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.     

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.     

On the main objectives of transmutation cycles for long-lived fission products and minor actinides

The present paper makes an effort to look at the problem of radiowaste from the view point of recent trends in fuel cycle development. Assuming nuclear fission as an energy source for a long-term perspective, the obvious goal of transmutation of fission products is to stop their accumulation or, in other words, to approach equilibrium state and keep this at easily manageable level. Characteristic time to approach equilibrium and loses in multirecycling are addressed in this paper as the most important criteria in selecting appropriate transmutation technology. For the minor actinides transmutation is proposed in a way to upgrade the proliferation resistance of the fuel cycles. Analysis given in the present paper reveals the favourable potential of external neutron sources in solving the transmutation problems.     

Challenge of transmutation of long-lived nuclides

Transmutation of radioactive nuclides into stable or short-lived ones has been under discussion as a measure to deal with the wastes of nuclear technology since its very beginning. There has been a lot of research activities world-wide with various approaches to transmuter design, matrix for waste incorporation and end waste form. This diversity comes from differently formulated transmutation priorities which, in their turn, originated in differently formulated strategy for development of nuclear fuel cycles. The present paper aims at surveying the goals of waste transmutation in view of trends identified in the past decade and address some new characteristics for estimating its radiological cost.     

长寿命裂变产物在聚变驱动次临界堆包层中嬗变的中子学优化分析

商用裂变堆乏燃料中高放长寿命裂变产物(LLFP)由于其具有很强的放射毒性,所以对于它们的嬗变处理非常重要。在对世界上关于LLFP嬗变处理的广泛调研的基础上,考虑到LLFP的同位素分离技术的发展水平,选择了LLFP中99Tc、129I和135Cs的嬗变处理(?)料的化学形式,分析了不同慢化剂材料对嬗变能力的影响,同时针对聚变驱动次临界堆的多功能双冷核废料嬗变包层(DWTB)进行了LLFP嬗变的中子学设计和优化分析。     

SIMS investigation of the spallation and transmutation products production in lead

The production of spallation and activation products in liquid metals (Pb or Pb-Bi) is an important issue in the frame of the MEGAPIE and other ADS studies. Although it is usually evaluated by well established codes like the MCNPX, experimental validations of the calculations in real conditions are rare. This work is an attempt to deliver experimental data using the material irradiated in the Swiss Spallation source (SINQ). A target composed of SS316L cladding tubes filled with Pb was irradiated in SINQ with a total proton charge of 10.03 Ah. A cross-section of one rod has been prepared for analysis in the PSI fully shielded secondary ion mass spectrometer (SIMS). Mass scans have been realized on one irradiated specimen and compared to a reference un-irradiated sample. The SIMS measurement delivers no absolute quantitative measurements but allow the determination of the mass distribution of the long lived spallation and activation products in real materials. The analysis shows the production of a raw of isotopes in the mass range 50-140 amu in agreement with calculation realized in model cases. The measurements across the specimen demonstrate also the homogeneity of the spallation and activation products content in the rod cross-section. This analysis provides useful information on the long lived isotopes production in lead based spallation targets like MEGAPIE.     

JENDL/ImPACT-2018: a new nuclear data library for innovative studies on transmutation of long-lived fission products

ABSTRACT

A new nuclear data library, JENDL/ImPACT-2018, was developed for an innovative study on the transmutation of long-lived fission products. Nuclear reaction cross-sections were newly evaluated for incident neutrons and protons up to 200 MeV for 163 nuclides focusing on long-lived nuclei such as ⁷⁹Se, ⁹³Zr, ¹⁰⁷Pd and ¹³⁵Cs, adopting some parts of JENDL-4.0. Our challenge was an evaluation of cross-sections for a number of unstable nuclei over a wide energy range where the experimental data were very scarce. We estimated cross-sections based on a nuclear model code CCONE by incorporating an advanced knowledge on the nuclear structure theory and a model-parameterization based on new experimental cross-sections measured by the inverse kinematics. Through comparisons with available experimental data on the stable isotopes, it is found that the present data give better agreements with them than those in the existing libraries. In a neutronics simulation by the PHITS code, we also found that the largest impact of the present library was seen on the estimated amount of isotope productions.     

Radiological hazard of long-lived spallation products in accelerator-driven system

The present paper focuses on analysis of radiological hazard of spallation products that appears to be an important factor that might affect the choice of beam/target performance in designing the accelerator-driven systems. The analysis is done in terms of toxicity expressed in units of Annual Limit on Intake (ALI). It reveals the significant contribution of alpha emitting rare earths (¹⁴⁶Sm, ¹⁴⁸Gd, ¹⁵⁰Gd, ¹⁵⁴Dy) into overall toxicity of spallation targets.     

Computational fluid dynamics analysis of spallation target for experimental accelerator-driven transmutation system

One of the key milestones in the roadmap of the European accelerator-driven transmutation system (ADS) is the design and construction of the European experimental ADS (XADS). The window spallation target unit in the lead–bismuth eutectic (LBE) cooled reactor system is one of the basic options considered in the preliminary design study of XADS (PDS-XADS). This paper presents the computational fluid dynamics (CFD) analysis and the main results achieved for this option focusing on the coolability of the window. Steady-state as well as transient behavior, including beam interrupts and three major accident scenarios, has been analyzed using the CFD code CFX 5.6 with an advanced turbulence model. The required boundary conditions were provided by a one-dimensional system code. Based on the CFD analysis, the window geometry was modified in order to achieve sufficient cooling capability of the window under normal operating conditions. The transient behavior of the window temperature under beam trip conditions shows the importance of the beam interrupt duration to the thermal stress load of the window structural material. Further transient analysis of three major accidental scenarios, i.e., beam focusing, loss of heat sink, and beam intensity jump, indicates that the beam focusing accident gives the most serious safety concern. In this case, window failure occurs in less than 1 s after the start of the beam focusing.     

Fusion-driven transmutation of elemental palladium-fission product

The paper deals with transmutation of elemental palladium separated from the spent fuel of fission reactors into the stable isotopes of silver and cadmium. The most efficient transmutation environment is achieved with resonance neutron spectrum in a blanket of fusion-driven transmuter. Three types of plasma conditioning are considered: DT-plasma with equal fractions of deuterium and tritium, DT-plasma with reduced tritium fraction and pure DD-plasma.     

Numerical analysis on element creation by nuclear transmutation of fission products

A burnup calculation was performed to analyze the Apr`es ORIENT process, which aims to create highlyvaluable elements from fission products separated from spent nuclear fuels. The basic idea is to use nuclear transmutation induced by a neutron capture reaction followed by a β-decay, thus changing the atomic number Z of a target element in fission products by 1 unit. LWR(PWR) and FBR(MONJU) were considered as the transmutation devices. High rates of creation were obtained in some cases of platinum group metals(44Ru by FBR,46 Pd by LWR) and rare earth(64Gd by LWR,66 Dy by FBR). Therefore, systems based on LWR and FBR have their own advantages depending on target elements. Furthermore, it was found that creation rates of even Z(= Z + 1) elements from odd Z ones were higher than the opposite cases. This creation rate of an element was interpreted in terms of "average 1-group neutron capture cross section of the corresponding target element σc Z defined in this work. General trends of the creation rate of an even(odd) Z element from the corresponding odd(even) Z one were found to be proportional to the 0.78th(0.63th) power of σc Z, however with noticeable dispersion. The difference in the powers in the above analysis was explained by the difference in the number of stable isotopes caused by the even-odd effect of Z.     

Volatile fission product and sodium release from liquids

For the improvement of radioactive source term calculations the computer code revols has been developed for the mechanistic modeling of the evaporative release of volatible species (e.g. water, sodium and volatile fission products as NaJ, Cs and Rb) from different hosts into an inert gas atmosphere. The code, showing a modular structure, has been developed to be coupled with reactor containment safety analysis codes as the contain / lmr and lmfbr version. In substituting existing constant-retention-factor formulations by introducing a geometry and state dependent, instationary retention factor, an improved aerosol and fission product source calculation can be obtained. The comparison of theoretical predictions with experimental results performed at the Karlsruhe Research Center shows good agreement.     

Evaluation of the specific radioactivity of 40 elements created by nuclear transmutation of fission products

A burnup calculation was performed to analyze Après ORIENT process which aims at creating highly-valuable elements by nuclear transmutation of fission products (FPs) separated from LWR spent nuclear fuels. In this paper, numerical evaluation of the specific radioactivity of 40 created elements, from reloaded each FP element, with atomic number from 31 to 70 at the end of the time of 5-year-cooling after the irradiation for 1125 days in each LWR and FBR was carried out. These 40 created elements were classified in 6 categories according to levels of the specific radioactivity and the length of additional cooling period, which was needed for the specific radioactivity to decrease below the exemption level defined by International Atomic Energy Agency. As a result, created ₃₁Ga, ₃₂Ge, ₃₃As, ₃₅Br, ₆₈Er, and ₇₀Yb did not contain any radioisotopes at the end of the 5-year-cooling. It should be noted that created ₃₇Rb, ₅₇La, and ₆₀Nd had much lower specific radioactivities than natural composition of them. Moreover, specific radioactivities of created ₄₀Zr, ₄₂Mo, ₄₄Ru, ₄₆Pd, ₄₉In, and ₅₄Xe were sufficiently lower than their exemption levels at the end of the 5-year-cooling. On the other hand, created ₃₉Y, ₄₅Rh, ₅₀Sn, ₅₂Te, ₅₈Ce, ₅₉Pr, ₆₅Tb, and ₆₆Dy needed additional cooling period less than 10 years until their specific radioactivities decreased below their exemption levels. Then, each additional cooling period required for created ₄₈Cd, ₅₁Sb, ₆₄Gd, and ₆₉Tm was estimated at 10–100 years. Additionally, specific radioactivities of other 13 created elements would not decrease below their exemption levels even if they had been stored for 100 years. There could be significance to create important elements as resources classified in first 4 of the 6 categories defined in this paper, by nuclear transmutation of fission products. In consideration of the efficiency of creation, the radioactivity, and the importance as resources of each product, ₄₄Ru, ₄₆Pd, ₅₂Te, ₆₀Nd, and ₆₆Dy were specially selected as the most important created elements to be more researched in the future Après ORIENT program.     

The reactions between sodium and plutonia,urania-plutonia and urania-plutonia containing fission product simulants

The kinetics of the reaction between sodium and solid solutions of urania-30% plutonia have been investigated over the temperature range 500 to 800°C, and a pseudo-activation energy for the reaction has been determined. The threshold plutonium valency for the reactions to occur was found to be dependent on temperature: at 800°C a value of 3.41 ± 0.02 was determined, and at 700°C a value of 3.46 ± 0.03. The effect of the addition of cations of the fission products to the urania-plutonia solid solution on the nature of the reaction with sodium has also been investigated. Pellets containing some of the fission product cations were found to break up on reaction with sodium. The addition of these cations also resulted in increased changes in volume and increase in the rate of reaction lat low temperatures with respect to those with urania-plutonia.     

The cross sections of reactions resulting in transmutation of long-lived radionuclides of exhausted nuclear fuel exposed to fast neutrons

IATE. Translated from Atomnaya Énergiya, Vol. 73, No. 4, pp. 300-305, October, 1992.