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Power Uprating and Side Effects in Nuclear Power Plant
The process of increasing the licensed power level of a commercial nuclear power plants (NPPs) is called a “power uprate.” power uprates are generally categorized based on the magnitude of the power increase and the methods used to achieve the increase.
Currently a significant number of the nuclear power plants have plans for power uprate by larger or smaller amounts. In most cases this is an economic way of producing more electricity in a nuclear power plant, and which has attracted interest due to increased electricity prices; a situation that is expected to remain. The increase in the electricity produced in a nuclear power plant can be achieved in two ways.
One way of increasing the thermal output from a reactor is to increase the amount of fissile material in use. Optimization of the reactor core can also be done. The amount of fissile material is increased either by increasing the degree of enrichment, or by increasing the density of the fuel. Optimization of the fuel reload aims at increasing the output from the fuel bundles with less power without affecting the high power bundles. This calls for the management of extra fuel bundles on every refuelling. It is also possible to increase the core power by increasing the performance of the high power bundles.
Safety margins can be maintained by either using fuels with a higher performance, or through the use of improved methods of analysis to demonstrate that the required margins are retained even at the higher power levels.
In the boiling water reactors, the increased core power is achieved by increasing the core feed water flows and steam flows. The degrees of re-circulation can be retained, with larger steam voids in the cores, or the steam volumes can be held constant by increasing the re-circulation flows. A combination of these measures can also be applied.
In the pressurized water reactors, the increased power outputs call for an increase either in the core coolant flows or in the mean coolant temperature rise across the cores, or both. In all cases the secondary steam production increases with increased electricity outputs being achieved by the turbo generators.
Report prepared within the framework of the Technical Working Group on Life Management of Nuclear Power Plants (TWGLMNPP) will be published in 2009.
References:
- Implications of Power Uprates on Safety Margins of Nuclear Power Plants, IAEA-TECDOC-1418, IAEA, Vienna (2004)