ML20002C459
| ML20002C459 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 12/21/1973 |
| From: | Sewell R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8101100328 | |
| Download: ML20002C459 (4) | |
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December 21, 1973
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'o Re: Docket 50-155
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Mr. John F. O' Leary
(~~3 License DPR-6 Director of Licensing
/p Big Rock Point US Atomic Energy Commissio -A Washington, DC 20515 6*g 4
Dear Mr. O' Leary:
By letter dated November 26, 1973, we reported that the water on the shell side of the emergency condenser (condenser) was found to contain an abnormal amount of short-lived activity in the form of short-lived fission gases. We further reported that there was no indication that a release of radioactivity to the environs had occurred and stated that further surveillance checks would be performed on a daily basis until the leak is repaired at the next cold shutdown.
The plant was placed in a cold shutdown condition on December 5, 1973 to repair the valve stem packing on a 1-inch valve on a steam drum level sensor column. During this shutdown, an investigation of the condenser was undertaken to determine the cause of the activity in the shell side water. This letter is written to inform you of the results of this investigation.
The tube side of the condenser was pressurized and an inspection was made on the shell side to detect leakage. From this inspection, it was concluded that three tubes were leaking in the vicinity of the tube sheet of the north tube bundle. The water box of the north tube bundle was removed and the leakage was determined to be due to tube-to-tube sheet-weld defects in three welds. These defects were determined, by dye penetrant testing, to be due to porosity in the welds. Weld repairs to eliminate these sources of leakage will be made prior to return-ing the plant to service.
When the water box was removed from the north tube bundle, the divider plate that separates the inlet from the outlet was de-termined to be slightly varped. The water box of the south tube bundle was then removed and its divider plate was also found to be warped. The divider plate acts to direct the inlet steam into the tubes and also separates the steam inlet side from the condensate outlet side of the tube bundle.
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i Mr. Jchn F. O' Leary 2
Big Rock Point December 21, 1973 Southwest Research Institute has been engaged as a consultant to help in determining the cause of the warpage and _to aid in the mod-ification of the divider plates to eliminate further warpage. Work is presently in progress to determine the cause of the warpage. On a very preliminary basis, the warpage appears to be related to the temperature transient across the divider plate upon condenser actuation, steady-state condenser operation and resultant cooldown. The water box is a carbon steel base metal with a stainless overlay and the divider plate is stainless steel. The divider plate is rigidly attached to the water box. Modifications to the divider plates will be performed in accor-dance with the provisions of 10 CFR 50.59 Modifications will be made prior to returning the plant to service which we are estimating will be achieved in one to two weeks.
The warpage of the divider plate (bowed downward toward the condensate side) resulted in a slight steam bypass to the condensate side. The exact bypass flow is unknown, but there has never been any noticeable reduction in the heat removal ability of the condenser. The condenser is occassionally used for routine plant cooldown.
The number of tubes (113 tubes in each of two bundles) in the condenser exceeds that required to achieve its design heat removal ability by 10%.
If the three leaking tubes are plugged, it would re-sult in less than a 3% decrease in heat transfer area in one tube bun-die.
The condenser is provided as a backup heat sink to the main condenser for removing reactor decay heat from the core. The Final Hazards Summary Report (FHSR) evaluated the effects of the loss of the main condenser without reliance on either of the condenser tube bundles as a heat sink. Therefore, it is concluded that the slight loss of heat removal capacity by having allowed some tube bundle by-pass flow to exist due to divider plate warpage did not present sig-nificant hazards considerations not described or implicit in the FHSR.
The performance of the leak detection system, during the period of time difficulties with the valve packing on the steam drum level sensor were being experienced, is worth noting, although not required to be reported by our operating license. The problem was first observed as a slight decrease in the water level on the water level instruments associated with one end of the steam drum.
Further investigations revealed the dev point of the containment exhaust air to be increasing. The leakage from the valve packing was then roughly located by operators listening at various locations outside the steam dr um enclosure. An entry into the recirculating pump room was then made and the precise location of the leak was determined. Since the leak was located such that a plant shutdown would be required to repack the leaking valve, a routine plant shutdown was initiated. All these events occurred over a 2-1/2-hour period.
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Mr. John F. O' Leary 3
. Big Rock Point
- December 21, 1973 Leak detection instrumentation responded as intended by design. The containment ventilation exhaust dev cell, the diffs: rent dew point recorder and the Continuous Air Monitor (CAM) sensed the increased leakage. The leakage rate was calculated to be 0.53 gpm-which is well within-all operating license limits. At no time while
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the leakage from the valve packing existed were personnel required to take any special precautions prior to entering containment.
Yours very truly,
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RBS/mel' Ralph B. Sewell Nuclear Licensing Administrator CC: JGKeppler, USAEC t
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AEC DIS'i' TUTION FOR PART 50 DOCKET MATEP h
10053 (TEMPORARY FORM)
, CONTROL NO:
FILE:
PROM:
DATE OF DOC DATE REC'D LTR MEMO RPT OTHER Con;umers Power-Company J:ckson, Mich. 49201 Mr. R.B. Sewell 12-21-73 12-28-73 X
TO:
ORIG CC OTHER SENT AEC PDR XXX SENT 1.0CAI. PDR N
J.F. O' Leary 1 signed CLASS UNCLASS PROP INFO INPUT NO CYS REC'D DOCKET NO:
XXX 40 50-155 DESCRIPTION:
ENCLOSURES:
Ltr ra their 11-26-73 ltr..... informing AEC cf the results of an investigation concern lockaga due to tube-to-tube sheet-weld defects
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in thr:e welds......
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