ML19327C041
| ML19327C041 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 11/09/1989 |
| From: | Michael Ray TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 8911150125 | |
| Download: ML19327C041 (8) | |
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- d. ef n TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 37401 SN 157B Lookout Place NOV 091989 U.S. Nuclear Regulatory Conwn)ssion ATIN: Document Control Desk c Washington, D.C. 20555 Gentlemen:
In the Matter of ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328 SEQUO/AH NUCLEAR PLANT (SQN) UNITS 1 AND 2 - NRC INSPECi10N REPORT NOS. 50-327, 328/88 UNRESOLVED ITEM (URI) 88-12-04
Reference:
NRC letter to TVA dated June 24, 1988, " Inspection Report ' Nos. 50-327/68-12 and 50-328/88-12" This letter provides TVA's response to URI 88-12-04, which was transmitted to TVA in the referenced letter. This URI addressed NRC's concern with the analysis used to generate the containment design basis accident (DBA) spectra. Specifically, TVA was requested to take two actions: (1) verify the adequacy of-the double differentiation technique adopted by the SUPRPOS computer program by comparing the response spectrum directly generated from the.SUPERSHELL computer program acceleration time history at the 0-degree azimJth nodes Wlth the corrtsponding response spectrum generated from the SUPrRSHELL displacement time history, and (2) verify that the existing DBA response spectra did not miss the real maximum response because of the analysis being cut off at the end of 0.9 second. As discussed in the enclosure, TVA has verified the adequacy of the double differentiation technique adopted by the SUPRPOS computer p'.ogiam by comparing the response spectrum directly generated from the SUPERSHELL comouter program
' acceleration time histories at the 0-degree azimuth, Elevation 763.68, with the corresponding response spectrum generated from the double differentiation of the SUPERSHELL displacement time histories, and has found them to be consistent. Also through evaluation of the pressure versus time plots for the DBA TVA has verified that tne existing DBA response spectra did envelop the i ,
maximum response. [ Please direct questions concerntrg this issue to B. S. Schofield at (615) 843-6172. Very truly yours, TENNESStE VALLEY AUTHORITY ! 8911150125 891109
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U.S. Nuclear Regulatory Commission NOV 091989 y cc (Enclosure): , Ms. S. C. Black, Assistant Director for Projects TVA Projects Olvision U.S. Nuclear Regulatory Conimission One White Flint. North 11555 Rockville Pike Rockville, Maryland 20852 Mr. B. A. H11 son, Ascistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NH, Suite 2900 > Atlanta, Georgia 30223 ' NRC Resident Inspector f Sequoyah Nuclear Plant 2600.19o0 Ferry Road i Soddy Daisy, Tennerree 37379
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- ENCLCSURE i
INTRODUCTION During NRC's integrated design inspection from June 1987 to Match 1988, NRC reviewed in detail the design basis accident (DPA) analysis of the steel ' containment vessel (SCV) performed by TVA. From that review came two NRC concerns: (1) the double differentiation method used by TVA in generating the ' amplified response spectra, and (2) the time history record cutoff of 0.9 second. NRC clored this issue for restart for Units 1 and 2, but labeled the finding as unresolved in Inspectfon Reports 50-327/88-12 and i 50-328/88-12. TVA was requested' to undertake two postrestert actionst (1). verify the adequacy of the double differentiation technique adopted by SUPRPOS by comparing the response spectrum directly generated from the ' SUPERSHELL acceleration time history at the 0-degree azimuth nodes with the corresponding response spectrum generated from the SUPERSHELL displacement time history, and (2) verify that the existing DBA response spectra did not misa the real maximum response because of the analysis being cut off at the end of 0.9 second. CONTAINMENT FINITE ELEMENT MODEL The SCV for SQN is a low-leakage, freestanding steel structure consisting of a cylindrical wall, a hemitcherical dome, and a bottom liner plate ancased in concrete. The cylindrical section of the SCV is approximately lik feet high and has an inside dirmeter of 115 feet. Its thickness varies from 1 3/8 inches at the base to 1/2 inch at the spring line. The hemispherical dome has an inside radius of 57.5 feet. The dome thicknese varies from 7/16 inch at the rpring line to 15/16 inch at the apex. -Circumfeacntial stiffeners are provided on approximately 20-foot cer.terc, while "ertical stiffeners are spaced at 4-degree intervals around the containment shell. A finite element model of the SCV was prepared using a Control Data Corporation version of the SUPERSHELL >:nmputer code. The mathematical representation of the SCV is an assembly of axisymmetric shell elemeiP9. Figure 1 shows the geometry of the model and alsc the order of the nodes and elements. Element orthotropic clastic properties have been modified to account for the effect of the vertical stiffeners. Element densities were increased to account for the mass of attached equipment, piping systems, cable trays, etc. LINEAR TRANSIENT DYNAMIC ANALYSIS A linear transient dynamic analysis (direct integration) of the SCV was performed to address NRC concerns using the model previously described and the pressure time history for the Final Safety Analysis Report main steam line break. Figure 2 provides a logic network of the steps to achieve this analysis. In the analysis, design basis damping, time step, etc., were invoked.
L ' L l t . , , l i L li LINEAR TRANSIENT DYNAMIC ANALYSIS (Continued) The dis,lacement time histories from the transient analysis were passed through.the SUPRPOS program where they were twice differentiated to provide acceleration time histories. Tbe time history at the 0-degree azimuth and Elevation 763.58 vas passed through the TVA computer. code RESPONSE VD to generate the accoleration response spectra. A similar calculation was < performed at the same czimuth and elevation on the acceleration tiwe history that is calculated directly by SUPERSHELL. A comparison plot of the tuo spectra is given in Figure 3. To verify the adequacy of the 0.9-seccud cutoff of the design oasis pressure time histories in the original DBA analysis, plots of typical SCV shell compartment pressure time histories are shown in Figures 4 and S. The I.evel 1 l compartmerts are adjacent to the reactor building base slab, while the Level 3 compartments are within the ice condenser main compartment. As shown on Figurc 4, the rapid rate of increase of pressure within Leve). I compartments ceases at approximately 0.9 second with a slow rate of increase of prassure up to the plot maximum time of 2.68 seconds. For the Level 3 compartments (Figure 5), the pressures peak at approximately 0.1 to 0.3 second, decrease at approximately 1.0 second, and slowly rise fo- the remainder of the 2.68-second ! plot duration. The dynamic response of the SCV is dominated by the sudden l increase in pressure durins the first 0.9 second. The slow rate of increase in pressure between 0.9 seconc and 2.68 seconds will not contribute to increasir.g the SCV dynamics generated in the first 0.9 second. Figures 4 j and 5 are typical plots of a Loor 1 hot leg design basis break and are consistent with the other design basis breaks.
,ONCLUSION C
The studies performed by TVA to address URI 88-12-04 have shown that response spectra generated by double differentiation displacement time histories are consistent with those generated from the acceleration time histories output directly by SUPERSHELL. I I Additionally, the pressure versus time plots generated by Westinghouse Electric Corporation (Figures 4 and 5) for the DBA breaks show that the
- dynamic response of the SCV is dominated by the sudden increase in.praasure i within the first 0.9 second. Therefore, the maximum response of the SCV has been calculated in che DBA analysis. (
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