A concept of a passive safety light water reactor system requiring reduced maintenance efforts

A reduction in human involvement in operations and maintenance thereby reducing human errors in reactor safety is essential to improving the safety of future light water reactors. For this reason, a passive safety reactor requiring reduced maintenance efforts is being proposed. In this concept, the nuclear steam supply system has an inherent matching nature of core heat generation and heat removal (inherent load-following capability) under a closed primary system. In-vessel control rod drive mechanisms (CRDMS) to eliminate chemical shim, a low-power density core to reduce the Doppler effect, and once-through steam generators (SGs) to minimize the change in SG exit temperatures were adopted. Accordingly, reactor power can be naturally reduced by reducing the feedwater flow rate or steam flow rate within an allowable steam temperature change. The CRDM is being developed for an advanced marine reactor design concept at the Japan Atomic Energy Research Institute. The reactor pressure vessel for a 660-MW(electric) plant is illustrated