Evaluation of higher K-modes of AHWR-LEU core and estimation of neutron flux at in-core detector locations

The Advanced Heavy Water Reactor LEU (AHWR-LEU) is a boiling light water cooled heavy water moderated reactor utilizing thorium based fuel. It has several passive safety features such as negative coolant void coefficient of reactivity and passive decay heat removal. The neutronic and thermal hydraulics is expected to be strongly coupled in the reactor core. A perturbation in the coolant conditions can give rise to power oscillations. Also the AHWR-LEU reactor core has a very large diameter. Slow xenon induced oscillations are possible in AHWR-LEU due to perturbation in reactor operation. The neutronic de-coupling of the reactor could lead to excitation of higher harmonics. It is very important to monitor the detailed spatial neutron fluxes. On-line flux mapping through SPNDs is one such measurement approach in power reactors. In an earlier simulation the fluxes at the detector locations were calculated for the AHWR reference core. Presently, the core had been redesigned with (Th-LEU) MOX fuel. In this simulation, the positions of the in-core instrumentation have not been changed. The LEU variant of the Advanced Heavy Water Reactor called AHWR-LEU has been designed to have on-line flux monitoring with the help of SPNDs using ⁵⁹Co, ⁵¹V or Platinum clad Inconel as the sensor. The neutron flux at those detector locations were calculated using the Transport Theory Code ATES3. (author)