NOVELTY - The fuel cell system comprises a fuel cell stack, and a fuel processor assembly coupled to the stack for producing a reformate for consumption by the stack. The fuel processor assembly includes an annular reformer, a thermal conduction mass coupled to the annular reformer, and a vaporizer coil coupled to the thermal conduction mass. The annular reformer has a first cylindrical wall portion surrounded by a second cylindrical wall portion to form an annular gap. Each wall portions has a wash-coated catalyst applied to a portion of a respective surface forming the annular gap.    USE - Used as a fuel cell system.    ADVANTAGE - The fuel cell system is lightweight, portable and affordable, and has strong mechanical force and thermal cycling and small temperature gradient.    DETAILED DESCRIPTION - The fuel cell system comprises a fuel cell stack, and a fuel processor assembly coupled to the stack for producing a reformate for consumption by the stack. The fuel processor assembly includes an annular reformer, a thermal conduction mass coupled to the annular reformer, and a vaporizer coil coupled to the thermal conduction mass. The annular reformer has a first cylindrical wall portion surrounded by a second cylindrical wall portion to form an annular gap. Each wall portions has a wash-coated catalyst applied to a portion of a respective surface forming the annular gap. The thermal conduction mass has an annular shape with a portion contacting a portion of the first cylindrical wall portion. The portion of the first cylindrical wall portion contacting the thermal conduction mass is fabricated from a heat conducting material. The thermal conduction mass is cast onto the vaporizer coil. The fuel cell system further comprises a combustion heater adjacent to the thermal conduction mass for burning a portion of the reformate to provide heat to the thermal conduction mass during normal operation, a heating element coupled to the thermal conduction mass for providing heat to the thermal conduction mass during a cold start, a feedback tube (134) mounted within the central passages for providing the portion of the reformate to the combustion heater and directing flow of the combustion gases, a hydrogen purification membrane coupled to an output of the reformer, a heater located within the central passage for heating the thermal conduction mass such that exhaust gases from the heater pass through the central passage to heat the thermal conduction mass, a housing (120) surrounding the annular reformer, thermal conduction mass and vaporizer to form a hot zone, an exhaust passage around the annular reformer and vaporizer, and an annular hydrogen purification membrane module (130) coupled to the annular reformer and having the thermal conduction mass partially nested in the module. Combustion gases from the combustion heater circulate through the thermal conduction mass to heat the thermal conduction mass. The thermal conduction mass has a central passage aligned with a central passage of the annular reformer. The combustion gases pass through the central passages. The thermal conduction mass is 20% nested within the annular reformer. The annular reformer includes a unit for improving catalytic reactions. The catalytic reaction improving unit is inserts, metal foam, a stack of annular metal screens, a roll of metal screens, a roll of perforated metal, a roll of perforated corrugated metal foil, catalytic granules and/or bulk material to form a catalytic bed. The thermal conduction mass and vaporizer are annular. The thermal conduction mass is nested within the annular reformer and vaporizer. The thermal conduction mass forms a central passage. The exhaust gases are counterflow through the exhaust passage with respect to the central passage, and transfer heat to the annular reformer and vaporizer. An INDEPENDENT CLAIM is included for an elongated fuel processor assembly.    DESCRIPTION OF DRAWING(S) - The diagram shows a perspective view of a reforming reactor assembly.    Reforming reactor (102)    Electric heaters (110)    Inlet header (114)    Housing (120)    Hydrogen-purification membrane module (130)    Feedback tube. (134)