ML20112B543

Responds to NRC 831230 Request for Addl Info.Assumption of Complete Mixing Not Concern from DNB Standpoint for Facility Since No Boiling Occurred in Hot Channel for Steam Line Breaks W/Different Mixing Factors

ML20112B543
Person / Time
Site:	Millstone
Issue date:	01/09/1985
From:	Counsil W NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	John Miller Office of Nuclear Reactor Regulation
References
A03722, A3722, B11402, TAC-54199, NUDOCS 8501100448
Download: ML20112B543 (2)

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General Offices

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(203) 665-5000 January 2,1985 Docket No. 50-336 B11402 A03722 Director of Nuclear Reactor Regulation Attn:

Mr. James R. Miller Operating Reactors Branch #3 U. S. Nuclear Regulatory Commission Washington, D. C. 20555

References:

(1)

K. L. Heitner letter to W. G. Counsil, dated December 30, 1983.

(2)

W. G. Counsil letter to 3. R. Miller, dated February 1,1984.

(3)

W. G. Counsil letter to 3. R. Miller, dated September 14, 1984.

Gentlemen:

Millstone Nuclear Power Station, Unit No. 2 Followup Actions to Amendment No. 90 to Operating License No. DPR-65 The NRC Staff forwarded Amendment No. 90 to Facility Operating License No.

DPR-65 in Reference (1). The amendment authorized Cycle 6 cperation for Millstone Unit No. 2. The NRC Safety Evaluation Report (SER) accompanying the amendment addressed various aspects of the core reload including the accident analysis evaluations submitted to support Cycle 6 operation. The Staff documented several concerns relating to the large break loss-of-coolant, steam line break and steam generator tube rupture accident evaluations submitted to support Cycle 6 operation of the plant following the core reload and thermal shield removal.

Northeast Nuclear Energy Company (NNECO) addressed the majority of the concerns identified in the Cycle 6 SER in Reference (2). The Staff concerns were further discussed at length with Mr. Jack Guttman and representatives from Argonne National Laboratories (ANL) during a meeting at NNECO corporate offices in February,1984.

Reference (3) addressed the remainder of the NRC concerns as clarified in the February meeting with NNECO, the NRC, and ANL. Additionally, in Reference (3), NNECO committed to provide the Staff the results of an evaluation of the steam line break event for Millstone Unit No. 2 to address Staff concerns regarding assumed mixing factors. The evaluation was performed assuming a range of mixing within the reactor vesselinlet and outlet plenums.

I 8501100448 850109 PDR ADOCK 05000336 P

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The purpose of this submittal is to provide the evaluation results as committed in Reference (3) as follows:

'A study of Departure from Nucleate Boiling (DNB) sensitivity to the mixing factors for a steamline break occurring at hot zero power conditions, with offsite power available, was performed for Cycle 6.

The mixing factors considered covered the range from perfect mixing to 10 percent mixing.. The DNB results, evaluated from THINC, demonstrated that nucleate boiling did not occur (void fraction = $) in the hot channel for all cases considered.

Therefore, no Departure from Nucleate Boiling Ratios (DNBR's) were calculated by THINC

- and no DNB sensitivity to the mixing factors could be obtained.

Consequently, the sensitivity study does not provide the one mixing factor yielding the lowest DNBR for Millstone Unit No. 2, such that this mixing factor could be utilized for analyses of future cycles if L

needed.

- The sensitivity study-provides conclusive evidence that, since no boiling occurred in the hot channel for steamline breaks with different mixing factors, the assumption of complete mixing is not a concern from a DNB standpoint for Millstone Unit No. 2.

This information is considered responsive to the. Reference (1) request for additional information concerning the mixing assumptions used in the steamline

- break event analyzed in support of Cycle 6 reload at Millstone Unit No. 2. -

We trust you find this information satisfactory.

Very truly yours, NORTHEAST NUCLEAR ENERGY. COMPANY v

IIM W. C.' Counsil Senior Vice President g

.