Part 21 Report - 1995-016
ACCESSION #: 9411280210
NTD-NRC-94-4344
Westinghouse Energy Systems Box 355
Electric Corporation Pittsburgh, Pennsylvania
15230-0355
November 15, 1994
U.S. Nuclear Regulatory Commission
Attn: Document Control Desk
Washington, DC 20555
Subject: Closeout of an Interim Report of an Evaluation of a
Deviation or Failure to Comply Pursuant to 10CFR21.21(a)(2)
Reference: (1) ET-NRC-94-4303, Interim Report of an Evaluation of
a Deviation or Failure to Comply Pursuant to
10CFR21.21(a)(2), dated September 19, 1994
The attached information is provided as a closeout to Interim Report
94-012. Preliminary information was previously provided per Reference
1 pursuant to the requirements of 10CFR Part 21 to submit an Interim
Report on issues that will not be completed within 60 days from the
discovery of the deviation or failure to comply.
A closeout to Interim Report 94-012 is enclosed for the following
Potential Issue under Westinghouse evaluation:
1. Reactor Coolant Pump (RCP) Support Column Tilt
If you have any questions regarding this matter, please contact Mr. H.
A. Sepp of my staff at 412/374-5282, or myself.
Sincerely,
N. J. Liparulo, Manager
Nuclear Safety Regulatory and Licensing Activities
Attachment
Westinghouse Electric Corporation
Energy Systems
P.O. Box 355
Pittsburgh, PA 15230-0355
Interim Report No. 94-012
Date: 11/16/94
SUBJECT:
Closeout to an Interim Report of an Evaluation of a Deviation or
Failure to Comply Pursuant to 10CFR21.21(a)(2).
TITLE:
Reactor Coolant Pump (RCP) Support Column Tilt
BASIC COMPONENT SUPPLIED BY:
Westinghouse Electric Corporation
NATURE OF DEVIATION:
As provided in the original issue of Interim Report 94-012,
Westinghouse identified a potential issue related to certain
reactor coolant pump (RCP) support columns that may be tilted
beyond design parameters. Specifically, certain three and four
loop plants have a loop piping layout in which the crossover leg
piping interferes with the front inside support column of the
RCP. The other columns on the RCP are oriented to be vertical in
the normal full power condition. This condition was recognized
by the support designer and changes were made to the column
layout to accommodate the interference between the column and the
crossover leg. The change consists of moving the base of the one
RCP column toward the reactor pressure vessel approximately 6-12
inches so that the tilted column no longer interferes with the
crossover leg piping. The required tilt is from approximately 2
to 5 degrees depending on the column length and amount of
movement. This condition was apparently reconciled during the
design phase and was not considered a significant issue. The
actual change in the value of the vertical stiffness is small,
but there is an impact on the thermal expansion of the system.
There are tolerances in the RCP columns that would potentially
absorb some of the vertical movement associated with the column
rotation.
SAFETY ASSESSMENT
Analyses have been performed to evaluate the impact of the RCP
column tilt on the plant with the most severe tilt. A plant with
a column tilt associated with a 12 inch movement of the column
base from the front inside pump column was chosen for this
evaluation.
The additional loadings associated with column tilt originate
from the use of a support stiffness that has been rotated from
vertical by a few degrees. This rotated stiffness at one of the
three column locations acts to restrain and rotate the RCP. For
a loop piping system thermal expansion
of approximately 1.8 inches, the vertical displacement associated
with the rotation of an RCP column will vary from about 10 mils
for a nearly vertical column to about 1.30 mils for an upper
bound tilted column. This difference in displacements at the
three RCP columns is what causes a rotation in the pump not
previously accounted for. This source of additional loading
varies from plant to plant based on the primary equipment support
design. There are plants with pin-ended columns that will not
have this type of additional loading. There are a number of
plants that have support details not of Westinghouse design.
Many of the Westinghouse designed supports have a tilt that is
approximately half of that analyzed as a part of this evaluation.
When this enhancement was made to the thermal analysis, different
system loadings resulted. The bending moment at the RCP outlet
nozzle for the example plant increased by more than 100%. The
RCP column loads also changed. The tilted column went from a
compression load to a tension load. The change in column loading
met applicable Code allowable limits. The loop Leak-Before-Break
(LBB) evaluation was of particular concern for system load
changes. The LBB evaluation is performed with the goal of
achieving certain margins. The new loadings were reviewed for
all 12 weld locations in the primary loop for the example plant,
and acceptable margins were maintained.
The loop evaluation performed for the example plant, for column
tilt loads, met acceptable stress levels. The column tilt for
the example plant is approximately twice (12 inches versus 6 or
6.5 inches) that of most other plants. It has been determined
that due to the overwhelming plant specific nature of both RCS
loops and the RCP column design, the example plant configuration
is not generic nor necessarily enveloping, but is representative
of a typical Westinghouse configuration. Every plant affected by
the RCP column tilt issue has a plant-specific loop analysis that
has a unique set of margins. Because loadings local to the RCP
can be quite different due to the inclusion of column tilt, those
plants that have small margins in this area may require
additional analysis. As mentioned, there are conservative
margins that are part of the licensing basis associated with LBB.
Even in the event that LBB licensing margins are not satisfied,
previous experience in the use of the margins associated with LBB
lead to the conclusion that the LBB design basis continues to
apply.
A review of the increased loadings on our example plant yielded
acceptable results in all areas reviewed. For the example plant
evaluation, there were significant margins available in the areas
where loadings increased. If specific modeling techniques are
the cause of lower margins, additional analysis may reduce some
of the potential conservatism that led to the low margins.
Westinghouse has determined that there is no RCS pressure
boundary integrity concern due to the RCP column tilt issue, and
as such, this issue is not reportable pursuant to 10 CFR part 21.
DATE OF DISCOVERY OF DEVIATION:
July 20, 1994
CORRECTIVE ACTIONS TO DATE:
Westinghouse has completed an extensive evaluation of this issue.
It has been determined that the RCP Column Tilt issue does not
pose a challenge to the reactor coolant system pressure boundary
and therefore, a substantial safety hazard does not exist.
Westinghouse has published a Nuclear Safety Advisory letter to
communicate this information to affected utilities.
EVALUATION COMPLETION SCHEDULE DATE
Complete
N. J. Liparulo, Manager
Nuclear Safety Regulatory and Licensing Activities
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