Modelling and Validation of CANDU Shim Operation Using Coupled TRACE/PARCS with Regulating System Response

In CANDU reactors, shim operation is used when the online refuelling capability becomes temporarily unavailable. Adjuster rods, normally in-core to provide flux flattening, are withdrawn in sequence additional reactivity as fuel depleted. a 900 reactor, up three of eight adjuster banks may be withdrawn, with power derated accordingly. this study, was modelled using combination TRACE_Mac1.1, PARCS_Mac1.1, and scripts modelling reactor regulating system, all running single coupled simulation. A driver script simulated steady-state, depletion, transient models. The results were compared operational data from nuclear plant, evaluating key figures merit. simulation extended beyond by reducing 59% FP withdrawing remaining adjusters, observe behaviour for deeper reactivity-driven transient. Sensitivity cases, including rod depletion uncertainty, also evaluated. This study able successfully reproduce general operation. Some discrepancies observed between dataset duration shim, particularly one bank out phase shim. Several potential causes early identified. When extended, model predicted that reduction below 60% would lead xenon poison adjusters depleted, timing sensitive depletion. Nodalisation PARCS had significant impact, due effect on nodalisation its area-of-effect respect actual locations. Nuclear uncertainty lesser but still noticeable effect. Other parameters, such distribution burnups core, only small