EP4P03

Section 1: TRUE/FALSE questions

1. The direction of flow of coolant in the PHT Main Circuit is from the ROH to the Steam Generator where it mixes with the light water of the feedwater system. / T / F
2.There must be at all times a continuous flow of heavy water coolant around the Heat Transport Main Circuit so as to provide cooling of the fuel. / T / F
3.Under normal operating conditions the reactor outlet header pressure setpoint for the CANDU 9 heat transport pressure control system is varied as a function of reactor power to minimize the impact of shrink and swell on the inventory of coolant in the main circuit. / T / F
4.The direction of flow of coolant in the PHT Main Circuit is from the Steam Generators to the inlet of the circulating pumps, and after the pumps to the Reactor Inlet Header. / T / F
5.There is a pressure drop as the PHT coolant flows across the steam generator and the pressure tubes of approximately 1.8 MPa due to fluid friction, that is compensated for by the main circuit circulating pumps. / T / F
6.The Pressurizer pressure setpoint is kept constant at 10 MPa for a CANDU 9 unit operating in the “at-power” range, and is used to control the pressure of the PHT Main Circuit. / T / F
7.In “Solid Mode” of Heat Transport Inventory Control deviations from the Storage Tank Level Setpoint determine the amount of feed and bleed flows. / T / F
8.Under normal operating conditions there is a free flow of heavy water between the Pressurizer and the Main Circuit that equalizes any pressure differences between the Main Circuit and the Pressurizer. / T / F
9.The term “Solid Mode” is used for a feed and bleed pressure control system that relies on the tensile strength of the vessels and piping of the main circuit, and on the very small compressibility of water. / T / F
10.All CANDU nuclear steam supply systems use a Pressurizer to control the pressure of the Main Heat Transport Circuit. / T / F

Section 2: Multiple-Choice Questions

1.Which of the following statements is the correct one?

  1. The Shutdown Cooling System is used to cool the heat transport heavy water to ambient temperatures via the steam generators.
  2. The Shutdown Cooling System is normally hot and pressurized so as to be ready to be brought into service as soon as there is a loss of Class IV power.
  3. With the Shutdown Cooling System isolation valves open, the Shutdown Cooling Pumps ON and the Main Circuit pumps OFF, the flow of heavy water is from the Reactor Outlet Headers through the Shutdown Cooling Pumps and Heat Exchangers, to the Reactor Inlet Headers
  4. With the Shutdown Cooling System isolation valves open, the Shutdown Cooling Pumps OFF and the Main Circuit pumps turned ON, the flow of heavy water is from the Reactor Outlet Headers through the Shutdown Cooling Pumps and Heat Exchangers, to the Reactor Inlet Headers.

2.Which of the following statements is the correct one?

  1. The PHT Main Circuit is designed to provide cooling of the reactor fuel under all operating conditions by transferring the heat from the fuel to the light water in the Steam Generators.
  2. Each heat transport pump has sufficient rotational inertia so that the rate of coolant flow reduction matches the rate of power reduction following a reactor trip if power to the pump motorsis lost.
  3. The assignment of pressure tubes to either of the two loops is random to ensure maximum redundancy and to allow flexibility in making the connections between pressure tubes and feeder pipes.
  4. In case of a loss of power to the PHT Main Circuit circulating pumps,such as when there is a total loss of Class IV power in the unit, bringing the Shutdown Cooling system into service as soon as Class III power is available, is the only method by whichthe removal of decay heat can be assured.

3.Which of the following statements is the correct one?

  1. The Pressurizer’s liquid and steam are kept at saturation, and at a pressure that keeps the reactor outlet header at its setpoint (10 MPa for CANDU-9 operating in the “at-power” range).
  2. Under normal “at-power” operating conditions the pressure in the Pressurizer is controlled to the Pressurizer Pressure Setpoint.
  3. The only means of reducing the pressure in the Pressurizer is by opening the Steam Bleed Valve(s) to allow flow from the Pressurizer to the Bleed Condenser.
  4. Under normal “at-power” operating conditions the pressure in the Pressurizer is controlled by changes in the bleed and feed flows.

4.Which of the following statements is the correct one?

  1. The Pressurizer Level Control System in “Normal mode” of pressure control is designed to keep the inventory of heavy water in the Pressurizer constant.
  2. A Pressurizer level above the setpoint is an indication of excess heavy water inventory in the Main Loop, so some bleed is taken into the Main Circuit from the D2O Storage Tank.
  3. The level setpoint in the Pressurizer is a function of reactor power so as to assist in accommodating the shrink and swell of the PHT coolant inventory resulting from changes in reactor power.
  4. In “Solid mode” of PHT Pressure and Inventory control Pressurizer Level is controlled via the main circuit feed and bleed valves.

5.Which of the following statements is the correct one?

  1. The Bleed Condenser at normal operating conditions contains heavy water and steam at saturation conditionsat the same pressure as the Pressurizer.
  2. The principal purpose of the Bleed Condenser is to reduce the pressure and temperature of the heavy water coolant from the Main Circuit and of the heavy water steam from the Pressurizer.
  3. Bleed Condenser pressure is controlled independently of the level in the Bleed Condenser by varying the amount of cool heavy water flowing in the reflux tube bundle and by spraying cool heavy water into the vapour space.
  4. The Over-pressure relief valve of the Bleed Condenser is used to release non-condensable gases, mostly nitrogen, that can accumulated in the Heat Transport coolant.

Section 3. With reference to the diagram below, explain the two main methods of cooling the fuel under Shutdown conditions, that is,when heat rejection via the Steam Generators is not available. Indicate the direction of D2O flow between the reactor headers via the Shutdown Cooling System.

What particular precaution must be exercised before placing he shutdown cooling pumps into service?