Power Reactor Benchmark Studies

The Light Water Reactor Pressure Vessel Surveillance Dosimetry Improvement Program (LWR-PV-SDIP) was established by the U.S. Nuclear Regulatory Commission (NRC) to improve, test, verify, and standardize the physics-dosimetry-metallurgy measurements and calculations used to predict the effect of neutron exposure to LWR pressure vessels and their support structures. As part of this effort the PCA and PSF experiments were initiated at Oak Ridge National Laboratory (ORNL) to allow accurate measurements adjacent to and through a pressure vessel mockup. It was recognized, however, that additional benchmark measurements would be needed to relate the PCA/PSF data to operating plants. Although measurements in operating plants could not be nearly as extensive as those in a mockup, only actual plant measurements can provide a test of the application of calculational techniques to the actual, more complex, LWR geometry. Therefore, in cooperation with vendors, utilities, and other laboratories, dosimetry measurements have been made in several operating plants. These measurements were carried out in the reactor cavities, adjacent to the outside of the reactor vessel, and, in one case, in a special capsule located at a surveillance position inside the vessel. The reactor measurement results provide a series of data points for validation of transport calculation methods. The value of the data lies in the evaluation of absolute magnitudes of flux through the vessel and in the information on azimuthal and axial flux variations. Application of calculational techniques to evaluation of various flux reduction schemes is of particular concern as regards these variations. Results from the power reactor benchmarks are generally consistent with bias trends observed in the mockup measurements. It is anticipated that future calculational improvements will utilize the power reactor benchmark data for verification.