The reactor is divided into 24 groups of rods, each containing 9 control rods. You can control each group independently. Once you start pulling rods on the main panel, you will notice that different groups heat up at different rates. This is mainly because they contain slightly different amounts of fuel. Also, you should notice some more patterns:
- core groups will heat quicker - this is due to the fact that they take neutrons from neighboring groups
- outside groups will heat slower - this is due they loose neutrons to the outside of the reactor (although some are reflected by neutron reflector)
- circulations flow will increase reactivity mostly in the part of the reactor where they force the circulation (flow 1 in the upper part of the diagram and flow 2 on the lower part)
- warmer groups will heat their neighbors while colder ones will cool them
You should try to balance these differences so that all groups operate at similar power levels. You can select any group or a set of groups and use the lever and speed switch in the same way as on the main panel. Furthermore, you can do this even while already moving rods on the main panel simultaneously. You can also choose from common predefined patterns.
The indicator screen will display the percentage of rods pulled in a given group and the percentage of the maximum group power. Starting from version 1.4, vertical power output is also simulated. You can select a single rod on the diagram and a level on the vertical display on the left side. This will provide you with a vertical diagram for the selected rod and a horizontal slice at the specified level. Colors represent relative power output compared to the selected rod/slice, and percentages indicate absolute power relative to the maximum reactor power output. Some parts can heat up to even 200% of power, which is normal as the core cannot be perfectly balanced, and there will always be some imbalance between certain parts of the core.