《CANDU堆介绍》-课件设计（公开）.ppt

2008 January CANDU Differences with PWR B. Rouben McMaster University EP 4P03/6P03 2008 Jan-Apr CANDU Reactor Heavy-water moderator Natural-uranium dioxide fuel Pressure-tube reactor CANDU is a PHWR CANDU-PWR Balance of Plant Balance-of-plant features in CANDU and PWR are very similar: Administration and maintenance facilities Pump house Reactor containment Turbine and generator Differences between CANDU and PWR are principally in reactor-core design Differences in Reactor-Core Design CANDU On-Power Refuelling Leads to: Constant global power shape, with localized “ripples” as channels are refuelled and go through their burnup cycle Constant in-core burnup Constant shutdown-system effectiveness Possibility of on-power removal of failed fuel, and therefore clean HTS Refuelling Excess Core Reactivity Refuelling Excess Core Reactivity Reactivity Devices In CANDU: Devices are in benign environment (moderator at low pressure and temperature) Pressure-driven ejection not possible Separate devices for control and safety Modest reactivity worth Maximum total reactivity rate 0.35 mk/s In PWR: Device worth is very high, to match high core excess reactivity Pressure-driven ejection must be considered in safety analysis Same for accidental boron dilution Reactivity Transients Reactivity Transients (cont’d) Reactivity Transients (cont’d) CANDU Caters to Void Reactivity by: Arranging heat-transport system to minimize rate of reactivity insertion on coolant voiding (e.g., subdividing the heat-transport system into 2 loops). Providing two fully capable Shutdown Systems that can individually overtake any reactivity transient. Core-Region Decoupling The CANDU core is more decoupled than a PWR core. This means that core regions or zones can behave somewhat independently of others to a greater degree in CANDU than in PWR: the spatial power distribution can be more easily tilted. Also, refuelling occurs daily, in various core regions. ? A spatial-control system is more