Abstract: Hydrogen ignitor and housing structure having high-strength and lightweight characteristics for surface mounting within a nuclear reactor containment vessel are disclosed. A unitary main body is formed from stainless steel sheet metal free of internal or external structural bracing to provide an open-ended enclosure for placement and interconnection of electrical transformer equipment for the hydrogen ignitor. The open end of the main body enclosure is hermetically sealed with a unitary stainless steel sheet metal cover plate which interlocks with the main body sidewall so that forces, due e.g. to changes of pressure, tending to distort the configuration of the sidewall or cover plate, are absorbed by both through such interlocking. Hermetic sealing of the enclosure is maintained while providing limited access for external placement of an ignitor glow probe and for line voltage power supply internally of the enclosure.