ML19261F183

LER 78-020/01T-0:on 780614,seven of Nine Control Rods in Group 3 Inadvertently Dropped Into Core,Causing Operation W/More than One Inoperable Rod.Caused by Shorted Diode in DC Hold Secondary Power Supply.Fuses & Diode Replaced

ML19261F183
Person / Time
Site:	Three Mile Island
Issue date:	06/28/1978
From:	Mitchell D METROPOLITAN EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19261F181	List: ML19261F180 ML19261F183
References
LER-78-020-01T, LER-78-20-1T, NUDOCS 7910250604
Download: ML19261F183 (3)

Text

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, LICENSEE EVENT REPORT CONTROL R, LOCK; l l l l l l (PLEASE PRINT OR TYPE ALL F ff R ED IN FO RMATION)

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EVENT OESCRIPTION AND PROB A8LE CCNSECUENCES h

] l On ik June 1973 'it 1006 hours0.0116 days <br />0.279 hours <br />0.00166 weeks <br />3.82783e-4 months <br />, seven of the nine centrol rods in cup 3 inadvertantlyl I I dropped into the ecre resulting in operatien with nere than ene inoperable red (as de- l

@ l fined in T.S. h.7.1.2) which is a violation of T.S. 3.5.2.2.a, anc' whiOh also violatest

] I the red index linits of T.S. 3.";.2.5.e. During the transient which fclieved, the quadt.

9 l rant pcVer tilt li=it of T.S. 3.5.2.h.a was exceeded but "as returned to an acceptablet

] [ value within fOur hcurs. Power was reduced to kO5 i=nediately and the centrol red l gl 1sy=setry was cleared within one hour with a shutdown nargin greater than 15 Ak/k. I a, ( cent . ) do SYSTE M CAUSE CAUSE COMP. VALVE CODE CCCE SUSCOCE COMPONENT CODE SU8COCE aV8COCE I $

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_ 21 22 23 24 26 27 N N 'O 31 32 AC' ION PUTURE E78ECT SMUTOCwN A TT ACHM E NT NP R O-4 PRIME COMP. COMPONENT TAKEN ACTION ON PLANT METHCO NCURS +4 SUBMITTED FORMbu8. SUP8 LIE R VANUFACTURER

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C#USE DESCRIPTION AND CCARECTIVE ACTICNS g ':h cause for the dropped rods was a shorteddicde in the DC Hold Secondary Pcver Sup- l g l ply. The shorted diede and resulting blevn fases caused icv voltage frem the Secen&/;

Supply. When the trip breakers for the Main Supply were trip tested during RPS sur-3  ; veillanca, the rods dropped because of the insufficient vcitage. 31cvn fuses and  ;

failed dicde vere replaced and the output wave ferns checked.

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a 9 90 p AciLITY METHCD OF STATUS  % PCWER OTHER STATUS OISCOVERY DISCOVERY OESC41PTICN 34

] lE l@ l 1l 0 l 0 l@l NA l l 3 l@l RPS Surveillance lead to Red urep l ACTIVITY CO TENT RELEASEO OF MLEASE AMOUNT CF ACTIVITY LOCATION OF RELEASE B 8l 3i .] @ L Z.J @ NA I I x^ l to 11 44 45 90 PERSCNNEl EXPQSURES NUM8ER TY8E OESCRIPTICN 3101 $ 9 01 ol@l 21@l2A 11 12 13 I

PER$CNNE L INJupt ES 30 NUM8ER GESCRiPTION I $1010l0l@l NA ni I 3 12 LOSS 11 OF OR OAMAGE TQ FACILITY Q k j

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i - NRC USE CNLY 8

] SSUEO@l [? l Weekly Nevs Release DESCRIPTION [ [l lltll11IIIl}

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NAME CF PREPARER D. G. Mitchell PHONE: (215) 929-3601 Ext. 169 ?

3 7910258[OY

t LER #78-20

1. 10 Event Descriptien and Probable Consequences Cent.

2.ere existed no threat to the health and safety of the public since =cre than the required shutdeva nargin existed during the occurrence.

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. . Attach =ent GQL 113h s  ;

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. AT"ACEEC "V LZ?. ~8-20 Cn l!. June 1978 at 1006 hours0.0116 days <br />0.279 hours <br />0.00166 weeks <br />3.82783e-4 months <br />, seven of the nine control reds in grcup 3 inadvertantly dropped into the cere. An F.PS surveillance was being perfer=ed at the ti=e which required manually tripping the trip breakers fer the DC Ecid Main Power Supply. The remaining DC Ecid Secendary ?cver Supply vill nor= ally held the reds, hcVever, the secccdary voltage was not sufficient to keep the reds latches because a shorted dicde resulted in blevn fases.

The unit var at 100T F.P. at the ti=e of the red drep. ?cver was r~duced i==ediately to h0% F.P. While plant conditiens vere being stabilized, core power distributions and other core physics data vere being analyzed. Frc= the Technical Specifications it was determined that cperation with =cre than ene inoperable red is not per=itted, and an crderly pcver reductica vas begun.

Meanwhile, the two reds which had net drcpped vere scved in and the reds which had dropped vere successfully latched. Within ene hcur after the reds had dropped, all nine rods in the group vere aligned thus clearing the asy=:etric red alarms. Within the next twenty =inutes the grcup 3 reds vere all loci vithdrawn.

Having returned the centrol reds to an acceptable configuration, the unit power reducticn was stopped with reactor power at apprcxi=ately 30% F.P. With ecndi-tiens stable, pcVer escalation began.

The present Unit 1 Technical Specifications does not define the time limit for shutting devn in this event. It has been noted that Standard Technical Specificatiens requires shutdevn within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. In the interi= until STS is i=plemented on Unit 1, Unit 2 Technical Specifications vill be used for guidance when an LCO is being viciated and no specific guidance is given in the Unit 1 Technical Specificaticas. Cperations Depar*=ent supervisien vill be familf arized with the reed to refer to Unit 2 Technical Specificaticus for additicnal guidance when required.

1481' 101