When its comprehensive test program was completed at the end of 1994, the Westinghouse AP600 became the most thoroughly tested advanced reactor design ever reviewed by the U. S. Nuclear Regulatory Commission. The results of the test program have now been documented and this paper looks at the results. While the overall plant design of AP600 follows in the decades-long tradition of Westinghouse two-loop pressurized water reactors, this design simplifies safety systems with passive functions which were always active in previous reactor designs. In the AP600, the principal safety functions of primary coolant inventory, reactivity control, reactor residual heat removal, and fission product containment are accomplished with systems relying on natural forces such as gravity, convection, and evaporation. The AP600 test program was a multi-discipline, multi-national effort with input from government, industry, and academic organizations. Its objectives were: To provide information to verify component designs To simulate the AP600 thermal-hydraulic phenomena and behavior of the passive safety systems To provide high-quality, qualified data to validate computer codes used in the Westinghouse safety analyses To support the U. S. Nuclear Regulatory Commission in its design certification review of the AP600. Each of these objectives was achieved. The test results confirm the exceptional behavior of the passive systems and have been instrumental in facilitating code validations. Tests were conducted in three general categories: component design verification tests, passive containment cooling system tests, and passive core cooling system tests. The success of the test program, long a major focus of Westinghouse and NRC discussions about AP600, puts the design of this advanced reactor systems well on its way to final design approval which is expected in 1997. While the NRC's review of the test program data is still being completed, the Commission has acknowledged the simplicity and safety of the design. In addition to providing fundamental engineering data to support the licensing process leading to NRC design certification, the test program imbues potential utility owners with confidence in the innovative aspects of the AP600.
