Chemical Module - Xenon generation and disintegration.

 Chemical Module - Xenon generation and disintegration

Patch notes: V 0.2.15.131

The following advances have been made in the implementation of Xenon generation and desintegration:

Xenon-135 (Xe-135) is always present during nuclear reactor operation. It is produced by uranium fission and has a half-life of 9.14 hours (9 hours in the game).

Effects of Xenon-135:

  • Absorbs neutrons: Reduces reactor reactivity, acting as a neutron poison.
  • Transient effect: Its concentration increases after a change in reactor power, which can cause a temporary power decrease (capped at 5 minutes in the game).
  • Xenon poisoning: If the reactor is shut down for an extended period, the Xe-135 concentration can increase considerably, making it difficult to restart the reactor (not yet implemented in the game).

Stabilization:

After 9 hours, the Xe-135 concentration reaches an equilibrium with its production and decay rate. At this point, the reactor power stabilizes.

Practical Example:

Initial situation:
  • The reactor operates at 10 MW power.
  • Control rods are partially inserted to maintain critical reactivity.
Objective: Increase power to 12 MW.

Action:
  • Increase the speed of the primary pumps to extract more heat from the reactor.
  • Partially withdraw the control rods to increase reactivity.
Secondary effect:
  • The increase in reactivity temporarily accelerates the consumption rate of Xenon-135 (Xe-135), a fission product that absorbs neutrons and reduces reactivity.
  • This causes a temporary power spike that exceeds the 12 MW target.
Power spike control:
  • Anticipation: In anticipation of the power spike, boric acid is injected into the reactor core. Function of boron: Boron also absorbs neutrons, temporarily compensating for the decrease in Xe-135 and counteracting the power spike.
  • Stabilization:
Once the Xe-135 concentration stabilizes at the new power level (12 MW), the boron is removed from the core. The control rods are readjusted to resume control of reactivity.

Analogy:
Imagine driving a car and you want to accelerate. Pressing the accelerator increases speed, but can also cause oversteer if not done carefully. To avoid oversteer, you can slightly turn the steering wheel in the opposite direction of the car's turn. This allows you to anticipate oversteer and counteract it in a controlled manner.

In the case of the nuclear reactor, boron acts as the steering wheel, counteracting the power spike that occurs when Xe-135 is burned.

There are two main strategies for handling xenon poisoning:

1. Boron operation:
  • The reactor is started without boron and allowed to reach xenon equilibrium (approximately 9 hours).
  • During this time, reactor power may decrease due to xenon poisoning.
  • After reaching equilibrium, boron is added to the core to absorb neutrons and compensate for the xenon effect.
  • The amount of boron added is adjusted to maintain the desired reactor power.
  • This strategy is more complex and requires precise boron control.

2. Boron-free operation:
  • The reactor is started with an initial boron concentration sufficient to compensate for the xenon effect during the first 9 hours.
  • This way, the power drop during the xenon poisoning period is avoided.
  • The operator gradually reduces the boron concentration as the xenon decays and reaches equilibrium to maintain critical reactivity.
  • This strategy is simpler, but requires a larger amount of boron at startup.

Does adding boron to the reactor reduce the xenon concentration?

No, adding boron to the reactor does not directly reduce the xenon (Xe-135) concentration. Boron acts as a neutron absorber, meaning it captures free neutrons in the reactor core.

Effects of boron on xenon:
  • Reactivity decrease: By absorbing neutrons, boron reduces reactor reactivity, meaning there are fewer neutrons available to initiate fission reactions.
  • Xe-135 production reduction: Fission is the main source of Xe-135 production in the reactor. By reducing fission, Xe-135 production is reduced.
  • Indirect effect on concentration: The reduction in Xe-135 production does not have an immediate effect on the Xe-135 concentration already present in the core.