Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9607170075
ANSYS [Registered ANSYS,Inc.
Trademark] Johnson Road Telephone 412.746.3304
Houston, PA 15342-1300 Facsimile 412.746.9494
July 11, 1996
Thomas Greene, NRR/PECB
U .S. Nuclear Regulatory Commission
Mail Stop 0-11E4
Washington, DC 20555-0001
Ref: 1. Accession 9601190322
2. ANSYS, Inc. letter dated June 24, 1996
3. Holtec Fax dated June 19, 1996
4. ANSYS, Inc. letter dated July 2, 1996
Subj: Request for a Technical Review of a Draft Information Notice
Regarding Erroneous Results from ANSYS 5.0A and ANSYS 5.1
Computer Codes
Dear Mr. Greene:
After investigation of item 2 of Holtec's 10CFR21 Notification (i.e.
disparate results for forces and displacements are obtained depending
upon the techniques employed to launch the analysis runs), the following
was determined:
- Using tho Holtec model as input, to ANSYS 5.1, minor changes in the
results were noted for cases run on Personal Computers using
different launch techniques.
- No changes were found when using different launch techniques for
cases run on workstations.
- No changes were found when using different launch techniques to run
ANSYS 5.2 on Personal Computers or workstations.
Comparisons of printouts of the ANSYS database using both launch
methods yielded no unexpected differences to the G 15.8 format used.
Similarly, comparisons of printouts of the ANSYS model, including Fortran
COMMON blocks, using both launch methods yielded only differences that
were expected.
Many changes were made to the ANSYS program between the 5.1 and 5.2
versions. However, the changes in run time libraries may have
contributed the most in causing the reported differences in results. Root
cause analysis and extensive study of the outputs show no evidence of an
error in either version of
ANSYS is a registered trademark of SASIP
Thomas Greene, NRR/PECB
U.S. Nuclear Regulatory Commission
Page Two
July 11, 1996
ANSYS. The reason for the reported differences obtained by using
different launch techniques is, again, the extreme numerical accuracy
required to solve Holtec's idealized problem.
As was the case for item 1 of Holtec's notification, if perfect
symmetry is destroyed the problem is resolved and the launch method has
no effect on the results when using ANSYS Revision 5.1.
The following summarizes our finding and recommendations on your
proposed draft notice:
Our investigation of Holtec's model found a perfectly symmetric
system that was inherently unstable, that physically could not
exist, and that required extreme numerical precision to maintain the
symmetry throughout the solution process. A slight change in the
model's dimensions resolves the problem immediately and results in
repeatable solutions on all platforms, with all launch methods.
We have found no evidence of an error in the ANSYS program and
therefore recommend that an Information Notice should not be published on
this matter.
Sincerely,
ANSYS, Inc.
William J. Bryan
Quality Assurance Manager
cc: Holtec, Inc. ANSYS, Inc.
A. Soler D. Looman
D. Conover
M. Ingrund
J. Bittner
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