<p>The nuclear safety industry makes extensive use of thermalhydraulics system analysis and computational fluid dynamics codes for validation and predictive purposes. These codes take different approaches to provide the user with reasonable estimates of system and component behaviors. With each displaying its own strengths, it is only logical to pursue coupled systems of these codes to create increasingly accurate, versatile, and more computationally efficient safety analysis tools. This work presents results of the attempted coupling of CD-ADAPCO's STAR-CCM+, a computational fluid dynamics (CFD) code, to Atomic Energy of Canada's CATHENA thermalhydraulics (TH) code. This coupled system is used in the simulation of the conditions within an inlet header of the RD-14M experimental facility under single phase conditions in the initial phase of selected test. This inlet header is removed from a modified CATHENA test B9401 deck and instead modelled in STAR-CCM+. Custom applications were written to allow information exchange at the newly created boundaries to provide an attempt at a coupled system. Results are provided through multiple stages of development of the coupled system, from the unmodified B9401 test case of CATHENA into a coupled system with header behavior predicted by STAR-CCM+. Though successful information transfer between codes was established at each desired time step and interval, the current technique was found to be insufficient for establishing acceptable steady-state conditions for the commencement of more complex (transient and two-phase) conditions.</p> / Master of Applied Science (MASc)

Inlet headers in the primary heat transport system(PHTS) of CANDU type reactors, are used to collect the coolant coming from the steam generators and distribute them into the reactor core via several feeders. During a postulated loss of coolant accident (LOCA), depressurization and vapor supplement into the core may occur, which results a deterioration in the heat transfer from fuel to the coolant. When a depressurization occurs, &ldquo / Emergency Coolant Injection(ECI)&rdquo / system in the PHTS in CANDU reactors, is automatically become active and supply coolant is fed into the reactor core via the inlet header and feeders. . This study is focused on the experimental and computational investigation of the ECI effect during a LOCA in a CANDU inlet header. The experiments were carried out in METU Two-Phase Flow Test Facility which consists of a scaled CANDU inlet header having 5 connected feeders. The same tests were simulated with a one dimensional two-fluid computer code, CATHENA, developed by Atomic Energy of Canada Limited(AECL). The average void fraction and the two phase mass flowrate data measured in the experiments are compared with the results obtained from CATHENA simulation. Although a few mismatched points exist, the results coming from two different studies are mostly matching reasonably. Lack of three-dimensional modeling for headers in CATHENA and experimental errors are thought to be the reasons for these dismatches.