ML17187A756
| ML17187A756 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 02/06/1997 |
| From: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML17187A754 | List: |
| References | |
| 50-237-97-03, 50-237-97-3, 50-249-97-03, 50-249-97-3, NUDOCS 9702100369 | |
| Download: ML17187A756 (7) | |
See also: IR 05000237/1997003
Text
U.S. NUCLEAR REGULATORY COMMISSION
Docket Nos.:
License Nos.:
Report Nos.:
Licensee:
Facility:
Location:
Dates:
Inspector:
Approved by:
9702100369 970206
ADOCK 05000237
a
REGION 111
50-237; 50-249
50-237 /97003(DRS); 50-249/97003(DRS)
Commonwealth Edison Company
Dresden Generating Station, Units 2 and 3
6500 North Dresden Road
Morris, IL 60450
January 14 - 15, and 23, 1997
M. S. Holmberg, Reactor Inspector
Wayne Kropp, Chief
Engineering Specialists Branch 1
Division of Reactor Safety
Report Details
II. Maintenance
M2
Maintenance and Material Condition of Facilities and Equipment
M2.1 Torus Inspections
a.
Inspection Scope (73753. 73755. 73052)
Degradation of protective coatings on containment structures had recently been
observed at *other reactor sites. Therefore, the inspector performed a walkdown of
the exterior of the Unit 2 and Unit 3 torus and reviewed past internal visual
inspection results to assess the integrity and materiel condition of this portion of
the containment structure.
b.
Observations and Findings
External Suppression Chamber Walkdown
The inspector identified several external areas (typically patches less than six inches
by six inches) of the suppression chamber on both units with missing paint and
light corrosion, (mostly at thermoweil penetrations and vacuum breaker line support
pads). Additionally, the inspector identified a minor gouge on the Unit 3 torus at
Bay 13 (at approximately the 492 foot elevation) and on the Unit 2 torus at Bay 4
(at the 496 foot elevation). These gouges were estimated by the inspector to be
less than 1 /1 6 inch deep. The engineering staff initiated condition reports for these
conditions. Preliminary evaluation of the minor gouges and areas of missing paint
with light corrosion by vendor and licensee engineering staff, indicated that these
conditions were not structurally significant. The inspector reviewed procedure
DTS 1600-11 "Primary Containment Structure General and Coating Inspections"
Revision 04, issued on December 3, 1996, which included implementation of
American Society of Mechanical Engineers Code,Section XI, 1992 Edition,
Class MC requirements for inspection of the torus (including the exterior). Since
this procedure revision was recently issued, the inspector could not-assess the
effectiveness of this new procedure, however the inspector considered that periodic
inspection of the torus exterior would be expected to result in an improved materiel
condition.
The inspector identified a pump mounted in a skid that was bolted to the Unit 2
torus basement floor (4 76 foot elevation) at Bay 10. The system engineer stated
that this pump was used to pump down the torus (an infrequent event). The
inspector reviewed drawing M5 "General Arrangement Basement Floor Plan"
. Revision G, which did not identify this pump. Engineering staff could not identify
an engineering modification, drawing revision or other documentation that
authorized the permanent mounting of this pump at Bay 10. Additionally, a written
safety evaluation had not been performed for installation of this pump.
The
licensee located a purchase order, which indicated that this pump had been
purchased in 1984. The inspector postulated that if the mounting of this pump
was inadequate, a seismic event could free this pump and damage the torus
2
suppression chamber. The licensee performed a walkdown of the area where the
pump was installed and determined that no potential seismic concern existed and
stated that no unreviewed safety question existed. The licensee staff stated that
they intended to initiate a 50.59 safety evaluation for installation of this pump and
were considering removal of this pump. The inspector considered the installation of
a pump in the Unit 2 torus basement (476 foot elevation), to be a change to the
facility as described in the Updated Final Safety Analysis Report (UFSAR)
Section 6.2 "Containment Systems." The failure to perform a written safety
evaluation in accordance with 10 CFR 50.59(b)(1) for.the installation of this pump
is considered a violation (50-237/97003-01 (DRS)).
Review of Internal Suppression Chamber Inspections
The inspector reviewed the Final Engineering Report (FER) FER-7 209 "Torus
Underwater Desludging, Inspection and Coating Repair for ComEd Dresden Nuclear
Power Station, Unit 2" prepared by S. G. Pinney and Associates, Inc., and dated
August 29, 1995. This report documented the 1995 inspection results from an
internal inspection of the Unit 2 torus for all sixteen Bays. Twenty-two areas of
pitting corrosion with pits that ranged from 0.0162 inches to 0.1062 inches deep in
the immersion areas of eight Bays were identified. Coating repairs had been made
on all areas with identified corrosion. Other minor deficiencies which included
blistered coating, rust sta:ning pinpoint rusting and localized corrosion cells were
recorded. No evidence of incipient general coating failure was identified.
In FER-7 209, results were also identified from an internal inspection of the Unit 2
torus immersion area that had been performed in February of 1993 which had been
documented in another FER entitled "Underwater Desludging, Inspection and
Coating Repair of the Torus Pressure Boundary." This inspection included six Bays
and had identified similar findings to the 1995 inspection, with corrosion pits that
ranged from 0.0145 inches to 0.1515 inches deep.
The inspector reviewed FER-7133 "Underwater Desludging, Inspection, Coating
Repair and Bolt Replacement" prepared by Underwater Engineering Services, Inc. a
subsidiary of S. G. Pinney and Associates, Inc., and dated July 15, 1994. This
report documented the 1994 internal inspection, repair and T-quencher bolt
replacement results for the Unit 3 torus. The inspection scope included a
- qualitative internal inspection of Bays one through five. Minor deficiencies were
recorded which included (blisters, rust staining, pinpoint rusting and localized
corrosion cells).
Pits were measured and recorded that ranged from 0.006 inches
to 0.1185 inches deep. Coating repairs had been made on* all areas with identified
corrosion. No evidence of incipient general coating failure was identified.
In UFSAR Section 6.2.1.2.3 the suppression chamber shell wall thickness was
.recorded as typically 0.585 inches above and 0.653 inches below the horizontal
centerline. No specific corrosion induced wall loss allowance was identified within
the UFSAR. Therefore, inspectors reviewed the following vendor Calculations
prepared for Commonwealth Edison:
,
3
CWE-084-218. "Dresden 3 Torus Pitting Evaluation." Revision 0. prepared
by NUTECH Engineers
This calculation evaluated the suppression chamber pitting (below the
horizontal centerline) for the Unit 3 torus identified during a 1991 inspection.
This calculation demonstrated that ASME Code Section Ill, Subsection NE
margins were maintained for pitting of 0.099 inch in depth, repaired by
contouring the pit edges with a four to one taper.
CWE084.0222, "Evaluation of Suppression Chamber Pitting at Dresden
Unit 2." Revision 0. prepared by NUTECH Engineers
This calculation evaluated the suppression chamber pitting (below the
horizontal centerline) for the Unit 2 torus identified during a 1993 inspection.
This calculation demonstrated that ASME Code Section Ill, Subsection NE
. margins were maintained for pitting of 0.1515 inch in depth, repaired by
contouring the pit edges with a four to one taper.
64.305.1027, "Evaluation of Torus Pitting Identified During D2R14,"
Revision 0. prepared by VECTRA
This calculation evaluated the suppression chamber pitting for the Unit 2
torus pitting identified during a 1995 inspection. This calculation provided
generalized curves for accepting torus pitting (in either unit) without repairs
(e.g., tapering of the edges) based on depth (maximum of 0.25 inches),
width of the pit and clustering of pits.
The coating deficiency records (from 1991 and 1993 inspections) reviewed by the
inspector, recorded only pit depth. No detailed information on* individual pit width
or clustering (spacing proximity to adjacent pits) had been recorded. Due to the
short duration of this inspection, the licensee staff were unable to provide repair
records (e.g., faring pit edges to a four to one taper) or documented
characterization/evaluation of this pitting as assumed in the bounding calculations.
Thus, the inspector was unable to determine:
if pits had been repaired with a four to one taper as assumed in Calculations
CWE-084-218 and CWE084.0222, or
if pit depth, width and clustering had been recorded and evaluated against
acceptance criteria found in Calculation 64.305.1027.
The inspector considered this issue to be an unresolved item (50-237 /97003-
02CDRS); 50-249/97003-01 (DRS)) pending further review by the licensee and NRC
of the documented corrective actions taken for the torus suppression chamber
pitting. The licensee staff agreed to look into this issue and stated that they would
respond to this issue within 60 days.
In FE Rs 7133 and 7 209 the carbon steel portions of the main steam relief valve
lines in the Unit 2 and Unit 3 torus immersion area were identified as being coated
with Carboline Carbo Zinc #11. Additionally, the emergency core cooling system
4
suction strainer cover shrouds for the Unit 2 torus were identified in FER 7209 as
being coated with inorganic zinc. UFSAR Section 6.1.2 allowed the use of
Carboline Carbo Zinc #11 on the containment and torus for touch up. UFSAR
Section 6.1.1.2, evaluated the affect on carbon steel corrosion rates from a
postulated event that results in introduction of sodium pentaborate solution into the
torus. However, the UFSAR did not include an evaluation of the potential effect of
sodium pentaborate solution with Carbo Zinc #11 nor inorganic zinc coating found
within the torus. The inspector's questions on the potential for hydrogen
generation from reactions with zinc based coatings and sodium pentaborate
solutions prompted the licensee staff to initiate a condition report on this issue.
The licensee subsequently provided the inspector a copy of an NRC letter "SEP
Topic Vl-1, Organic Materials and Post Accident Chemistry, Dresden Nuclear Power
Station, Unit 2" dated June 30, 1982, which indicated that this issue had been
considered and Unit 2 had been found to meet the current licensing basis criteria for
this topic. The inspector had no further concerns on this issue.
Conclusion
The inspector identified a pump installed in the Unit 2 torus basement that lacked
installation documentation and for which an installation safety evaluation had not
been performed. The inspector considered the undocumented installation of a.
pump in the Unit 2 torus basement to be a change to the facility as described in the
UFSAR, without a written safety evaluation to ensure that an unreviewed safety
question did not exist.
Past licensee inspections had identified inside diameter pitting of the torus
suppression chamber in both units, for which vendor supplied calculations had been
performed to demonstrate the acceptability of these conditions.* Due to the short
inspection period, the licensee staff were unable to provide repair records or
documented characterization/evaluation of this pitting as assumed in the bounding
calculations. Thus, the inspector was unable to determine if appropriate corrective
actions (pitting repairs and/or pitting characterization) had been performed as .
assumed in the bounding engineering calculations. The inspector also identified
missing paint and minor gouges on the exterior of the torus which indicated that
more effort may be needed in this area. The inspector considered the
implementation of the ASME Code,Section XI, Class MC requirements, in
containment coating inspection procedures, to be a positive step toward
maintaining the torus and containment materiel condition.
Ill. Engineering
E2
Engineering Support of Facilities and Equipment
E2.1
Inspector Updated Safety Analysis Report Review
While performing the inspections discussed in this report, the inspectors reviewed
UFSAR sections:
6.1
Engineered Safety Feature Materials
5
6.2
Containment Systems
The inspectors identified one UFSAR discrepancy related to an undocumented
installation of a pump in the Unit 2 torus basement (see Section M 2.1 ).
V. Management Meetings
X1
Exit Meeting Summary
At the conclusion of the inspection on January 15, 1997, and final phone exit on
January 23, 1997, the inspector met with licensee representatives identified herein
and summarized the scope and findings of the inspection activities. The inspector
questioned licensee personnel as to the potential for proprietary information in the
likely inspection report material discussed at the exit. No proprietary information
was identified.
PARTIAL LIST OF PERSONNEL CONTACTED
Commonwealth Edison Company <ComEdl
E. Carroll
B. *casey
A. Casilla
R. Freeman
P. Holand
R. Radke
Regulatory Assurance
ISi Coordinator -
Design Engineering
Engineering Manager
Supervisor Regulatory Assurance
Plant Engineering
F. Spangenberg
Manager Regulatory Assurance
System Engineering lead
G. Tietz
J. Williams
D. Winchester
T. Woodroffe
Plant Engineering
SOV Director
System Engineering
U. S. Nuclea"r Regulatory Commission (NRC)
J. Hansen, Resident Inspector
IP 73753:
IP 73755:
IP 73052:
INSPECTION PROCEDURES USED
lnservice Inspection
lnservice Inspection, Data Review and Evaluation
lnservice Inspection, Review of Procedures
6
~*-
ITEMS OPENED, CLOSED, AND DISCUSSED
Opened
50-237 /97003-01 (DRS)
50-237 /97003-02(DRS)
50-249/97003-01 (DRS)
Undocumented installation of a pump in the Unit 2
torus basement
Review of the corrective actions taken for torus pitting
7
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