ML19344B049

LER 80-059/03L-0:on 800720,control Room Operators Noticed NI-1 Startup Rate Peg High,Then Low.Source Range Indication for NI-1 Went to Zero.Cause Not determined.Pre-amp Gain Link Readjusted to Raise Signal Pulses

ML19344B049
Person / Time
Site:	Davis Besse
Issue date:	08/18/1980
From:	Powers T TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19344B048	List: ML19344B047 ML19344B049
References
LER-80-059-03L, LER-80-59-3L, NUDOCS 8008250483
Download: ML19344B049 (3)

Text

{{#Wiki_filter:U. S. NUCLEAR REGUL ATORY COMMISSION P.RC FORM 36G (7 77)

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     -                                                                      LICENSEE EVENT REPORT                                                                              j i

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 ?       8                      60            61              DOCKET NUMB ER EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h                                                                                                         ,

l o l a l i (NP-33-80-72) On 7/20/80 at 0425 hours and on 8/9/80 at 1710 hours, the control l

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Source range l 1 o 13 l I room operators noticed NI-1 startup rate peg high, then peg low. l9l4ll indication for NI-1 also went to zero, and the instrument was declared inoperable. i

 ;ol3j        lSince the unit was in mode 5, the action statement *of Tech Spec 3.3.1.1 was not                                                                            l I o is l l entered. There was no danger to the health and safety of the public or station                                                                                l lOl7ll personnel. Redundant source range instrument NI-2 was operational throughout both                                                                                 l l

1o I8 l 1 occurrences.

• 80 E CODE . S SC E COMPONENT CODE SU8 CODE SU E io19i lI lD lh (_E_jh W h l I l N l S l T l R l U lh (E_jh (Z_j h 13 18 19 20 8 9 10 11 12 Y

OCCURRENCE REPORT REVISION SEQUENTIAL REPORT NO. CoOE TYPE No. EVENT YE AR O aE LE R 'Ro so Q _ 23 l8l6l 22 [-j 23 l0lSl9l 24 26 l/l 27 10 l 31 M M W 30 [--] 31 l 0] 32

                                                                                       ' HOURS           S8 iT         FOR      8.      SUPPLIE             MANUFACTURER KN AC           N          ON PL NT              ME

[1J@Lx.J@ l_z.J@ Lz_]@ loIaIeIeI LIJ@ LN_j@ [Z_jh lZ l9 l9 l9 l@ 44 47 3b A 31 40 41 42 43 33 34 CAUSE DE3CRIPTION AND CORRECTIVE ACTIONS 1 li l o l l In both cases the instrumentation returned to normal within minutes on its own. i i lST 5091.01 was successfully completed at 0920 hours on 7/21/80 and at 2345 hours on 1

   ,,,,,l8/9/80, respectively. Under MRO-IC-572-80, investigation found weak signal pulses                                                                                _l jfrom a pre-amp. The pre-amp gain link was re-adjusted which raised the signal pulses ]

lco prevent it being lost in the noise clutter and being cut off by the discrimination. 80l 8 9 AQQ1 Clonal System cneckout is bein conducted under this MO. 7 oTHER STATUS IS O RY DISCOVERY OESCRIPTION SA S  % POWER i 5 [_H_jh l 0 l 0 l 0 lh! NA l (A_jh!ControlRoomIndication l ACTIVITY CO TENT LOCATION OF RELEASE RELE ASED OF RELEASE AMOUNT OF ACTIVITY l NA  ! 1 6 l NA l 7 8

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h [Z_}@11 10 44 45 80 PERSONNEL E XPOSURSS NUMBER TYPE DESCRIPTION l

li l 71 10 1 0101@l Z l@l" NA *

                  , ERSONNEL        IN,u'JIES NU.,e E n              OESCniPnON@                                                                                                                         l i a      10 101 Ol@l12NA 7      8 9                  11 LOSS OF oR DAMAGE To FACILITY Q TYPE        DESCRIPTION                     N./

l 7 1 9 8 9 d hl 10 NA NRC USE ONLY 80 l PUBLICITY

     , R     ggr'c;'"~                                                         800825of33                                                 i 68 e1 i i i i i i iiiiiiii    80 E Trent Powrc                                              PHONE:       259-5000          Ev. t . ?11 fMMjlf0f_2BGMtER _

I TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-80-72 i l i FACILITY: Davis-Besse Unit 1 DATE OF OCCURRENCE: July 20, 1980 and August 9, 1980. IDENTIFICATION OF OCCURRENCE: Failure of NI-1 instrument indication Conditions Prior to Occurrence: The unit was in Mode 5 with Power (MRT) = 0 and Load (Gross MWE) = 0. Description of Occurrence: At 0425 hours on July 20, 1980, control room operators noticed NI-1 startup rate peg high, then peg low. Source range indication for NI-1 also went to zero, and the instrument was declared inoperable. The Instrument and Control Foreman was informed of the situation and sent an I&C mechanic to investi-gate. By the thee the mechanic arrived in the con' trol room, the instrument appeared to be indicating properly, and the decision was made not to conduct any troubleshoot-ing until ST 5091.01, Source Range Monitor Functional Test, was performed on the instrument. At 0920 hours, ST 5091.01 was satisfactorily completed on the instrument, and NI-1 was declared operational. At 1710 hours on August 9, 1980, control room operators again noticed the NI-I startup rate peg high and then low along with source range going to zero. The instrument was declared inoperable. At 1725 hours NI-1 returned to normal on its own. ST 5091.01, Source Range Monitor Functional Test was successfully run at 2345 hours on August 9, 1980, and NI-1 was declared operable. Technical Specification 3.3.1.1 Table 3.3-1 requires a minimum of one channel of source range instrumentation to be operable while in Mode 5. Since NI-1 being inop-erable did not violate the minimum channels operable requirements of Technical Speci-fication 3.3.1.1, no action statement was entered. l Designation of Apparent Cause of Occurrence: Since it nc;mally restores itself within minutes, it has been difficult for I&C personnel to check it in a failed state. A check on August 15 did show that.the signal pulses from the pre-amp were only -0.35 to -0.40 volts which was less than " l the -0.5 to -1.0 volts called for in IC 2002.04, Source Range Detector High Voltage and Discrimination Setting Procedure. This may have resulted in these lower signal pulses being lost in noise clutter and being cut off by the dis- " criminator. This could explain th: Insa of indication. t Analysis of Occurrence: ! There was no danger to the health and safety of the pub j The thermal power level was maintained at less thanamps 10-{fe on the to station personne the intermediate range flux instrumentation. The redundant source range instrument NI-2 was in service and operational throughout the occurrence. s LER #80-059

    '* T0LEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE PACE 2 SUPPLEMENTAL INFORMATION FOR LER NP-33-80-72
       ' Corrective Action:

In both cases the indications returned to norual before troubleshooting could begin. In both cases ST 5091.01 was satisfactorily completed and NI-l was declared operable at 0920 hours on July 21, 1980 and at 2345 hours on August 9, 1980, respectively. Under Maintenance Work Order IC-572-80, it was discovered that the signal pulses from the pre-amp was -0.35 to -0.4 volts which was less than the -0.5 to -1.0 volts called for in IC 2002.04. The pre-amp gain link was re-adjusted from X10 to X20 which taised the signal pulses to about -0.8 volts. IC 2002.04 was then performed to establish new Source Range High Voltage and discriminator setpoints. This resulted in much stronger signal pulses to and through the source range count amp. Failure Data: Short duration failures of NI-1 have been repetitive, but the cause is not yet known. Previous reports on similar failures are Licensee Event Reports NP-33-77-79, NP-33-77-88, NP-33-77-100, NP-33-78-110 (78-093), NP-33-79-87 (79-078), and

,         NP-33-80-65 (80-054) .

LER #80-059 l l I l I

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