ML20035B152

Forwards Staff Comments on Key Phenomena Identified for AP600 Core Makeup Tank Separate Effects Tests

ML20035B152
Person / Time
Site:	05200003
Issue date:	03/26/1993
From:	Borchardt R Office of Nuclear Reactor Regulation
To:	Liparulo N WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
References
NUDOCS 9303310241
Download: ML20035B152 (4)

Text

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March 26,1993 i

Docket No. S0-003 Mr. Nicholas J. Liparulo, Manager Nuclear Safety and Regulatory Activities i

Westinghouse Electric Corporation P.O. Box 355 Pittsburgh, Pennsylvania 15230 i

SUBJECT:

COMMENTS ON WESTINGHOUSE'S IDENTIFICATION OF KEY PHENOMENA FOR THE AP600 CORE MAKEUP TANK SEPARATE EFFECTS TESTS Enclosed are the staff's comments on the key phenomena identified for the AP600 core makeup tank separate effects tests. These comments have resulted from the review of your submittals, the presentation material obtained during the February 25, 1993, meeting on this test program, and input from the United States Nuclear Regulatory Commission the Office of Nuclear Regulatory Research.

If you have any questions regarding this matter, you can contact the project i

manager, Thomas J. Kenyon, at (301) 504-1120.

Sincerely, Or?na10pd by Richrd w.Borchardt i

Richard W. Borchardt, Acting Project Director Standardization Project Directorate Associate Director for Advanced Reactors and License Renewal Office of Nuclear Reactor Regulation

Enclosure:

i As stated l

cc w/ enclosure:

See next page l

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i Mr. Nicholas J. Liparulo Westinghouse Electric Corporation-Docket No.52-003 AP600-cc:

Mr. B. A. McIntyre'.

Advanced Plant Safety & Licensing

~ Westinghouse Electric Corporation i

Energy Systems Business Unit P.O. Box 355 i

Pittsburgh, Pennsylvania 15230 Mr. John C. Butler Advanced Plant Safety & Licensing Westinghouse. Electric Corporation Energy Systems Business Unit 1

Box 355 Pittsburgh, Pennsylvania 15230 Mr. M.-D.; Beaumont Nuclear and Advanced Technology Division Westinghouse Electric Corporation One Montrose Metro l

3 11921 Rockville Pike I

Suite 350

. 20852 Rockville, Maryland i

Mr.- Sterling Franks U. S. Department of Energy NE -

Washington, D.C.

20585' Mr. S..M. Modro I

-EG&G Idaho Inc.

-l Post Office Box 1625

~

Idaho Falls, Idaho 83415 Mr. Steve Goldberg l

Budget Examiner i

725 17th Street, N.W.

Room 8002 4

Washington, D.C.

20503 i-t Mr. Frank A..Ross U.S. Department of. Energy, NE-42 i

Office of LWR Safety and Technology 19901 Germantown Road 1

Germantown, Maryland 20874 l

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Comments on Westinghouse's " Key Phenomena" to be Studied in CMT Tests The " key phenomena" to be investigated during the core makeup tank separate effects tests are listed on p. 4 and p. 8 of the handout distributed by Westinghouse at the meeting of February 25, 1993. The two lists are slightly different, but generally consistent with one another. Additional objectives are also covered in the handout; one that should be added is the assessment of the performance of the heated-thermocouple level sensors that will be used to trigger ADS initiation in the AP600. The staff recognizes that these sensors will not be used to trigger the depressurization sequences to be simulated as part of the CMT tests. Nevertheless, their performance is of substantial interest to the staff, since this will be the first opportunity to observe the operation of the prototypic instrument.

The phenomena identified by Westinghouse appear to cover adequately the appropriate aeneral issues that should be studied in the tests.

It must be remembered that these tests are designed to be only separate effects experiments, and that, for the most part, investigation of system-related behavior and interactions will be included in the SPES and OSU integral systems tests. However, while the lists of phenomena appear to be reasonably complete, they are also quite general in nature.

In order to perform the scaling analysis requested by the staff, Westinghouse will have to consider specific thermal-hydraulic behavior that may occur as subsets of the general phenomena.

For instance, one general " key phenomenon" (p. 4) is " natural circulation and flow behavior between CMT balance line and tank." When the different phases of an accident are considered, however, it can be seen that there are several different scaling issues that arise:

single-phase natural convection recirculation (single-phase hot water flowing from the cold leg to the CMT, with single-phase cold liquid flowing to the reactor vessel; possible two-phase natural convection recirculation (two-phase mixture in the cold leg flowing to the CMT, with single-phase liquid flowing to the vessel; CMT drain-down (steam flowing to the CMT from the cold leg or pressurizer balance line, with water--or possibly a two-phase mixture--flowing to the vessel); and possible dynamic effects (water hammer, flow oscillations due to two-phase flow in a balance line, transitional behavior shifting from recirculation to draining mode). The governing equations and/or dimensionless parameters may be different for these various modes of operation, and it may, in fact, be impossible to satisfy all of the different scaling parameters in a single facility. Thus, a ranking of phenomena (PIRT) needs to be performed, and the facility and the test matrix should be designed to represent properly the most important phenomena.

In this regard, Westinghouse needs to assess the major weaknesses of its systems codes; the importance of a specific phenomenon needs to be a function of (1) its prevalence in influencing the behavior of the CMT subsystem and (2) the adequacy with which it is modeled in the codes. We recognize that Westinghouse has performed this type of evaluation in general in developing its design certification test program; what is now needed is a narrower focus strictly on CMT behavior.

Enclosure

' In conjunction with a scaling analysis, it is also strongly advisable for Westinghouse.to examine the existing models in.its systems codes-to determine if they are applicable over the ranges of the pertinent parameters that will exist in the AP600. Natural circulation, and the relatively low flows that result in the AP600, may produce thermal-hydraulic conditions.outside the databases for correlations or. semi-empirical models used for conventional plants. As part of the code review for AP600, the staff will determine.

whether the models in Westinghouse's codes are. appropriate to represent the behavior in the plant. This issue is a generic one as far as the AP600 is concerned, and is not limited only to the behavior of the CMTs; however, it is of particular importance for unique design features.of the AP600, which is clearly the case for the CMT/high-pressure ECC system.

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