ANSI/ANS 19.6.1-2019 applies to the reactor physics tests that are performed following a refueling or other core alteration of a pressurized water reactor (PWR) for which nuclear design calculations are required. This standard does not address the physics test program for the initial core of a commercial PWR. This standard specifies the minimum acceptable startup reactor physics test program to determine if the operating characteristics of the core are consistent with the design predictions, which provides assurance that the core can be operated as designed. This standard does not address surveillance of reactor physics parameters during operation or other required tests, such as mechanical tests of system components (for example, the rod drop time test), visual verification requirements for fuel assembly loading, or the calibration of instrumentation or control systems (even though these tests are an integral part of an overall program to ensure that the core behaves as designed). Keywords: LWR, Light Water Reactor, Nuclear Safety, PWR, Pressurized Water Reactor, Reactor Physics