Once-through thorium cycle

Milgram, M.S. 1982. Once Through Thorium Cycles in CANDU Reactors, Atomic Energy of Canada Limited Report, AECL-7516. 

The once-through thorium (OTT) cycle in HWRs provides an evolutionary approach to exploiting some of the energy potential of thorium without recycling. The optimal OTT cycle is economical today in terms of money and in terms of uranium resomces. This cycle creates a mine of valuable U, safeguarded in the spent fuel, for future recovery if desired. 

Once-through thorium (OTT) cycle in HWR (n/kb or neutron per kilobarns is a measure neutron flux averaged over time). 

The fuel cycle options for the VBER-150 are the same as for the VBER-300 they include a once-through uranium fuel cycle (basic option), a uranium-thorium once-through fuel cycle to reduce specific plutonium production (Radkowsky Thorium Fuel — RTF — cycle), and a closed fuel cycle with MOX fuel, for details see [IV-1]. 

Fuel cycle options, alternative Radkowsky Thorium Fuel (RTF) once-through fuel cycle with heterogeneous fuel layout bimetallic enriched uranium (<20%) seed subassemblies thorium dioxide blanket subassemblies ... 

Scale of deployment. Reactors with once-through fuel cycles (AHTR and VHTR) can be rapidly deployed on a large scale. Creation of the fuel cycle requires only constmction of a relatively low-cost fuel fabrication plant (at most a few tens of milhons of dollars). Reactors that require SNF recycle [5] will require many decades to deploy on a large scale and involve very large expenditures of resources because (1) economics demands constmction of large-scale facilities to recover fissile material from SNF and (2) the current inventories of fissile material in SNF are limited. The limited fissile inventories imply that many decades will be required to obtain the neeessary materials for deployment of sufficient reactors on a scale that makes a major impact on the world s H2 production. Such fuel cycles require very-large-scale commitments over very long time periods but, require very little uranium or thorium to operate. 

Fission energy can be obtained from uranium, using the uranium once-through option and the uranium-plutonium fuel cycle, and from thorium, by the thorium-uranium fuel cycle. Each fuel cycle offers a number of alternative routes with respect to reactor type, reprocessing, and waste handling. Although the uranium based cycles are described with special reference to light water reactors, the cycles also apply to the old uranium fueled gas cooled reactors. 

Thorium-to- U breeders with actinide recycle would produce several orders of magnitude less transuranic waste than a conventional LWR once-through cycle and significantly less than even a U-Pu fast breeder (based on 0.1% losses during fuel processing). This leads to the radiotoxicity of waste being less than the equivalent uranium ore used in LWRs within a few hundred years. 

Fuel cycle options, alternative - Plutonium burner mode using plutonium-thorium MOX and a fully thorium- U fuelled mode in a closed fuel cycle - Synergy with fast breeder reactors and accelerator driven systems Once-through/ low enrichment U in advanced fuel forms, e.g., micro-particles in metallic matrix... 

A once-through Radkowsky Thorium Fuel (RTF) cycle is selected as an alternative for the VBER-300 (for more details, see Annex VII). 

---