[en] This analysis is a submission by AECL to the IAEA/INPRO Collaborative Project SYNERGIES (Synergistic Nuclear Energy Regional Group Interactions Evaluated for Sustainability), 2012-2014, to be included as an ANNEX in the final report of this work group. It is shown that, assuming an efficient market, reprocessed uranium from LWRs could be sold to HWRs at more than double the current price of natural uranium. If reprocessed uranium is a byproduct of MOX reprocessing, this would represent pure profit to the reprocessor. The existence of such a market would severely impact another potential use for reprocessed uranium which is discussed in a different ANNEX of this report - mixing it with Am-241 to produce a natural uranium equivalent for use in HWRs. (author)

[en] The good neutron economy and online refuelling capability of heavy water moderated reactors enable them to use many different fuels types such as: low enriched uranium, plutonium, or thorium, in addition to their traditional natural uranium fuel. The toxicity and radiological protection methods for these proposed fuels, unlike those for natural uranium, are not well established. This study uses software to evaluate the composition and toxicity of three irradiated advanced heavy water reactor oxide fuels as a function of post-irradiation time. All three fuels use plutonium assumed to be recovered from light water reactor (LWR) fuel via reprocessing. The first heavy water reactor fuel investigated is a homogeneous thorium-plutonium fuel designed for a once-through fuel cycle. The second fuel is a heterogeneous thorium-plutonium- ²³³U bundle, with graded enrichments of ²³³U in different parts of a single fuel assembly, assumed to be part of a recycling fuel cycle in which ²³³U from previous cycles is recovered. The third fuel is one in which plutonium and ²⁴¹Am is mixed with natural uranium. Each of these fuels turns out to be considerably more radiotoxic, for several years after reactor shutdown, than standard natural uranium reactor fuel would be, and it is shown that initial plutonium content is the most important factor affecting final radiotoxicity. For natural uranium, the isotope ²³⁹Pu is a significant contributor to the internal dose from exposure, and evaluating its presence in urine using mass spectrometry is sufficient to estimate internal doses as low as 1 mSv - the level required by regulation. If this method is extended so that ²⁴⁰Pu is also measured, then the combined amount of ²³⁹Pu and ²⁴⁰Pu is sufficiently high in the thorium-plutonium fuel that internal exposure to this fuel can be monitored using this method, but the fraction of these isotopes in the other two fuels is sufficiently low that they would remain below the detection limit. Thus, new techniques such as faecal measurements of ²³⁹Pu (or other alpha emitters) will be required for these fuels. (author)

[en] The online refueling capability of Heavy Water Reactors (HWRs), and their good neutron economy, allows a relatively high amount of neutron absorption in breeding materials to occur during normal fuel irradiation. This characteristic makes HWRs uniquely suited to the extraction of energy from thorium. In Canada, the toxicity and radiological protection methods dealing with personnel exposure to natural uranium (NU) spent fuel (SF) are well-established, but the corresponding methods for irradiated thorium fuel are not well known. This study uses software to compare the activity and toxicity of irradiated thorium fuel ('thorium SF') against those of NU. Thorium elements, contained in the inner eight elements of a heterogeneous high-burnup bundle having LEU in the outer 35 elements, achieve a similar burnup to NU SF during its residence in a reactor, and the radiotoxicity due to fission products was found to be similar. However, due to the creation of such inhalation hazards as U-232 and Th-228, the radiotoxicity of thorium SF was almost double that of NU SF after sufficient time has passed for the decay of shorter-lived fission products. Current radio-protection methods for NU SF exposure are likely inadequate to estimate the internal dose to personnel to thorium SF, and an analysis of thorium in fecal samples is recommended to assess the internal dose from exposure to this fuel. (author)

[en] The good neutron economy and online refuelling capability of the CANDU® heavy water moderated reactor (HWR) enable it to use many different fuel types such as: low enriched uranium (LEU), plutonium, or thorium, in addition to its traditional natural uranium (NU) fuel. The toxicity and radiological protection methods for these proposed fuels, unlike those for NU, are not well established. This study uses software to compare fuel composition and toxicity of irradiated NU fuel against those of two irradiated advanced HWR fuel bundles as a function of post-irradiation time. The first bundle investigated is a CANFLEX® low void reactor fuel (LVRF), of which only the dysprosium-poisoned central element, and not the outer 42 LEU elements, is specifically analyzed. The second bundle investigated is a heterogeneous high burnup (LEU,Th)O₂ fuelled bundle, whose two components: LEU in the outer 35 elements, and thorium in the central 8 elements, are analyzed separately. The LVRF central element was estimated to have a much lower toxicity than that of NU at all times after shutdown. Both the high burnup LEU and the thorium fuel had similar toxicity to NU at shutdown, but due to the creation of such inhalation hazards as: ²³⁸Pu, ²⁴⁰Pu, ²⁴¹Am, ²⁴²Cm and ²⁴⁴Cm (in high burnup LEU), and ²³²U and ²²⁸ Th (in irradiated thorium), the toxicity of these fuels was almost double that of irradiated NU after 2700 days of cooling. New urine bioassay methods for higher actinoids, and the analysis of thorium in faecal samples, are recommended to assess the internal dose from these two fuels. (author)

[en] One of the key challenges in the development of a CANDU pressure-tube supercritical water-cooled reactor (SCWR) is the selection of materials appropriate for in-core use. Such materials must be able to withstand the high-temperature, corrosive environment, and effects of irradiation encountered in the core, while at the same time minimizing parasitic neutron absorption. Achieving the appropriate balance between reactor physics and materials requirements necessitates knowledge of both materials properties of candidate alloys and their impact on lattice physics. In this paper, lattice physics calculations have been performed for the CANDU-SCWR for several categories of candidate in-core materials. In addition, a simple relation is derived that can be used to estimate the relative influence of in-core materials on lattice reactivity and fuel discharge burnup, based on material chemical composition and density. (author)

[en] The CANDU supercritical water-cooled reactor (CANDU-SCWR) is a pressure tube reactor intended to operate with a coolant pressure of 25 MPa and temperatures ranging between 350°C (core inlet) and 625°C (core outlet). Along the length of a fuel channel, there is a drastic decrease in the coolant density and dielectric constant, which is expected to result in a rapid decrease in the solubility of corrosion products. Therefore, it is anticipated that corrosion product deposition onto the cladding and liner in an SCWR fuel channel will be much greater than in conventional water-cooled reactors operating below the critical point of water. While optimized materials selection and chemistry control strategies may mitigate corrosion and corrosion product deposition to some degree, it may not be possible to completely eliminate corrosion product deposition within SCWR fuel channels. Corrosion product deposition on fuel cladding will have a negative impact on the neutron economy of the CANDU-SCWR because of parasitic absorption of neutrons within the deposited material. In this paper, lattice physics calculations are used to assess the impact of corrosion product deposition on fuel exit burnup, based on corrosion product deposition rates estimated for prototypical SCWR conditions. (author)

[en] The CANDU® supercritical water-cooled reactor (SCWR) is Canada's primary contribution to the Generation IV International Forum (GIF). The goals of GIF include the development of next-generation reactors with enhanced safety, resource sustainability, economic benefit and proliferation resistance. There is great potential for enhancing the sustainability of the nuclear fuel cycle by extending the availability of current resources through the use of thorium fuel cycles. Recent studies of thorium-based fuel cycles in contemporary CANDU reactors demonstrate the possibility for substantial reductions in natural uranium (NU) requirements of the fuel cycle via the recycling of U-233 bred from thorium. As thorium itself is not fissile, neutrons must be provided by adding a fissile material, either within or outside of the thorium based fuel. Various thorium fuel cycles can be categorized by the type and geometry of the added fissile material. The simplest of these fuel cycles are based on homogeneous thorium fuel designs, where the fissile material is mixed uniformly with the fertile thorium. These fuel cycles can be competitive in resource utilization with the best uranium-based fuel cycles, while building up an inventory of U-233 in the spent fuel for possible recycling in thermal reactors. When U 233 is recycled from the spent fuel, thorium-based fuel cycles can provide substantial improvements in the efficiency of energy production from existing fissile resources. In this paper, two homogeneous CANDU-SCWR thorium-based fuel cycles using reactor-grade plutonium as the fissile driver material have been examined. As the CANDU-SCWR reactor concept is still in the early development and design stages, various lattice and channel parameters can be varied to optimize the reactor for a specific fuel type. The impact of varying some of these parameters to optimize for thorium fuel has been studied. In this paper, thorium fuel cycle options are examined and compared with respect to initial Pu driver fuel requirements, U-233 recycling, and exit burnup. (author)

[en] With world stockpiles of used nuclear fuel increasing, the need to address the long term utilization of this resource is being studied. Many of the transuranic (TRU) actinides in nuclear spent fuel produce decay heat for long durations, resulting in significant nuclear waste management challenges. These actinides can be transmuted to shorter-lived isotopes in CANDU reactors to reduce the decay heat period. Many of the design features of the CANDU reactor make it uniquely adaptable to actinide transmutation. The small, simple fuel bundle facilitates the fabrication and handling of active fuels. Online refueling allows precise management of core reactivity and separate insertion of the actinides and fuel bundles into the core. The high neutron economy of the CANDU reactor results in high TRU destruction to fissile-loading ratio. This paper provides a summary of actinide transmutation in CANDU reactors, including both recent and past activities. The transmutation schemes that are presented reflect several different partitioning schemes and include both homogeneous scenarios in which actinides are uniformly distributed in all fuel bundles in the reactor, as well as heterogeneous scenarios in which dedicated channels in the reactor are loaded with actinide targets and the rest of the reactor is loaded with fuel. (author)

[en] Projections of the total world nuclear electricity demand for the next century show that existing natural uranium (NU) resources will be severely challenged by 2070. One way to meet this challenge is to recycle spent plutonium from Light Water Reactors (LWRs) as starting fissile material in thorium-fuelled Heavy Water Reactors (HWRs). This arrangement obtains more total energy per unit of NU mined since no NU is required by the HWR fleet, which instead gets its fissile material from LWR spent fuel and from U-233 bred into the thorium. Modeling shows that world NU requirements up to the year 2130 can be reduced by 10% for a once-through Th-Pu fuel cycle and by almost 20% in a Th-Pu-U-233 fuel cycle where the U-233 in spent HWR fuel is recovered and used to top-up the initial fissile material. As an added benefit, the total decay heat of spent fuel in repositories, a limiting factor, is reduced by more than one third by the transmutation of LWR plutonium. (author)

[en] First, starting from a relativistic d'Alembert's principle for a one-particle system, it is shown that whenever a classical Lagrangian formulation exists for one observer in terms of his space-time variables, a corresponding formulation exists for any Lorentz-related observer. The relationship is unique and guarantees the correct description of any physical one-particle problem for all such observers. One is then able to identify unambiguously the relativistic scalar, vector, etc. interactions classically. Second, some simple one-dimensional exactly solvable problems are discussed in order to illustrate the differences in the motions caused by relativistic scalar and vector interactions. One of the scalar interactions suggests the possibility of quark confinement classically. Finally, some generalizing comments are presented