ML17252A534
| ML17252A534 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 06/18/1974 |
| From: | Stephenson B Commonwealth Edison Co |
| To: | O'Leary J US Atomic Energy Commission (AEC) |
| References | |
| BBS Ltr. #439-74 | |
| Download: ML17252A534 (3) | |
Text
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Mr. J. F. O'Leary, Director Directorate of Licensing U. S. Atomic Energy Conmiss ion Washington, D. C.
20545 Eb Cy~
- 50~249
SUBJECT:
. LICENSE DPR-25, DRESDEN NUCLEAR POWER STATION, UNIT #3, REPORT OF ABNORMAL OCCURRENCE PER SECTIGN 6.6.B.l.a OF THE TEalNICAL SPECIFICATIONS.
NIPPLE FAILURE ON FEEDWATER PUMP DISQIARGE LINE..
References:
Notification of Region III of AEC Regulatory Operations Telephon~: F. Maura, 1325 hours0.0153 days <br />0.368 hours <br />0.00219 weeks <br />5.041625e-4 months <br /> on 6/10/74 Teleg*am: J. Keppler, 1345 hours0.0156 days <br />0.374 hours <br />0.00222 weeks <br />5.117725e-4 months <br /> on 6/10/74
Dear Mr. O'Leary:
This letter is to report a condition relating to the operation of the unit at about.1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br /> on June 10, 1974. At*this time, station personnel n~ted a leak in a 3/4 inch test line which was welded to the feedwater pump discharge line.
The unit was shutdown to effect repairs.
The leakage associated with the failure fell directly to the turbiile build-ing floor and flowed into a nearby turbine building drain from which it was pumped to Radwaste.
No airborne radioactivity.resulted and no personnel exposur~ was experienced due to the leak.
This malfunction is reportable according to section 1.A. 5 of the Technical Specifications which defines an abnormal occurrence as an abnormal degradation of one of the several boundaries which are designed to contain the radioactive materialS resulting from th,e fission process.
The problem was discovered at approximately 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br /> on June 10, 1974, when station personnel noted water spraying from a newly installed vibration test line located on the reactor feedwater pump discharge header.
At the time, the unit was operating at 440 MWe.
The carbon steel line was leak4ng through a crack in the 3/4 inch nipple which connected the feedwater header to the two valves in the test line. After discovery of the crack, it was determined that the test line could not be isolated without draining the feedwater header line 3-3201-24".
This action i~ turn necessitated a plant shutdown.
The unit was shutdoWll in an orderly fashion with the turbine 5778
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v Mr. J. F. O'Leary June 18, 1974
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being taken off-line at 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> on June 10, 1974. After shutdown, the feedwater discharge line was drained and the leaking vibration test line was cut out of the feedwater line. - A plug was welded in its place and the weld was dye-penetrant tested.
By 0100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> on June 11, 1974, the repairs were completed and preparations for the unit startup were begun.
INVESTIGATION Visual inspection of the nipple showed the failure *to be a crack in the nipple body itself, -not in welds.
The crack was located on the side of the nipple~ was vertical in nature, and extended for approximately 1/4 inch.
Very near the crack itself was a deep pit or gouge in* the nipple.
This gouge was due to the welder striking his arc on the nipple before welding the two valves to the nipple.
It_ is very probable that this veld strike arc is the site for the start of the crack and that the crack pro-pogated under the surface of the nipple until it surfaced* approximately
- J/8 of an inch from the strike arc. The nipple. will be sent out for tests to confirm this.
Although the strike arc was the primary cause* of the failure, several.other contributory causes were noted during the investigation.
These include:
1.. The strike arc gouge was in a beat affected zone of the nipple.
- This further weakened the metal in this area.
There was no
-_post-weld heat_ treatment of the area.
_ 2. *The feedwater header was cold* and level.when the test line was-installed *. Upon operating conditions, *the header moved downward by approximately 1 inch.
Since the test line was secured to the ceiling by a pipe hanger, a large stress was induced in-t_he test 1 ine.
- 3. ; The feedwater header was known.to be vibrating vertically during startup and operat-ional conditions. _This induced a second, cyclic stress on the test line_.
CORRECTIVE ACI'IONS Upon discovery of the leaking nipple, and determination that the
- leak co~ld not be isolated_ without isolating the feedwater head.er, the unit
- was--shutdown in a controlled manner.
The feedwater heade.r was i$olated after unit shutdown and the leaking test connection was cut out of the feedwater header. Aplug was
- welded into the resultant bole and the weld was dye penetrant tested.
O'Leary -* June 18, 1974 Similar test conq_e_c_tions-on-the-feedwater-header were--checked and-
---none-:-w*=e=r=e-r=igidly -held_in_ place, independent of :the feedwater line to which it was welded.
This occurrence did not jeopardize the safety of the plant or the public and resulted in no significant contamination problems.
The nature of the failure is such that in-service hydrostatic testing, as is accepted by the codes, is sufficient to prevent or minimize failures of this type on similar equipment.
This type of hydrostatic test was performed on this test connection.
Because of the nature of the failure, no_corrective acti~ can be affected to prevent repetition of the occurrence on this and other equipment.
Cumulative experience regarding contaminated water line leaks of this*nature is minimal.
Por this reason, the corrective actions are con-sidered effective and satisfactory.
(. -.*
.l BBS:JMD:do
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Sincerely, *
- . phenson *
- : ~.
enden~
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