CTF is a modernized version of the thermal-hydraulics subchannel code COBRA-TF that was originally developed in the early 1980s at Paciﬁc Northwest National Laboratory. CTF uses a two-ﬂuid, two-phase ﬂow modeling approach for modeling ﬂuid ﬂow and heat transfer. Flow can be modeled as three independent ﬁelds: continuous liquid, vapor, and liquid droplets. CTF also provides a set of solid thermal conduction modeling capabilities that can be used for tubes, cylinders, and nuclear fuel rod geometries. CTF is used primarily for modeling in-core light water reactor ﬂuid ﬂow and heat transfer in normal and oﬀ-normal operating conditions. CTF has been adopted for use in the Virtual Environment for Reactor Applications Core Simulator (VERA-CS) being developed by the Consortium for Advanced Simulation of Light Water Reactors (CASL). This has resulted in improvements to software quality assurance measures, code testing, closure models, integration into the VERA-CS environment, and coupling to other VERA-CS physics packages.
As part of the CASL program, numerous improvements have been made to CTF, including:
- Implementation of new closure models and user features in support of CASL challenge problems including departure from nucleate boiling (DNB), crud-induced power shift (CIPS), and reactivity insertion accident (RIA)
- Extensive verification and validation testing of the code
- Coupling to the neutron transport code, MPACT, the crud-chemistry code, MAMBA, and the fuel performance code, BISON
- Code performance improvements, including a domain decomposition parallelization of the code using the Message Passing Interface (MPI)
- Integration into the VERA-CS environment, allowing CTF models to be developed from the VERA common input file and CTF results to be visualized in the VERAView visualization tool
- Expansion of the code documentation suite to include a software assessment manual, software requirements, lifecycle process, and a training and change control plan
- Integration of an automated code build and testing system
ORNL jointly maintains CTF with North Carolina State University (NCSU) and participates in the CTF User Group, which is responsible for distributing the code to users outside of CASL, providing user support, and providing a forum for users of the code to share code-related research and improvements.
CTF prediction of liquid enthalpy distribution at most limiting point of main steamline break transient with stuck control assembly
Example of modeling resolution of CTF for a 4-loop PWR when used as part of VERA