Part 21 Report - 1996-210

ACCESSION #: 9601300209 NUMERICAL APPLICATIONS, INC. Engineering Software Development and Applications 825 GOETHALS DRIVE, SUITE A o RICHLAND, WA 99352 o TELEPHONE (509) 943-0861 TELECOPY (509) 943-6617 January 16, 1996 Director, Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Dear Sir: This letter is to inform you of a reportable defect under 10CFR Part 21. The defect is in the early versions of the GOTHIC and FATHOMS computer programs for containment and general thermal-hydraulic analysis and is described in the attached error notification being sent to all users of record with the affected versions. The notification applies to all organizations with current or future use of GOTHIC 3.1 or earlier and all versions of FATHOMS. The defect was confirmed on January 15, 1996 and all affected users are being notified. Version 3.2 of GOTHIC (July 1990) eliminated the identified problem. Earlier code versions with the identified problem are not frequently used. Modifications are available from NAI to correct the problem. If there are any questions, please contact me at the number shown above. Sincerely, Thomas L. George January 15, 1996 GOTHIC ERROR NOTIFICATION - GOTHIC.3.1.34 To: GOTHIC Users An error has been discovered in GOTHIC_S 3.1 and earlier versions, and all versions of the precursor code FATHOMS, that may effect the accuracy of some calculations. The error does not exist in version 3.2 or later of GOTHIC. The error may result in an overprediction of the vaporization of water in superheated environments. GOTHIC 3.1 and earlier versions, including FATHOMS, use a single energy equation for the combined liquid and drop phases and correspondingly a single source term for the total vaporization rate of drops and liquid. In certain analyses, e.g., a steam line break, there should be a minimal amount of drops in the atmosphere. However, the code selected initial value for the drop surface area and a small drop area source term associated with the break in these early code versions, results in a substantial drop surface area during the blow-down, even though the drop mass is negligable. Because the drop and liquid vaporization are combined, the large drop area combined with the significant liquid from condensation on heat sinks, results in a high estimate for the vaporization rate. This vaporization cools the atmosphere and results in lower peak containment temperatures and pressures. This effect does not cause a problem in steam/water blowdowns because the significant drop injection quickly leads to realistic values for the drop surface area and the total rate of phase change. Any safety analyses performed with these early code versions should be reviewed with regard to the identified error. Necessary corrections may be obtained from NAI. NAI considers this error to be a reportable defect under 10CFR Part 21 and an error notification has been sent to the NRC. *** END OF DOCUMENT ***

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