Computer-Based Simulation Methods for Boiling Water Reactors (BWR)

A computer-implemented simulation method of predicting local concentrations of constituents in coolant water anywhere along fuel rods within any fuel assembly mechanical design of a Boiling Water Reactor, BWR, potentially resulting in crud deposits on said fuel rods, the method is based on a sub-channel approach of predicting local mass fluxes of vapor and liquid in coolant water anywhere along fuel rods within any fuel assembly mechanical design of a Boiling Water Reactor, BWR, for given steady-state or transient boundary conditions, the sub-channel approach is based on the solution of mass, momentum and energy conservation equations for the vapor phase and the liquid phase, the liquid phase is represented by more than one field variable, and is specifically represented by three fields, with the vapor phase as a fourth field, consisting of droplets, a liquid base film, and disturbance waves, wherein the method comprises solving individual mass, momentum and energy conservation equations, for said four fields, and solving the necessary closure relations describing the transfer of mass between the said fields, completed by mass conservation equations for constituents dissolved in the liquid phase and transported by each of the said fields individually, and wherein the method comprises:

• simulating steady-state or transient boundary conditions for the condition of interest to the fuel assembly, such as inlet coolant water flow into said sub-channels, temperature, pressure, rod power distribution, and assembly power, the coolant water flow may have a predetermined flow velocity variation,
• analyzing predefined parameters of said disturbance waves and base film, including wave velocity, wave frequency and base film thickness, and
• analyzing liquid base film thickness between consecutive passing disturbance waves, to calculate local instantaneous impurity concentrations based on said simulated boundary conditions, the calculation is made for each fuel rod of the fuel assembly, wherein, for each fuel rod, the method further comprises comparing said calculated local instantaneous impurity concentration to a crud compound precipitation limit, and during the time said concentration is higher than said precipitation limit, crud is considered to have occurred.

A computer-implemented simulation method, based on a sub-channel approach of predicting local mass fluxes of vapor and liquid in coolant water anywhere along fuel rods within any fuel assembly mechanical design of a Boiling Water Reactor, BWR, for given steady-state or transient boundary conditions, the sub-channel approach is based on the solution of mass, momentum and energy conservation equations for the vapor phase and the liquid phase, the liquid phase is represented by more than one field variable, and is specifically represented by three fields, with the vapor phase as a fourth field, consisting of droplets, a liquid base film, and disturbance waves, the method comprises solving individual mass, momentum and energy conservation equations, for said four fields, and solving the necessary closure relations describing the transfer of mass between the said fields, completed by models describing local phenomena being base film dryout, clad temperature increase or drop entrainment from waves, wherein the method further comprises:

• simulating steady-state or transient boundary conditions, such as any postulated scenarios relevant to BWR operation relevant to BWR operation with respect to the potential appearance and rewetting of dry patches between waves, associated dry time and clad temperature increase, and
• analyzing predefined parameters of said disturbance waves and liquid base film, including wave velocity and frequency, and base film thickness.