6.1. Introduction

The SAS4A/SASSYS‑1 control system model was developed for the design and analysis of control systems in LMR plants. The model is described in Ref. 6-1 while application of the model is described in Ref. 6-2. In this chapter, the model is described and guidelines for using the model are given. Essentially, the user should be able to set up an input deck and run the model using the material in this section and in Section 6.8.

The model is very flexible, allowing the user to select any number of plant variables for input to the control system as measured quantities. These signals can then be processed by a user defined network of mathematical blocks that implement the control equations. The output from these blocks can then be used to drive various actuators already existing in SAS4A/SASSYS‑1 or they can be used to directly control plant variables in SAS4A/SASSYS‑1. The model has a steady- state solution finder that can be used to determine initial values for demand signals and state variables that place the control system in a steady state that is consistent with the plant steady state as calculated by SAS4A/SASSYS‑1. The control system model can also be used to calculate auxiliary variables and print their values.

The model is an integral component of SAS4A/SASSYS‑1 and is accessed through the input deck in a manner similar to the other reactor component models. Before using the model however, one must write the mathematical equations that describe the desired plant control system and identify the plant variables that are to be measured and controlled. The user then transforms the equations and variables into a block diagram where the individual component blocks are basic mathematical elements such as integrators and summers. The input deck is prepared directly from this block diagram with each block definition occupying an input card and each plant variable that links with the control system also occupying an input card. Several other cards must also be entered to specify how the control system initial conditions are to be calculated and to assign values to parameters that control the accuracy and stability of the transient solution. A set of parameters also exists for controlling the printing of debug data. This output is useful for diagnosing input errors.

This section describes the basic model; it also gives some general guidelines for using the model. The section assumes the reader has a knowledge of power plant control systems and is able to write the equations that describe their system. The organization of the material is as follows. In Section 6.2 the general equation form that can be represented is given. It is very probable that the user’s model fits this form but this should be verified. The solution techniques used to solve the block diagram equations are described in Section 6.3. Section 6.4 presents some general guidelines for selecting values of solution control parameters and describes some of the model features and how they are used. The input description is given in Section 6.8.