Operational Events Noted for Power Uprated Plants and Potential Safety Implications

During the past several decades the US Nuclear Regulatory Commission (NRC) has reviewed and approved in excess of 50 licensee requests for power uprates, most of which have been in the range of 1–6% increase. More recently the agency has received License Amendment Requests (LARs) for significant power increases, in the range of 15–20%, which are under current review. Although each uprate request is evaluated to assure that current regulatory requirements are satisfied, concerns have developed regarding the safety implications of power uprates of this magnitude for the aging population of US-LWR plants. Such concerns stem from operational events noted for plants having received power uprates, including failure to fully-insert control rods in high-power/high-burnup PWR fuel assemblies, piping failures, and reactivity anomalies. Of particular concern is the potential for synergistic/compounding effects, for example higher core power when combined with system/component degradation via plant aging for plant license renewal, or higher power in conjunction with fuel life extensions to elevated burnup. This paper examines a number of operational events for uprated plants and potential safety implications of such events.