Adaptation of PROTHOS to the once-through steam generator

The PORTHOS Mod-01 computer code, developed by the Electric Power Research Institute, is a three-dimensional, transient thermal-hydraulic analysis tool for simulating two-phase flow in recirculating-type steam generators. Under the sponsorship of the Babcock & Wilcox (B&W) Owners Group, the PORTHOS code was modified for use in analyzing the Once-Through Steam Generator(OTSG). The goal has been. to develop a tool to assess the effects of plugging tubes on the distributions of moisture and fluid velocities within the tube bundle under steady-state operating conditions in the OTSG. The Mod-Ol version of PORTHOS was modified to account for differences between the recirculating and once-through generators, particularly differences in the geometry and the operating heat-transfer regimes. Coding changes include (1) new routines for initializing the solution field, (2) revised flow boundary conditions to reflect the OTSG geometry, and (3) additions to heat transfer routines to model the film-boiling and steam superheat processes. The modified coding allows the user to optionally include the OTSG steam annulus as part of the solution domain and the bleed port as a boundary condition. Pre- and post-processors were developed to automatically generate geometry input to the code and produce data output files to facilitate visualizing the flow-field solution with use of PATRAN. Favorable results have been obtained in comparing the predictions of the OTSG-modified PORTHOS code with test data PORTHOS results and test data agree well for both model boiler and full-size steam generator temperature profiles within the OTSG tube bundle. Good agreement has also been obtained for the predicted velocity distributions at the exit of the tube bundle in comparison with data from scale model tests.