05000338/LER-1979-035-01, /01T-0 on 790319:valve Weights for 14 Check Valves Supplied by Vendor Were Higher than Originally Specified. Caused by Erroneous Design Specs by Vendor.One Pipe Hanger Identified as Unsatisfactory Will Be Modified

/01T-0 on 790319:valve Weights for 14 Check Valves Supplied by Vendor Were Higher than Originally Specified. Caused by Erroneous Design Specs by Vendor.One Pipe Hanger Identified as Unsatisfactory Will Be Modified

ML19273B426
Person / Time
Site:	North Anna
Issue date:	04/02/1979
From:	Benson D VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19273B423	List: 05000338/LER-1979-035, Forwards LER 79-035/01T-0 05000338/LER-1979-035-01, /01T-0 on 790319:valve Weights for 14 Check Valves Supplied by Vendor Were Higher than Originally Specified. Caused by Erroneous Design Specs by Vendor.One Pipe Hanger Identified as Unsatisfactory Will Be Modified
References
LER-79-035-01T, LER-79-35-1T, NUDOCS 7904060343
Download: ML19273B426 (4)

LER-1979-035, /01T-0 on 790319:valve Weights for 14 Check Valves Supplied by Vendor Were Higher than Originally Specified. Caused by Erroneous Design Specs by Vendor.One Pipe Hanger Identified as Unsatisfactory Will Be Modified

Event date:
Report date:
3381979035R01 - NRC Website

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North Anna Unit No. 1 License Number NPF-4 Attachment page 1 of 2 Docket Number 50-338 Report Number LER 79-035/OlT-0 Event Date.

March 19, 1979

Description of Event

The licensee was notified by the NSSS vendor for North Anna Unit No. I th at valve weights specified for certain check va!ves, supplied by the in error.

Specifically, 14 check valves originally specified

vendor,

--.e as weighing 22S pounds each actually weigh 450 pounds each.

Immediately following this notification, the licensee directed the architect engineer for North Anna Unit N 3.

I to reanalyze the port ions of piping systems containing the subject check valves to determine if the design was adequate for the higher valve weights.

Eight individual pipe stress problems we re involved.

In al.1 cases, reanalysis indicated minor increases in pipe stresses due to the heavier valves but all values remained below code allowables (ASME B 31.7).

However, analysis of the 6 inch hot leg safety injection line to "A" reactor coolant loop indicated that one pipe hanger was overstressed. The piping arrangement and overstressed hanger location are shown in Figure 1.

Additionally, five other hangers, while not overstressed, were found to be below the original design margins.

While these hangers require some adjust-ment or modification to restore the original design margin, they would remain functional under all conditions.

Since the overstressed hanger could no longer be considered functional under accident condi icns, the A-E was directed to reanalyze the piping system assuming that the overstressed hanger was not installed. This was to determine the adequacy of the piping and remaining hangers under accident conditions assuming cenplete f ailure of the overstressed hanger.

This approach is conservative since a significant amount of the energy of the initial upset motica would be dissipated in failing the hanger. The results of this analysis indicated that, without the hanger, the piping will be stressed slighti:- 'reycad code allowables in three locations.

The three locations, node prin:s 2, 3, and 21, are indicated on Figure 1.

The stresses calculated from Z;ustion (9) of the code versus the code allowables are listed in Table 1.

The code allowable, 1.5 (Sm), is based on the assumed generic yield s:renz:h for time type of material; specifically, Sm =.9 (yiele st rength).

ke have reviewed the initial material test result s for the specific piping used at North Anna and have calculated an Sm value specifically for :' e caterials used. The resulting allowables based on the n

pipe specific y;e;d strengths are also listed in Table 1 (Column 3).

TABLE 1 Calculated Stress (1.5 Sm)

(1.5 Sm)-

PSI - Eqn (9)

Code-Generic MILL. CERT. SPECIFIC Point 2 25,761 25,620 31,320 Point 3 26,720 25,020 31,320 Point 21 35,215 30,000 34,900

North Anna Unit No. 1 License I: umber NPF-4 Attachnent page 2 of 2 Docket Number 50-338 Re po r t Number LER 79-035/01T-0 Event Date:

March 19, 1979 When the inethodology of the code is applied based on the specific yield strengths for the piping naterials involved, ali points are below 1.5 Sm.

Based on this information it was concluded that the subject piping would remain intact and functional under all accident conditions.

This event is r e p'a r t a b le pursuant to Technical Specificat ion 6,9.1.8.i.

Probable Consequences of Occurrence As described above, reanalysis for the heavier valve weights indicates' that, while minor modifications are necessary to achieve strict code compli-ance, the existing piping system will remain intact and funct ional under accident conditions.

Concurrent with the piping reana hrsis, we conducted a review of the operational implications of any failure in this line.

The subject line is inactive until about 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> following a LOCA, at which time safety injection flow is redirected from the cold legs to the hot legs to prevent precipitation of boron within the system.

Based on analysis completed by the NSSS vendor, if the subject piping segment did rupture sa result of the seismic event and a LOCA occurred concurrent with this rupture, the hot leg recirculation system function would not be degraded below minimum requirements for long term LOCA mitigation.

At the initiation of hot leg recirculation, approximately 250 gpm is required to be deliveced to the core to compensate for boil-off.

Assuming only one hot Icg reeirculation branch path delivers to the core, appcoximately 1000 gpm will be provided to compensate for boil-off. This assumes one branch path spills to the broken loop (LOCA) and one branch path spills as a result of the postulated hot leg branch line rupture.

Thus a coolant flow of 4 times the required flow would remain available ender the worst accident scenario. The re fo re, the health and safety of the general public were not affected.

Cause of Occucrence The weights :riginally specified by the NSSS vendor for the subject check valves were ir error.

The initial pipe stress calculations performed on the piping ecn:aining the check valves was based on the erroneous valve weights.

Reana'_f 5_s was required to determine if the existing piping sys tem was adequate for the heavier valve weights.

Reanalysis identified the inadequate hanger.

Corrective Actier The pipe '.:nger identified as overstressed will be modified to meet all i

code req u i reme n: s by April 16, 1979.

The other bangers will be adjusted or modified to restore original design cargins 22 operations and materials availability permits.

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