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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 *** END OF DOCUMENT ***