ML20035H272

Forwards Comments on Core Makeup Tank Test Matrix Supporting AP600 Design Certification Application

ML20035H272
Person / Time
Site:	05200003
Issue date:	04/29/1993
From:	Kenyon T Office of Nuclear Reactor Regulation
To:	Liparulo N WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
References
NUDOCS 9305040060
Download: ML20035H272 (4)

Text

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April 29,1993 T

Docket No.52-003 Mr. Nicholas J. Liparulo Nuclear Safety and Regulatory Activities Westinghouse Electric Corporation P.O. Box 355 Pittsburgh, Pennsylvania 15230

SUBJECT:

COMMENTS ON CORE MAKEUP TANK TEST MATRIX SUPPORTING THE AP600 DESIGN l

CERTIFICATION APPLICATION The staff.has reviewed the core makeup tank (CMT) tests as presented in the handout provided at the February 25, 1993, meeting on those tests, and have developed the enclosed comments. We request that your staff consider these comments in the final development of the CMT test matrix.

If you have any questions regarding this matter, you can contact me at (301) 504-1120.

Sincerely, i

Originct swa tw Thomas J. Kenyon, Project Manager Standardization Project Directorate Associate Director for Advanced Reactors and License Renewal Office of Nuclear Reactor Regulation l

Enclosure:

As stated cc w/ enclosure:

See next page

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DISTRIBUTION:

Docket File PDST R/F DCrutchfield RBorchardt PDR TEssig TKenyon RHasselberg GGrant, EDO JMoore, 15B18 PShea Alevin, 8E23 -

MRubin, 8E23 ACRS (11) w/o encl.

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DOCUMENT NAME: COMMENTS.CMT k\\

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

Mr. B. A. McIntyre Advanced Plant Safety & Licensing Westinghouse Electric Corporation Energy Systems Business Unit P.O. Box 355 Pittsburgh, Pennsylvania 15230 Mr. John C. Butler Advanced Plant Safety & Licensing Westinghouse Electric Corporation Energy Systems Business Unit Box 355 Pittsburgh, Pennsylvania 15230 Mr. M. D. Beaumont Nuclear and Advanced Technology Division Westinghouse Electric Corporation t

One Montrose Metro 11921 Rockville Pike Suite 350 Rockville, Maryland 20852 Mr. Sterling Franks U. S. Department of Energy NE-42 Washington, D.C.

20585 Mr. S. M. Modro EG&G Idaho Inc.

Post Office Box 1625 Idaho Falls, Idaho 83415 L

Mr. Steve Goldberg Budget Examiner 725 17th Street, N.W.

Room 8002 Washington, D.C.

20503 Mr. Frank A. Ross U.S. Department of Energy, NE-42 Office of LWR Safety and Technology 19901 Germantown Road Germantown, Maryland 20874 f

s 4.

r COMMENTS ON CORE MAKEUP TANK TEST MATRIX SUPPORTING THE AP600 DESIGN CERTIFICATION APPLICATION i

1.

The staff is concerned about the overall emphasis of the test matrix.

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About 70 percent of the specified tests (28 out of 41, excluding repeats) involve either condensation behavior only or constant pressure draining. Only nine tests involve draining and depressurization, and only six of those include the natural circulation phase of core makeup tank (CMT) transient response. While condensation behavior is important in the early states of a transient, its significance will likely i

decrease as the CMT water and structure heat up during the recir~culation k

phase of operation. Characterization of the CMT draining behavior is 1

clearly important, but almost 20 constant pressure tests (which may not actually be conducted at constant pressure) would appear to be neces-i sary; some of this type of data may be obtainable during the hot-shakedown portion of the test program, leaving additional tinte open in i

the matrix testing for more complex tests.

l

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In Tests 36-41, only two states of the CMT are investigated:

corrpletely i

heated and half heated. There is no justification given for ther,e two choices.

In the AP600, the total volume of each CMT is roughly.16,000 gallons. At a CMT recirculation rate of the order of 750 gpm (total l

from two CMTs) (which would tend to decrease as the CMTs became heated),

l it would take more than 20 minutes to replace half the volume of both CMTs. While for some scenarios, especially very small LOCAs, the CMTs may recirculate for an extended period of time, many events involve,a 3.

considerably shorter recirculation period. This would result in a much smaller volume of hot water entering the CMTs. The fractional hot water volume in the CMT may have a significant impact on both draining t

(through density and condensation effects) and depressurization (flash-ing) behavior-. However, it is not clear what volume of hot water in the CMT results in the most limiting behavior of the system, when consider-ing the interactions of the CMTs with the primary system and the relationship of CMT level to the operation of the automatic depressuriz-ation system (ADS).

For instance, a relatively small hot water layer could flash and then mix with the remaining cold CMT water, causing substantial pressure and level oscillations; large hot water layers

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might in contrast behave relatively smoothly. Rather than limit the tests to only two situations with large amounts of hot water, it would be valuable to acquire data over a range of stratified conditions.

Therefore, it is suggested that Westinghouse consider adding tests with i

hot water volumes comprising between about 10 and 30 percent of the CMT i

4 prior to draindown and depressurization.

2.

In the design of the AP600, the reactor water chemistry could f

potentially have an impact on the behavior of the CMT.

For instance, a j

hydrogen overpressure will be maintained in the reactor to control i

dissolved oxygen. - The hydrogen may tend to come out of solution in the l

• Estimate based upon INTEL RELAP5 calculations reported in NUREG/CR-5853.

j Enclosure l

f k

pressurizer and collect in the upper head of the pressurizer, from which it might then be transported to the CMT and diffuse into the CMT water.

Upon depressurization of the CMT, for example, the hydrogen could come out of solution and affect the response of the system. The hydrogen would also tend to collect in the pressure balancing line, and this non-condensible volume could affect the response of the system as it is introduced into the CMT during its initial draining (before. initiation of the first stage of the ADS, when the pressurizer pressure balancing line check valves would close). This behavior could also be affected by operation of the pressure balancing line drain valve and associated piping.

It is not clear from the test specification whether this effect has been accounted for in the design and testing of the CMT facility.

Therefore, it is suggested that Westinghouse evaluate the potential for the presence of hydrogen in the pressurizer pressure balance line and for hydrogen dissolution in the CMT water, and that reactor water chemistry be simulated as closely as is practical in the test facility.

While it may not be practical to test with hydrogen itself, consider-ation should be given to introducing other non-condensible gases. The choice of the non-condensible(s) may depend upon molecular weight, impact on condensation, and/or solubility.

3.

The depressurization rates to be used in the tests that involve depress-urization are not well-specified in the test matrix. The rates chosen should be considered carefully.

In the AP600, there is a dependence of this parameter not only on the ADS operation, but also on the size and location of the break of the reactor coolant system (RCS). The rate of depressurization can affect the CMT response due to its impact on the rate of vapor evolution in the tank and in the RCS itself. An appro-priate range of depressurization rates needs to be specified in more detail, considering (a) available ADS vent area, including possible failures of Stage 1 or Stage 2 ADS valves; (b) break size and location; and (c) other system parameters that could affect depressurization

behavior, 2-