ML19225C811

LER 79-010/01T-0 on 790714:design of Main Steamline Restraints Did Not Consider Steam Hammer Transient Forces. Review Performed.Overstressed Area Will Be Modified

ML19225C811
Person / Time
Site:	Arkansas Nuclear
Issue date:	07/27/1979
From:	Shivley C ARKANSAS POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19225C790	List: ML19225C789 ML19225C797 ML19225C811
References
LER-79-010-01T, LER-79-10-1T, NUDOCS 7908020475
Download: ML19225C811 (4)

Text

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N RC F O R M 366 (7 77) U S NUCLE AR REGUL ATORY COMMISSION

, LICENSEE EVENT REPORT EXHIBIT A CONTROL BLOCK. l l l l l l lh PLE ASE PRINT OR TYPE ALL REQUIRED INFORMATIONI I 6 i

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s1 Lload ratine or design limits in main steam lines. A review has extended _this 90 I to mainfeed water and pressurizer surte lines. Main steam line break wasI a i l analyzed in FSAR.

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1 o LReview was performed. The affected snubbers / restraints will be i ii i iredesigned and/or replaced. The over stressed area will be i i >

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9 l-Reportable Occurrence Report No. 50-313/79-010

2. Report Date: 07-27-79 3. Occurrence Date: 07-14-79 4 Facility:

~ Arkansas Nuclear One - Unit One Russellville, Arkansas 7,~ 8 01

5. Identification of Occurrence:

Design deficiency in the main steam line restraints and snubbers.

6 Conditions Prior to Occurrence:

Steady-State Power Reactor Power Mhth lie t Stan 2y Net Output 0 We Cold Shutdown X Percent of Full Power 0 i Refueling Shutdown Load Changes During Routine Power Operation Fautine Startup Operation R utine Shutdown Operation Other ( spec i fy )

7. Description of Occurrence:

During a design review of the main steam piping (MSP) inside the reactor building, it was discovered that the piping restraints were not designed considering steam hammer transcient forces. The MSP is subjected to steam hammer transcient forces as a result of the turbine stop valves closing rapidly following a turbine trip.

435 028

Reportabic Occurrence Rept t No. 50-313/79-010

8. Designation of Apparent Cause of Occurrence:

Design X Procedure hbnufacture Unusual Service Condition Including Environmental Installation /

Construction Component Failure (See Failure Data)

Operator Other (specify)

9. Analysis of Occurrence:

The review and analysis predicts that the piping stress exceeds the code allowable stress at one location (integrally welded pipe attachment to the 36 x 36 x 24 tee on the north line). Also all thermally rigid pipe support and pipe restraint loadings exceed the design limit, or for hydraulic snubbers, exceed the manufacture's load rating.

435 029

, Reportabic Occurrence Report No. 50-313/79-010

10. Corrective Action:

A review of the existing pipe supports / restraints to determine adequacy was performed. The review identified 11 snubbels and -

2 restraints in the main steam piping that were inadequate. 2 snubbers in the main feedwater and 1 snubber in the pressuri:er surge line were found to be inadequate. These snubbers and restraints are:

Pressurizer Main Steam Main Feedwater Surge Line 11S - 3 HS-17 11S - 4 6 HS-60 HS-4 HS-IS HS-4S 115 - 5 11S - 1 9 IIS-6 11S - 2 0 11S - 7 MS-13S 115 - 1 5 MS-141 IIS-16 The above supports / restraints will be modified, redesigned, and/or replaced as needed. The local over stress will be corrected by modification of the weldcd attachment. Nondestructive testing of the welded attachment and a walkdown of the piping support will be performed to identify any signs of distress.

11. Failure Data:

NA 435 030

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