| CPC G21C 7/26 (2013.01) [G21C 7/06 (2013.01); G21C 9/033 (2013.01)] | 12 Claims |

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1. A reactor control system for a nuclear reactor, the reactor control system comprising:
one or more hollow tubes comprising a neutron absorbing material, each of the one or more hollow tubes having a first end and a second end;
a pump connected to the first end of each of the one or more hollow tubes and operable to control an amount of a first fluid within that hollow tube, the first fluid comprising a neutron moderator,
wherein:
the reactor control system is configured to control the pump based on a level of reactivity in the nuclear reactor, and
the second end of each of the one or more hollow tubes is in fluid communication with a second fluid, the second fluid having a neutron moderating capacity lower than 10% of that of the first fluid.
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