On December 12, 1952, one of the world's first major reactor accidents occurred in the NRX reactor at AECL's Chalk River Laboratories, when a combination of human and mechanical error led to a temporary loss of control over the reactor's power level. Undercooling of the fuel channels led to a partial meltdown. This caused a hydrogen-oxygen explosion inside the calandria. Several fuel bundles experienced melting and ruptured, rendering much of the core interior unusable. The reactor building was contaminated, as well as an area of the Chalk River site, and millions of gallons of radioactive water accumulated in the reactor basement. This water was pumped to a waste management area of the Laboratories and monitored. Hundreds of military personnel from Canada and the U.S. (including naval officer and later U.S. President, LT James "Jimmy" Carter) were employed in the cleanup and disposal of the reactor debris.[http://www.ccnr.org/paulson_legacy.html]