Rx Start-Up Knowledge Flashcards
Why do we perform an ICRR Plot?
- Backup to calculated ECP to ensure reactor is not brought critical with the control rods below the 0 power rod insertion limit.
- To provide the operator with another mechanism for evaluating / predicting the point at which criticality can be expected.
What can effect the ECP?
- Changes in RCS Boron Concentration
- Changes in RCS T-avg
- Delay in Startup Xenon Effects
- Delay in Startup ECP validity
If Xenon is present, and a large delay occurs, what must be done?
A new calc must be made
What does it mean when there is a doubling of counts?
The distance from the initial Keff to Keff = 1 is halved
What is the definition of SDM?
The amount of reactivity by which the reactor is sub critical
A doubling also means….
You added half the reactivity necessary to achieve criticality to the core.
How many doubling are expected before reaching criticality?
5-7 doubling
What is subcritical multiplication?
The effect caused by the combination of a neutron source and a SUBCRITICAL reactor that produces a steady state neutron population greater than the population of source neutrons alone.
How long is the average neutron generation time?
About 0.1 seconds
As Keff gets closer to 1, the number of generations….
Increase significantly
When can criticality be expected?
** At any time
Approx 5-7 doublings
How can you determine if the reactor is critical?
Reactor is actually slightly super critical.
Indicated by a + SUR and a steadily increasing count rate with no rod movement.
Why do we choose 10E-8 amps to collect critical data?
- Well above SR, so source neutron effects are negligible
2. Below POAH. Doppler and Moderator Temperature effects are not present.
What is the POAH?
Point where thermal output of the core exactly equals system losses.
What are the primary and secondary indications that the POAH has been reached?
- Lowering SUR
- T-avg Rising
- PZR Pressure and Level Rising
- SG Pressure and Level Rising
- Raise in steam dump demand
