NOVELTY - A hydrogen gas generator comprises a cartridge containing casing having outer housing, internal compartment (300) comprising two end caps (310) containing solid material impermeable to gas flow and gas permeable side wall(s) (320) restrictive of liquid and solid material transport, and hydrogen outlet valve in the casing, hydrogen flow path, solid reactant material (302) arranged within the internal compartment comprising hydrogen containing material capable of releasing hydrogen gas when contacted with a liquid reactant, fluid distribution network(s) (304) and fluid injection system.    USE - Hydrogen gas generator is used in fuel cell systems e.g. hydrogen fuel cell reactors, used for generating power (all claimed).    ADVANTAGE - The generator has improved water efficiency, reduced flow velocity and increased temperature within the internal compartment reaction volume which improves the efficiency of the generator. The gas generation in the generator stops very quickly when liquid injection ceases, improving control and safety. The radial construction of the generator minimizes the chance of clogs and restrictions. The side walls provide further containment for byproducts. The fluid distribution networks provide for improved restart capability because the distribution network gradually moves toward unused materials allowing the system to restart more easily because mass transport can be reduced.    DETAILED DESCRIPTION - A hydrogen gas generator comprises a cartridge containing a casing having an outer housing, an internal compartment comprising two end caps containing solid material impermeable to gas flow and gas permeable side wall(s) impermeable to liquid and solid material transport, a hydrogen outlet valve in the casing, a hydrogen flow path from a volume between one of internal compartment side wall(s) and the outer housing to the hydrogen outlet valve, a solid reactant material arranged within the internal compartment, fluid distribution network(s) arranged within the internal compartment to deliver the liquid reactant to the solid reactant material and a fluid injection system to controllably provide the liquid reactant through end cap(s) and into fluid distribution network(s). The solid reactant material contains a hydrogen containing material capable of releasing hydrogen gas when contacted with a liquid reactant. INDEPENDENT CLAIMS are included for the following:    (1) fuel cell system;    (2) generation of hydrogen gas; and    (3) method of generating power.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of gas generating system.    Internal compartment (300)    Solid reactant material (302)    Fluid distribution networks (304)    End caps (310)    Side walls (320)