The ZEEP (Zero Energy Experimental Pile) reactor was the first reactor outside of the USA to go critical. This event occurred at Chalk River on 05 September 1945. The reactor vessel was surrounded by various-sized blocks of reactor-grade graphite which acted as a neutron reflector. Three of the blocks have been donated as artifacts to the Society. They have a square cross-section 19 cm on a side (nominal 7.5”) and are 76 cm (nominal 30”) long. Nuclear graphite is defined as having a “density of at least 1.5 g/cubic centimeter” hence the blocks weigh approximately 41 kg.
