CANFLEX develops fuel cycle options for CANDU31 March 1999
The Canadian heavy water reactors operate at lower enrichment levels than PWRs. Atomic Energy of Canada Ltd sees many possibilities in integrating the processes of the two main Western power reactor designs.
The most significant event in recent Canadian research and development has been the loading of 16 CANFLEX fuel bundles into the New Brunswick Power’s Point Lepreau CANDU reactor. The bundles were loaded into two of the 380 channels that make up the Point Lepreau core and according to Atomic Energy of Canada’s Ian Hastings they have performed well so far.
“The first 4 high powered bundles were discharged on 26 March, an important milestone for the programme,” he said.
The CANFLEX bundles were manufactured by Zircatec Precision Industries in Ontario. They have been developed over a 12 year design phase. Initially an AECL project, in 1991 the Korean Atomic Research Institute (KAERI) became involved.
The aim of the demonstration irradiation at Point Lepreau is to establish the irradiation performance of the bundles in a power reactor, as well as the production processes of fuel fabrication for the new design. The CANFLEX bundle is designed to improve critical channel powers (CCP), which can offset the drop in performance in ageing reactors as a result of pressure tube creep and boiler tube fouling.
The CANFLEX bundles contain 43 elements, compared with 37 in the current CANDU fuel bundles. However the bundles are designed to be fully compatible with the CANDU-6 fuel handling system, and with similar pressure drop and xenon transient levels, it is possible for operators to introduce CANFLEX bundles during normal on-power refuelling.
CANFLEX bundles offer improved performance through enhanced thermohydraulic performance and flatter radial power distribution, leading to a 6-8% improvement in CCP when compared with standard 37 element fuel.
CANFLEX bundles are also part of AECL’s strategy to address the problems currently inherent within the fuel cycle and it intends to use both slightly enriched uranium (SEU) and recycled uranium (RU) in the bundles. AECL anticipates introducing SEU of between 0.9% and 1.2% into the CANFLEX bundles, below the point at which restrictions and complications due to criticality issues come into play. Enrichment at this level should reduce fuel cycle costs by about 25% compared to natural uranium fuel in CANDUs. It should also lead to 30% savings in spent fuel disposal costs.
In the medium term it may be possible to use RU from spent LWR fuel, offering the possibility of a highly economic supply of SEU. A detailed assessment of the use of RU in CANFLEX bundles is currently being carried out by AECL, British Nuclear Fuels and KAERI. AECL anticipates this option becoming available in 2004-5.
The possibility of using RU in CANDU reactors offers a potential synergism between CANDU and PWR reactors. Spent PWR fuel has a higher fissile concentration than natural uranium CANDU fuel.
According to P Boczar of the Chalk River Laboratories in Ontario, who gave a paper on the subject to IAEA Technical Committee Meeting on Fuel Cycle Options for LWRs and HWRs in April 1998, CANFLEX bundles and CANDU reactors offer potential solutions to some of the difficulties LWR operators have with spent fuel.
“The ability to use low-fissile fuel make possible a unique synergism with LWRs, that offers the potential of fuel recycling having a high degree of proliferation resistance, using simpler and potentially cheaper technologies than conventional reprocessing,” he said.
In his address, Boczar described AECL’s wider vision for addressing fuel cycle problems. As well as burning RU in CANFLEX bundles, he argued that CANDU reactors are also suitable for MOX fuel as the reactors’ higher neutron economy would result in approximately double the energy recovered from plutonium in MOX fuel, when compared with PWRs. CANDUs could also burn actinide wastes.
AECL is also promoting the concept of the Direct Use of Spent PWR Fuel in CANDU, the DUPIC processes, which further exploit CANDU reactors’ ability to use fuel with a low fissile content.
“Such is the neutron economy of the CANDU reactor, that the fissile content of the spent PWR fuel can be used as-is, without enhancement. Indeed even removal of the fission products from spent PWR fuel is not required in order to achieve an appreciable burn-up,” said Boczar. Benefits of the DUPIC cycle over traditional reprocessing include the lack of wet chemistry, simplicity and cost. However considerable technical work is needed to make the DUPIC cycle a practical option. A further major attraction is the high level of proliferation resistance. This would be a result of no purposeful separation of isotopes, dilute plutonium concentration and the high radioactivity of all stages of the process and the DUPIC fuel bundles which would make physical access to the materials extremely difficult.