ML20012B384
| ML20012B384 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 03/01/1990 |
| From: | Lohmeier A, Mcbrearty R, Strosnider J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | |
| Shared Package | |
| ML20012B382 | List: |
| References | |
| 50-029-90-03, 50-29-90-3, NUDOCS 9003140301 | |
| Download: ML20012B384 (5) | |
See also: IR 05000029/1990003
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U.
S.' NUCLEAR REGULATORY' COMMISSION
REGION I
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Report'No.- 50-29/90-03
Docket.No.
50-29
License No._
D_PR-3
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Licensee:
Yankee Atomic Electric Company
580 Main Street
Bolton, Massachusetts 01740-1398
Facility Name: . Yankee Rowe
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Inspection At:
Rowe, Massachusetts
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Inspection Conducted:- February 5-9, 1990
Inspectors:
-JAN#
R.
NcBrearty, Reactor Engineer
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,A.pnmeier,ReactorEngineer
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Approved by:
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. Strosnider, Chief, MPS, EB, DRS
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Inspection Summary:' Inspection on February 5-9,1990 (Report No. 50-29/90-03);
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Areas Inspected: A routine, announced inspection was conducted of licensee
activities regarding safety injection tank cracking problems.
-Results: On January 10, 1990 a leak was discovered in the Yankee Rowe safety-
infaction-tank.
Inspections have revealed other cracks in the tank. Daliy
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inspections of the leaking crack are being performed by the licensee and
criteria have been established at which actions including plant shutdown would
be taken.
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Repair or replacement of the tank is being considered by the licensee, and the
resulk of the'. metallurgical analysis of samples which will be removed from the -
tank and of an examination of the inside surface of the tank will be used to
decide if the tank is acceptable for continued operation past the next scheduled
refueling outage. Acceptability of the tank for continued operation beyond the-
next refueling outage is an unresolved item.
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Details
1.0 Persons Contacted
Yankee Atomic Electric Company
- T. Henderson, Acting Plant Superintendent
B. Holmgren, Engineer
- J. Kay, Technical Services Manager
- D. King, Maintenance Support Supervisor
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- J. Lance, Plant Support Department Manager
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- R.
Mellor, Technical Director
- R. Mitchell, Maintenance Manager
R. Rossman, Lead I&C Engineer - Yankee Project
- N. St. Laurent, Acting Manager of Operations
- J. Thayer, Project Manager - NSD
Structural Integrity Associates (SIA)
- J. Copeland, Consultant
Nuclear Regulatory Commission
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- M. Markley, Resident Inspector
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- Indicates those present at the exit meeting,
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- Telephone contact.
2.0 Safety Injection Tank (92700)
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The safety injection tank at Yankee Rowe is 30 feet high and 30 feet in
diameter.
It is fabricated of aluminum plate with a maximum thickness
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of 7/8" and a minimum thickness of 3/8".
The plate is type 5052
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(B-178GR20A). The tank, fabricated in 1957, was constructed in accordance-
with API 650 and consists of three major sections:
the top and bottom
ellipsoidal heads and a-middle barrel or shell section. ~The top and
bottom heads each contain three circumferential welds, and the shell
section contains one circumferential barrel weld for a total of seven
circumferential welds.
There is no documented tank leakage prior to September 30, 1988, although
the licensee is aware of leakage prior to 1984 which occurred through the
tank reinforcing "tell tale" holes. The first documented case of leakage
was on September 30, 1988 when leakage was observed on the bottom
ellipsoidal head to shell circumferential weld. The leak was found to
emanate from a 0.4" long transverse crack at approximately a 270' azimuthal
location. The crack was monitored for approximately three months with no
measurable change in size during that time.
During the 1988/1989 refueling
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outage the crack was removed and the tank was repaired by welding.
Sub-
sequent to the repair a visual examination of the accessible, exterior
areas of the lower head revealed no observable leakage. On March 8, 1989
during routine auxiliary operator rounds another area was noted showing
evidence of leakage at the 200' azimuthal area on the bottom head cap
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weld. An examination using a 5x glass showed two longitudinal cracks,
0.050"'and 0.100" in length. The locations were monitored on a weekly
basis with no. measurable change in length. Additionally, the leakage ratt
was too small to measure. Subsequent to the March 8, 1989 finding, a
visual examination of the lower head accessible areas failed to reveal any
other leakage or boron buildup.
On January 10, 1990, an auxiliary operator reported a boron buildup at
the 135' azimuthal location on the longitudinal weld connecting the bottom
head cap weld and the bottom head middle circumferential weld.
Leakage at
the rate of 204 ml/ hour was measured coming from a longitudinally oriented
crack approximately 2.6" in length. When first detected, the crack
length and leak rate was monitored every 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
No measurable change
in length or leak rate was noted.
Presently, the condition is monitored
on a daily basis and, at the time of this inspection, no change in crack
length or rate of leakage was observed.
Subsequent to the discovery of the 2.6" long crack, a visual examination
of the bottom head accessible areas was performed and three additional
weld areas showing evidence of leakage (boron buildup) were found as
follows:
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Bottom head cap weld at the 55 azimuthal location. The crack is
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oriented transverse to the weld axis, 0.3" long, and has no measur-
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able leakage.
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108' azimuthal location on the longitudinal weld connecting the
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bottom head cap weld to the bottom head middle circumferential weld.
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The crack is oriented transverse to the weld axis,1.0" long, and has
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no measurable leakage.
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Bottom head to shell weld at the 270' azimuthal location. The crack
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is oriented transverse to weld axis, 0.5" long, and has no measurable
leakage.
The licensee has established guidance to monitor for propagation of the
2.6" long crack or increased leakage from the crack. The crack length and
leak rate are being monitored on a daily basis. The licensee has stated
that if any increase in crack length or leak rate is observed, a
reassessment of tank operability will be performed and if the crack
extends " beyond the present 2.6", a plant shutdown will be initiated.
Because of the weid configuration (double "V" prep with an as welded
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crown) nondestructive testing methods have not been able to characterize
the extent of cracking in the welds.
Ultrasonic thickness measurements
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have; however, shown' that there is no generalized thinning of the tank
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plate material adjacent to the welds.- The licensee has not performed an
inspection of the inside surface of the tank.
During the next refueling outage the licensee plans to drain the tank,
perform an inspection of the inside surface, and remove metallurgical
samples for analysis to assess the acceptability of the tank for continued
operation. Options presently under consideration by the licensee include
repair or replacement of the tank.
The. inspectors visually inspected the bottom head outside surface paying
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particular attention to the areas where known through wall cracks exist,
and to the support areas where boron buildup is evident. Additionally,
the report on the crack evaluation performed by Structural Integrity
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Associates (SIA), the licensee's consultant, was reviewed.
Regarding the evaluation, the licensee was aavised that the methodology
used in the critical flaw size determination is believed to be
conservative, but the prediction of critical flaw size is uncertain for
the following reasons:
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1.
The governing fracture toughness properties were not specifically-
identified for the flaw in the weld material.
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The residual stress level for the as welded structure in the area of
the crack was not considered.
The issue of the safety injection tank structural integrity and accept-
ability for continued operation beyond the next refueling outage is
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considered an unresolved item pending evaluation of additional information
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from the planned tank inspections and metallurgical evaluations and addi-
tional information regarding critical flaw size for the specific material
and the residual stress level in the safety injection tank (90-03-01). Of
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major importance in the tank inspection during the next shutdown, will be
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the determination of the true cause of initial cracking and assessment of
the means to repair the cracks and mitigate future crack formation.
3.0 Unresolved Items
Unresolved items are matters about which more information is required to
ascertain whether they are acceptable items or violations. An unresolved
item is discussed in paragraph 2.
4.0 Exit Meeting
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The inspectors met with licensee representatives (denoted in paragraph 1)
at the conclusion of the inspection on February 8,1990.
The inspectors
summarized the scope and findings of the inspection.
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At no. time'during the inspection was written material provided by the -
inspectors to the licensee. The-licensee did not indicate that
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proprietary information was involved within the scope of this inspection.
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