ML20235D617

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Aos:On 710420,26 & 0502,condenser Pressure Switches Isolated,Msiv Closed Too Slowly & Automatic Pressure Relief Sys Fuses Found Missing,Respectively.All Conditions Corrected
ML20235D617
Person / Time
Site: Monticello, 05000000
Issue date: 05/19/1971
From: Duncanson R
NORTHERN STATES POWER CO.
To: Morris P
US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20235B311 List: ... further results
References
FOIA-87-111 NUDOCS 8709250284
Download: ML20235D617 (4)
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NSm> NORTHERN STATES POWER COMPANY-Minneapolis, Minnesota 55401 , May 19, 1971 51 

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Dr. Peter A. Morris, Director i4 J,'

4) ~3 j Division of Reactor Licensing '
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United States Atomic Energy Commission h, u ) "; ./37/ __ j Washington, D.C. 20545 7 Cj,'.jpg 

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Dear Dr. Morris:

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M0tHICELLO ti) CLEAR GENERATIPG PLANT Docket No. 50-263 License No.. DPR-22 - Rept ts? 

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File Cy. Reporting of Unusual Occurrences Three conditions have occurred recently at the Monticello f4; clear Generating Plant which we interpret to be reportable to your office in accordance with Section 6.6.0 of A Provisional Operating License 22. DPR:ppendix A, Technical The three occurrences are: Specifications, of the

1. Isolation of Condenser Low Vacuum Scram Pressure Switch PS-5-11A.

(4-20-71)

2. Slow Closure of Main Steam Isolation Valve 2-868. (G26-71)
3. Automatic Pressure Relief System Backup Power Supply Fuses Missing.

( 5-2-71 ) Occurrences 1 and 3 are being reported under Section 6.6.0.4 of the Technical Specifications and occurrence 2 is beina reported under Section 6.6.C.1.of the Technical Speci fications. The Region Ifl Compliance Office has been previously noti fied of the occurrences. On-site investigations of the occurrences have been completed and the Operations Committee has reviewed each occurrence. The attached reports describe the occur-rences and summarize the actions taken to prevent future similar occurrences. Yours ver truly, R.0. Duncanson, r. P. E. Gen. Supt. of Power Plants Mechanical 03 Chairman-Monticello Safety Audit Committee c) c ROD /CEL/ car pg O 

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MONTICELLO tOCLEAR GENERATItG PLAT,T Vay 18,1971

Subject:

Isolation of Con' denser Low Vacuum Scram Pressure Switch PS-5-11A.

1. Summary Description and Analysis of the Occurrence On Ap ril 20, 1971, during' a plant restart following a turbine trip from 20% power, the condenser low vacuum trip in trip system A did not immediately reset when condenser vacuum was established. It was then discovered that the manual isolation valve' for the low condenser vacuum scram pressure 4 switch PS-5-11 A was seal wired closed, making the switch inoperable. The  ;

isolation valve was apparently erroneously seal wired closed after the completion of surveillance testing on the vacuum scram switches on April 16th. As a result of this occurrence, switch PS-5-11A was not operable for a period of April 16 to A pril 20th. Surveillance testing performed on April 16 and April 20th demonstrated that the B, C, and D switches were operable and that a reactor scram would have resulted if a condenser low vacuum condition occurred.

2. Corrective Actions 1

On April 20, 1971, following the discovery of the inoperable low condenser vacuum scram pressure switch, a surveillance test of all four. vacuum scram switches was porformed. ' All switches were found in calibration and verified to be in an operable condition after the completion of the surveillance testing. Actions Taken in Prevent Future Similar Occurrences 

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3. The occurrence was reviewed with all members of the instrumentation crew to further explain to them the significance and importance of properly per- ) forming calibration and surveillance testinE+ i the importance of a previously initiated program to revise the applicable Also,illance surve procedures has been re-emphasized and a higher priority for t completion of this work has been established. Applicable surveillance 4 procedures will be revised to include instrument system checks to assure that { each system has been returned to its normal operating condition following the completion of surveillance testing. ] t 

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MONTICELLO WCLEAR GENERATito PLANT May 18,1971

Subject:

Slow Closure of Main Steam isolation Valve 2-86B

1. Summarv Descrio+ ion or the Occurrence On April 26, 1971, while performing a test at 25% power involving the simultaneous. closure of all Main Steam Isolation Valves, MSIV 2-868 closed in approximately 6 seconds.. The allowable closure times of the MSIVs is 3 to 5 seconds.
2. Acenun+ and Analysis of the Occurrence On A p ril 26,1971, at 0809 hours, a full MSIV isolation test was performed while operating at 25% power. All of the valve closure times were within the allowable 3 to 5 seconds except for the outboard valve, MSIV 2-868, on the B steam line, which took 6.1 seconds to close. The inboard valve, NGIV 2-808, on the same steam line closed in 3.8 seconds. After the full isolation. test and resultant scram, MSIV 2-868 was tested and had a closure time of 5.3 seconds.

Prior to the full isolation test, each of the MSIVs was closed individually. The closure times for the B steam line isolation valves were 3.3 seconds for the inboard valve, LGIV 2-808, and 5.0 seconds for the outboard valve, N6IV 2-868. The main steam line isolation valves are designed such that steam flow assists in closing the valves. It is believed that the rapid closure of 

                                                           .the B steam line inboard N61V resulted in the slower closure of the out-board MSIV due to the sudden stoppage of steam flow. The di fference in closure times between the two individual closures for LSIV 2-86B measured before and after the full MSIV isolation is attributed to the absence of steam flow after the full isolation was performed.

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3. Corree+ive Action The closure time for MSIV 2-86B was adjusted using the flow control valve on the MSIV oil dashpot. The valve was cycled two times after the adjustment was {'

made and times of 3.6 and 3.8 seconds were recorded (no steam flow). The valve was subsequently timed at the 25 and 50 percent reactor power levels and the closure times were found to be 3.5 and 3.24 seconds, respectively. < Tn. present surveillance testing of the MSIVs requires individual MSIV closure tests monthly. The results of the MSIV closure testing performed 

                                                           - at 25 percent power indicate that it takes longer to isolate a steam line when the inboard and outboard MSIVs are simultaneously closed than it does                                  1 if a single MSIV is closed, 11 is therefore planned that if relatively i

slower single valve closure times are measured during the monthly surveillance i testing, simultaneous closure testing of the inboard and outboard MSlVs will be conducted to determine that the MSIVs close in 5 seconds or less under any condition. j i

p 1... f MONTICELLO NJCLEAR GENERATING PLANT May 18,.1971

Subject:

. Automatic Pressure Relief System Backup Power Supply Fuses Missing
1. Sucrnarv Descriefion or +he Occurrence
  . o                                                           On May 2, 1971                            it was discovered that the backup power supply fuses for the Auto Pressure 3elief System were missing. The backup. power supply is -

required to supply power to the ARS if the normal power source .is not avail-able.- - 1

2. Acenun+'or the Occurrence j
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On May.'2,1971, during a startup after a maintenance outage,: a station { battery ground existed. During the investigation to locate the ground, two fuses (2E-F9 and 2E-F10) in panel C-32 in the; cable spreading room were foune to be missing. J An inspection for missing fuses conducted on August 30, 1970 prior to the- j initial fuel loading had veri fied that the fuses were installed at' that time. I Plant records do not show any documentation' or possible reason for the removal of the fuses since that time and the plant electricians cannot recall any time when the fuses were removed. It cannot- be determined when or why the -{ fuses were removed. 

                              . 3.                               Corree+ive Action 1

The missing fuses were-immediately replaced and the backup power source- a for -the ARS system was verified to be functional. An inspection-for missing j fuses in the cable spreading room and the control room was completed and a couple of additional non-essential utility circuit fuses were found missing. , The administrative requirement to record the removal of fuses in the dumper and Bypass Log has been reviewed with the plant and construction electricians. u I l 

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