Identification of thermal neutron flux in central thimble of TRIGA 2000 reactor with experimental method

The TRIGA 2000 reactor has just completed its latest reshuffling and refueling process, i.e. 100-core configuration. This reshuffling and refueling changed the fuel configuration in the TRIGA 2000 core reactor. In this 100-core configuration, new fuel elements (fresh fuel) and instrumented fuel elements (IFE) are added. Generally, routine neutron flux measurements are carried out every time the reactor core configuration is changed. Neutron flux measurements have the purpose to determine the effect of changes in the new core configuration on the value of the thermal neutron flux with an axial position. The value of the neutron flux is used to make data on the distribution of the neutron flux in the reactor core. Hence, in performing services at various existing irradiation facilities, the irradiated sample could use the position that has the most optimal value of the neutron flux. The measurement method uses the gold activation method by irradiating small pieces of gold on the central thimble in the reactor core’s middle position. There were 2 pairs of samples placed on the CT pipe which were inserted into the different aluminum containers. All samples were irradiated in the reactor core with a power indicator on the display during the operation of 600 kW for 5 hours. The sample is then transferred using a container into the hot cell. One month after irradiation, the samples were removed from the container and then counted. The thermal neutron flux measurement results obtained a value of 4.928×10⁹ neutrons/cm²s and 6.511×10⁹ neutrons/cm²s at the position of 21 cm and 35 cm, respectively, from the base of the core. The value of the thermal neutron flux measured by the experimental method in this study is generally on the order of 10⁹ neutrons/cm²s. This experimental research showcases that the thermal neutron flux profile in the reactor core with the latest configuration has a higher flux value at the axial center position. Moreover, it can provide an initial description of the reactor core’s thermal neutron flux profile, which is useful in further studies.