Nuclear Power Chap. 11 8. Although the steam cycle is simpler in a BWR, explain why the capital costs of BWR and PWR plants are very competitive. Solution: The simplicity of a single steam/water cycle in a BWR compared to the double primary/secondary cycles in a PWR is offset by the increased complexity of the BWR components. Although a BWR does not require steam generators and a pressurizer, the reactor pressure vessel is much more complex. A BWR vessel must include steam dryers in the top and penetrations for control rods and instrumentation in the bottom of the vessel. Two- phase flow through the core requires a very detailed thermal-hydraulic design. For example, fuel assemblies are shrouded (Fig. 11.21) to prevent cross flows. F\1rthermore, differing sized orifices are required in the entries to coolant channels to adjust flow rates to assure that steam quality is uniform across the core. More important, A BWR core has a power density (W /liter) about half that of PWRs, and, for the
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