ML20148H879

Advises That Util Mods of Components in Barrel/Baffle Region of Reactor Vessel to Upflow Design & Remove of Fuel Thimble Plugs During Sixth Refueling Outage Acceptable

ML20148H879
Person / Time
Site:	Beaver Valley
Issue date:	03/23/1988
From:	Tam P Office of Nuclear Reactor Regulation
To:	Sieber J DUQUESNE LIGHT CO.
References
TAC-66287, NUDOCS 8803300108
Download: ML20148H879 (3)

Text

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March 23,1988 1

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l Docket No. 50s&&& DISTRIBUTION:

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' <pocret;FTie JPartlow I NRC PDR ACRS (10) l Local PDR Gray File l Mr. J. D. Sieber, Vice President SAVArga Duquesne Light Company BABoger Nuclear Group SPNorris Pos+. Office Box 4 PSTaM Shippingport, PA 15077 OGC-WF EJorde.n

SUBJECT:

BEAVER VALLEY UNIT 1 - MODIFICATION DURING THE SIXTH REFUELING OUTAGE (TAC 66287)

By letters dated September 15, and December 7,1987 you informed us of the following planned modifications to the unit during its sixth refueling outage:

1. Components in the barrel /bafile region of the reactor vessel to be modified from the current downflow design to an upflow design.

2. Fuel thimble plugs to be renoved.

We have reviewed the submittals. The upflow modification has been implemented at a number of Westinghouse plants to eliminate the baffle jetting problem, which was observed during the last refueling outege. The upflow conversion consists of plugging of the core barrel inlet flow holes and to provide holes in the top former plate. This changes the flow path from being downflow between the core barrel and baffle plate to upflow and has the effect of increasing the core bypass flow.

The elimination of the thimble plugs effects a decrease'in active flow since the hydraulic resistance is decreased, thereby also increasing the core bypass flow. The combined effect of the two modifications would increase the core bypass flow from 4.5% to 6.5%. There will be an offset due to an increase in total flow because of a decrease in overall core resistance. However, the net effect is a decrease in active core flow. The decrease in active core flow decreases the fuel thermal margins for minimum departure from nucleate boiling ratio (FDNBR),' fuel melt, and peak clad temperature (PCT).

• You have presented an analysis that relates to these modifications. We have reviewed your analysis and conclude that the modifications do not result in an unreviewed safety-concern. We have Earlier .found the resulting increased core bycass flow acceptable (Letter, P. Tam to;J. D. Sieber, dated Deceniber 29,1987).

We further note that similar nodifications have been performed at Farley, Trojan, Point Beach and Prairie Island.

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8803300108 880323 PDR P

ADOCK 05000334 PDR

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'I g Mr. J. D. Sieber. a

/t This review was performed b'y G. Thomas of our Reactor Systems Branch.

Sincerely, a

orignal signed by' -

. Peter S. Tam, Projtict Manager Project Directora_te I-4 Division of Reactor Projects I/II .

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. [i hr.J.Sieber Beaver Valley Fower Station Duquesne Light Ccapany Units 1 & 2 Cc:

Bureau of Radiation Protectior.

Jay E. Silberg, Esquire Pennsylvania Departirent of Environtrental j Shaw, Pittman, Potts and Trowbridge Resources L 2300 N Street, N.W. ATTN: R. Janati Washington, DC 20037 Post Office Box 2063 ,

Harrisburg, Pennsylvania 17120 Kenny Grada , Manager Mayor of the Borrough of ,

Nuclear Safety Shippingport Duquesne Light Company Post Office Box 3 P. O. Boy ? Shippingport, Pennsylvania 15077 Shippingport, Pennsylvania 15077 William Lacey, Manager Ashley C. Schannauer Nuclear Operations Departroent Assistant City Solicitor Post Office Box 4 City of Pittsburgh Duquesne Light Company 313 City-County Building ~

Shippingport, Pennsylvania 15077 Pittsburgh, Pennsylvania 15219 John A. Lee Esquire Regional N ministrator, Region I Duquesne Light Cortpany U.S. Nuclear Regulatory Comission 475 Allendale Pcad One Oxford Centre ,

301 Grant Street King of Prussia, Pennsylvania 19406 Pittsburgh, Pennsylvania 15279 W.F. Cant.ichael, Comissioner Resident Inspector Cepartment of Labor U.S. Nuclear Regulatory Commissien 1800 Washington Street East Post Office Box 181 Charlesten, West Virginia 25305 Shippingport, Pennsylvania 15077 <

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John D. Borrows Director, Pennsylvania Errergency Director, Utilities Departirent Management Agency Public Utilities Commistion Post Office Box 3321 120 East Broad Street Harrisburg, Pennsylvania 17105-3321 Columbus, Ohio 43266-0573

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