Utilization of spent PWR fuel-advanced nuclear fuel cycle of PWR／CANDU synergism

High neutron economy, on line refueling and channel design result in the unsurpassed fuel cycle flexi-bility and variety for CANDU reactors. According to the Chinese national conditions that China has both PWR and CANDU reactors and the closed cycle policy of reprocessing the spent PWR fuel is adopted, one of the advanced nu-clear fuel cycles of PWR/CANDU synergism using the reprocessed uranium of spent PWR fuel in CANDU reactor is proposed, which will save the uranium resource (-22.5%), increase the energy output (-41%), decrease the quantity of spent fuels to be disposed (-2/3) and lower the cost of nuclear poower, Because of the inherent flexibility of nuclearfuel cycle in CANDU reactor, and the low radiation level of recycled uranium(RU), which is acceptable for CANDU reactor fuel fabrication, the transition from the natural uranium to the RU can be completed without major modifica-tion of the reactor core structure and operation mode.It can be implemented in Qinshan Phase Ⅲ CANDU reactors with little or no requirement of big investment in new design. It can be expected that the reuse of recycled uranium of spent PWR fuel in CANDU reactor is a feasible and desirable strategy in China.     

CANDU堆先进燃料循环的展望

介绍ＣＡＮＤＵ堆的天然铀燃料循环以及最近开发的适合未来近期的先进燃料循环。高中子经济性,不停堆换料以及简单的燃料束设计,使得ＣＡＮＤＵ堆具有非常优良的燃料循环灵活性和多样性。     

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.     

Radiation Characteristics of Fuel and Wastes in the Uranium–Plutonium and Thorium–Uranium Fuel Cycle

The radiation characteristics of fuel cycles of various reactors – replacement candidates in the future nuclear power – are compared. Proceeding from the basic requirements (safety, fuel supply, and nonproliferation of fissioning materials), inherently safe fast reactors of the BREST type can be used as the basis for large-scale nuclear power. Thermal reactors, which can burn enriched uranium, thorium–uranium fuel, or mixed uranium–plutonium fuel with makeup with fissioning materials from fast reactors, will operate for a long time simultaneously with fast reactors in the future nuclear power. VVÉR-1000 and CANDU reactors are examined as representatives of thermal reactors; for each of these reactors the operation in various variants of the fuel cycle is simulated. It is shown that with respect to radiation characteristics of the fuel and wastes the thorium–uranium fuel cycle has no great advantages over the uranium–plutonium cycle.     

Proliferation-resistant fuel options for thermal and fast reactors avoiding neptunium production

Sustainable nuclear energy production requires reuse of spent nuclear fuel while avoiding its misuse. In the paper we assume that plutonium with sufficiently high content of the Pu-238 isotope (about 6% or more) and americium from spent nuclear fuel are proliferation-resistant. On the other hand, neptunium should be considered as material that is fissionable in a fast neutron spectrum and could be misused.We also assume that plutonium denatured by Pu-238 can be produced in nuclear reactors of, e.g. nuclear weapon states and used for fuel fabrication there or in multilateral reprocessing and re-fabrication centers as suggested by IAEA. Then the fabricated fuel can be utilized in nuclear reactors everywhere provided that the reactors may operate safely and the fuel remains proliferation-resistant after utilization. Options to meet these criteria are investigated in the paper for two reactor types: pressurized water reactors (PWRs) and fast reactors (FRs).In PWRs, the investigated fresh fuel compositions include denatured plutonium and depleted uranium mixed with a small amount of U-233, thorium and, optionally, with americium, presence of U-233 making the coolant void effect negative. In FRs, use of americium makes plutonium denatured, both for the burner (without fertile blanket) and breeder options. It is shown that the proposed design and fuel options are proliferation-resistant, the generation of neptunium being very low. Safety parameters are acceptable. Advanced aqueous or pyrochemical reprocessing for plutonium/thorium/uranium fuel and related fuel re-fabrication technology applying remote handling may become necessary to realize the considered fuel cycles.     

PWR/CANDU联合核燃料循环研究

根据我国已拥有PWR和CANDU核电站的具体情况 ,提出一种PWR/CANDU联合核燃料循环的策略 ,即把压水堆的乏燃料后处理后的回收铀 (RU)用作为CANDU堆的核燃料 ,既可节约铀资源 ,提高燃料的能量输出 ,又减少了废燃料的处置量 ,可大大降低核电成本。由于CANDU堆对核燃料循环的固有灵活性 ,堆芯结构及运行方式不需作重大改变 ,即可完成从天然铀到RU的过渡。又由于RU较低的放射性活度 ,这对CANDU堆的燃料制造是可以接受的 ,因而只需对现有燃料制造生产线稍加屏蔽措施 ,对运输和运行中燃料管理操作等都勿须改变。因而这一策略是具有重大经济效益和吸引力的     

Nuclear power technologies at the stage of sustainable nuclear power development

It is not simple to solve the problem of competitiveness of nuclear power technologies in evolutionary upgrading the conventional nuclear power plants (NPP) such as light water reactors (LWR), which requires high expenditure for safety. Moreover, the existing LWRs cannot provide nuclear power (NP) for a long time (hundreds of years) because the efficiency of use of natural uranium is low and closing the nuclear fuel cycle (NFC) for those reactors is not expedient.The highlighted problem can be solved in the way of use of innovative nuclear power technology in which natural uranium power potential is used effectively and the intrinsic conflict between economic and safety requirements has been essentially mitigated.The technology that is most available and practically demonstrated is the use of reactors SVBR-100 — small power multi-purpose modular fast reactors (100 MWe) cooled by lead-bismuth coolant (LBC). This technology has been mastered for nuclear submarines’ reactors in Russia.High technical and economical parameters of the NPP based on RF SVBR-100 are determined from the fact that the potential energy stored in LBC per a volume unit is the lowest.The compactness of the reactor facility SVBR-100 that results from integral arrangement of the primary circuit equipment allows realizing renovation of power-units LWRs, the vessels’ lifetime of which has been expired. So due to this fact, high economical efficiency can be obtained.The paper also validates the economical advantage of launching the uranium-fueled fast reactors with further changeover to the closed NFC with use of plutonium extracted from the own spent nuclear fuel in comparison with launching fast reactors directly with on uranium-plutonium fuel on the basis of plutonium extraction from spent nuclear fuel of LWRs.     

Nuclear and materials aspects of the thorium fuel cycle

This paper is an attempt to assess and review the materials aspects of the thorium fuel cycle. It starts with an examination of the nuclear aspects of the thorium fuel cycle, meant as an introduction for materials scientists and engineers who may not normally be familiar with the concepts and terms involved. After defining and describing the thorium and uranium fuel cycles, the reasons for the resurgence of interest in the thorium fuel cycle and the technical and economic considerations that support its early adoption are examined. The reactor physics and fissile economics aspects of the thorium and uranium cycles are then compared. The specific reactor types suitable for the adoption of the thorium cycle are briefly examined and described. Subsequent sections of the paper are devoted to a detailed discussion of the materials aspects of the thorium fuel cycle. Available information on fabrication, refabrication and irradiation performance of thorium-based fuels for light water reactors, heavy water reactors, high temperature gas-cooled reactors, molten salt breeder reactors and fast breeder reactors is critically reviewed and analysed. Materials problems related to cladding and structural materials are also discussed whenever these are unique to the thorium cycle.     

A perspective on fast reactor fuel cycle in India

The growing energy needs of India can be fulfilled only by judicious mix of all the fuel resources. It is possible to achieve energy security and sustainability through the introduction of fast reactors in an expeditious manner and closing the fuel cycle. This approach is inevitable in view of the limited uranium resources in India. The Fast Breeder Test Reactor (FBTR) built by India uses mixed carbide as fuel and the 500 MW(e) Fast Breeder Reactor Project (PFBR), to be operational in 2010, will use mixed oxide as fuel. It has also been decided that fast reactors beyond 2020, with enhanced safety features and having better economy, will use metallic fuel. Having successfully operated FBTR with carbide fuels, we need to develop the fuel cycles for both the mixed oxide fuel in the near future and the metallic fuel expeditiously. The progress achieved so far and the plans for implementation are discussed in this paper.     

核能生产人工辐射源对中国大陆公众的辐射照射

总结了核燃料循环和核电生产放射性流出物释放对中国大陆公众的辐射照射，所涉及的活动主要包括铀矿开采和冶炼、铀转化和铀浓缩、核燃料元件生产、核反应堆发电对中国大陆公众的影响。评估结果表明，对于中国铀矿开采和冶炼、铀转化和铀浓缩、核燃料元件生产、压水堆核电生产、重水堆核电生产，按照5年期（2001—2005）平均的归一化集体有效剂量分别为0.81、5.16×10^-3、2.09×10^-3、2.91×10^-3和1.84×10^-1人•Sv/（GW•a），中国核能生产的某些环节的放射性流出物排放和所致的归一化集体有效剂量比全球平均值高，值得进一步分析和研究。     

重水堆钍铀燃料增殖循环方案研究

论文的目的是研究重水堆钍铀燃料增殖循环方案。基于前期设计的技术路线,以CANDU-6堆芯为参考堆芯,研究了钍基堆芯燃料管理策略,分析了中子学特性,并对乏燃料特性进行了评估,包括放射性毒性、衰变热和伽马射线。在此基础上,建立了钍铀燃料增殖循环方案,其在可持续性关键指标方面优于常规天然铀一次通过循环。     

Use of weapons plutonium in VVÉR-1000 reactors

One scenario for using excess Russian weapons plutonium is to load it into VVéR-1000 reactors. It is proposed that up to 40% of the fuel assemblies with uranium fuel be replaced with structurally similar fuel assemblies with mixed uranium-plutonium fuel. The stationary regime for burning fuel has the following characteristics: the run time is about 300 or 450 eff. days, the yearly plutonium consumption reaches 450 kg, the neutron-physical characteristics are close to the corresponding regimes with uranium fuel. The nuclear safety criteria and the irradiation dose for workers handling fresh and spent mixed fuel remain within the limits of the normative values. The use of mixed fuel makes it necessary to upgrade certain systems at nuclear power plants. A substantial quantity of weapons plutonium can be loaded every year into VVéR-1000 reactors, effectively using the energy potential of this plutonium. __________ Translated from Atomnaya énergiya, Vol. 103, No. 4, pp. 215–222, October, 2007.     

The status of the Canadian nuclear power program and possible future strategies

Canada is fortunate in having developed a versatile and flexible power reactor concept—one which can be kept economically competitive into the distant future, while at the same time offering opportunities for large reductions in uranium requirements. The one CANDU concept provides a range of alternatives, at least as extensive in terms of adaptation to changing economic and uranium supply conditions as that of most other nuclear power programs consisting of two or more distinct reactor types.The range includes reduced capital costs through use of boiling light water and organic cooled options, better thermal efficiency through use of the organic cooled option, and the ability to minimize the impact of changing economic parameters and improve uranium utilization through use of Pu recycle and/or thorium fuel with uranium recycle.AECL has devoted considerable effort over the last few years to study of advanced fuel cycles in the various CANDU reactor types. Very few feasibility questions have been uncovered.A detailed conceptual study of our currently favoured vehicle for Pu recycle, CANDU-BLW (PB), a plutonium burning, boiling light water cooled CANDU, has indicated that it could be initiated with no major problems. Development would be required in a number of areas—notably, fuel design and computational methods for fuel management. The results indicate a savings of some 15–20% in plant capital costs over the natural uranium CANDU-PHW and a reduction of almost a factor of two in uranium requirements.More general studies of thorium fuelled concepts are also encouraging. The reactor designs are almost identical to those for uranium CANDU reactors and so no new feasibility problems are introduced. We recognize feasibility problems associated with specific fuels in specific CANDU types, but there appear to be none in the areas of reactor physics, control, safety and fuel management. These concepts are competitive with CANDU-PHWs even for current economic conditions over a fairly wide range of reprocessing costs and/or separative work cost. Increasing uranium prices tend to favour the thorium fuelled reactors. The uranium requirements as a function of time depend on system growth rate but for any reasonable values the saving is at least a factor of two. As the growth rate slows this factor increases. In fact we envisage the possibility of thorium cycles with uranium recycle, which are self sufficient at equilibrium. This means a limited natural uranium requirement to establish and maintain a given electrical capacity. Requirements as low as 1 Mg (natural uranium)/MWe seem possible. We are currently studying these self-sufficient thorium cycles in more detail.We feel that the question is not so much whether the CANDU concept can be adapted to suit any particular set of economic and uranium supply conditions, but rather one of matching and timing. A large amount of work is required to determine the best system to match a given set of economic conditions or, with more difficulty, a given uncertainty band of economic conditions. The substantial time delays associated with any major adaptation make anticipation of future economic conditions important. Indeed at any time, the best system to design and build may be one which can be used with a variety of fuels rather than the optimum system for any one fuel. In order to capitalize on our present enviable position we will have to keep on top of these problems.In the U.S. the study of strategies for various plausible scenarios is important for long term planning, to provide a basis for decisions on types of reactors to develop. For Canada such studies are important for long term planning of development programs but will also likely be important for determining optimum operation of facilities.Some of the initial work detailing what I have been saying appears in our paper. The time seems ripe for serious consideration of Pu recycle and use of thorium, and yet in Canada there seems to be no need for undue haste in implementing these. Therefore we can contemplate an orderly research and development program which will put us in a position to adopt one or more of the many options in 10–20 yr time.Since our major uncertainties are in the areas of fuel reprocessing and active fuel fabrication these will be an important part of this program.It is not clear how our experience relates to U.S. problems. Certainly there are many conditions which are quite different in the two countries. The two most important are:

1. (i) We have developed heavy water power reactors and the U.S. has not.

2. (ii) The U.S. has a fast breeder program and we do not.

I would like to stress the fact though that we really believe our program is a fully valid alternative (at least for us).We are quite willing then to explore with you the question of whether Canadian experience has any pertinence to problems associated with the U.S. nuclear power program.     

On the potential use of F2Be-molten-salt for hybrid reactors

Breeder reactors are considered a unique tool for fully exploiting natural nuclear resources. In current Light Water Reactors (LWR), only 0.5% of the primary energy contained in the nuclei removed from a mine is converted into useful heat. The rest remains in the depleted uranium or spent fuel. This evident need to improve resource-efficiency has stimulated interest in Fast-reactors, and with it, boosted the need to answer many of the remaining safety issues attached to such systems (i.e. coolant positive void coefficients). Among the existing candidates to overcome this fundamental drawback, the F₂Be-molten-salt, has proved to feature outstanding neutronic properties. In previous studies, in an analysis that took into account requirements for criticality, for breeding, and for safety, it was demonstrated that a design window could be found in the definition of an F₂Be-cooled system, where the safety requirement was met for a critical breeder reactor.     

Energy sustainability and economic stability with Breed and Burn reactors

The purpose of the present study is to evaluate the impact a successful development of Breed and Burn (B&B) fast reactors and their fuel reconditioning technologies could have on the uranium ore utilization, uranium enrichment capacity, nuclear waste and energy security. It is found that a successful development of B&B reactors will offer 40-folds increase in the uranium ore utilization versus that presently achieved. A successful development of a fuel reconditioning technology could increase the attainable uranium utilization to 100-folds its present value. The growth rate of the installed capacity of B&B reactors possible to achieve using the “spawning” mode of operation is estimated to be nearly 4% per year. The amount of natural uranium required for starting a fleet of B&B reactors that will reach an electricity generation capacity of 1000 GWe by the end of this century is estimated to be the equivalent of 10 years of supply to the presently operating commercial fleet of LWRs in the US (86 GWe). No natural uranium and no enrichment capacity will be required to support this fleet beyond the later part of this century. The energy value of the depleted uranium stockpiles (“waste”) that will be accumulated in the US by that time is equivalent to, when used in the B&B reactors, up to 20 centuries of the total 2010 supply of electricity in the USA. It is therefore concluded that a successful development of B&B reactors and associated fuel reconditioning could provide a great measure of energy security, proliferation resistance and cost stability.     

Burnup optimization of once-through molten salt reactors using enriched uranium and thorium

The advantages of once-through molten salt reactors include readily available fuel,low nuclear proliferation risk,and low technical difficulty.It is potentially the most easily commercialized fuel cycle mode for molten salt reactors.However,there are some problems in the parameter selection of once-through molten salt reactors,and the relevant burnup optimization work requires further analysis.This study examined once-through graphitemoderated molten salt reactor using enriched uranium and thori...     

Evaluation of uranium thorium and plutonium thorium fuel cycles in a very high temperature hybrid system

In recent times, there is a renewed and additional interest in thorium because of its interesting benefits. Thorium fuel cycle is an attractive way to produce long term nuclear energy with low radiotoxicity waste. In addition, the transition to thorium could be done through the incineration of weapons grade plutonium or civilian plutonium. Th-based fuel cycles have intrinsic proliferation-resistance and thorium is 3–4 times more abundant than uranium. Therefore, thorium fuels can complement uranium fuels and ensure long term sustainability of nuclear power.In this paper, the main advantages of the use of fuel cycles based on uranium-thorium and plutonium-thorium fuel mixtures are evaluated in a hybrid system to reach the deep burn of the fuel. To reach this goal, the preliminary conceptual design of a hybrid system composed of a critical reactor and two Accelerated Driven Systems, of the type of very high temperature pebble-bed systems, moderated by graphite and cooled by gas, is analyzed.Uranium-thorium and plutonium-thorium once-through and two stages fuel cycles are evaluated. Several parameters describing fuel behaviour and minor actinide stockpile are compared for the analyzed cycles.     

Recycling of uranium from spent RBMK fuel in the nuclear fuel cycle

It is shown that there is promise in using the uranium product obtained by reprocessing spent nuclear fuel from RBMK reactors as a non-initial fuel source for thermal reactors. A technical path for spent nuclear fuel from RBMK reactors is proposed: radiochemical reprocessing and obtaining oxides of recycled uranium. Oxides of the category RBMK-poor are packed and then stored in a near-surface storage facility; oxides of the category RBMK-rich are fluoridated, and UF₆ is fed into separation production for additional enrichment to the required content of ²³⁵U. Additional advantages of recycled RBMK uranium as a source of non-initial ²³⁵U are the low content of ²³²U and the relatively low activity of spent fuel, which simplifies its reprocessing.     

Concept of Erbium Doped Uranium Oxide Fuel Cycle in Light Water Reactors

This paper is aimed at the development of a fuel cycle concept for host countries with a lack of nuclear infrastructure. To minimize plutonium proliferation concern the adoption of long-life core with no fuel radiochemical treatment on site is suggested. Current investigation relies upon light water reactor technology and plutonium-free fresh fuel. Erbium doped to uranium oxide (enrichment 19.8%) fuel is selected as the reference. Such a high enrichment is selected in attempt to approach the longest irradiation time in one batch mode. In addition to that, uranium enriched up to 20% does not consider as a nuclear material for direct use in weapon manufacture. A sequence of two irradiation cycles for the same fuel rods in two different light water reactors is the key feature of the advocated approach. It is found that the synergism of PWR and pressure tube graphite reactor offers fuel burnup up to 140GWd/tHM without compromising safety characteristics. Being as large as 8% in the final isotopic vector, fraction of ²³⁸Pu serves as an inherent protective measure against plutonium proliferation.     

Study of the radiotoxicity of actinides recycling in boiling water reactors fuel

In this paper the production and destruction, as well as the radiotoxicity of plutonium and minor actinides (MA) obtained from the multi-recycling of boiling water reactors (BWR) fuel are analyzed. A BWR MOX fuel assembly, with uranium (from enrichment tails), plutonium and minor actinides is designed and studied using the HELIOS code. The actinides mass and the radiotoxicity of the spent fuel are compared with those of the once-through or direct cycle. Other type of fuel assembly is also analyzed: an assembly with enriched uranium and minor actinides; without plutonium. For this study, the fuel remains in the reactor for four cycles, where each cycle is 18 months length, with a discharge burnup of 48 MWd/kg. After this time, the fuel is placed in the spent fuel pool to be cooled during 5 years. Afterwards, the fuel is recycled for the next fuel cycle; 2 years are considered for recycle and fuel fabrication. Two recycles are taken into account in this study. Regarding radiotoxicity, results show that in the period from the spent fuel discharge until 1000 years, the highest reduction in the radiotoxicity related to the direct cycle is obtained with a fuel composed of MA and enriched uranium. However, in the period after few thousands of years, the lowest radiotoxicity is obtained using the fuel with plutonium and MA. The reduction in the radiotoxicity of the spent fuel after one or two recycling in a BWR is however very small for the studied MOX assemblies, reaching a maximum reduction factor of 2.