ML19261F204

Nonroutine 10-Day Rept Re Inability to Sufficiently Decrease Reactor Power/Imbalance Setpoint.Caused by Design Inadequacy.Faulty Rod Drive Motor Stator Replaced.Design Changes Under Review

ML19261F204
Person / Time
Site:	Three Mile Island
Issue date:	11/29/1974
From:	METROPOLITAN EDISON CO.
To:
Shared Package
ML19261F200	List: ML19261F199 ML19261F204
References
74-06, 74-6, NUDOCS 7910250623
Download: ML19261F204 (2)

Text

ENCLOSURI Metropolitan Edison Cc=pany

- Three ! Ele Island Nuclear Station, Unit 1 (TMI-1)

Dcc%et No. 50-289 Operating License DFR-50 Nenroutine 10-Day Report Th-C6 Report of Inability to Sufficiently Decrease the Reactor Fever /I: balance Setpcint Descriptien of Event On November 17,197h, a defective Centrol Red Drive Meter stater vinding caused a drcpped centrol red ecndition which resulted in a maximu: quadrant power tilt of 215. Appropriate precautions vere taken with regard to this condition, except that it was discovered that the pover/ imbalance reacter trip envelope could net be decreased to the appropriate value as defined by Secticn 3 5.2.h.b.l. and figure 2.?-2 of the TMT-1 Technical Specifications (Note: Fcr this event the trip setting needed to be decreased frc: a value which would ensure a reacter trip prior to 1C8% reactor pcVer, to c value which would ensure a reacter trip prior to 6o5 reactor pcver; i.e. 1C85 - 2x(215) = 665. The trip setpoint was, hcVever, cLpable of t ing reduced only to an indicated trip set-point of 725 reactor power).

Upon determing that the dropped rod could not be utilized to reduce quadrant power tilt , and after atte= pts to reduce quadrant power tilt with part length axial pcver shaping rods proved unsuccessful, the reactor was shutdevn.

Apparent Cause of Event The apparent cause of the event was inadequate design, in that the reactor power trip circuitry does not have a grea*, encugh range to permit reduction of the reactor pcVer trip setting to the point which ecrrespends to the naximu:

allevable quairant power tilt of 25% (ref: TMI-l T.S. Section 3 5 2.h.6.).

Analysis of Event Neither the health nor safety of the public was threatened as a result cf this event, in that

a. ence the control rod had dropped, reactor power inmediately decreased to less than 60%, which was less than the quadrant tilt limiting level of 66%, and never again exceeded 60% until after the reactor was shut-down and repairs verc made en the central rod drive =cter,

b. during the period of this event, the maxi =u= heat rate experienced was 6 KJ/ft, which is well telow the Technical Specificatien limit of 19.6 E4/ft, and the lowest DNER (Departure frc Nucleate Boiling Ratio) was 8.1, which is well abeve the Technical Specification Limit of 13, and

c. sufficient added precautions, including heat balances taken at 15 minute intervals, were taken to check the accuracy of the indicated pcVer levels.

?91onsa 1481 138

. .ENCLCSURE Page 2 Corrective Acticns Following reacter shut-down , the faulty red drive motvr stator was replaced, and an investigati<., was conducted to determine what design changes could be made to the pcwer/istalar.ce reactor pcVer trip =cdule to allev the trip setpoint to be set to a value correspcnding to the maxinu allevable quadrant power tilt of 255 This investigaticn is still in progress.

Failure Data

a. Sailey Meter Cetpany System S80 Euffer Anplifier.

b. Although not related to che inadequate design of the abcve referenced module , identifying data for the centrol red drive

=ct';r that failed is as fc11cvs:

Red Drive Motor Stator - Diamend / Reyal Industries Number 12CJ-3hl-I Serial EPOL 1481 139