ML20028B682

Responds to 820827 Question 7 Re Two Loop Operation.Revised Table of Sequence of Events for Major Rupture of Main Steam Pipe Encl

ML20028B682
Person / Time
Site:	Beaver Valley
Issue date:	11/22/1982
From:	Carey J DUQUESNE LIGHT CO.
To:	Varga S Office of Nuclear Reactor Regulation
References
TAC-10386, NUDOCS 8212030142
Download: ML20028B682 (3)

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Telephone (412) 4564000 Nuclear Division P.O. Box 4 Shippingport, PA 15077 6 November 22, 1982 Director of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Attn:

Mr. Steven A. Varga, Chief Operating Reactors Branch No. 1 Division of Licensing Washington, DC 20555

Reference:

Beaver Valley Power Station, Unit No. 1 Docket No. 50-334, License No. DPR-66 Request for Additional Information on Two Loop Operation Gentlemen:

Our letter of October 8,1982, provided additional information with regard to N-1 loop operation as requested in your letter of August 27, 1982.

In that submittal, we stated that additional time would be required to permit the Westinghouse Electric Corporation to study their analysis with respect to the time it takes the 20,000 ppm boron to reach the loops.

This submittal provides a response to Question No. 7 and as such completes our submittal responding to your original seven questions.

Question 7 For steam line breaks with an isolated loop, the time to attain criticality and the time to empty the pressurizer are longer than for normal operation (see Table 2.5-2 of the License Amendment Reques t).

By contrast, the time to reach 2,000 ppm boron is much shorter for N-1 operation.

Please provide a detailed explan-ation of this behavior.

Response

In a steam line break accident, the time to empty the pressurizer I

is directly proportional to the cooldown rate.

The cooldown rates dif fer slightly between N and N-1 loop analyses and are the cause of the small difference between N and N-1 in the time to empty the pressurizer.

The time to attain criticality is directly proportional to the shutdown margin a nd the cooldown rate.

For N-loop analyses, a shutdown margin of 1.772 Ak was assumed, while for N-1 loop analysis, a shutdown margin of 2.40% dk was used.

Because of the additional 0.63%d k shutdown margin available for N-1 loop, more reactivity F212030142 021122 PDR ADOCK 05000334 p

PDR

) Bravar Valley Powar Station, Unit No.1 Dockat No. 50-334, Licenze No. DPR-66 Request for Additional Information on Two Loop Operation Page 2 insertion is required to remove this additional negative reactivity.

Since the reactivity insertion rates are approximately the same for N and N-1, more time is required to attain criticality in the N-1 loop cases.

The time for 20,000 ppm boron to reach the core, as shown on TABLE 2.5-2 of the License Amendment Request, was originally analyzed using the computer code MARVEL for the N-loop case and the computer code LOFTRAN for the N-1 loop case.

Some differences in the models do exist and this is the prime reason for the time differences seen between N and N-1 loops for borated water reaching the core. In order to be consistent with the original FSAR analysis (MARVEL), the N-1 loop times for borated water to reach the core have been adjusted. A revised table is included with t.his submittal as an attachment.

If you have any questions on this subject, please contact my office.

Very truly yours, J. J.

arey Vice President, Nuclear

Attachment:

Table 2.5-2 cc:

Mr. W. M. Troskoski, Resident Inspector U. S. Nuclear Regulatory Commission Beaver Valley Power Station Shippingport, PA 15077 U. S. Nuclear Regulatory Commission c/o Document Management Branch j

Washington, DC 20555 i

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TABLE 2.5-2 TIME SEQUENCE OF EVENTS FOR MAJOR RUPTURE OF A MAIN STEAM PIPE EVENT TIME (SEC)

TIME (SEC) 3-LOOP 2-LOOP 1.

Case a Steam Line ruptures 0

0-Criticality attained 18 32 Pressurized empty 15 18 20,000 ppm boron reaches loops 44 40

• 2.

Case b Steam line ruptures 0

0 Criticality attained 11 15 Pressurizer empty 15 12 20,000 ppm boron reaches loops 44 40

• 3.

Case c Steam line ruptures 0

0 Criticality attained 22 38 Pressurizer empty 16 21 20,000 ppm boron reaches loops 54 50

• 4.

Case d Steam line ruptures 0

0 Criticality attained 14 19 Pressurizer empty 16 13 20,000 ppm boron reaches loops 55 51

• For two loop cases, this is when boron reaches core