ISO/PWI 25799

Reactor technology — Pressurized water reactor — Assessment of the potential for Two-Phase-Flow-Instability in passive residual heat removal systems

Scope

This document gives guidance on assessing the potential for two-phase flow instability (CLOs) in PWR PRHRSs. The assessment is based on both steady and unsteady analytical solutions for the two-phase natural circulation loop model in terms of the condensate water level in the vertical feedwater pipe section.

The document specifies a simplified model of the PWR PRHRS for analysis, along with the analytical solutions of steady and unsteady condensate water level, and acceptance criteria to determine whether the systems would be threatened by the two-phase flow instability.