RBMK Simulator Startup Manual

This is a step-by-step startup guide for the RBMK Simulator on how to bring it up to full power. Note that this is work in progress, you might want to come back to this manual and check for updates.

The simulation starts in a full shutdown state after some maintenance was done. The reactor is cooled by natural circulation and the decay heat is removed by the Blowdown/Cooldown system.

You will notice that there are a lot of alarms active and the rector is locked by the reactor protection system (RPS).

Preparations

As deaerators and steam drums are both on low fill levels, we need to fill those systems with fresh water and ensure they have the correct levels. This also helps to get to know the systems and how they are operated.

You will now control multiple systems that are controlled with Control Widgets and the result can be see on Mnemonic Displays or some diagrams. Take your time to explore those before doing each step. You can use the “Hotwell/DA/Drum Level” preset in the Control Window or arrange everything as you need it.

• Bring one makeup pump online (see Simulator Usage on how pump assemblies are operated). Those pumps pump fresh feedwater from the cold condensate storage into the hotwell. You can then manually open the hotwell fill valve and observe how the hotwell level will start to rise. Switch the fill valve to Auto mode. Make sure the hotwell level does not fall below 5 cm as this will trigger a safety shutoff of the pumps connected to the hotwell.
• You need to fill the deaerators (DA) by using the condensate path from hotwell to the DAs. Bring one condensate pump online, open the bypass of the main ejectors and bring one booster pump online. You now have pressure on the DA flow valves. You can open them manually and fill the DAs with those. Take your time, fill one DA first and observe the hotwell and its fill valve. Fill both DAs to 100 cm (this is also set as setpoint). You will note that the hotwell gets refilled with the automatic regulation by the fill valve. Make sure not to drain the hotwell. Do not switch the DA flow valves to auto as this will fully open them and the hotwell fill valves might not supply enough water to the hotwell, effectively draining them.
• After filling both DAs to about 100 cm, switch both DA flow valves to Auto mode. They will now, together with the hotwell fill valve, provide sufficient levels in the DAs.

Congratulations, you gained your first experience in power plant operations. Such procedures are common as the automatic modes might only cover the full load operation and situations such as startup might require manual overrides from time to time.

In the same way we filled the hotwell and the DAs, we will now fill up both steam drums. Note that there is already hot water circulating in the reactor so you can observe some temperature changes during filling.

• Bring one feed pump per side online. This will revoke the feed pressure alarms.
• There are 3 valves in series for startup: A reducing valve, a shutoff valve and a regulation valve. Those valves are on the lower left of the feedwater control widget. Fully open the startup reducing valves and open the startup shutoff valves. Note that the shutoff valves might be blocked if there is no pressure on them so the order in which you do things here are important. Carefully open the startup regulation valve manually on one steam drum and observe how the steam drum starts to fill up. Open the other valve too and observe how the hotwell fill valve automatically fills the hotwell and the DAs get refilled by the DA flow valves.
• You can switch on the Blowdown level Balance now, this uses the blowdown return valves to keep the level values equally in both drums.
• When a level of 0.0 is reached, close the startup regulation valves, do not put them on auto mode (there will be level fluctuations when turning on the MCPs later which we do not want the automatic regulator to compensate).

To allow the reactor to be operated, the reactor protection system needs to be reset. This is possible with pressure on feedwater pumps as well as pressure on condensate system pumps and a sufficient flow through the reactor. We still need flow through the reactor.

Make yourself familiar with the Blowdown/Cooldown system. To prevent high flow through the cooldown system when the MCP is turned on, we will shut off the blowdown pump and use the bypass for passive flow through the aftercooler.

The MCPs get their water from the bottom of the steam drum with the cold feedwater mixed into the steam drum outlet. During operation, the water mixture is cooled down and cavitation is avoided that way. You can see a cooldown value in Kelvin on the MCP control panel, this refers to the boiling point of water on given pressure. As we can not add cold water when no steam leaves the steam drum, we now have to trim the MCP flow by closing the trim valves to about 40 %. This reduces flow and prevents cavitation. You can do this on all pumps before starting them.

• Open all suction valves on all MCPs
• Set trim valve positions to 40 %

After preparing the trim valves, prepare the blowdown system for switching on the MCP.

• Disable Pump 2 of the blowdown system
• Open “Passive Flow” valve
• Open “Pumps to regenerator” valve
• Reduce coolant flow to about 400 kg/s (Aftercooler coolant valve)

Note how the temperature in both steam drums immediately starts to rise as soon as there is no flow through the blowdown/cooldown system in this constellation.

Switch on one MCP per side and close the reactor bypass afterwards. You might want to watch the levels in the steam drums as with only one pump on one side and no pump on the other side, the water will be taken from only one side but returned to both sides. After one MCP per side is running, switch on a total of 3 MCP per side. The blowdown balance control will compensate the level imbalances. 3 Pumps with 40 % trim will still throw a LOW1 flow warning, which is acceptable during startup.

As soon as both steam drum levels are balanced, turn off the blowdown balance control and put both startup feedwater valves to auto mode. After turning off the blowdown balance control, the valves must be set to the same position on both sides (just fully open them both).

You should now have a condition with stable temperatures around 40 °C in both steam drums.

Heatup and first steam generation

Before heating up the system we need to make sure the heat can be properly removed. So far, the coolant through the aftercooler (and the aux condenser) is provided by the coolant aux pump. Start one main coolant pump to ensure circulation of cold water from the cooling pond through the condenser.

• Bring 1 main coolant pump online
• Open “Main to Auxiliary” valve to also provide water to aftercooler and aux condensers with the main coolant pumps. Note how flow suddenly drops in aftercooler.
• Switch off the Aux coolant pump.
• Adjust aftercooler valve (the pressure is now lower).

To allow smooth and controlled heatup, a portion of the steam will be removed steadily and the pressure will be controlled with the “Auxiliary Condensation” system. A small portion of steam can be used to heat up the deaerators, this ensures steam flow through pipes and also warms them up.

• Open Steam Supply from Main Steam to DA on both sides to about 10 %
• Manually open the DA steam valves (labeled “DA Press”) to 20 %

The pressure setpoint is defined as a function of thermal power of the reactor during startup. This can be viewed with a X/Y diagram. The auxiliary condensation will try to keep the pressure setpoint for each drum. Prepare the aux condensation system as follows:

• Open coolant valves to 30 %. Note how coolant flow through the aftercooler drops as they use the same coolant source.
• Set the aux condenser level setpoint to about 65 cm (someone seems to have forgotten this).
• Open the hotwell valve
• Turn on one condensate pump
• Switch both aux condenser level control valves to automatic (they will now drain a portion of the condensate in the aux condensers)
• Switch on automatic regulation on both Steam valves (switches on the left to the steam valve buttons)

The auxiliary condensation system is now ready to use.

Heatup

Heat from the core is at this moment still removed by using the blowdown system. To start heating up the core with its decay heat, we put the blowdown system in operation with the regenerator in place, this will reduce the removed heat amount.

• Open “Regenerator to Cooler” valve
• Close “Pumps to regenerator” and “Pumps to cooler” valves
• Open “Regenerator to drums”
• Close “Treatment bypass”
• Close Aftercooler coolant valve to about 30 % as we have less flow now to cool down

The temperature in the core and the steam drums will now slowly start to rise and hit the boiling temperature eventually. Small amounts of steam will flow to the deaerator and heat up the system. You can either wait for a long time for the system to reach the pressure setpoint of 5.0 bar or start with the reactor immediately. As soon as 5.0 bar is reached, the auxiliary condensers will use their steam valves to keep that pressure. Note that the steam drum level is rising due to the expansion of the water.

If you notice deviations in levels before the evaporation removes some of the water, try to enable the blowdown balance control again to keep those levels balanced. A high deviation of pressure will force the water from one side to the other side. Avoid having both the feedwater and the balance control controlling the levels at the same time.

The aux condensation can handle the steam on this level. The drums will cool down if cold feedwater is added, so be patient. The pressure is too low to properly operate the startup ejectors to generate vacuum in the condenser so the turbine bypass can not be used.

Reactor Startup

Head over to the reactor controls and push the reset button on the RPS. The red light must disappear.

The reactor control has a neutron setpoint which controls the neutron flux between 0 and 100 %. There is also a display for reactivity and a neutron flux log gauge which shows the neutron flux on very low neutron amounts.

We will try to get the reactor critical and use the automatic rods to control the reactivity. You could also use some manual rods if you like but we try to remove a certain amount of rods so the auto rods stay in their middle position to be able to control in both directions. Note that the reactor will scram itself if the auto rods are unable to get the reactivity below 0.0.

• Select all auto rods and remove them by about 1/3
• Select one manual rod on the outside and fully remove it. Watch the reactivity display.
• Remove more rods until you get to a positive reactivity reading or near zero. Initially this should be about 5 rods.
• Select the auto rods and pull them up until you have a reactivity reading of about +0.00100. Watch the core activity display showing activity.
• The neutron population will start to grow now, this can be seen on the flux log gauge which shows readings below 1 %. Be careful with with the neutron rate. Reduce reactivity by moving the auto rods as soon as the little red light on the neutron rate meter flashes up.

You can try to reach a neutron flux of 2 % and switch to automatic mode to hold that flux. To switch to auto mode after reaching a certain neutron flux:

• Enable Global Control
• Select automatic rods which should be used by the control (you can just select them all).
• Push the “Auto” button.

After those steps, global control is now active and keeps the current neutron setpoint. Set your desired target setpoint in % and enable “Transient” and “Target” switches. This makes the global control ramp to the selected target.

Bring the reactor to 150 MWth which is a neutron setpoint of 4.8 %N. The auxiliary condensers will be able to handle that amount of steam to condensate. The increase of power will automatically raise the pressure setpoint.

Vacuum

We need to use the main condenser for further steam condensing, which is full of air at the moment. We will evacuate it by using the startup ejectors. Once you reach the pressure setpoint of 15 bars

• Open both startup ejector valves to 100 %. Watch the condenser vacuum gauge.
• As soon as condenser is evacuated, switch the turbine bypass valves to automatic mode.
• You will notice that nothing happens as we still have the auxiliary condensers regulating the pressure and condensing all the steam.
• Close the auxiliary condenser steam valves. Note how the turbine bypass valves are opening and holding the pressure now.

Turbine Warmup

The Turbine has 4 predefined hold points on which the warming up can be done. It is recommended to not operate the turbine on different speeds for a long period of time as vibrations outside those hold points will occur. There is a recommendation for steam parameters for each hold points. With the steam pressure setpoint from reactor thermal power output in use, each steam parameter can be achieved with a certain power level of the reactor.

At this point, we should already have our steam parameters near the first hold point.

Speed (1/min)	Pressure	Reactor Power	Neutron Setpoint
750 1/min	15 bar	140 MWth	4.7 %N
1500 1/min	27 bar	206 MWth	7.0 %N
2250 1/min	38 bar	263 MWth	8.8 %N
3000 1/min	50 bar	326 MWth	10.9 %N

Note that the pressure setpoint is generated from actual reactor thermal power output, not from neutron setpoint. It is not necessary to exactly have the given values, they are only a recommendation.

• Reset the turbine protection system.
• Open all 4 fast closing valves.
• Select 750 1/min target speed
• Switch both startup valves to Auto mode

The turbine will now start to spin up.

[To be continued] – increase power, set next hold point and so on and sync. Reheater will be used when sync is done. watch alarms

use 2 main ejectors at 15 % load

enable feedwater preheater at 20-30 % load, start with first, should work on full auto