ML20005A434

Final Deficiency Rept Re Overturning of Primary Shield Wall During Const Movement.Base Plate Is Being Reworked to Restore to Original Design Conditions.Attachments to Base Plate Will Be Replaced

ML20005A434
Person / Time
Site:	River Bend
Issue date:	06/23/1981
From:	Draper E GULF STATES UTILITIES CO.
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
10CFR-050.55E, 10CFR-50.55E, RBG-10618, NUDOCS 8106300323
Download: ML20005A434 (4)

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's 4.Y GULF STATES UTELZTEES COMPANY E*h

• CST OFFICE 8ox29*.

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• TEFA$ 777cd AREA Coct 7:3 232 3143 June 23, 1981 P3G - 10616 File Code G9.5, G9.25.1 '

Mr. K. V. Seffrit, Director / .//- f V

U.S. Nuclear Regulatory Co::ission W~ ( .g 9 'g \

Region IV, Office of Inspection & Enforcemen:

611 Ryan Plaza Drive, Suite 1000

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Arlington, Texas 76011 '.- ,, /-

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Dear Mr. Seyfrit:

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River Send 5:ation - Uni: ;

Docket No. 50-l.58 Gulf States Utilities Co:pany (CSU) has ccepleted its investigation of the reportable 10C7R50.55(e) deficiency concerning the ever:urning of the Primary Shield Wall during a construe: ion =overen:. The final results of our assess =ent and the correc:ive actiers taken are attached.

The princical area of damage to the shield vall was limited to :he base pla:e. Repairs are being made in the field te res:cre :he shield vall to i:s specified design conditions.

GSU has reviewed the procedures involved and has ::ncludcd tha: this type of incident was an isolated case and shculd nc: recur. Since the investiga:icn revealed no significant darage, GSU has deter =ined tha: the safety of operations vill ne: he adversely affec:ed a: :he River lend Sta:icn.

Sincerely, E. 1. inn Draper, a..

Vice Presiden:

Nuclear Technology ELD /RJK/te A::ach=ent cc: Direc:c of Inspec:1on and Enforce en:, U.S. Nuclear Regulatory Co=:sission , Washington, D. C. 20535 uw s 810 6 30 0 sa P00R [i E

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• j ATTACIDfENT )

1. Description of Deficiencv

a. Cause of Accident The front transporter of the rig carrying the shield wall strayed to the edge of the road and was about 3 feet onto the shoulder. In this position the load assumed the full transverse slope of the road.

The king pin joining the transporter body and the swivel bolster was assembled with vertical play which allosed the plate to partially lift off the transporter body.

The bolster swivel plate assembly was stressed due to the moment caused by the inclined shield wall. The top flange of the angles welded to the bolster plate started to yield and then buckled. The bolster swivel plate ultimately failed in a brittle manner.

The. bolster frame connecting the front and the rear transporters twisted due to the moment of the inclined shield wall.

The above events gradually and cumulatively increased the inclination of the shield wall from the vertical. Consequently:

1. The restraining moment due to the transporter weight was unavailable to resist the overturning moment until the vertical play in the king pin assembly was completely taken up.

2. The redistribution of the load to the edge of the transporter tread due to the eccentric loading increased the intensity of loading on the soil in the shoulder. The shoulder was not capable of supporting the high inter.sity local loading and yielded.

. 3. The increasing inclination of the load combined with the local soil yeidling at the edge of the tread, resulted in the transporte / load pivoting about the edge of the tread and overturning.

b. Damage to the Shield Wall As reported earlier, the base plate of the shield wall was locally damaged where it tore from the clips holding the wall to the bolster frame. Several attachments welded to the shield wall were bent. The base plate was bent in a few other areas.

The shield wall was impacted in two areas of the shell as it hit the railroad and the West Creek embankment. There was no observed damage to the shell due to the impact.

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paEe 2 of 3 2 .. Safety Evaluation The safety functions performed by the shield wall from the view points of structural integrity and radiation shielding were enumerated in our Letter No. RBG-9739.

The structural integrity of the shield wall has not been impaired by the accident. The radiation shielding safety has not in any way been affected because the high density concrete material which provides the shielding had not been placed in the shield wall compartments at the time of the accident.

3. Corrective Action

a. Rework of Damages The base plate is being reworked to restore it to its original design conditions. Portions of the baseplate which were torn are being replaced using originally specified material and approved welding and inspection procedures.

The base plate will be ground cff to remove the undulations from one face and built up to the design thickness by weld deposition on the other.

The attachments which were bent were removed and the base metal was inspected by magnetic particle testing.

Replacement attachments fabricated to the original

-specification requirements will be installed.

The rework of the damaged baseplate is being performed at the River Bend Job Site,

b. Evaluation of the Impact on the Shell The shell was evaluated in the following manner to verify the visual observation of no damage caused by the impact:

1. The overturning and fall of the assembly of the transporting rig and the shield wall was 3 analytically modeled; the soil properties in and around the impact area were determined and utilized to derive the reaction pressure on the wall; and a stress analysis was pertarmed on the structure.

The structural analysis has established that the stress levels in the shell were sufficiently low as not to create any permanent deformations.

2. Dimensional checks of the shell diameter have proved that the circularity of the shell has not been affect d. The shell diameters measured in the fabrication shop and after the accident were found to be comparable and within design tolerances. ,

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.The impacted contact areas on'the shell plus'a

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surrounding area extending to a distance equivalent to one compartment of the structure were inspected by magnetic particle testing methods. Both the inner and outer skin plates were_ inspected in this manner. There were no cracks detected, providing additional assurance that the impact _due to the accident did not affect the structural integrity of the shield wall.

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