Microreactor with control neutron absorber assembly including a control neutron absorber rod

A microreactor configured to produce nuclear energy, comprising:

• a reactor core including a fuel region;
• a top flange that defines a top head of an upper core barrel and includes one or more instrumentation penetrations;
• and
• a Control Neutron Absorber (CNA) assembly including:
• an inner housing extending from the top flange and through the fuel region, the inner housing configured to receive a CNA rod;
• an outer housing extending from the top flange coaxially with the inner housing and positioned radially outward and offset from the inner housing, the inner housing, the outer housing, and the top flange defining a cavity therebetween;
• the CNA rod including a neutron absorbing rod including a first neutron absorbing material, the neutron absorbing rod being positioned within the inner housing and configured to move axially relative to the inner housing;
• and
• a burnable absorber including a second neutron absorbing material, the burnable absorber exhibiting a neutron absorbing strength that is less than that of the neutron absorbing rod, the burnable absorber positioned within the inner housing and configured to receive the neutron absorbing rod therein, and a combined neutron absorption of the neutron absorbing rod and the burnable absorber is sufficient to shut down a nuclear reaction in the reactor core.