Journal of Sol-Gel Science and Technology

, Volume 9, Issue 3, pp 285-294

First online:

Sol-gel microsphere pelletisation process for fabrication of (U,Pu)O2, (U,Pu)C and (U,Pu)N Fuel pellets for the prototype fast breeder reactor in india

  • C. GangulyAffiliated withRadiometallurgy Division, Bhabha Atomic Research Centre
  • , P. V. HegdeAffiliated withRadiometallurgy Division, Bhabha Atomic Research Centre

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A “dust-free” sol-gel microsphere pelletisation (SGMP) process has been developed for fabrication of (U,Pu)O2, (U,Pu)C and (U,Pu)N fuel pellets containing around 15% plutonium for the forthcoming prototype fast breeder reactor (PFBR) in India. The objective was to produce homogeneous sintered pellets of ∼85% T.D. with a predominantly open-pore structure. Hydrated gel-microspheres of UO3+PuO2 and UO3+PuO2+C have been prepared from nitrate solutions of uranium and plutonium by the “ammonia internal gelation” process, using hexamethylene tetramine (HMTA) as an ammonia generator and silicone oil at 90±1°C as gelation bath. For oxide fuel pellets, the hydrated UO3+PuO2 gel-microspheres were calcined at around 700°C in Ar+8% H2 atmosphere to produce “non-porous”, “free-flowing” and coarse (around 400 micron) microspheres which could be directly pelletised at 550 MPa to green pellets. The mixed oxide pellets were subjected either to low temperature (∼1100°C) oxidative sintering (LTS) in N2+air containing ∼1500 ppm O2 or to high temperature (1650°C) sintering, (HTS) in Ar+8% H2. For monocarbide and mononitride pellets, hydrated gel-microspheres of UO3+PuO2+C were subjected to carbothermic synthesis in vacuum (∼1 Pa) and flowing nitrogen (flow rate: 1.2 m3/h) in the temperature range of 1450–1550°C respectively. The monocarbide and mononitride microspheres thus produced were relatively hard and required higher compaction pressure (∼1200 MPa) for making reen pellets which could be sintered to 85% T.D. in Ar+8% H2 at 1700°C. The sintered oxide, monocarbide and mononitride pellets had a “blackberry” “open” pore microstructure with fine grain size. The microspheres retained their individual identity in the sintered pellets because during sintering densification took place mainly within and not between the microspheres.


fast reactor fuel mixed uranium plutonium oxide monocarbide and mononitride sol-gel microsphere pelletisation internal gelation cold-pelletisation open-pore microstructure