ML17037B953

Letter Requesting Information Relating to a Review of Unit 2 and Radial Cracks Which Have Occurred in the Blend Radii of Reactor Vessel Feedwater Nozzles

ML17037B953
Person / Time
Site:	Nine Mile Point, North Anna
Issue date:	07/30/1976
From:	Vassallo D Office of Nuclear Reactor Regulation
To:	Rhode G Niagara Mohawk Power Corp
References
Download: ML17037B953 (4)

Text

JUL 3 0 1976 Docket No. 50-410 Niagara Mohawk Power Corporation, ATTN; Hr. Gerald) R.

Rhode Vice President - Engineering 300 Erie Boulevard, West

Syracuse, New York 13202 Gentlemen:

Distribution Docket File HR 84 Fl e

NRC PDR Local PDR DBVassallo CMoon llKane MServiee JKnight ELD IE (3)

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RCDeYoung On May 7, 1975 we were informed by a pressurized water reactor plant licensee, Virginia Electric 5 Power Company, that the as~1 etric loads resulting from a postulated pipe rupture at a particular location in the reactor coolant system had not been taken into account in the original design of the reactor vessel support system for North. Anna ~U'nits 1 and 2.(Docket Nos.

50-33/8 and 50-339).

As you may be aware, we hav~e been purs'ping this subject on a generic basis with pressurized water reactor plant (liicensees and applicants f'r the past several months.

Althaugh we are aware that the loads for this postulated condition are ~not limiting for boiling water reactor plants and can be properly accounted for, in the final des'l'gn, we will require such verification (at the final design stage.

The attachment to this letter outlines the information< that we will requi~e3 in our review,,of this matter for Nine flile Point Nuclear Station-Unit 2.

Another generic matter which we have been reviewing on operating plants, deals with radial cracks which have occurred in the blend radii of reactor vessel feedwater nozzles.

The attachment to this letterl'oOitlines the information that we will require in our review of this matter for Nine Nile Point Nuclear Station - Uhit 2.

He request that you provide us with a schedule for providing the requested informatio~3within 2 weeks from your receipt of this letter.

Should you require any clarification of this matter, contact the staff's assigned Licensing Project Manager immediately.

Sincerely, Original signed l X

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ATTACHMENT 1.

With respect to the reactor vessel and its supports:

(a)

Provide drawings of the reactor support system sufficient to show the geometry, dimensions of all principal elements and the type of material they are fabricated from.

(b)

Demonstrate that the analytical

methods, models, and load considerations have adequately considered the dynamic forces that result from:

Transient asyanetric differential pressure loadings on the reactor internals.

Asymnetric loadings from transient differential pressures that exist around the exterior of the reactor vessel resulting from postulated pipe rupture considered(separately>,",for each of the main coolant lines at the reactor vessel nozzle safe end.

The main steam, feedwater, and reactor recirculation discharge and suction lines should be considered.

2.

Several of the boiling water reactor plants have reported finding radial cracks in the area of the blend radii,on the reactor vessel feedwater nozzles.

In one of the plants, the cracks were reported again after they were ground out and the degree of thermal cycling was reduced by changing the sparger sleeve.

Describe any planned design modifications to eliminate this condition or any plans to assure safe reactor operation coupled with continuous examination of the area of the feedwater nozzles where the cracking has occurred.

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