CANDU Control Programs & Process Systems

1. CANDU Control Programs & Process Systems B. Rouben McMaster University EP 4P03/6P03 2013 Jan-Apr

2. Plant Control Software • There are 5 main control programs (software) executing at all times in the CANDU power-plant computers: • Unit Power Regulator (UPR) • Steam-Generator (or Boiler) Pressure Control: SGPC (or BPC) • Steam-Generator (or Boiler) Level Control: SGLC (or BLC) • Heat-Transport Pressure & Inventory Control (HTP&I) • Reactor Regulating System (RRS) • These 5 programs control the plant’s main process systems. Their task is to keep everything running smoothly.

3. Process Systems & Control Software

4. Unit Power Regulator • The Unit Power Regulator (UPR) has control of the plant’s electrical output,but only when the plant is in the NORMAL mode of operation: • In this mode, it measures the plant’s electrical output and compares it to the setpoint. If there is a power error, UPR will take action to remove the error: • It will incrementally change the opening of the governor valves to the turbine, to change the volume of steam allowed into the turbine, and hence drive the power to the setpoint at the operator’s specified rate.

5. Steam-Generator Pressure Control • Steam-generator pressure is a parameter easy to measure, and it is convenient to use it as a “communication tool” to co-ordinate electrical output with reactor power. • Steam-Generator Pressure Control (SGPC, or BPC) has as task to maintain the steam-generator pressure to a constant value (4.7 MPa). • Steam-generator pressure will tend to change in response to changes in governor-valve opening and also to changes in reactor power. • If there is a steam-generator-pressure error, SGPC manipulates the reactor power setpoint (in NORMAL mode) or the governor-valve opening (in ALTERNATE mode) to remove the error.

6. Steam-Generator Level Control • Steam-Generator Level Control (SGLC, or BLC) has as task to maintain a constant inventory of (light) water in the steam generators, to ensure a constant heat sink. • The steam-generator-level setpoint is changed as a function of reactor power, to take into account volume changes of water with temperature. • If there is a steam-generator-level error, SGLC manipulates the feedwater flow into the steam generators to remove the error.

7. Heat-Transport Pressure & Inventory Control • Heat-Transport Pressure and Inventory Control (HTP&I) has as task to maintain constant the outlet coolant pressure and the inventory of coolant in the primary coolant system. • The outlet coolant pressure needs to be maintained constant to ensure that the coolant does not boil (or boils very little) in the fuel channels: a pressurizer connected to the outlet headers ensures this. • The inventory of coolant needs to be maintained constant to ensure adequate cooling of the fuel. A “feed & bleed” system feeds coolant into (or bleeds coolant from) the primary heat-transport system to maintain the inventory constant (taking into account volume changes with reactor power).

8. Reactor Regulating System • The Reactor Regulating System (RRS) has as task to control the total reactor power to the required value, as well as to control the distribution of power (i.e., the power shape) to the reference shape. • In ALTERNATE mode, the reactor-power setpoint (and the target rate of change) are set by the operator. • In NORMAL mode, the reactor-power setpoint is set automatically, in response to the steam-generator-pressure error, so that the desired electrical output can be generated. • The RRS manipulates reactivity by means of a panoply of reactivity devices: zone-control compartments, adjuster rods, mechanical control absorbers, and boron poison.

9. Table of Main CANDU Plant Software *Note: HTP&I measures also the Pressurizer level!

10. Reactor-Power Maneuvering Rates The following Table shows the maximum allowable reactor-power maneuvering rate in the CANDU 9 (note: FP  Full Power) The overall plant-power maneuvering rate is limited to 5-10% FP/min

11. END