ML20235E330

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Requests Submittal of Plans & Program to Rectify Operating Deficiencies at Plant,Based on Listed Events & Discussions W/Representatives of Util.Handling & Resolution of Many Events Appears Inadequate
ML20235E330
Person / Time
Site: Monticello, 05000000
Issue date: 10/18/1971
From: Morris P
US ATOMIC ENERGY COMMISSION (AEC)
To: Dienhart A
NORTHERN STATES POWER CO.
Shared Package
ML20235B311 List: ... further results
References
FOIA-87-111 NUDOCS 8709280066
Download: ML20235E330 (3)
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," t CCT 181971 Docket No. 50-263 Northern States Power Company ATTN: Mr. Arthur V. Dienhart 414 Nicollet Mall Minneapolis, Minnesota 55401 Gentlemen:

In reviewing the operation record of the Monticello Nuclear Generating Plant since the provisional operating license No. DPR-22 was issued, we note that there have been a number of unusual occurrences that have had safety implications. %e hanuling or resolution' of many of these items 'does not appear to have been adequate, which leads us to conclude that your Operations Committee and Safety Audit Connaittee have not functioned properly in discharging their responsibility to assure the high level of operational competence required.

On May 12, 1971, you reported that while you were testing at 507, power, you ' determined that all four main steam line flow restrictors exhibited

.a significant discrepancy between measured differential pressure and the vendor's calculated calibration curve. Following telephone conversations with DRL and Compliance staff' members, you submitted a second interim report on July 2,1971, stating that additional tests had been approved and that the reason for the anomaly was not yet determined. At that time, the setpoints of the high flow sensors equivalent to 140% of rated flow had been reduced from 122 psid to 43 paid. Se new setpoint was justi-fied by extrapolation of measured data. In our letter of July 26, 1971, we expressed our concern that since the measured pressure drop across the flow restrictor is much less than expected, and therefore the restrictor may not restrict flow to the extent assumed in the safety evaluation, the high flow setpoint based on extrapolation of measured data may not be valid.

We requested that the operation of the sensors be tested at the Technical Specifications setpoint of 1407,of rated flow. We instructed you to submit as soon as possible your plans and the methods you will use to conduct the

, tests safely. We also asked you to submit your plans for determining the cause of the anomalous behavior of the sensors end. for taking any required I

remedial actions. In the interim period until the tests have been performed, you were asked to set the setpoints of the high flow sensors not above pre-viously tested levels (1137. of rated flow). We have not received any infor-mation on this subject from you since our July 26 letter,

' i i i l h l 8709280066 870921' PDR FOIA ,

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. t Northern States Power Company 2 on July,14, 1971, while operating at approximately 907. of rated power, a reactor isolation occurred. After clearing the isolation, while evacuating the condenser, apparently a pressure surge in the 30-minute delay,line blew

'out the air ejector- off-gas loop seal. As a result, activity  !

levels of approximately 35,000 pC1/see were measured at the off-gas stack and levels of 20,000j4Ci/see were calculated at the reactor building vent

.steck. The liquid activity in the discharge canal reached 2.5 x 10-6 tC1/ce,

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possibly exceeding the limits of 10 CFR Part 20 As a result of thisf incident, you made several modifications in your operating and emergency procedures; a new control switch that will allow the operator to manually  ;

isolate the off-gas line loop seal was installed; and an interlock has been added to the control switch in the off-gas line so that steam supply to the air ejectors will be blocked when there is no ses flow. >

On August 4,1971, in discussions on this matter, we informed you that the precautions you had taken would not prevent future similar releases  !

and that a means to prevent the loss of the off-gas loop seal should be l provided. As of this date, we have not been informed of the disposition of this potential problem.

..By TWX on Apri1~28, 1971, you informed us that the High Pressure Coolant ~

Injection (HPCI) system became inoperable on April 22, 1971 and stated that you 1971.

would operate the plant with the HPCI system inoperable until Hay 5, In our reply' dated April 29, 1971, we informed you'of the importance l of the availability of safety- systems and that your request for extended '

plant operation beyond the seven days in which the HPCI was not available was not acceptable. On September 5,1971, during an incident involving loss of instrument air, the HPCI was declared inoperable. By letter dated September 28, 1971, you informed us that the HPCI system was  !

again declared inoperable from September 18, 1971, to September 24, 1971.

In the name letter, you state that the main reason for the unavailability of the HPCI is the erroneous indication of high flow in the steam supply line to the HPCI elbow tapa, caused by turbulence. A high flow signal {

isolates the HPCI. Your solution to this problem is to isolate the "B" steem line while testing the HPCI. This will require a reset action by an operator within the 45-second time delay to bring the system back into operation. Your solution is not acceptable bscause automatic actuation of all engineered safety features is required. Also, your solution may isolate the HPCI when needed. The operation of the HPCI is assumed in our finding of no undue risk to the health and safety of the public.

We request that you determine the cause of the trouble and then eliminate it in such a way that the existing safety and reliability of the plant is not affected.  ;

We understand that on September 5, 1971, while operating at 907 power and ths HPCI declared inoperable, after the incident involvina loss of instru-menta$r,thefeedwa$erpumpsstopped. Therepctorscrammepon"lowlevp1" 4

Northern States Power Company 3 and " low low level" was annunciated. As a result the primary system was isolated. However, approximately 45 seconds later, all eight stesa line isolation valves opened. The reactor was restarted before investi-gating the causes of these occurrences, as the operators were unaware that the steam isolation valves had opened. We understand that you attribute the opening of the steam valves to' inadvertent operation of the reset switch by an operator. Fortunately, even though the HPCI was declared inoperable, it performed its function, since under the existing circumstances the Automatic Pressure Relief System would not have actuated automatically, and therefore none of the automatically actuated safety features were available. (Our own evaluation shows that a short circuit in the reset switch located in the control room would negate the isolation required for the health and safety of the public.)

Your letter reporting this occurrence was received on October 8, 1971.

If we require additional information regarding this incident we will be in touch with you in the near future. ,

Based on the instances enumerated above and our discussions with representatives of the Division of Compliance and representatives of the Northern States Power Company on seversi recent occasions, we conclude that additional management attention is necessary to assure safe operation of the Monticello plant. We request that within 10 days of receipt of this letter you submit your plans and program to rectify the operating deficiencies at the Monticello plant, and to improve the management and control system and the overall technical surveillance by the company to assure that similar deficiencies are avoided in the future.

Sincerely, Peter A. Morris, Director Division of Reactor Licensing cc: Gerald Charnoff, Esquire Shaw, Pittman, Potts, Trowbridge ,

) & Hadden 910 17th Street, N.W.

Washington, D.C. 20006 Distribution:

See attached 1

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