Part 21 Report - 1997-811
ACCESSION #: 9711030183
ABB
October 30, 1997
LD-97-031
Document Control Desk
U.S. Nuclear Regulatory Commission
Washington, DC 20555
Subject: Report Pursuant to 10 CFR 21 Regarding Incorrect Nut And Washer
Plate Material for ECCS Suction Strainer Bolted Connections
Gentlemen:
The purpose of this letter is to notify the Nuclear Regulatory Commission
of a defect pursuant to 10 CFR 21, "Reporting of Defects and
Noncompliance." The identified "defect" is the use of incorrect material
in the fabrication of nut plates and washer plates for Peach Bottom Unit
3 Emergency Core Cooling System (ECCS) suction strainer bolted
connections.
The nut plates and washer plates were fabricated from incorrect material
and delivered to the Peach Bottom Unit 3 site. US Tool and Die Company
fabricated the parts as a subvendor to ABB-CE. During receipt inspection
by Philadelphia Electric Company (PECO), it was determined that the nut
plates and washer plates were fabricated with SA-240, Type 304 material
instead of the specified 17-4 PH material, SA-564, SA-693, or SA-705,
Grade 630 in H1150 condition per ASME Code Section III, Class 1,
Subsection NF, 1989 Edition, no addenda. These parts are used as part of
the bolted connection when two or more strainer modules are joined
together to form a strainer train. High strength bolts are threaded into
the nut plates and torqued to a level that results in a bolt preload that
exceeds required operational bolt loads. This assures that the strainer
train remains continuous for all loading cases, and that no unacceptable
gaps develop between strainer modules. The SA-240, Type 304 material has
lower yield and tensile properties than the specified material.
These nut and washer plates were never installed, and replacement parts
have been provided which have the required material properties. This is
the first application of this design and, therefore, no previous
applications exist.
ABB Combustion Engineering Nuclear Operations
Combustion Engineering, P.O. Box 500 Telephone (203) 688-1911
Inc. 1000 Prospect Hill Road Fax (203) 285-9512
Windsor, Connecticut
06095-0500
LD-97-031
Page 2
An evaluation was performed to determine the potential conditions that
might have existed if this material discrepancy had not been discovered
and the parts fabricated of incorrect material had been installed in the
strainers. Three potential conditions could have existed.
1. The threads in the SA-240 Type 304 nut plates would have been
subjected to shear forces that exceed the ASME code allowable
values. The threads may have sheared during the installation
torquing process, in which case the material discrepancy would
have been discovered prior to plant operation.
2. The threads in the SA-240 Type 304 nut plates would have
locally yielded and strain hardened, but would have held the
applied torque and resulting bolt preload. The preload was
specified at a level that exceeds specified operational
loadings up to and including Level D loadings. Since the
temperature at operation is well below the threshold for creep
relaxation, the bolt preload would remain as intended during
use. Shop testing by US Tool and Die Company indicates that
this is the most likely result.
3. During installation at high torque values, some SA-240, Type
304 threads may have yielded and galled. Galling of the
threads during installation could result in a failure to
achieve the design bolt preload, even though the proper torque
is applied. The propensity for galling of these incorrect
materials is about the same as for the specified materials for
lower torque values. It is the greater potential for local
yielding at high torque values that increases the risk of
galling of the incorrect materials in this application.
Failure to achieve the proper bolt preload could result in the
strainer modules separating by more than the design limit of
1/8 inch during some loading cases. It should be noted that
shop torque testing at US Tool and Die Company of nut and
washer plates fabricated from the incorrect materials did not
result in galling at torque values equal to or higher than that
prescribed.
The Attachment contains information specifically required by 10 CFR 21.
Very truly yours,
COMBUSTION ENGINEERING, Inc.
Ian C. Rickard, Director
Operations Licensing
cc: M. F. Barnoski (ABB-CE)
Attachment to
LD-97-031
1
ABB Combustion Engineering Nuclear Operations
10 CFR 21 Report of a Defect or Failure to Comply
The following information is provided pursuant to 10 CFR 21.21 (c)(4):
(i) Name and address of the individual informing the Commission:
Ian C. Rickard, Director
Operations Licensing
Combustion Engineering
2000 Day Hill Road
Windsor, CT 06095-0500
(ii) Identification of the facility, the activity, or the basic
component supplied for such facility or such activity within
the United States which fails to comply or contains a defect:
The basic components are nut plates and washer plates for ECCS
suction strainer bolted connections.
(iii) Identification of the firm constructing the facility or
supplying the basic component which fails to comply or contains
a defect:
The nut plates and washer plates were supplied to ABB-CE by US
Tool and Die Company, and were subsequently provided to the
nuclear plant identified in item (vi) below by:
Combustion Engineering, Inc.
2000 Day Hill Road
Windsor, CT 06095-0500
(iv) Nature of defect or failure to comply and the safety hazard
which is created or could be created by such defect or failure
to comply:
The defect is the use of incorrect material in the fabrication
of nut plates and washer plates used in ECCS suction strainer
bolted connections. The incorrect material could result in
failure to achieve proper bolt preload, potentially resulting
in strainer modules separating by more than the design limit of
1/8 inch during some loading cases.
2 Attachment to
LD-97-031
(v) The date on which the information of such defect or failure to
comply was obtained:
ABB-CE received information regarding incorrect nut plate and
washer plate material on September 18, 1997.
(vi) In the case of a basic component which contains a defect or
fails to comply, the number and location of all such components
in use at, supplied for, or being supplied for one or more
facilities or activities subject to the regulations of this
part:
ABB-CE supplied 208 nut plates and 208 washer plates to PECO
for use at Peach Bottom Unit 3. The incorrect material was
discovered during receipt inspection by PECO, and the affected
nut plates and washer plates were not installed.
(vii) The corrective action which has been, is being, or will be
taken; the name of the individual responsible for the action;
and the length of time that has been or will be taken to
complete the action:
ABB-CE is preparing training classes to strengthen its own
internal review processes to prevent a recurrence of this
error. These training classes will be held by the end of
December, 1997. US Tool and Die Company is currently revising
its internal procedures to prevent a recurrence of this error.
US Tool and Die Company has initiated a requirement that all
contract material be receipt inspected in accordance with
approved customer documents.
(viii) Any advice related to the defect or failure to comply about the
facility, activity, or basic component that has been, is being,
or will be given to purchasers or licensees:
ABB-CE intends to provide an information copy of this 10 CFR 21
report to PECO Energy, Stone and Webster Engineering
Corporation, and utilities owning an ABB-CE designed NSSS.
Within the scope of ABB CE's activities, this issue applies
only to PECO Energy's Peach Bottom Unit 3.
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