ML16224A215

NRC Confirmatory Test Program in Support of the AP600 Design Certification

ML16224A215
Person / Time
Issue date:	11/18/1993
From:	Wilkins J Advisory Committee on Reactor Safeguards
To:	Selin I NRC/Chairman
References
D931118
Download: ML16224A215 (3)

Text

D931118 The Honorable Ivan Selin Chairman U.S. Nuclear Regulatory Commission Washington, D.C. 20555

SUBJECT:

NRC CONFIRMATORY TEST PROGRAM IN SUPPORT OF THE AP600 DESIGN CERTIFICATION During the 403rd meeting of the Advisory Committee on Reactor Safeguards, November 4-6, 1993, we reviewed selected aspects of the NRC Office of Nuclear Regulatory Research (RES) experimental program to be conducted at the Japan Atomic Energy Research Institute's (JAERI's) Large-Scale Test Facility (LSTF) in support of the NRC design certification of the Westinghouse (W) AP600 passive plant. Our Subcommittee on Thermal Hydraulic Phenomena met on October 28, 1993, to review this matter. During this review, we had the benefit of discussions with representatives of the NRC staff. We also had the benefit of the documents referenced.

In a September 16, 1992 Staff Requirements Memorandum, the Commission requested that the ACRS review selected aspects of the ROSA-V test program prior to its initiation. Specifically, the Committee was asked to review the test matrix and the facility modifications and additions, including instrumentation and controls. The following comments are offered in response to that request:

The modified LSTF has been designated as ROSA-V. Despite the modifications, a number of atypicalities and scaling distortions exist in the ROSA-V configuration relative to the AP600 design. Some of the atypicalities in ROSA-V are: the use of one cold-leg per reactor coolant system (RCS) loop instead of two; the geometry and heat transfer characteristics of the steam generators; the existence of a four foot loop seal in the RCS; excess metal mass (in particular, for the core makeup tank (CMT)); the volume and geometry of the in-containment refueling water storage tank (IRWST); the primary residual heat removal (PRHR) system; and the configuration of the pressurizer surge line. RES staff representatives stated that they understand the impact these atypicalities will have on system performance. The RES staff has not, however, presented a convincing argument that it understood the impact.

RES should do so and document the results.

Despite the facility shortcomings, we believe that ROSA-V will generate useful data to support validation of the relevant computer codes. This validation, however, may be inconclusive given the above atypicalities, especially those existing in the CMT, the PRHR system, and the IRWST. We recommend that the staff be urged to resolve the issues resulting from the atypicalities discussed above by additional analyses and, if

necessary, by separate effects tests.

The instrumentation proposed in support of the planned test program appears adequate for code assessment when dealing with single-phase phenomena. It is not clear that it is adequate for the measurement of key phenomena under conditions of two-phase flow. It is inadequate for determining some of the heat transfer characteristics of the PRHR system.

The AP600 automatic depressurization system (ADS) will be activated by decreasing water level in the CMT. This level will be measured with heated junction thermocouples (HJTCs).

The three AP600 integral system test facilities (ROSA-V, APEXýAdvanced Plant Experimentýand SPES-II) will use differential pressure (DP) cells to measure this level.

Activation of the ADS using DP cells rather than HJTCs could result in significant test distortions, given the inherent time delay associated with the use of HJTCs. The RES staff believes that these differences can be addressed. We were told by RES that JAERI has installed HJTCs of its own design at ROSA-V. We recommend that the RES staff use these HJTCs for ADS control for at least one properly chosen test, even if they are of a different design from those planned for use on the AP600.

The ROSA-V test matrix is based on examination of transients and design-basis accidents for existing PWR designs. A number of the tests in the ROSA-V Phase I matrix have counterparts in the test matrices of the W SPES II and APEX facilities. These three facilities are scaled differently and have atypicalities of differing natures. We believe that the data obtained from these facilities will prove adequate for the necessary computer code validation by providing a broad range of challenges for simulation, given that the separate effects test programs supply sufficient information for code model development.

Recently, RES modified the Phase I test matrix in response to a request from NRR to include some very small breaks and some "beyond-DBA" type events. We support this modification, but note that the capability of the relevant computer codes to model very small-break LOCAs is weak. This may lead to difficulties when code validation is attempted.

Sincerely, J. Ernest Wilkins, Jr.

Chairman

References:

1. U.S. NRC Report, NUREG/CR-6066 (Draft), "Analysis of LSTF Scaling for AP600 Testing," M. Ortiz, et al., June 11, 1993 (Draft Predecisional)

2. Memorandum dated December 23, 1992, from G. Rhee, NRC, to P.

Boehnert, ACRS, transmitting INEL Report by T. Boucher, et al., "Description of Design Requirements for ROSA Modifications to Simulate AP600 Phenomena" (Revised September 1992)

3. U.S. NRC Report, NUREG/CR-5853, "Investigation of the Applicability and Limitations of the ROSA Large-Scale Test Facility for AP600 Safety Assessment," M. G. Ortiz, et al.,

December 1992

4. ACRS report dated July 17, 1993, "Integral System and Separate Effects Testing in Support of the Westinghouse AP600 Plant Design Certification"

5. Staff Requirements Memorandum dated September 16, 1992, from S. J. Chilk, Office of the Secretary, to J. M. Taylor, EDO, "SECY-92-219 - NRC-Sponsored Confirmatory Testing of the Westinghouse AP600 Design"

6. SECY-92-219, Memorandum dated June 16, 1992, from J. M.

Taylor, NRC Executive Director for Operations, for the Commissioners,

Subject:

NRC-Sponsored Confirmatory Testing of the Westinghouse AP600 Design