CTF Theory Manual (V.4.2)

Abstract

Coolant-Boiling in Rod Arrays-Two Fluids (COBRA-TF) is a thermal/hydraulic (T/H) simulation code designed for light water reactor (LWR) vessel analysis. It uses a two-fluid, three-field (i.e. fluid film, fluid drops, and vapor) modeling approach. Both sub-channel and 3D Cartesian forms of 9 conservation equations are available for LWR modeling. The code was originally developed by Pacific Northwest Laboratory in 1980 and had been used and modified by several institutions over the last few decades.COBRA-TF also found use at the Pennsylvania State University (PSU) by the Reactor Dynamics and Fuel Modeling Group (RDFMG) and has been improved, updated, and subsequently re-branded as CTF. As part of the improvement process, it was necessary to generate sufficient documentation for the open-source code which had lacked such material upon being adopted by RDFMG. This document serves mainly as a theory manual for CTF, detailing the many two-phase heat transfer, drag, and important accident scenario models contained in the code as well as the numerical solution process utilized. Coding of the models is also discussed, all with consideration for updates that have been made when transitioning from COBRA-TF to CTF. Further documentation outside of this manual is also available at RDFMG which focus on code input deck generation and source code global variable and module listings.

Assessment of the Effect of Prototypic High-Burnup Operating Conditions of Fuel Fragmentation, Relocation, and Dispersal Susceptibility

“…First, LHRs were selected as surrogates to characterize fuel rod temperature behaviors. Fuel rod temperature estimates calculated by VERA's thermal-hydraulics module, CTF [6], [7], are available in the HDF5 files. However, these results were expected to be less realistic than the LHRs calculated by VERA's neutronics module, MPACT [8], [9].…”

VERA 4.3 Release Notes

“…• experimental capability to perform jump-in calculations for BWRs using ORIGEN • BWR transverse in-core probe (TIP) detector inputs and processing • additions to summary file for BWR-related quantities such as void, thermal limits, etc. CTF, an updated version of the COBRA-TF code, is a subchannel T/H code that uses a two-fluid, threefield (i.e., fluid film, fluid drops, and vapor) modeling approach for single-and two-phase steady-state and transient condition [5]. CTF includes a wide range of T/H models important for LWR safety analysis and modeling of normal LWR operating conditions-including flow regime-dependent, two-phase wall heat Virtual Environment for Reactor Applications 13 ORNL/SPR-2022/2533 transfer, inter-phase heat transfer and drag, turbulent mixing, two-phase pressure drop, spacer grid effects, and void drift.…”

“…A T/H capability is provided with CTF, an updated version of COolant Boiling in Rod Arrays -Two Fluid (COBRA-TF) [5], that allows T/H subchannel analyses for single and multiple fuel assemblies using the simplified VERA Common Input (VERAIn). This distribution also includes coupled neutronics, T/H, and depletion capabilities to allow calculations using MPACT coupled with CTF and ORIGEN, and it includes a fuel rod temperature model in CTF that provides intra-pellet temperature coupling with MPACT for Doppler feedback to the neutronics.…”