ARIANT

The acronym ARIANT stands for AlgoRIthm for Analysis of Network Thermalhydraulics. The ARIANT code was developed by Atomic Energy of Canada Limited (AECL), now the Canadian Nuclear Laboratories (CNL).

The thermalhydraulic code ARIANT was developed primarily for the analysis of postulated upset conditions in CANDU reactors; however, the code has found a wider range of application for the modelling of thermalhydraulic test facilities such as RD-14M. An overview of the ARIANT thermalhydraulic code numerical methods and constitutive relations is given in ARIANT Theoretical Background Manual.

Code Overview:

ARIANT uses a transient, one-dimensional two-fluid representation of two-phase flow in piping networks. In the thermalhydraulic model, the liquid and vapour phases may have different pressures, velocities, and temperatures. The thermalhydraulic model consists of solving six partial differential equations for the conservation of mass, momentum and energy for each phase. The thermalhydraulic model in ARIANT includes pipe, volume, reservoir, T-junction and tank components.

Interface mass, energy and momentum transfers between the liquid and vapour phases are specified using constitutive relations obtained either from the literature or developed from separate-effects experiments. The accuracy and applicability of the constitutive relations available in ARIANT can only be assessed by the code user after familiarisation with the code verification base.

The code uses a staggered-mesh, one-step, fully-implicit, finite-difference solution method, which is not transit time limited. In the numerical solution method used, a non-linear system of finite-difference equations is constructed as a result of the time and spatial integration of the partial differential mass, momentum and energy conservation equations over finite time steps and finite space (nodes or links). In the ARIANT numerical method, the time step is selected based on the rates of change of a set of parameters including pressure and void fraction.

The ARIANT code includes thermophysical properties for both light water, H₂O and heavy water, D₂O. The pressure range of application of the fluid properties is from the triple-point pressure ( 611.73 and 660.1 Pa for H₂O and D₂O respectively) to the critical pressure (22.0 and 21.66 MPa for H₂O and D₂O respectively). The temperature range of light water properties is from 0°C to 2000°C. The temperature range of the heavy water properties is from 0°C to 800°C. The thermodynamic properties for light water are within 1.5% of values obtained from the US National Bureau of Standards (NBS) steam table generating functions, Kestin et al [2], and property derivatives are within 5%. For vapour temperatures above 2000°C the properties are obtained using the ideal gas approximation. The thermodynamic properties for heavy water are within 1.5% of the values obtained from the generating functions of Hill et al [3] and the property derivatives are within 5%. For temperatures above 800°C the ideal gas approximation is used.

The comprehensive solid heat-transfer package used to model pipes or fuel in contact with the fluid has been given the acronym HTP which stands for Heat Transfer Package. The heat transfer package includes radial, circumferential and axial conduction. Contact conduction between solid surfaces is modelled. A thermal radiation model is currently under development. The heat-transfer package allows the connection of multiple solid surfaces to a single thermalhydraulic node or multiple thermalhydraulic nodes to a single heat transfer model. As a result, very detailed modelling of a CANDU channel containing horizontal fuel bundles can be performed. Testing of ARIANT/HTP has shown high computational efficiency, as well as the advantage of closely coupling thermalhydraulic and fuel-channel behaviour. Heat transfer in deformed geometries (pressure tube/calandria tube/moderator, fuel element and pressure tube, etc.) may be modelled. One code, ARIANT, may be used for modelling the system thermalhydraulics, as well as detailed heat transfer modelling of a CANDU fuel channel.

ARIANT code also includes system models for components such as pumps, valves, user definable junction resistances, and separators. Also included in the set of system models is a point-reactor kinetics model, a break-discharge model and a heat-balance calculation model. An extensive control system modelling capability is also provided. Complex control systems can be defined in LUA scripts by the user. ARIANT is capable of interfacing with user LUA scripts to model almost an unlimited variety of system control models. In addition, a general code interface to external executable programs is also provided through the PVM (Parallel Virtual Machine) data passing software.

The code holder of ARIANT is the Systems and Safety Analysis Branch at CNL.

Further information on ARIANT can be obtained through the ARIANT website (www.ARIANT.cnl.ca).

Operating System Requirements:

ARIANT is supported on Microsoft Windows and RedHat Linux.