History of ARIANT

Development of a thermalhydraulic simulation code began in 1975 at the then Whiteshell Nuclear Research Establishment (now Whiteshell Laboratories), christened RAMA (Reactor Analysis IMplicit Algorithm).  This was a homogeneous EVET (Equal Velocity Equal Temperature) code. Early on it was realized that proper CANDU analysis would require a two-fluid code in which the liquid and vapour phases could have unequal temperatures and unequal velocities (UVUT), especially for CANDU channel analysis under stratified flow conditions. Following from this the RAMA-EVUT (Equal Velocity Unequal Temperature) variant was developed in 1977/78 and RAMA-UVUT (Unequal Velocity Unequal Temperature) in 1979/80.

These versions of RAMA used a characteristic finite-difference solution algorithm. Although this solution scheme had some important advantages over other techniques, it also suffered from some serious deficiencies, most notably conservation of mass was not enforced. These difficulties could not easily be resolved and therefore this technique was abandoned.

In 1984, a new code, ATHENA, was created which used a more conventional upwind staggered-mesh finite difference method. ATHENA was renamed CATHENA (Canadian Algorithm for THErmalhydraulic Network Analysis) later in 1985 to distinguish it from an ATHENA package available in the United States. CATHENA is currently in maintenance mode at the Canadian Nuclear Laboratories (Chalk River, ON).

Development of the ARIANT code commenced in 2010, driven by CNL's requirements as part of the CANDU licensing process and future reactor projects, and in response to feedback from the customer base. ARIANT is developed from ground up with an entirely modern code architecture. It employs a fully-implicit numerical integration scheme and has been coded in the modern Fortran 95/2000 language with 2008 extensions. It employs dynamic memory allocation in all internal models resulting in unlimited problem size.