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and i t,

4 45 minutes earlier that the valve was still oper., closed the [

l block valve and stopped the reactor ccelant leak.  ;

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Workin.? cn Cendensste System ,

Three Mile Island Unit 2 was operating at 97,4 power {

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at this power level ter three weeks.

t Prior to the accident, a Shif t Fereman and 6n A2x111ary (

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Operator were worging to transfer resin fron a cendenoste polisher t tank to the resin regeneration tank. This work had teen in j

precress fer spproximstely 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> prict to the turbine trip.

l Operaters were extremely sensitiva to the fact that ner:41 l h

operst.ing cenditions of the cendtnsste/reeduster system were "try near the design limits at full pcrer.

Ststien pereennel stated that water in the instrument att system at the ecndensste pc11 hing system will cause the condeneste polisher air crersted effluent valves to close.

01esure c; the cendencate relisher effluent valves will ster cenden:ste flow and cause o turbine trip.

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The Station had problems with water in the condensat" relisher air liies on October 19 197*/ and en May 12, 1978. i l

On November 3,197F an instrument technician caused a l reactor trip frem 90; power when he mistakenly opened a breaker causing the condensate polisher outlet valves to close, a loss of [

condensate and feedwater, and turbine trip., i

'n'ork continued the night of March 27 and 28 with attempts [

by the Operstors to free up and transfer the resin. At 040U. l service air (at 80 to 100 psig) was being used to fluff the j resin in the tank, and deminerali;:ed water (at 160 peig) was being h

~l used to transfer the resin. The service air and instrument j

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l air systems were cross-ecnnected.

l Af ter the accident, a frc:en open check valve was found l in the service air line approximately 115 feet from condensate  ;

l l resin tank. The shut off valve in that line is open khe7 resin l l

transfer is in progress. The cpen shut off valve 9nd open check valve allcwed a path fer water to enter the station service air-instrument air system en March 28, 1979. Significant emeunts of water were found in the statien serv

• ce air and instrument air receivers af ter the accident. [

At the announcement of the turbine trip /reaeter trip, the condensate po11ther panel indicators showed conden;ste polisher ,

f isolation which *ndicates no condensate flow. Condensate flew

(

< charts confirm an a',rupt t>rmination of ficw.

The Shift Superviser in centinuing the attempt to l l

transfer resin over a period of 11 hcurs under the circumstances i enumerated abcVe: (1) did not give careful consideratien to the l

{ FC'ential consequences of the work en the condensste polisher cr; A

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(2) accepted the risk of the consequences of a turbine trip and reactor scram; or (3) was following orders or policy for plant operations.

Corrective Action If the Operating License / Technical Specifications had been adhered to by the Operators at rhree Mile 1sland, the block valve for the electromagnetic relief valve would have been closed before 0400 March 28, 1979, as required by Station Epergenev Procedure 2202-1.6. Then the loss of coolant accident and subsequent core damage at Three Mile Island Unit 2 on March 28, 1979, would not have occurred even though Operators persisted in attempting to perform en operation bi the secondary plant at a high power level which risked and then caused a turbine trip and reactor scram.

To prevent loss of coolant accidents at Three Mile Island, perators should be directed by Metropolitan Edison Corporate Management to follow the requirements of the Plant's Operating License / Technical Specificetions.

Design Defect Maintaining the integrity of the reactor coolant system is a prime objcetive of the design of this system.

t Opening the electromagnetic relief valve bre' aches the reactor coolant system.

To bro'ach the integrity of the reactor coolant system by an opening relief valve for a purpose other than to preserve the structural integrity of the system, is counter to the design objective.

d 4

. The electromagnetic relief valve of Three Mile Island Unit 2 freqc.ently opens on plant emergencies. (Examples:

November 3,1978; not ember 7,1978) . This is a design defect in the reactor plant.

This dsaign defect may or may not have been a factor in the Three Mile Island accident.

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