Recycling as an option of used nuclear fuel management strategy

The paper presents recycling as an option of used nuclear fuel management strategy with specific focus on the Slovenia. GEN energija is an independent supplier of integral and competitive electricity for Slovenia. In response to growing energy needs, GEN has conducted several feasibility and installation studies of a new nuclear power plant in Slovenia. With sustainable development, the environment, and public acceptance in mind, GEN conducted a study with AREVA concerning the options for the management of its’ new plant's used nuclear fuel.After a brief reminder of global political and economic context, solutions for used nuclear fuel management using current technologies are presented in the study as well as an economic assessment of a closed nuclear fuel cycle. The paper evaluates and proposes practical solutions for mid-term issues on used nuclear fuel management strategies. Different scenarios for used nuclear fuel management are presented, where used nuclear fuel recycling (as MOX, for mixed oxide fuel, and ERU, for enriched reprocessed uranium) are considered. The study concludes that closing the nuclear fuel cycle will allow Slovenia to have a supplementary fuel supply for its new reactor via recycling, while reducing the radiotoxicity, thermal output, and volume of its wastes for final disposal, reducing uncertainties, gaining public acceptance, and allowing time for capitalization on investments for final disposal.     

Radioactive Waste Arisings from Various Fuel Cycle Options

This study examines all kinds of waste volumes from various fuel cycle options including DUPIC (Direct Use of Spent PWR Fuel In CANDU) fuel cycle and compares each other. The fuel cycle option considered the PWR (Pressurized Water Reactor) once-through cycle, the PHWR (Pressurized Heavy Water Reactor) once-through cycle and the thermal recycling option using an existing PWR with MOX (Mixed Oxide) fuel. This study focuses on the radioactive wastes including mill waste, low-level waste and high-level waste generated by all fuel cycle steps, which can be one of the effectiveness measures of waste management. All waste disposition volume is estimated in terms of m³/GWe-yr. We find in the estimation of radioactive waste volume that PWR-MOX option has the lowest mill tailings and spent fuel volumes among the options, but the option has high volume of ILW and HLW. Mill tailings and spent fuel volumes of the DUPIC fuel cycle are lower than those of other competitive options such as PWR-PHWR once-through cycle. PWR once-through cycle has the lowest LLW and ILW volume among the options, but has high mill tailings and spent fuel volume. The data obtained in this study would be helpful to further estimate environmental effect and/or waste disposition costs in various fuel cycle options.     

Radionuclide inventories in the discharged fuels of PHWR-220, BWR-160, VVER-1000 and the conceptual ATBR-600 reactors – A case study

Radionuclides content in the discharged fuel of the conceptual thorium breeder reactor ATBR-600 has been assessed and compared against other thermal power reactors considered in Indian nuclear power programme. The contribution of actinides and the fission products inventories in the discharged fuels are separately estimated and assessed. The ATBR-600 reactor is suggested for closed fuel cycle option. The relatively large presence of the unspent plutonium would in fact be recycled. Nonetheless, the data has been presented in the event of operating ATBR-600 like other present day power reactors in a once through fuel cycle mode.     

A view of strategies for transmutation of actinides

Developments in the field of recycling and transmutation of actinides are discussed. Three general strategies are discriminated: (i) an evolutionary strategy based on gradual implementation of partitioning and transmutation techniques in the fuel cycle; (ii) a radical strategy based on implementation of partitioning and transmutation in the fuel cycle, once all steps of this technology are proven; (iii) plutonium incineration, based on the conversion, with existing reactor types, of separated plutonium into a spent fuel form that is suited for direct storage.     

Dynamic analysis of a thorium fuel cycle in CANDU reactors

The thorium fuel recycle scenarios through a Canada deuterium uranium (CANDU) reactor have been analyzed for two types of thorium fuel: homogeneous ThO₂UO₂ and heterogeneous ThO₂UO₂–DUPIC fuels. The recycling was performed with dry process fuel technology which has a proliferation resistance. For the once-through fuel cycle model, the existing nuclear power plant construction plan was considered up to 2016, while the nuclear demand growth rate from the year 2016 was assumed to be 0%. After setting up the once-through fuel cycle model, a thorium fuelled CANDU reactor was modeled to investigate the fuel cycle parameters. In this analysis, the spent fuel inventory as well as the amount of plutonium, minor actinides and fission products for the multiple recycling fuel cycle were estimated and compared to those of a once-through fuel cycle.     

行波堆平准化发电成本分析

本文通过平准化发电成本的方法,以燃料循环作为研究对象,对行波堆一次通过式燃料循环和二次通过式燃料循环的经济性进行了研究,并选取10个重要的经济和技术参数进行成本敏感性分析。研究结果表明,行波堆的平准化发电成本低于现有压水堆和快堆,其中,行波堆一次通过式燃料循环方式的平准化发电成本最低。敏感性分析表明,贴现率、燃耗深度、隔夜价和反应堆热效率是影响行波堆经济性最重要的参数,而燃料价格和废物处置的价格由于占成本的比例较小,对行波堆经济性的影响不大。     

Some aspects of risk reduction strategy by multiple recycling in fast burner reactors of the plutonium and minor actinide inventories

This paper shows the impact of recycling light water reactor (LWR) mixed oxide (MOX) fuel in a fast burner reactor on the plutonium (Pu) and minor actinide (MA) inventories and on the related radioactivities. Reprocessing of the targets for multiple recycling will become increasingly difficult as the burnup increases. Multiple recycling of Pu + MA in fast reactors is a feasible option which has to be studied very carefully: the Pu (except the isotopes Pu-238 and Pu-240), Am and Np levels decrease as a function of the recycle number, while the Cm-244 level accumulates and gradually transforms into Cm-245. Long cooling times (10 + 2 years) are necessary with aqueous processing. The paper discusses the problems associated with multiple reprocessing of highly active fuel types and particularly the impact of Pu-238, Am-241 and Cm-244 on the fuel cycle operations. The calculations were performed with the zero-dimensional ORIGEN-2 code. The validity of the results depends on that of the code and its cross-section library. The time span to reduce the initial inventory of Pu + MA by a factor of 10 amounts to 255 years when average burnups are limited to 150 GW · d t⁻¹ (tonne).     

Some aspects of risk reduction strategy by multiple recycling in fast burner reactors of the plutonium and minor actinide inventories

The paper shows the impact of recycling LWR-MOX fuel in a fast burner reactor on the plutonium (Pu) and minor actinide (MA) inventories and on the related radio activities. Reprocessing of the targets for multiple recycling will become increasingly difficult as the burn up increases. Multiple recycling of Pu + MA in fast reactors is a feasible option which has to be studied very carefully: the Pu (except the isotopes Pu-238 and Pu-240), Am and Np levels decrease as a function of the recycle number, while the Cm-244 level accumulates and gradually transforms into Cm-245. Long cooling times (10 + 2 years) are necessary with aqueous processing.The paper discusses the problems associated with multiple reprocessing of highly active fuel types and particularly the impact of Pu-238, Am-241 and Cm-244 on the fuel cycle operations. The calculations were performed with the zero-dimensional ORIGEN-2 code. The validity of the results depends on that of the code and its cross section library. The time span to reduce the initial inventory of Pu + MA by a factor of 10, amounts to 255 years when average burn ups are limited to 150 GWd t⁻¹.     

The economic effects of the deferred disposal of spent fuel in Korea

The present study analyzes the economic effects concerning deferred disposal of spent fuel through long-term storage. According to the cost analysis, a scenario that a 90-year deferral of an HLW (High-Level Waste) repository construction in favor of a long-term storage of spent fuel would be economically preferable to another scenario based on the year 2040 chosen as the starting point for construction on a repository. That is, the former scenario would cost about 1/2 of the latter. This finding is an estimated result from an economic perspective only, assuming the disposal of 20,000-ton PWR spent fuel and 16,000-ton CANDU spent fuel. Still, it seems necessary to elicit proper term of storage for radioactive waste in order to comply with the so-called Polluter-Pays principle that the current generation cannot pass on its radioactive waste to the next generation.     

Development of a multi-tiered recycling strategy with a sodium-cooled Heterogeneous Innovative Burner Reactor

The Sodium-Cooled Heterogeneous Innovative Burner Reactor (SCHIBR) model created at the University of South Carolina uses heterogeneous minor actinide targets. To improve minor actinide transmutation, a hybrid fuel management scheme is utilized involving initially moderated assemblies on the core periphery followed by a second period of irradiation in a fast flux with the moderating rods removed. A multi-tiered recycling strategy was developed to increase plutonium utilization in the SCHIBR model through the recycle of the driver fuel. An equilibrium fuel cycle was evaluated with the computer code ERANOS to determine the improvements in fuel utilization, reduction in high level waste, and safety of the SCHIBR design. Fuel depletion studies were conducted to determine the composition of input and output streams in order to develop reactor recipes for use in the fuel cycle simulation code, VISION. The once-through SCHIBR model reduces the radiotoxicity of high level waste by 66% of the once-through LWR model after 300 years in storage. The multi-tiered recycling strategy offers improvements over the previous once-through SCHIBR model by reducing the radiotoxicity by 86% after 300 years in storage.     

Evaluation of multiple, self-recycling of reprocessed uranium in LWR

The multiple recycling of uranium in light-water reactors is evaluated to understand its sustainability in multiple recycling scenarios and to evaluate its impact on fuel design and the fuel cycle. Two recycling scenarios were evaluated. One involves the mixing of repU with natU prior to reenrichment. A second involves the mixing of repU with 19.9% EU to provide the new reactor fuel. The equilibrium concentrations of troublesome isotopes such as U-232 and U-236 are evaluated along with the required overenrichment of U-235. It was confirmed that a U-235 overenrichment factor of 0.28 applied to the U-236 concentration is sufficient to meet the cycle reactivity requirements and yields equilibrium enrichments of 5.06% and 5.52% for the two cycles, respectively. The impact on plutonium production and cycle reactivity is further evaluated to ensure the new fuel can meet the desired burnup requirements. Here, the plutonium production was found to be greater and the reactivity swing less in recycling scenarios with higher U-236 concentration.     

A Study of Plutonium Recycle in a Gas-Cooled,Graphite-Moderated Reactor, (III)

Reactor physics characteristics related to plutonium recycling in a gas-cooled, graphite-moderated reactor were investigated and correlated to those for the case without plutonium recycling, using the fuel cycle analysis code FUELMOVE. It was found that, in the initial stages of irradiation, plutonium recycled fuel shows a thermal spectrum harder with respect to neutron temperature and a higher slowing down density, but that differences become smaller as the burnup progresses. A notable difference between the cases with and without recycling Hes in the resonance fission rate which proves to be roughly 20 to 35% higher in the former case.     

Risk-benefit evaluation of nuclear power plant siting

An assessment scheme is described for the risk-benefit analyses of nuclear power versus conventional alternatives. Given the siting parameters for the proposed nuclear plant an economic comparison is made with the most advantageous competitive conventional production scenario. The economic benefit is determined from the differential discounted annual energy procurement cost as a function of the real interest rate and amortization time. The risk analysis encompasses following factors: radiation risks in normal operation, reactor accident hazards and economic risks, atmospheric pollutants from the conventional power plants and fuel transportation. The hazards are first considered in terms of probabilistic dose distributions. In the second stage risk components are converted to a compatible form where excess mortality is used as the risk indicator. Practical calculations are performed for the power production alternatives of Helsinki where district heat would be extracted from the nuclear power plant. At the real interest rate of 10% and amortization time of 20 yr the 1000 MW(e) nuclear option is found to be $9.1 m per yr more economic than the optimal conventional scenario. Simultaneously the nuclear alternative is estimated to reduce excess mortality by 2–5 fatal injuries annually.     

The effectiveness of full actinide recycle as a nuclear waste management strategy when implemented over a limited timeframe – Part II: Thorium fuel cycle

Full recycling of transuranic (TRU) isotopes can in theory lead to a reduction in repository radiotoxicity to reference levels in as little as ∼500 years provided reprocessing and fuel fabrication losses are limited. However, over a limited timeframe, the radiotoxicity of the ‘final’ core can dominate over reprocessing losses, leading to a much lower reduction in radiotoxicity compared to that achievable at equilibrium. In Part I of this paper, TRU recycle over up to 5 generations of light water reactors (LWRs) or sodium-cooled fast reactors (SFRs) is considered for uranium (U) fuel cycles. With full actinide recycling, at least 6 generations of SFRs are required in a gradual phase-out of nuclear power to achieve transmutation performance approaching the theoretical equilibrium performance. U-fuelled SFRs operating a break-even fuel cycle are not particularly effective at reducing repository radiotoxicity as the final core load dominates over a very long timeframe. In this paper, the analysis is extended to the thorium (Th) fuel cycle. Closed Th-based fuel cycles are well known to have lower equilibrium radiotoxicity than U-based fuel cycles but the time taken to reach equilibrium is generally very long. Th burner fuel cycles with SFRs are found to result in very similar radiotoxicity to U burner fuel cycles with SFRs for one less generation of reactors, provided that protactinium (Pa) is recycled. Th-fuelled reduced-moderation boiling water reactors (RBWRs) are also considered, but for burner fuel cycles their performance is substantially worse, with the waste taking ∼3–5 times longer to decay to the reference level than for Th-fuelled SFRs with the same number of generations. Th break-even fuel cycles require ∼3 generations of operation before their waste radiotoxicity benefits result in decay to the reference level in ∼1000 years. While this is a very long timeframe, it is roughly half that required for waste from the Th or U burner fuel cycle to decay to the reference level, and less than a tenth that required for the U break-even fuel cycle. The improved performance over burner fuel cycles is due to a more substantial contribution of energy generated by ²³³U leading to lower radiotoxicity per unit energy generation. To some extent this an argument based on how the radiotoxicity is normalised: operating a break-even fuel cycle rather than phasing out nuclear power using a burner fuel cycle results in higher repository radiotoxicity in absolute terms. The advantage of Th break-even fuel cycles is also contingent on recycling Pa, and reprocessing losses are significant also for a small number of generations due to the need to effectively burn down the TRU. The integrated decay heat over the scenario timeframe is almost twice as high for a break-even Th fuel cycle than a break-even U fuel cycle when using SFRs, as a result of much higher ⁹⁰Sr production, which subsequently decays into ⁹⁰Y. The peak decay heat is comparable. As decay heat at vitrification and repository decay heat affect repository sizing, this may weaken the argument for the Th cycle.     

Management of actinide waste inventories in nuclear phase-out scenarios

The improvement of the “radiological cleanliness” of nuclear energy is a primary goal in the development of advanced reactors and fuel cycles. The multiple recycling of actinides in advanced nuclear systems with fast neutron spectra represents a key option for reducing the potential hazard from high-level waste, especially when the fuel cycle is fully closed. Such strategies, however, involve large inventories of radiotoxic, transuranic (TRU) nuclides in the nuclear park, both in-pile and out-of-pile. The management of these inventories with the help of actinide burners is likely to become an important issue, if nuclear energy systems are eventually phased out, i.e. replaced by other types of energy systems.     

Advanced fuel cycle scenarios for High Temperature Gas Reactors

This study evaluates nuclear fuel cycle scenarios which are based on recycling spent nuclear fuel for the sustainability of nuclear energy. Three fuel cycle scenarios, the Light Water Reactor (LWR)–Advanced Recycling Reactor (ARR) recycle, the LWR–High Temperature Gas Reactor (HTGR)–ARR recycle, and the HTGR partial recycling fuel cycle, are assessed for their mass flow and electricity generation costs and the results are compared to those of the LWR once-through fuel cycle. The spent fuels are recycled in both the Consolidated Fuel Treatment Center and the Actinide Management Island, which are capable of reprocessing spent fuels by Uranium Extraction and Pyrochemical processes, respectively. The mass flow calculations show that the Transuranics (TRU) which have a long-term radiation effect can be completely burned in the recycling fuel cycles, resulting in 350, 450 and 6 times reduction of TRU inventory for the LWR–ARR, LWR–HTGR–ARR and HTGR partial recycling fuel cycles, respectively, when compared to the once-through fuel cycle. The electricity generation costs of these fuel cycle scenarios were estimated to be 39.1, 34.9 and 25.7 USD/MW h(e), which are comparable to or smaller than that of the once-through fuel cycle. Although the candidate fuel cycles adopt reprocessing options which raise fuel cycle cost, increase in uranium cost and the advanced design of the HTGR can further reduce the advanced fuel cycle costs of the HTGR.     

Irradiation behavior of HTGR coated particle fuel at abnormally high temperature

Irradiation behavior of high temperature gas-cooled reactor (HTGR) coated particles under temperature transient conditions was investigated in accordance with a design-base accident scenario for HTTR, a 30 MWth HTGR under construction at JAERI. One of the scenarios predicts that the fuel temperature of the block-type fuel elements rises to abnormally high temperature by blocking a coolant channel with some foreign substance. For simulating this scenario the fuel compacts incorporating the coated particles were irradiated at normal temperature in three capsules, followed by temperature transient up to a maximum of approximately 2000°C. The post-irradiation examinations, including surface inspection, metrology, ceramography and a measurement of coated particle failure were applied to the fuel compacts to investigate the thermal-transient effect on the fuel integrity. Integrity of the fuel compact was also assessed by an estimation of tangential stress introduced into the compact by the temperature transient.     

混合能源堆裂变包层核燃料成本分析

混合能源堆裂变包层燃料管理策略是:对乏燃料做后处理,得到的回收燃料作为下一循环的燃料,据此开展裂变包层的燃耗性能分析。在此基础上建立了针对混合能源堆的燃料循环成本分析模型:建立核燃料循环图,进行物料衡算,并分析燃料管理方案的单位发电量的燃料消耗量,根据市场价格,得到最终的核燃料成本。根据燃料循环成本分析结果,对影响较大的因素,如天然铀采购单价、乏燃料后处理单价、燃料制造单价等参数进行敏感性分析,得到燃料成本根据各价格参数变化规律。     

Investigation on spent fuel characteristics of reduced-moderation water reactor (RMWR)

The spent fuel characteristics of the reduced-moderation water reactor (RMWR) have been investigated using the SWAT and ORIGEN codes. RMWR is an advanced LWR concept for plutonium recycling by using the MOX fuel. In the code calculation, the ORIGEN libraries such as one-group cross-section data prepared for RMWR were necessary. Since there were no open libraries for RMWR, they were produced in this study by using the SWAT code. New libraries based on the heterogeneous core modeling in the axial direction and with the variable actinide cross-section (VXSEC) option were produced and selected as the representative ORIGEN libraries for RMWR. In order to investigate the characteristics of the RMWR spent fuel, the decay heat, the radioactivity and the content of each nuclide were evaluated with ORIGEN using these libraries. In this study, the spent fuel characteristics of other types of reactors, such as PWR, BWR, high burn-up PWR, full-MOX-PWR, full-MOX-BWR and FBR, were also evaluated with ORIGEN.

It has been found that about a half of the decay heat of the RMWR spent fuel comes from the actinides nuclides. It is the same with the radioactivity. The decay heat and the radioactivity of the RMWR spent fuel are lower than those of full-MOX-LWRs and FBR, and are the same level as those of the high burn-up PWR. The decay heat and the radioactivity from the fission products (FPs) in the spent fuel mainly depend on the burn-up and the burn-up time rather than the reactor type. Therefore, the decay heat and the radioactivity from FPs in the RMWR spent fuel are smaller, reflecting its relatively long burn-up time resulted from its core characteristics with the high conversion ratio. The radioactivity from the actinides in the spent fuel mainly depends on the ²⁴¹Pu content in the initial fuel, and the decay heat mainly depends on ²³⁸Pu and ²⁴⁴Cm. The contribution of ²⁴⁴Cm is much smaller in RMWR than in MOX-LWRs because of the difference in the spectrum. In addition, from the waste disposal point of view, the characteristics of the heat generation FP elements, the platinum group metals, Mo and the long-lived FPs (LLFPs) were also investigated.     

Experimental studies on the upward fuel discharge for elimination of severe recriticality during core-disruptive accidents in sodium-cooled fast reactors

In order to eliminate the energetic potential in the case of postulated core-disruptive accidents (CDAs) of sodium-cooled fast reactors, introduction of a fuel subassembly with an inner-duct structure (FAIDUS) has been considered. Recently, a design option of FAIDUS which leads molten fuel to upward discharge has been considered as the reference core design of the Japan Sodium-Cooled Fast Reactor (JSFR). In this study, a series of experiments which consisted of three out-of-pile tests and one in-pile test were conducted to obtain experimental knowledge of the upward discharge of molten fuel. Experimental data which showed a sequence of upward fuel discharge and effects of initial pressure conditions on upward discharge were obtained through the out-of-pile and in-pile test. Preliminary extrapolation of the present results to the supposed condition in the early phase of the CDA in the JSFR design suggests that the sufficient upward flow rate of molten fuel is expected to prevent the core melting from progressing beyond the fuel subassembly scale and that the upward discharge option will be effective in eliminating the energetic potential.