The AHWR Fuel

The initial core will be made up of entirely (Th, Pu-239) MOX fuel assemblies.

• The U233 bred in the 54 pin (Th, Pu-239) MOX fuel pin will be progressively recovered and recycled as (Th, U233) MOX.
• At equilibrium, the core of AHWR will consist of composite fuel assemblies each having 24 nos. of (Th, Pu239) MOX pins and 30 nos. of (Th, U233) MOX pins arranged in three consecutive rings having fissile material compositions as shown hereunder:
  (i) 12 (Th-U233)O2 pins with U233 enrichment of 3.0% in inner most or 1st ring.
  (ii) 18 (Th-U233)O2 pins with U233 enrichment of 3.75% in intermediate or 2nd ring.
  (iii) 24 pins consists of (Th-Pu)O2 pellets with plutonium enrichment of 3.25% in outermost or 3rd ring.
  Fissile isotopes content of plutonium will go down from initial 75% to 25% level at equilibrium discharge burn-up level (which would not be possible to recycle in AHWR but can be recycled to FBR or ADSS with fast neutron spectrum).

To reduce the overall inventory of waste, it is envisaged that Th and U233 will be recycled in AHWR. Even though U234 produced (along with U235 and U236) by neutron capture in U233 has negative influence on reactivity, it might be possible to recycle U233 in AHWR with only a marginal penalty of less than 1000 MWd/Te on discharge burn-up for each recycling.
The initial core characteristics and equilibrium characteristics on AHWR are shown in Table 2 and Table 3 respectively. Plutonium in AHWR burns faster due to large absorption cross section

that leads to loss in reactivity. An option is kept available in AHWR to reconstitute the fuel cluster after an averaged discharge burn-up of 24,000 MWd/Te. In reconstitution, only plutonium pins in outer rings are replaced by fresh fuel. Rest of the fuel cluster remains as it is. It is possible to obtain an additional burn-up of upto 20,000 MWd/Te from the reconstituted cluster. The cluster reconstitution improves U233 production and reduces the reprocessing load due to increase in average cluster burn-up. Reconstitution of fuel cluster involves multiple enrichments for the (Th-Pu)O2 pins, which will affect the fuel fabrication. However, reconstitution improves fuel conversion and hence economics of fuel cycle.
The fuel cycle time of AHWR is 8 years : 4 years for residence in reactor residence and two years for cooling (to allow for >99.9% conversion of Pa-233 to U233), 1 year of reprocessing and 1 year for refabrication. For the initial few years, annual reload would consist of (Th-Pu)O2 clusters only.