ML20086S378

SR-S2-74-01:pipe Restraints on Three Safety Injection Accumulator Discharge Lines Experienced Some Degree of Shock & Vibration.Caused by Flashing & Water Hammer Shock Experienced During Early Operation

ML20086S378
Person / Time
Site:	Surry
Issue date:	11/29/1974
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
SR-S2-74-01, SR-S2-74-1, NUDOCS 8403010537
Download: ML20086S378 (7)

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O tij, VInoxxzA Er.ccrate Axo PowEn Cox1=An p{ggj.gg 3 Rtcuxoxo.ViaorxtA 20261 November 29, 1974 ggg 4 t9p' p C1 5 LS U nic n a;g cm;2m H

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,p am:my Eall k:as ,}.g s* w Mr. Norman C. Moseley, Director Serial No. 337 Directorata of Regulatory Operations PO&M/JTB:clw United States Atomic Energy Co::: mission Region II - Suite 818 Docket No. 50-281 230 Peachtree Street, Northwest License No. LPR-37 Atlanta, Georgia 30303

Dear Mr. Moscley:

Pursuant to Surry Power Station Technical Specification 6.6.B.1, the Vir;; inia Electric and Power Co=pany hereby submits forty (40) copies of Special Report SR-S2-74-01.

Tha substance of this report has been reviewed by the Station Nuclear Safety and Operating Coc=1ttee and will be.placed on the agenda for the next meeting of the System Nuclear Safety and Operating Co=ittee. -

Very truly yours, Orig *nal Signed BY.

ST.*J.I.EY EAZ3 ,?

C. M. Stallin;;s '

Vice President-Power Supply and Production Operations Enclosure cc Mr. K. R. Goller (39 copics) 12251 8403010537 741129 PDR ADOCK 05000281 S PDR COPY SENT BR(iION , j

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1 O O SPECIAL REPORT SR-S2-74-01 SAFETY INJECTION PIPE SUPPORTS DOCKET NO. 50-281 4

LICENSE NO. DPR-37 t.

NOVEMBER 4, 1974 SURRY POWER STATION VIRGINIA ELECTRIC AND POWER COMPANY l

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, G s I. INTRODUCTION During the recent outage of Unit No. 2 for turbine maintenance, it was discovered that the pipe restraints on the three (3) safety injection (SI) accumulator discharge lines had experienced some degree of shock and vibration. This was evident by the damaged condition of the grouting and concrete support structure. The AEC was notified and an investigation was initiated by the licensee. The results of that investigation are reported herein.

II. DISCUSSION Pipe restraints H-4, H-9 and H-15 rigidly support SI accumulator discharge lines SI-245, SI-246 and SI-247, respectively. The pipe re-straints are designed to withstand loads (including seismic) during normal system operation. Each restraint is constructed of three (3) built-up stainless steel beams, joined to a stainless steel ring reinforcement which is welded to the pipe line it supports. The restraint legs are arranged in a " tee" configuration, with two (2) of the beams joined diametrically opposite each other on the ring reinforcement, and the third beam situated at right angles to each beam. Each beam is welded to its stainless steel baseplate which is anchored to a two-foot thick concrete floor. Rigid attachment of the baseplate to the concrete floor is designed to be accomplished by the insertion of bolt anchor fasteners in the concrete, the insertion of six (6) inch long studs into the anchor f asteners and finally installing nuts and washers to hold the baseplate to the concrete.

A bed of grouting, one (1) inch thick (as per the original specification),

is placed between the baseplates and the concrete floor.

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r O O Inspection of the pipc restraints revealed cracking of the grouting under the pipe support bedplates of -SI loops A and C, and crumbling of the grouting under the pipe support baseplate for loop B. The majority of the anchor hex nuts were loose, with some nuts inch from properly contacting the baseplate. The length of the studs varied from four to six inches. All baseplates were carefully examined for possible defor-mations, but no discrepancies were noted.

During the physical inspection of the anchor supports, it was noted that the grout under the baseplates was approximately 2 inches thick instead of the 1 inch specified in the original design; therefore, the baseplate anchor bolts may have penetrated less concrete than originally specified. This, coupled with varying stud lengths may have resulted in a reduction of the pipe supports' capability to resist upward loads or bending movements. The increased thickness of grout was placed during construction primarily to accommodate the-prefabricated anchor.baseplates for the SI piping.

To determine what caused the damage to the pipe restraint system, a review of the unit's operational history was conducted. During early unit start-ups from cold shutdown, drain lines connected to the SI accu-mulator discharge lines were experiencing' erratic flow indications. The erratic flow indications were believed caused by rapid boiling-(flashing) during leak testing of . accumulator discharge check valves. While performing the leak test, per Operating Procedure OP-7.1 ' (Safety Injection System), the pressure in the accumulatoridischarge line was reduced _below the saturat' ion pressure of the water it contained, resulting in the boiling or flashing.

The operating procedure was modified to insure that adequate pressure-l (above. the- saturation pressure) was maintained in accumulator discharge

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-lines.during testing. LFollowing~the procedural modification.to OP-7il, b . _. __ _ __1

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u's no further erratic flow indications were detected. In view of the above described operational experience the licensee postulates that due to sizeable volume expansion from water to steam, when flashing occurred, the SI accumulator discharge piping was subject to tension stresses.

Flashing created a steam void in the line. When the accumulator discharge valves were subsequently opened, the relatively high pressure water of the accumulator would have collapsed the previously formed steam void, causing water hammer shock. The combination of stresses from flashing and shocks from water hammer are believed to have damaged the pipe restraint system.

Non-destructive tests have been conducted to determine if damage had occurred to adjacent piping and welds. . Visual inspection revealed no discrepancies other than the subject pipe restraint grouting damtge.

Liquid penetrant tests of the welds from the second SI accumulator discharge ,

check valve to the reactor coolant loop were conducted, but no significant indications were noted. Radiographic tests were performed on the welds of the "B" Si line, from the accumulator to the reactor coolant loops. The test results indicated no defects.

An evaluation has been performed to determine if the SI piping or accumulator nozzles have been overstressed as a result of pipe motion or shock. All pipe supports adjacent to the damaged restraints were in-spected, but no discrepar.cies other than those anticipated were found.

The large hydraulic 'suppressors located on the piping adjacent sto the accumulator nozzles would preclude any load being-transferred'to'the nozzles..

A computer analysis of the stresses developed at 30 points along the-accumulator discharge piping was performed. The analysis was based'on a h inch vertical line surge; this-surge was. determined.by. physical evidence;

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at loop pipe restraint, i.e. the maximum clearance between the bottom of the anchor hex nuts and the top of the pipe restraint baseplate was inch. The results of the analysis indicate that the greatest stress developed was at a point on the discharge of the 90 degree elbow prior to joining with the reactor loop. The stress at this point was 8,200 psi, or approximately 47 per cent of the allowable stress and was not considered ,

to be significant. Based on the above findings, it was concluded that the SI lines were not overstressed as a result of the water hammer induced shocks and motion.

All SI baseplate anchors were removed and have been replaced with 3/4 x 8b x 10 inch Hilti-Kwik bolts. The 10 inch long anchor bolts will give additional penetration depth, enabling the new anchors to develop full strength against normal system loads (including seismic). The increased penetration of the concrete floor does not compromise the floor's integrity.

Following the installation of all anchor bolts and tightening of nuts, a new bed of grouting was poured between the concrete floor and restraint baseplates.

III. CONCLUSION The damaged restraints were the result of flashing and water hammer shock experience? during the early operation of the unit. Since the modifications were made to the operating procedure, the water hammer has not recurred. With the increased penetration of the new anchor bolts, the ability of the pipe restraints to function as originally intended is maintained. The licensee therefore feels that the solutions proposed above will prevent future occurrences of a similar nature.

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4 The licensee will investigate the pipe restraints for accumulator discharge piping in Unit No. I during the refueling outage, and will issue an additional report, based on the findings.

The events described herein did not affect the safe operation of the station or the health or safety of the general public.

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