ISO/NP 25799

​​​​Reactor technology — Pressurized water reactor — Assessment of Potential condensate level oscillatory instability in passive residual heat removal systems​

Scope

​​This document provides guidance on assessing the potential for condensate level oscillatory (CLO) instability in passive residual heat removal systems (PRHRSs) for pressurized water reactors (PWRs).

​The assessment is based on steady and unsteady analytical solutions for the two-phase natural circulation loop model in terms of the condensate level in the vertical feedwater pipe section.
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​The document outlines a simplified model of the PWR PRHRS for analysis, including analytical solutions for steady and unsteady condensate water levels and acceptance criteria to determine whether CLO instability poses a threat to the system.​