ML19312B652
| ML19312B652 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 10/10/1979 |
| From: | TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML19312B651 | List: |
| References | |
| NCR-MEB-79-01, NCR-MEB-79-1, NUDOCS 7911050289 | |
| Download: ML19312B652 (2) | |
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4 ENCLOSURS SEQUO'lAH NUCLEAR PLCT UNITS 1 AND 2 I
PCTLNTIAL EXCES317; WATER SAMMER FORCES i
IN Tile R\\IN FEEDh*ATER S~lSTE'!
NCR MEB 79-1 REVISED FINAL REPORT 4
Description of Deficiency Westinghouse informed TVA of the potential for excessively high water hammer forces associated with the main feedwater line check valves.
I luia deficiency involves excessively high water hammer forces gener-
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ated by slamminh of the three main feedwater line check valves as a result of a postulated pipe rupture in the other main feedwater line.
The water hammer force caused by slamming of the three check valves might be high enough to adversely affect the integrity of those three check valves or feedwater piping and hence lead to a multiple steam geaurator blowdown.
4 Toe failure of TVA to evaluate in detail at the design stage the capability of the c.ain feedwater check valves and feedwater piping ta absorb the water haemer forces associated with a closure of those valves following a postulated break in one. leg of the main f eedwater system piping resulted in this deficiency.
1 Safety implicatio n If this deficiency had remained uncorrected, a maia feed ater line cr.ak in the feedwater line to one steam. generator would have had no afverse effee. on the safety of the plant.
A line break could lead either to a single staam generator blowdown or loss of the main feed-so.er :.ystem's ability to supply the four steam 'generatots, dependent on break location.
however, these accidents have been analyzed (see FSAA chapter 15) and the ability of the plant to reach a safe snutdown condition is not adversely affectad.
Corrective Actions
!"A ima completed a detailed study of the main feedwater check valves im:talled at Sequoyah Nuclear Plant.
Evaluations of the chack valves were made using,two procedures.
The first procedure was a comparison of the energy level that the Sequoyah feedwater check valves are capable of sustaining with the energy levels that similar design
' check valves used in the main steam system at several other TVA nucicar facilities and at other non-TVA nuclear facilities are 7 911050 A f 7 d
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capable of sustaining. The second procedure of the evaluation con-sisted of analysia of the main feedvater chuck valve discs by equating the disc strain energy to the. disc kinetic energy at closing. A fluid transient analysis of the pipe break / water hammer event was performed to determine the disc kinetic energy at closure. This evaluation l
shows the closing kinetic energy to be less than the potential strain i
energy capacity of the disc and a stress slightly above yield at the disc center.
This study has shown that the main feedwater check valves at Sequoyah would maintain their integrity and would continue to func-tion as designed following the most severe main feedwater line break postulated.
Based on these studies and analyses TVA is satisfied with the adequacy of the Sequoyah main feedwater check valves to per-form their intended functi'on 'ander all expectcd accident conditions.
i The allowable pipa peak pressure calculated in accordance with ASME lection II, paragraph NC-3611.2 is 3,3C0 psi, compared to worst case l
calculated transient pressure of 2.730 psi.
Circumferential prassure I
stress produced by the calculated 2,750 psi pressure is 26,097 psi ecm-rared to a mini 5cm material yield stress of 30,000 psi et system operating temperacare.
Means Taken to Prevent Recurrence i
l The analyses of the main feedwater line' check valves for all of TVA's future nuclear plants will be docur.ented at the design stage. A veri-iiestion of the capability of the main feedwater check valves to sus-Lain the water hanner forces resulting from a closure of those valves i
following a postulated break in one leg of the main feedwater system
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piping will be made and documented for each of TVA's nuclear plants now under construction.
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