Colloquially named for the Soviet five-kopeck coin, the pyatachok (П'ятачок) was the operational surface of Chornobyl’s RBMK-1000 unit 4 reactor. Its 1,872 interlocking steel blocks each capped a pressure tube or control rod channel, shielding radiation and bearing the machinery above while the reactor ran beneath. Plant engineers described how, in the seconds before the April 1986 explosion, the 80kg blocks appeared to ‘dance’ from the immense rising steam pressure. Viewed in person, the disordered and partially dismantled reactor plate of unit 2 suggests a scaled city plan or a geological formation; the decay of an ordered system observed at the moment of its own undoing.