IN-CORE NEUTRON DETECTORS FOR CHARACTERIZING HIGH TEMPORAL-RESOLUTION REACTOR TRANSIENTS

摘要

The technology required to measure fast transient needs to be small enough to quantify near point-like measurements and needs to acquire sufficient amounts of data over the typical span of a fast transient, which can be as small as 20ms. For this purpose, a detector system has been developed that can measure neutron flux levels between fuel elements at various heights. The structural system designed for this system is a versatile system that minimally impacts the reactor operation but allows the movement of a detector within the structure essentially without restriction. Detailed thermal-hydraulic simulations were performed to ascertain the impact of this structure on the safety of the reactor especially with regards to me Minimum Departure from Nucleate Boiling Ratio (MDNBR). The geometry of the detector featured a detector diameter of 0.4 cm and a height of 1.9 cm, with the high voltage and coaxial signal cable fitted within an aluminum tube with an internal diameter of 0.95 cm. This detector tube would then fit into the detector structure that allowed detector tubes with a maximum outer diameter of 1.067 cm. Data acquisition is achieved at a rate of 250 MHz which allows very detailed characterization of fast transients.