ML20058K929

Discusses Planned Mods to HPCI Sys Steam Line Flow Sensing Device

ML20058K929
Person / Time
Site:	Monticello
Issue date:	03/02/1972
From:	Mayer L NORTHERN STATES POWER CO.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9104260283
Download: ML20058K929 (3)

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NORTHERN STATES POWER COMPANY M IN N E A PO LI S, M S N N E S OTA M5401 N N

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Dr. Peter A Morris, Directox s @ ft 6 jo M > 5 S ' , S Ge0 Division of Reactor Licensing "

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Dear Dr.113rris:

co MONTICELLO NUCLEAR GENERATING PIANT Docket No. 50-2o3 License No. DPR-22 Planned Modifications to the High Pressure Coolant Injection System Steam Line Flow Sensing Device As reported in our letter of September 15, 1971, during an operability test of the High Pressure Coolant Injection (HPCI) system, the HPCI steam line isolation valves tripped closed from a false high steam flow signal. Backflushing of the flow elbow sensing lines appeared to correct the observed increase in the differ-ential prassure measurements from the HPCI steam line elbow taps; however, fre-quency of testirg of the HPCI system was increased to once per week, after its return to service, with additional recording of elbow tap pressures to detemine that the observed change in flow elbow differential pressure was not a recurrirg problem.

On the first weekly test on September 18, 1971, following the return to service of the EPCI system, and while operating at 90% power, it was found that the flow elbow differential pressure had again increased, causing the HPCI steam line to isolate. A review of EPCI tests previous to these two showed that all success-ful testing had been completed under low main steam flow conditions and that the unsuccessful tests were conducted with approximately 90% of rated steam flow.

Based upon this new informtion, it was demonstrated that the differential pres-sure at the HPCI steam line flow elbow, which is directly connected to a saddle on the HPCI steam line, will be affected by the flow in the main steam line.

These effects become so pronounced above 50% of rated flow in the main steam lines, that when testing the EPCI system it automatically isolates after 45 sec-onds because the differential pressure indications remain higher than the reset  !

values of the 150,000 lb per hour flow sensors. This effect on the flow elbow differential pressure prevents full completion of the EPCI system flow rate tests under conditions of high reactor power; however, the conditions under which the HPCI is required to function (low-low reactor water level and high drywell pressure) also result in a reactor scram and a main steam line isolation. Thus, e, . , -

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9104260283 720302 CF ADOCK 05000263 j ,#;

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NC THERN STATES POWER $ MPANY

. ., . T>r. 7 A Marris h rch 2, 1972 for an automatic HPCI initiation, the main steam flow vill drop to zero within 5 seconds and allow the 150,000 lb per hour flow sensors to reset well before the end of the 45 second time delay.

Pending further review of means for development of a practicable method for re-solving the flow disturbance effects on the HPCI system steam line elbow taps, quarterly flow rate testing of the HPCI system was planned to be conducted with the "B" steam line isolated for the short period of time required to complete this test. If conditions develop requiring HPCI initiation during the period of testing, proper functioning of the HPCI system will occur as required.

Engineering studies have been completed on various methods to eliminate the flow l

disturbance effects on the HPCI system steam line elbow taps and the preferred  ;

alternate has been determined. We have initiated detailed engineering and pro-curement of materials to install a Universal Venturi Tube piping section to re-place the piece of piping between the existirg HPCI steam line flow elbow and HPCI isolation valve Mo-Co34 as shown on the attached sketch. The new flow device vill utilize the existing control logic and where compatible, the exist-ing equipment. The BIF Universal Venturi Tube primary flow metering device vill provide sufficient accuracy and reliability, as a replacement for the elbow f1cw measuring device, to permit flow rate testing of the HPCI system without the need for "B" steam line isolation.

The delivery time for the Universal Venturi Tube is about 16 to 20 weeks. We plan to make this modification at the first scheduled outage at Manticello for refueling (or poison curtain removal), or at an earlier unscheduled outage which might be expected to persist for a time period long enou6h to allow the new flow measuring device to be installed. In the meantime, quarterly flow rate testirg of the HPCI system vill be performed with the "B" steam line isolated.

Yours very truly, L o m yer, P.E.

Director-Nuclear Support Services LoM/br ec: B H Grier Attachment l

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