Nuclear reactor core having outer portion coolant passages of larger diameter than inner portion coolant passages

A nuclear reactor core, comprising:

• a plurality of fuel elements;
• and
• one or more moderator blocks to form a nuclear reactor core inner portion and a nuclear reactor core outer portion, wherein:
• the nuclear reactor core inner portion includes an inner moderator matrix formed of a plurality of inner holes that include:
• a plurality of inner fuel openings with one or more of the fuel elements disposed therein, and
• a plurality of inner coolant passages to flow a coolant;
• the nuclear reactor core outer portion includes an outer moderator matrix formed of a plurality of outer holes that include:
• a plurality of outer fuel openings with one or more of the fuel elements disposed therein, and
• a plurality of outer coolant passages to flow the coolant;
• each of the inner coolant passages has an inner coolant passage diameter;
• each of the outer coolant passages has an outer coolant passage diameter;
• the outer coolant passage diameter exceeds the inner coolant passage diameter;
• and
• each of the inner coolant passages are located closer to a nuclear reactor core radial center than each of the outer coolant passages.