ML20056B813

Ro:On 710303,omission of One Rod Group Occurred When Withdrawing Control Rods

ML20056B813
Person / Time
Site:	Monticello
Issue date:	04/02/1971
From:	Duncanson R NORTHERN STATES POWER CO.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9102110393
Download: ML20056B813 (4)

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NORTHERN STATES POWER COMPANY Minneapolis, Minnesota 55401 April 2,1971 . p'g A

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\ Neusslar Dr. Peter A. Morris, Director Division of Reactor Licensing 4' AD 7 s

United States Atomic Energy Comission -

Washington, D.C. 20545 1

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Dear Dr. Morris:

L0ffTiCELLO t/JCLEAR GENERt.TlTG PLANT E-5979 i

Docket No. 50-263 License No. DPR-22

{ Omission of One Rod Group When Withdrawing Control Rods An error in the withdrawal sequence of control rods occurred 5

at the Monticello Nuclear Generating Plant on March 3,1971 i during low power reactor testing. We interpret this occurrence to i be reportable to your office in accordance with Section 6.6.C.4 of i

Appendix A, Techaical Specifications, of the Provisional Operating j

License DPR-22. The Region 1II Compliance Of fice has been previously i notified of the occurrence.

i An on-site Unusual Occurrence investigatien of the occurrence t

has been completed and the written report has been reviewed by the site Operations Comittee. The attached report, "0 mission of One Rod Group When Withdrawing Control Rods", describes the occurrence and sumarizes the actions taken to prevent future similar occurrences. f,.

, Yours very truly, 4 # M ca s r Gen. Supt. of Power Plants - Mechanical -

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Chairman - Monticello Safety Audit Comittee 30 -

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i March 18,1971  :

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Subject:

Omission of One Rod Group When Withdrawing Control Rods

{ 1. Sumarv Descrinfion of the Occurrence I 1 g. y y 4 py j

On March 3,1971, control rods were being withdrawn from the reactor

to irscrease power while the Rod Worth Minimizer (RWM) was bypassed. '

One group of four rods remained partially inserted in the. core out of ,

j sequence with the specified rod withdrawal program. The situation  ;

was undetected for approximately five. hours and was corrected within

! approximately eight hours. Since the rods were peripheral rods havin  !

very low worth, there were no specific _ results from this occurrence. g  !

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2. Sumary of P!ani Conditions i

l j During the course of the occurrence, the reactor was operated in the range j of 15 to 200 ME to provide the necessary conditions for startup testing.  ;

Reactor pressure was at 1000 psig, the reactor water level was norri.al i

j at +37 inches, bypass valves. and steam was being dumped to the condenser through the

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j 3. Account of the Ocmcrence -

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The following sequence of events occurred on March 3,1971.  !

i 0137 i Reactor power was reduced by inserting control rod groups 17,16, 15 and 14 to their group insert limits.

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) 0410 The RWM was bypassed for control rod scram testing. _ (NOTE: This l

was necessary because special roo patterns were being use.d to 1 allow the withdrawal of control rods fo. scram testing. The

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special rod patterns were specified by test engineers and the rod I programming was being verified by a knowledgeable employee.)

0645 The REM was returned to servii.e on completion of the scram testing.

, 0700 1 At the shift change time, an operator who was beginning his shift ast.ignment made the following reactor lo l 1-14 at normal ' A' sequence posi tions". g. entry, "All CR groups

0900 The RWM was bypassed to allow friction testing of control rods.

(NOTE:

l Unmlated to the developing occurrence, the Engineer, Nuclear, ws investigating previously reported RWM problems. 3 3 foluwing the completion of the control rod friction testing, i the RWM remained out of service for trouble shooting of the re-ported problems.) '

! 0950 A, . persior began increasing power by withdrawing group 15 rods. -  !

A se jor licensed engineer was veri fying the rod withdrawal seg;ence.

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1500 The on-duty shift, in the process of verifying the rod patternt ,

i discovered the rod withdrawal segaence error. The rod group positions were correctly recorded as "Grps 1-13 at s l 3

positions, Grps 15-20 at specified positions ....." pect and fied the ~i i information was reported to the Engineer, Nuclear. The j attached figure shows the location of the control rod group's

. involved.

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1 i 1747 Control rod groups 15-20 were inserted and group 14 rods withdrawn.

i The RWM was returned to servic.e and was functioning properly.

j (NOTE: At the time of the discovery of the sequencing errer, i heat balance data was being taken and nuclear instrumentation-j calibrations were in progress. It was determined that this work .

l could be completed prior to correcting the rod sequence error.)'

l 4. Analysis of the Occurrence ._

4 j Three factors contributed to the cause of this occurrence. First, an j incorrect entry was written in the log. Secondly, an operator failed to j verify the rod pattern prior to withdrawing rods resulting in a rod

withdrawal sequence error. Thirdly, the individual assigned to follow

' the rod sequencing while the FW was bypassed, failed to verify the

! existing rod pattern prior to the withdrawal of out-of-sequence rods.

I Administrative procedures were not adequate to prevent a deviation from )

the planned rod sequence. j

5. Actions Taken to Prevent Future Similar Occurrences

The Operations Committee has reviewed the occurrence report and has taken the j following actions to prevent future similar occurrences.

! a. All required actions must be taken promptly, when necessary, to have the llod Worth Minimizer available during all reactor operations below l 10% power.

b. The following administrative actions will be formally stated through

! the issuance of a Volume F mmo (to amend the Operations Manual

procedu res):

l 3 1) When control rods are being moved and the FM is bypassed, the name of the operator at the reactor controis and the name of the person assigned to verify the rod sequence must be entered in the reactor log.

2 i 2) Each shift must verify the correct- rod pattern when they come on duty and enter in the reactor log that the correct rod pattun .

has been verified.

c. The Engineer, Nuclear will periodically audit the control room records i to verify that proper procedures are being followed.

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O l 27 48 48 6 48 6 48 6 48 6 40 6 48 49

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48 ef 48 I 02 06 10 .14 18 22 26 30 34 38 42 46 50 1 -

] Rod Pattern after Withdrawal of Group 13

a - Group 14 withdrawal (Designated rods to be withdrawn from position 24 to 48) a 10 - 43 42 - 43 10 - 11 42 - 11 i

b - Group 15 withdrawal (Designated rods to be withdrawn from position 00 to 24) i 14 - 47 46 - 39 j  % - 15 38 - 07 t

c - Group 16 withdrawal (Designated rods to be withdrawn from position 00 to 24)

06 - 39 38 - 47 ~

14 - 07 46 - 15~

). d - Group 17 withdrawal (Designated rods to be withdrawn f' rom position 06 to 12)

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10 - 27 26 - 11 e - Group 18 withdrawal (Designated rods to be withdrawn from position 06 to 10) 1 18 - 35 M - 35

18 - 19 34 - 39 j f - Group 19 withdrawal (Designated rod to be withdr

wn from position 06 to 08) 26 - 27 .

g - Group 20 withdraival (Designated rod to be withdrawn from position 06 to 12)

18 - 43 42 - 35 10 - 19 34 - 11 1

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