Self-Consistent Nuclear Energy System Research Articles

Fusion-driven transmutation of selected long-lived fission products

The long-term radiological burden associated with nuclear power production is usually attributed to long-lived fission products (LLFP). Their lifetime and large equilibrium mass and hence radioactivity accumulated in the course of fission energy generation make their storage a rather formidable task to solve. Therefore the idea of artificial incineration of LLFP through their transmutation has been quite naturally incorporated into the concept of self-consistent nuclear energy system (SCNES) based primarily on fast breeder reactor technologies. However it is now acknowledged that neutron environment of fission facilities including fast breeder reactors does not seem most appropriate for LLFP transmutation. The issue has been then extensively developed within the framework of multi-component self-consistent nuclear energy system (MC-SCNES). Neutrons of specific quality required for LLFP transmutation are proposed there to be of non-fission origin. Given neutron excess available and neutron quality, a fusion neutron source (FNS) is appearing as the candidate No. 1 to consider for LLFP transmutation. Research on LLFP transmutation by means of FNS has very long history and has received an additional boost during the decade passed. In the present study, potential of thermal flux blanket of FNS is exemplified by transmutation of 93Zr and 126Sn, the most difficult LLFP to transmute. It is shown that transmutation of 93Zr is effective even with a rather modest neutron loading of 1 MWt·m −2, typical for ITER project. Transmutation of 126Sn, however, requires neutron loading of as high as 3 MWt·m −2 for DD fusion and is quite unattractive for DT fusion. In the latter case, transmutation through the threshold (n,2n) reaction may be preferable.

Feasibility study of large MOX fueled FBR core and applicability of various coolants and fuels aimed at the Self-Consistent Nuclear Energy System

The potential of a large MOX fueled fast breeder reactor (FBR) is evaluated with regard to its ability to transmute radioactive nuclides and its safety when incorporated in the self-consistent nuclear energy system (SCNES). The FBR's annual production amounts of selected long -lived fission products (LLFPs), Se-79, Tc-99, Pd-107, I-129, Cs-135 and Sm-151, can be transmuted by using a radial blanket region and part of a lower axial blanket region without any significant impact on the reactor's nuclear and safety characteristics. The other LLFPs are confined in the system. The hazard index level of the LLFPs per one ton of spent fuel from the system after 1000 years is as small as that of a typical uranium ore. To realize self-controllability (passive safety), the proposed FBR core concept employs gas expansion modules and a sodium plenum above the core. To realize self-terminability, even if MOX fuel melting should cause a core compaction, re-criticality of the core can be avoided by a fuel dilution and relocation module. The results show the MOX fueled FBR core has potential applicability to the SCNES. The fundamental applicability of various coolants and fuels is evaluated based on neutron balance toward the final goal of the ideal SCNES. The results show that gas coolant has a potential for increasing the transmutation efficiency of LLFPs. And an improved SCNES with several conventional FBRs and a FP transmutation reactor is also studied.

Nuclear energy system for a sustainable development perspective — Self-Consistent Nuclear Energy System-

In developing science and engineering and introducing it to society, it is not easy to view the future by studying technological aspects alone. However, the ongoing dispute over nuclear science and engineering seems to be biased too much toward technological aspects. We live in an age where technology cannot always solve all of our problems. Social or economic benefits are important factors to consider; society will not choose anything that lacks economic benefits. This point should be kept in mind from the beginning, namely, from the development stage. Although economic or social benefits are given a higher priority than technology, it is still difficult to view the future clearly. Scientific thinking that can develop into abstract or philosophical thinking will be more appropriate for viewing the future. At the turn of the century, scientific thinking should be developed to view the total picture of comprehensive nuclear science and engineering and its long-term perspective. This is the approach that society should support in determining the future direction of nuclear science and engineering as we head into the 21st century.

Feasibility study on nitride fuel core and recycling system toward Self-Consistent Nuclear Energy System

The concept of a nuclear fuel recycle system with a nitride fueled FBR core has been investigated as a part of related studies towards the Self-Consistent Nuclear Energy System (SCNES). Nitride fuel has been given attention because of its relatively high fuel density and high thermal conductivity. To materialize the SCNES concept, it is important to adequately use the excess neutrons produced in the chain reaction. The high fuel density of the nitride fuel brings out more of the excess neutrons and has a higher potential to transmute the long-lived fission products (LLFP's). The high thermal conductivity, in addition, provides margin of fuel melting, and gives negative feedback due to the Doppler reactivity in unprotected loss of flow accidents. In this paper, we discuss good use of nitride fuel in the SCNES.

A metallic fuel cycle for Self-Consistent Nuclear Energy System (SCNES)

A fast reactor core and fuel cycle concept has been discussed for Self-Consistent Nuclear Energy System (SCNES) concept. This paper discussed loading material candidates for long-lived fission products (LLFPs) and removal of stable nuclides from radioactive nuclides with isotope separation using tunable laser. Some of LLFPs were possible to be loaded in metal of the generated form. The potential for LLFP-confinement in the reactor system is discussed along with a metallic fuel cycle concept. The proposed fuel cycle scheme is a successful candidate for SCNES concept.

The implication of high-flux fusion neutron source for the self-consistency in multi-component nuclear energy system

Among fission products (FP) discharged from a fission reactor, long-lived fission products are considered as of primary concern. Their transmutation has been of high priority to reduce the long-term consequences of nuclear energy generation. A self-consistent nuclear energy system (SCNES) in which we center fast breeder reactor may not have enough degree of excess neutron sources to transmute the fission products that potentially would poses environmental hazards in long-term period if they are buried in geologic disposal. Here we propose a so-called multi-component SCNES in which fission reactor systems can be combined with fusion reactor systems mainly for compensating the loss of enough capability for the transmutation. Amongst long-lived fission products, major concern has been paid for iodine and technetium and little attention was given to radioactive 93Zr, although its hazard appears to be rather substantial. The importance of 93Zr transmutation is emphasized and the transmutation capability was examined with fusion neutron sources by incorporating adequate moderation structures. As a result, we have demonstrated that the fusion neutron sources with high-flux blanket can be applied to transmute 93Zr sufficiently and resolve the problem of its accumulation within the time period of several decades.

A metal fuel fast reactor core for the Self-Consistent Nuclear Energy System

Feasibility of transmutation of the major long-lived FPs (I, Pd, Tc, Sn, Se, Zr, Cs) while maintaining fuel breeding capability for the Self-Consistent Nuclear Energy System is evaluated based on the actinide recycle metal fuel core of a fast reactor. It is shown that I, Pd, Tc, Sn, Se, and Zr can be transmuted simultaneously by an aid of the isotope separation of Pd-107, Zr-93, Sn-126 and Se-79. Cs, which is difficult to transmute with the other FPs, is planned to be utilized as an in-reactor shielding material to confine in the system The overall assessment based on those results indicates that the developed system has the great potential toward the Self-Consistent Nuclear Energy System.

Elimination of recriticality potential for the Self-Consistent Nuclear Energy System

The ultimate safety goal of the Self-consistent Nuclear Energy System (SCNES) is to eliminate the recriticality-problem based on a simple safety logic. The principle of the elimination of the recriticality-problem is the Controlled Material Relocation (CMR) to establish the neutronic shutdown by removing the molten fuel to the out of core before a large scale pool formation which has potential of energetics driven by a super prompt criticality. The CMR concept should be reliable without significant impact on the core neutronic performance. As the typical core concepts to enhance this CMR characteristic, several design options are under consideration. They are fuel assemblies with inner duct structure (FAIDUS), fuel assemblies with hollow fuel pins in the axial blanket region (ABLE) for MOX fueled cores, and fuel assemblies without fuel pin bundle structure in the lower axial blanket region (ELAB) for the metallic fueled core. Based on the core design study and accident analyses, these CMR-oriented concepts have been found feasible without significant degradation of the neutronic performance In order to experimentally confirm the effectiveness of the CMR concept for the MOX fueled core, the EAGLE project has been started in 1998 by Japan Nuclear Cycle Development Institute (JNC) and The Japan Atomic Power Company (JAPC). The EAGLE project is the experimental program utilizing the out-of pile test facility and in-pile facility IGR of the National Nuclear Center of the Republic of Kazakhstan (NNC/RK).

Multi-Component Self-Consistent Nuclear Energy System for sustainable growth

Environmental harmonization of nuclear energy technology is considered as an absolutely necessary condition in its future successful development for peaceful use. Establishment of Self-Consistent Nuclear Energy System, that simultaneously meets four requirements — energy production, fuel production, burning of radionuclides and safety, strongly relies on the neutron excess generation. Implementation of external non-fission based neutron sources into fission energy system would open the possibility of approaching the Multi-Component Self-Consistent Nuclear Energy System (MC-SCNES) with unlimited fuel resources and zero radioactivity release. This provides strong evidence that nuclear energy could be considered as a base for the future sustainable growth in long perspective.

Neutron economy and nuclear data for transmutation of long-lived fission products

In the study of Self-Consistent Nuclear Energy System, the following 29 long-lived fission products (LLFPs) have been selected to be transmuted into stable or short-lived nuclides: 106Ru, 102Rh, 109Cd, 125Sb, 134Cs, 146,147Pm, 154,155Eu, 171Tm, 85Kr, 90Sr, 93mNb, 113mCd, 121mSn, 137Cs, 151Sm, 152Eu, 108mAg, 158Tb, 166mHo, 79Se, 93Zr, 94Nb, 99Tc, 107Pd, 126Sn, 129I, 135Cs. In the present study, the number of neutrons necessary for the transmutation of the 29 LLFPs with an FBR was evaluated, and the present status of the (n, γ) and (n,2n) cross section data of the 29 LLFPs in JENDL-3.2 and ENDF/B-VI was investigated. The main results of the present study are as follows: (1)only 0.25 neutron per fission is necessary for the transmutation of the 29 LLFPs with isotopic separation, whereas 6.8 neutrons are necessary with chemical separation, (2)the accuracy of the cross sections is 30 to 100% except for the (n, γ) cross sections of limited nuclides in limited incident neutron energy regions.

Inherent and Passive Safety Sodium-Cooled Fast Reactor Core Design with Minor Actinide and Fission Product Incineration

A self-consistent nuclear energy system (SCNES) can be a promising option as a future nuclear energy source. An SCNES should fulfill (a) efficient energy generation, (b) fuel production or breeding, (c) burning minor actinides with incinerating fission products, and (d) system safety. We focus on the system safety and present a simple evaluation model for the inherent and passive power stabilization capability of intact fast reactor cores under the conditions of an anticipated transient without scram (ATWS), i.e., self-controllability.The simple evaluation model is referred to as the “reactivity correlation model.” The model assesses self-controllability of a core based on the capabilities of reactivity feedbacks to stabilize transient power and maintain temperatures within predefined safety limits. Here the safety limits are “no fuel failure” and “nonboiling of coolant.”The reactivity correlation model was used to survey the self-controllability for metallic-fueled fast reactor cores. The survey was performed by selecting the core volume fractions of fuel, coolant, and structure; the arrangement of material compositions; and core configuration. A variety of reactor cores were examined, ranging from a standard 100-cm height to a flat 40-cm height. The effect of additions of sodium plena and channels, increased/decreased fuel volume fraction (Vf), loading 0 to 10 wt% minor actinides, and installing fission product-burning assemblies was also examined. The core performances were evaluated relative to tolerances against typical ATWSs, i.e., unprotected transient overpower and unprotected loss of flow. An optimum fast reactor core with the self-controllability as well as well-balanced tolerance against ATWSs resulted. The performance of this optimal core was examined for the other three prerequisites of a self-consistent nuclear energy system.

An application of metal fuel cycle technology toward Self-Consistent Nuclear Energy System (SCNES) concept

A fast reactor core and fuel cycle concept has been discussed for Self-Consistent Nuclear Energy System (SCNES) concept. This paper discussed loading material candidates for long-lived fission products (LLFPs) and LLFPs burning capability. Some of LLFPs were possible to be loaded in metal of the generated form. The potential for LLFP-confinement in the reactor system is discussed along with metallic fuel cycle concept. The proposed fuel cycle scheme is a successful candidate for SCNES concept.

Feasibility study of large MOX fueled FBR core aimed at the Self-Consistent Nuclear Energy System

The potential of a MOX fueled fast breeder reactor (FBR) is evaluated with regard to its ability to transmute radioactive nuclides and its safety when incorporated in the so-called self-consistent nuclear energy system (SCNES). The FBR's annual production amounts of selected long-lived fission products (LLFPs), Se-79, Tc-99 Pd-107, I-129, Cs-135 and Sm-151, can be transmuted by using a radial blanket region and a part of a lower axial blanket region without any significant impact on its nuclear and safety characteristics. The other LLFPs are confined in the system. The hazard index level of the LLFPs per one ton of spent fuel from the system after 1000 years is as small as that of a typical uranium ore. To realize self-controllability (passive safety), the proposed FBR core concept employs gas expansion modules and sodium plenum above the core. To realize self-terminability, even if MOX fuel melting should cause a core compaction, recriticality of the core can be avoided by a fuel dilution and relocation module. The results show the MOX fueled FBR core has potential applicability to the SCNES. With the final goal of the ideal SCNES, fundamental applicability of various coolants and fuels is evaluated based on neutron balance. It is shown that the harder the core spectra is, the larger the potential for transmuting LLFPs would be.

Toward Zero-Release of Radioactive Wastes. The Expectation and Role of Fusion Neutron Sources.

The Establishment of a Self-Consistent Nuclear Energy System (SCNES) attempts to meet the following four requirements -energy production, fuel production, the burning of radionuclides, and system safety with a strong reliance on excess neutron generation. Based on several milestone studies, it has been pointed out that a fast fission reaction provides an appreciable neutron excess to incinerate fission products, while MA (Minor Actinides) may be treated as a fuel along with Pu in this system. To improve both the quality and quantity of neutron excess for the transmutation of radiowastes, neutron generation in the external neutron sources based on accelerator and/or fusion technologies was evaluated. Our results suggest that multi-component SCNES supplemented by accelerator-driven and fusion-based neutron sources may approach the final goal of the development of a nuclear energy system that is safe, wasteless, and supported by reliable fuel resources.

A feasibility study on FP incineration for self-consistent nuclear energy system (SCNES)

A fast reactor core and fuel cycle concept is discussed for the future “Self-Consistent Nuclear Energy System (SCNES)” concept. The present study mainly discussed long-lived fission products (LLFPs) burning capability and recycle scheme in the framework of metal fuel fast reactor cycle, aiming at the goals for fuel breeding capability and confinement for TRU and radio-active FPs within the system. Combining neutron spectrum-shift for target sub-assemblies and isotope separation using tunable laser, LLFP burning capability is enhanced. This result indicates that major LLFPs can be treated in the additional recycle schemes to avoid LLFP accumulation along with energy production. In total, the proposed fuel cycle is a candidate for realizing SCNES concept.

Feasibility study of nitride fuel core and recycle system toward self-consistent nuclear energy system

A concept of nitride core and recycling system in relation to SCNES (1) has been investigated and it has been found that the safety of intact core is enhanced by zero burnup reactivity and negative feedback at ULOF (Unprotected Loss of Flow) and ULOHS (Unprotected Loss of Heat Sink). The self-actuating modules are examined so as to eliminate recriticality of degraded core. The nitride core can employ transuranics-added fuels and burn long life radioactive fission products after isotope-separation of FPs. The enrichment of 15N and the laser isotope separation seem to need about 2.4% of produced electric energy in the preliminary evaluation.

Applicability evaluation to a MOX fueled fast breeder reactor for a self-consistent nuclear energy system

The potential for a MOX fueled fast breeder reactor (FBR) is evaluated with regard to its ability to transmute radioactive nuclides and its safety when incorporated in a self-consistent nuclear energy system (SCNES). The FBR's annual production amounts of selected long-lived fission products (LLFPs), Se-79, Tc-99, Pd-107, I-129, Cs-135 and Sm-151, can be transmuted by using a two layer radial blanket region without a significant impact on core nuclear and safety characteristics. The other LLFPs are confined in the system. The hazard index level of the LLFPs per one ton of spent fuel from the system after 10 2 years is as small as that of a typical uranium ore. Regarding self-controllability in the system's safety, the proposed FBR core concept has an inherent negative reactivity feedback with a gas expansion module, sodium plenum above the core and burnup reactivity compensation module. So sodium boiling and fuel melting will be avoided in anticipated transient without scram events. Regarding self-terminability, even if the MOX fuel melting should cause a core compaction process, re-criticality of the core can be avoided by a fuel dilution and relocation module.

Isotope separation methods for self-consistent nuclear energy system

It is known that for transmutation of fission products(FPs) in the concept of self-consistent nuclear energy system(SCNES) based on fast neutron reactor it is necessary to apply isotope separation of some FPs to keep neutron balance (to decrease parasitic capture of neutrons by stable isotopes). It is a question whether such FPs isotope separation can be feasible or not within amount of nuclear fission energy production. So it is necessary to consider isotopic content of FPs after fast reactor and to choose energetically appropriate isotope separation method for each radioactive FPs taking into account safe radioactivity level of FPs. In this paper we discuss about isotope separation method for SCNES. Isotopic composition of FPs was calculated using tables of fission yields from 239Pu fission. It isshown that concentrations of radioactive isotope in the main FPs to be isotopically separated are significant and vary from 2% in ruthenium up to 74% in iodine. We consider new isotope separation methods developed recently such as plasma separation process (PSP) based on selective ion cyclotron resonance heating and atomic vapor laser isotope separation (AVLIS) as a possible candidates. It seems to be energetically profitable to combine various methods to achieve desired separation characteristics. Since the most of FPs have a high initial concentration of radioactive isotope, PSP method seems to be a good candidate for first stages of separation process. We consider the main parts of energy expenditure in one PSP module and its separation characteristics. Estimations of energy consumption in multistage isotope separation process of FPs give maximum value 100keV/fiss. using PSP only and 3MeV/fiss. using AVLIS only. We can significantly decrease these values using AVLIS after PSP when concentration of target isotope in separation cascade will become sufficiently low. We can affirm that energy consumption in isotope separation of FPs is less than 60 MeV of electricity per one fission in nuclear reactor.

Long-lived FP burning based on the actinide recycle metal fuel core

Feasibility of burning of the major long-lived FPs (I, Pd, Tc, Sn, Se, Zr, Cs) while maintaining fuel breeding capability for the Self-Consistent Nuclear Energy System is evaluated based on the actinide recycle metal fuel core of a fast reactor. It is shown that I, Pd, Tc, Sn, Se, and Zr can be burnt simultaneously by an aid of the isotope separation of Pd-107, Zr-93 and Se-79. Cs, which is difficult to burn with the other FPs, should be utilized as an in-reactor shielding material to confine in the system. The selection of the target FPs to be burnt are also validated by using the Burden Index. The overall assessment based on those results indicates that the developed system has the great potential to achieve the goal of the Self-Consistent Nuclear Energy System.

Safety characteristics of the SCNES core

The core concept of the Self-Consistent Nuclear Energy System (SCNES) and its safety characteristics have been investigated from the view point of the elimination of recriticality. The recriticality potential can be eliminated based on characteristics of self-controllability to prevent the core damage and self-terminability to limit the propagation of core disruption. These two characteristics are simultaneously achieved by the radial heterogeneous two region core with different height. This core consists of leading and driver zones where hybrid metallic fuels with different melting point are installed. The self-controllability can be achieved by decreased coolant density effect due to the above core sodium plenum at the leading zone. The self-terminability is achieved by the Controlled Material Relocation (CMR), which is essentially the preceding downward in-pin fuel relocation selectively generated at the leading zone. U-Pu-1Zr alloy is used to the leading zone fuel due to lower melting point (900°C) than the driver fuel of U-Pu-10Zr(1100°C). Based on the quantitative investigations, it was emphasized that the recriticality potential can be eliminated by the in-pin fuel CMR even for severe unscrammed events such as a total pump stick for the primary coolant system and a total control rods withdrawal.