NOVELTY - Radial flow reactor comprises a shell with first and second ends, a process fluid inlet at the first end for receiving a process fluid, and a process fluid outlet at the second end for discharging a reacted or decontaminated process fluid, and elongate containment units within the shell for containing a particulate catalyst or sorbent. Each containment unit comprises two perforate members defining a space in which the particulate catalyst or sorbent may be placed. The perforate members are mounted between two process fluid-impermeable end members.    USE - The radial flow reactor is useful for converting component of gaseous process fluid; and for water-gas shift reaction, especially sour-shift water gas shift reaction used to increase or decrease hydrogen content of synthesis gases.    ADVANTAGE - The use of the containment units offers the potential for an improved packing density of the catalyst or sorbent versus a conventional radial bed. Improved packing leads to improved performance. By providing containment units, the reactor also has the advantage that the containment units may be pre-filled and so installed already filled into the reactor, which speeds up installation and offers improvement in consistency of catalyst packing. Pre-filling also permits the catalyst or sorbent to be subjected more readily to any pre-treatment such as a reduction treatment or sulfidation. The containment units are preferably detachably mounted on the header assembly, e.g. by a flange assembly, to allow removal of the containment units individually from the header for repair, replacement or replenishment.    DETAILED DESCRIPTION - Radial flow reactor comprises a shell with first and second ends, a process fluid inlet at the first end for receiving a process fluid, and a process fluid outlet at the second end for discharging a reacted or decontaminated process fluid, and elongate containment units within the shell for containing a particulate catalyst or sorbent. Each containment unit comprises two perforate members defining a space in which the particulate catalyst or sorbent may be placed. The perforate members are mounted between two process fluid-impermeable end members, where one end member extends across the containment unit to provide a closed end and the other end member closes the space thus providing an open end through which a process fluid may enter or exit the containment unit, and a header assembly is connected to the open ends of the containment units and either the process fluid inlet or the process fluid outlet. An INDEPENDENT CLAIM is included for a process of using the reactor which involves: (i) passing a process fluid to a process fluid inlet of a reactor, the reactor comprises a cylindrical shell with first and second ends, the process fluid inlet at the first end and a process fluid outlet at the second end; (ii) passing the process fluid from the process fluid inlet to elongate containment units within the shell, each containment unit comprising two perforate members defining a space in which a particulate catalyst or sorbent is placed, the perforate members mounted between two process fluid-impermeable end members, where one end member extends across the containment unit to provide a closed end and the other end member closes the space thus providing an open end, and a header assembly connected to the open ends of the containment units and either the process fluid inlet or the process fluid outlet; (iii) passing the process fluid radially through the catalyst or sorbent contained within the containment units to form a reacted or decontaminated process fluid; (iv) passing the reacted or decontaminated process fluid from the containment units to the process fluid outlet; and (v) recovering the reacted or decontaminated process fluid from the process fluid outlet.