Building Control Systems
Read Chapt 3 in the TRACE
User's Guide. Scan Sections
6.4.5, 6.4.6, 6.4.8, and 6.4.9 to get a feel for the range of
The ability to use control blocks
separates the amateur from the
master analyst. This class forms
a basis for the active control that you will introduce into later
system models for homework and
your final project.
Now prepare for an in-class exercise
by making a folder for your
results, and downloading this
TRACE input file to that
folder. Import the file into the SNAP Model Editor, then in the
Component Navigator window right click "Control Systems" and select
"Create View". Examine the signal variables and control blocks,
tell me what control block 600 represents. Next find a simpler
way to get the same result.
- Basic Definitions
- Signal Variables are values of physical parameters (pressure,
etc) that are extracted from user specified locations in the systems
as input to Trip and Control Block operations.
- Trips are simple tests that compare signal variables to
thresholds and provide
simple signals to the code (on, off, on reverse) indicating that
- Control blocks are in effect a programming language for the
analyst. They accept
output from signal variables and other control blocks as input, and
operation on the input to produce an output. Control block output may
be used to
drive component behavior such as pump speed, boundary condition
valve areas, and reactor power.
- History and comparison of various codes
- The early development of best estimate codes (TRAC and RELAP5)
on analysis of Large Break Loss of Coolant Accidents. Requirements for
modeling of plant control systems were relatively minimal. In TRAC this
handled with a combination of Trips and features such as rate factor
tables in the
- With the advent of TMI a much broader range of accidents were
opened to best
estimate analysis and a more complete control capability was required.
original Control system coding now seen in TRACE was developed at INEL
for use in TRAC-B.
Coding was picked up by LANL for use in TRAC-P and extended to include
specific blocks for PI and PID controllers. The functional capabilities
within INEL to the RELAP5 effort, resulting in a very similar structure
that code. TRACE captures all of the capabilities found in
RELAP5, TRAC-B, and TRAC-P.
- Primary uses of trips and control systems
- Simulating real reactor control systems
- Remember the implementation in the code is digital not analog
as are most
real reactor control systems. Also keep in mind the digital sampling
period is the time step for the integration of the flow and heat
equations. When this is too large it may introduce control
that are not present in the real control system.
- Functionality of the reactor control system should be
usually you should not attempt to replicate the elements of a control
system on a block by block basis as provided in a control system
- Driving the system to a steady state in preparation for
- Sometimes this involves a plant control system
- Usually it's a user created or code default control unrelated
to a real
- Performing simple sanity checks such as giving pressure drops
- Provide desirable indirect data such as enthalpies or
integrated mass flows (can be
- Provide simulation of actual instrumentation response. Random
generators can simulate signal noise. Offsets and delays in the
instruments to physical conditions can also be modeled.
- Provides a method for extracting key numbers in English rather
than SI units.
- Control blocks are basically a programming language
approximately at the assembly code level) available to the user to
certain aspects of the code. Special control block functions are not
required in the
French code CATHARE, since the entire input is effectively a
- Control block Specifications
- Note alphabetic ordering, in the documentation.
- Two Broad classes of functions
- Actual Logic Circuits and elements in control circuits
- Useful functions and operations.
- The SNAP Model Editor uses a finer classification of control
- Arithmetic Blocks
- Calculus Blocks
- Controller Blocks
- Logical Blocks
- Manipulation Blocks
- Time Related Blocks
- Trignometric Blocks
- The General Rule is not to build detailed controller. Build a
- Capabilities are reproduced well in TRACE and RELAP5. RETRAN is
- Special Steady State control included in TRACE
- Adjust pump speed to get desired flow.
- Adjust valve area to get desired upstream pressure or desired
- Adjust heat transfer area to give desired temperature or
volume fraction at the outlet of a heat exchanger
A cleaner version of this input deck is the basis for Homework
7. Use the remainder of your time in the computer lab to work on Homework 7.
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