ML20056B805
| ML20056B805 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 05/12/1971 |
| From: | Duncanson R NORTHERN STATES POWER CO. |
| To: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9102110375 | |
| Download: ML20056B805 (2) | |
Text
~
9 Regulatory File Cy.'
NORTHERN STATES POWER COMPANY l
Minneapolis, Minnesota 55401 y'\\ 0W ci
~
May 12, 1971 f,
q, 3 S.
'k -
hgF
/((l b 01 m
N, 4.-
V st l 9h 5 &,t,4
'G 4 4 h,>
V Dr. Peter A. Morris, Director f
Division of Reactor Licensina United States Atomic Energy dommission%
9 2[
~
p Washington, D.C.
20545 N
m E __.,'
Dear Dr. Morris:
MotRICELLO tOCLEAR GEfERATI f6 PLANT 1
Docket No. 50-263 Li cense No. DPR-22 l
Inoperability of Main Steam Line 4
High Flow Sensors lt has been determined that the high flow sensors for main steam line 8 have been inoperable during the startup test program to the 50% power level.
We are reporting this occurrence in accordance with section 6.6.B of Appendix A, Technical S eci fications, of the Provisional Operating License DPR-22. The p
Region 111 Compliance office has been previously notified in accordance with section 6.6. A of the Technical S ecifications.
p Summnrv Descrintion of Occurrence On May 3,1971, while operating at 50% power, it was discovered that the high and low pressure sensing lines for the steam flow instruments associated with main steam line B were connected in reverse order. Thus, four of the hi h steam flow sensors which initiate main steam isolation were inoperable.
E The main steam isolation valves for steam line B were imediately closed and the instrument piping was corrected.
Following correction of the reversed sensing lines it was found that the differential pressure being sensed by all of the steam flow instruments is apparently less than that predicted by the flow nozzle calibration curve.
The setpoints of all 16 high flow sensers in the main steam isolation logic were immediately lowered to assure that they are within the Technical S ec-p i fication limits.
Investigation of this discrepancy is currently in progress.
Dalailed Descrintion and Analvsi_s During startup testing at 25% power the total steam flow indication was found to be low and the indicated individual steam line flows were unsteady and unequal. At that time, the problem was attributed to instrument calibration discrepancies and the fact _ hat the flow was well below 20%
of full scale. Prior to operation at higher power levels the instrumentation was recalibrated.
~
9102110375 710512 CF ADOCK O 263 2340 1-o
I x
e During the initial rise to 50% power on A ril 28, 1971, the steam flow p
rmte r for steam line B indicated zero flow.
That evening the reactor was brouBht to the cold shutdown condition for operator licensing examinations and scheduled maintenance.
investigation during the outage revealed a blown fuse in the flow instrumentation. The fuse was replaced prior to returning to power operation.
On May 3,1971, the reactor was again at 50% power and it was found that the B steam line flow meter indication was downscale. The four high steam flow di fferential pressure indicating swi tches (DPIS-2-117A, B, C, D) for steam line B were found to be indicating a negative differential.
It was concluded that the high and low pressure sensing lines from the B sicam line were connected in reverse order.
Thus, the four high steam flow sensors had been inoperable.
The main steam isolation valves for the B steam line were immediately closed. The instrument piping was corrected, the high steam flow sensors were made operable, and the isolation valves were reopened wi thin approximately six hours.
Following correction of the reversed sensing lines, the flow indication for all four steam lines were found to be reasonably eg;al.
However, the total indicated steam flow was approximately 2,400,000 lb/hr while the actual steam flow, based on feedwater flow and confirmed by gross electrical power output, was about 3,100,000 lb/hr.
The di fferential pressure at the various flow instruments was found to average about 5 psid. According to the flow nozzle calibration curve approximately 12.5 psid would be expected at steam flows corresponding to 50% power.
Immediately following this discovery (equivalent to 140% of rated flow based on the flow nozzle the setpoints of the high flow sensors were reduced from 122 psid calibration curve) to 40 psid. The 40 psid setting should assure that the Technical S ecification limit of 140% of rated flow is not exceeded.
p Investigation of the discrepancy is currently in progress. Preliminary cFecks of flow nozzle design data and the physical installation have not indicated any All of the flow instruments are being recalibrated with special error.
attention to the lower quarter of the scale range.
Additiona14P measurements at various flows will be obtained as the startup test program progresses.
i Yours very rul y, R. O. Duncanson, Jr., P. E.
Gen. Supt. of Power Plants - Mechanical l
Chai rman-Monticello Safety Audit Committee ROD /!MC/caf 1
l l
l f
I