Abstract: In a nuclear reactor, a drainage channel for the safety injection and spray circuits of the reactor is arranged in the bottom of the annular gap between two substantially vertical walls surrounding the pressure vessel of the reactor, the drainage channel comprising filter panels disposed vertically along each side of a central horizontal solid lower panel at the bottom of the annular gap and between two lateral horizontal solid upper panels so as to bound a central channel having vertical lateral filter walls communicating with two lateral chambers which communicate by substantially horizontal passages with a central collecting chamber disposed below the central lower panel and having an outlet for connection to the main intake of the safety circuit.