Transmutation Of Long-lived Fission Products Research Articles

Monte Carlo analysis of the long-lived fission product neutron capture rates at the Transmutation by Adiabatic Resonance Crossing (TARC) experiment

The design of Accelerator Driven Systems (ADS) requires the development of simulation tools that are able to describe in a realistic way their nuclear performance and transmutation rate capability. In this publication, we present an evaluation of state of the art Monte Carlo design tools to assess their performance concerning transmutation of long-lived fission products. This work, performed under the umbrella of the International Atomic Energy Agency, analyses two important aspects for transmutation systems: moderation on Lead and neutron captures of 99Tc, 127I and 129I. The analysis of the results shows how shielding effects due to the resonances at epithermal energies of these nuclides affects strongly their transmutation rate. The results suggest that some research effort should be undertaken to improve the quality of Iodine nuclear data at epithermal and fast neutron energy to obtain a reliable transmutation estimation.

Fast Accelerator Driven Subcritical System for Energy Production Using Burned Fuel

Accelerators Driven Systems (ADS) are an innovative type of nuclear system, which is useful for long-lived fission product transmutation and fuel regeneration. The ADS consist of a coupling of a sub-critical nuclear core reactor and a proton beam produced by a particle accelerator. These particles are injected into a target for neutrons production by spallation reactions. The neutrons are then used to maintain the fission chain in the subcritical core.The aim of this study is to investigate the nuclear fuel evolution of a lead cooled accelerator driven system used for energy production and high-level waste transmutation. The fuel studied is a mixture based upon 232Th-233U and Pu-MA extracted from PWR spent. The target is a lead spallation target and the core is filled with a hexagonal lattice. In order to reduce the negative reactivity caused by the presence of protactinium, moderator is not used.In this work is used the Monte Carlo code MCNPX 2.6.0, that presents the depletion/burnup capability, combining a ADS source and kcode-mode. The keff evolution, the neutron energy spectra in the core and the nuclear fuel depletion during the burnup are evaluated. Keywords: ADS, thorium, MCNPX.

Experimental and numerical study on lead–bismuth heat transfer in a fuel rod simulator

As a task of the EU project IP EUROTRANS towards development of an Accelerator Driven System (ADS) dedicated to the transmutation of long-lived fission products, experiments and simulations were performed on the TALL test facility at KTH to investigate thermal hydraulics along a single fuel rod simulator cooled by lead–bismuth eutectic (LBE). The fuel rod simulator is concentrically inserted in a tube, so that an annular channel is formed for LBE flow. This paper presents the measured temperature profiles in the annular channel, and the comparisons with the simulation results of the CFX code. The primary objective is to help understanding the LBE heat transfer characteristics and qualifying the turbulence and heat transfer modeling for LBE application. The quantitative comparison between the calculated and measured temperatures of the LBE indicates that the simulation underestimates the experiment at most radial and axial positions. Finally the uncertainties in measurement and the deficiency in turbulence models resulting in such a disagreement were discussed, which will be directive and beneficial to future work in the field.

Study on the LLFPs transmutation in a super-critical water-cooled fast reactor

The performance of the super-critical water-cooled fast reactor (Super FR) for the transmutation treatment of long-lived fission products (LLFPs) was evaluated. Two regions with the soft neutron spectrum, which is of great benefit to the LLFPs transmutation, can be utilized in the Super FR. First region is in the blanket assembly due to the ZrH 1.7 layer which was utilized to slow down the fast neutrons to achieve a negative void reactivity. Second region is in the reflector region of core like other metal-cooled fast reactors. The LLFPs selected in the transmutation analysis include 99Tc, 129I and 135Cs discharged from LWR or fast reactor. Their isotopes, such as 127I, 133Cs, 134Cs and 137Cs were also considered to avoid the separation. By loading the isotopes ( 99Tc or 127I and 129I) in the blanket assembly and the reflector region simultaneously, the transmutation rates of 5.36%/GWe year and 2.79%/GWe year can be obtained for 99Tc and 129I, respectively. The transmuted amounts of 99Tc and 129I are equal to the yields from 11.8 and 6.2 1000 MWe-class PWRs. Because of the very low capture cross section of 135Cs and the effect of other cesium isotopes, 135Cs was loaded with three rings of assemblies in the reflector region to make the transmuted amount be larger than the yields of two 1000 MWe-class PWRs. Based on these results, 99Tc and 129I can be transmuted conveniently and higher transmutation performance can be obtained in the Super FR. However, the transmutation of 135Cs is very difficult and the transmuted amount is less than that produced by the Super FR. It turns out that the transmutation of 135Cs is a challenge not only for the Super FR but also for other commercial fast reactors.

Fission of heavy Λ hypernuclei with the Skyrme–Hartree–Fock approach

Fission-related phenomena of heavy Λ hypernuclei are discussed with the constraint Skyrme–Hartree–Fock + BCS (SHF + BCS) method, in which a similar Skyrme-type interaction is employed also for the interaction between a Λ particle and a nucleon. Assuming that the Λ particle adiabatically follows the fission motion, we discuss the fission barrier height of U Λ 239 . We find that the fission barrier height increases slightly when the Λ particle occupies the lowest level. In this case, the Λ particle is always attached to the heavier fission fragment. This indicates that one may produce heavy neutron-rich Λ hypernuclei through fission, whose weak decay is helpful for the nuclear transmutation of long-lived fission products. We also discuss cases where the Λ particle occupies a higher single-particle level.

Modification of PROMETHEUS Reactor as a Fusion Breeder and Fission Product Transmuter

This study presents the analyses of the fissile breeding and long-lived fission product (LLFP) transmutation potentials of PROMETHEUS reactor. For this purpose, a fissile breeding zone (FBZ) fueled with the ceramic uranium mono-carbide (UC) and a LLFP transmutation zone (TZ) containing the 99TC and 129I and 135Cs isotopes are separately placed into the breeder zone of PROMETHEUS-H design. The neutronic calculations are performed by using two different computer codes, the XSDRNPM/SCALE4.4a neutron transport code and the MCNP4B Monte Carlo code. A range of analyses are examined to determine the effects of the FF, the fraction of 6Li in lithium (Li) and the theoretical density (TD) of Li2O in the tritium breeder zone (TBZ) on the neutronic parameters. It is observed that the numerical results obtained from both codes are consistent with each other. It is carried out that the profiles of fission power density (FPD) are flattened individually for each FF (from 3 to 10%). Only, in the cases of FF ≥ 8%, the system is self sufficient from the point of view of tritium generation. The results bring out that the modified PROMETHEUS fusion reactor has capabilities of effective fissile breeding and LLFP transmutation, as well as the energy generation.

Immobilization of strontium, cesium and rhenium into .ALPHA.-SiAlON ceramics assisted with co-doping of yttrium

Immobilization of long-lived fission products (LLFP) such as radioactive Tc, Cs and Sr into α-SiAlON ceramics was evaluated using stable isotopes instead of radioactive isotopes, and the applicability of α-SiAlON ceramics as the inert matrix for transmutation of LLFP was investigated. In the case of single addition of SrO, SrCΟ 3 , Cs 2 CO 3 or ReO 2 to the starting materials, α-SiAlON single phase was not formed after hot-pressing. When Y 2 Ο 3 was added with SrO, SrCO 3 or Cs 2 CΟ 3 to the starting materials (α-Si 3 N 4 , AlN and α-Al 2 O 3 ) in optimum compositions, α-SiAlON single phase was obtained after hot-pressing at 1700°C or 1800°C. From the EDS analysis, Sr and Y were detected from grains. It is suggested that Y would assist the expansion of interstices of α-SiAlON lattice, resulting in the incorporation of Sr 2+ into α-SiAlON lattice. In the case of Cs addition with Y, Cs was not incorporated into interstices due to much larger ionic radius of Cs + . Bulk density of hot-pressed α-SiAlON ceramics obtained in this study was higher values and densification proceeded well. From these results, it was found that the immobilization of Sr in α-SiAlON was successfully achieved with co-doping of Y, and α-SiAlON ceramics would be an inert matrix for transmutation of long-lived radioactive Sr.

Time-dependent Neutronic Analysis for High Level Waste Transmutation in a Fusion-driven Transmuter

This study presents time-dependent transmutations of high-level waste (HLW) including minor actinides (MAs) and long-lived fission products (LLFPs) in the fusion-driven transmuter (FDT) that is optimized in terms of the neutronic performance per fusion neutron in our previous study. Its blanket has two different transmutation zones (MA transmutation zone, TZMA, and LLFP transmutation zone, TZFP), located separately from each other. High burn-up pressured water reactor (PWR)-mixed oxide (MOX) spent fuel is used as HLW. The time-dependent transmutation analyses have been performed for an operation period (OP) of up to 10 years by 75% plant factor (η) under a first-wall neutron load (P) of 5 MW/m2. The effective half-lives of the MA and LLFP nuclides can be shortened significantly in the considered FDT while substantial electricity is produced in situ along the OP.

China ADS sub-critical experimental assembly—Venus-1 and preliminary experiment

China’s accelerator-driven sub-critical system (ADS) sub-critical experimental assembly—Venus-1 and the preliminary experiment is presented. The core of Venus-1 is a coupled one of a fast neutron zone and a thermal neutron zone. The fast neutron zone is at the centre of the core and formed by natural uranium fuel. A fast neutron spectrum field can be produced in the fast neutron zone and used for the transmutation of minor actinides (MAs). The thermal neutron zone surrounds the fast neutron zone and is formed by low-enriched uranium fuel. It is a fission zone. An epithermal neutron zone between the fast neutron zone and the thermal neutron zone can be established for the transmutation of longlived fission products (LLFP). On July 18, 2005, the first fuel element was loaded into the Venus-1 sub-critical assembly and some preliminary experiments about the sub-critical neutronics were performed. The Venus-1 can be driven by an Am-Be source or other steady neutron source (Cf-252, D-D reaction and D-T reaction) to study the effect of the external neutron source with different energies or a D-T pulsed neutron source on the dynamic characteristics.

Fusion-driven hybrid system with ITER model

Neutron calculations have been carried out for a fusion–fission (FF) hybrid reactor system, focused on the Japanese situation, to be realized as soon as possible. The ITER facility configuration has been taken as basis for the calculations. In the blanket region reprocessed plutonium and natural uranium oxide were taken as nuclear fuel for neutron/energy multiplication and lithium oxide with beryllium for tritium breeding. The plasma conditions were derived from the JT-60 experience. The neutron analysis has been done with a three-dimensional Monte Carlo code and a point burnup code. As a result, it was found that the proposed FF concept can be operated for at least 5 years with acceptable good performance from the point of view of tritium breeding, sub-criticality, energy multiplication and used for transmutation of long-lived fission products without nuclear fuel exchange and shuffling.

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.

Transmutation of Long-Lived Fission Products Driven by D-T and D-D Fusion: Specific Neutronics and Radiological Consequences

In view of the poor transmutation environments in fission reactors, elimination of long-lived fission products (FPs) remains an unresolved problem in the quest for a harmonized nuclear energy system. Since plasma fusion technology could provide effective neutron support, it is important to elaborate the qualities, features, and dimensions of a fusion neutron source exclusively oriented to FP transmutation, and this forms the main objective of this paper. Recent trends in fusion technology are examined to shape the conceptual blanket design features for D-T- and D-D-driven transmuters that match the demanding set of transmutation requirements. Material behavior under neutron irradiation in these blankets constitutes the central issue underlying this paper and yields the operational limits and radiological cost of FP incineration.

Present status and future prospects of the work on the Moscow meson factory

The current status and prospects of work on the Moscow meson factory are described. The maximum energy obtained at the present time is limited by the existing powerful klystrons and is 247 MeV. The maximum beam intensity is 150 μA. The accelerator beam is used for fundamental research and for solving applied problems. The average duration of the sessions is 2000 h per year. Three of the five branches of the proton channel which are provided in the design are in operation in the experimental complex. This includes the branch on the multifunctional neutron complex, which is to be used for, among other things, research on nuclear transmutation of long-lived fission products, Np, Am, Cm, and the electronuclear method of generating electricity. The first phase of the proton therapy complex is under construction.

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.

Study on multi-recycle transmutation of LLFP in light water reactor

The effectiveness of transmutation for long-lived fission products (LLFP) in light water reactors (LWR), i.e. both BWR and PWR, considering the large capture cross-section of FPs in thermal region was evaluated. Calculation results of iodine and technetium transmutation in BWR and PWR suggested an effective use of BWR as compared to PWR. To obtain transmutation fraction [TF] of 30 to 40%, the irradiation period needed for 99Tc transmutation was estimated as 10 to 15 years, and the period for 129I transmutation was estimated as 30 to 40 years, respectively. The evaluations bring a new concept of multi-recycle LLFP transmutation using LWRTR (LWR for transmutation).

Accelerator-driven system for transmutation of high-level waste

The accelerator-driven transmutation system has been studied at the Japan Atomic Energy Research Institute. This system is a hydrid system which consists of a high intensity accelerator, a spallation target and a subcritical core region. In the conceptual design study, two types of system concepts, sodium cooled and lead-bismuth cooled system, are being studied. In this study, we fucus on our lead-bismuth cooled accelerator-driven transmutation system to investigate basic characteristics. The fuel compositions were optimized for efficient transmutation of minor actinide. The transmutation of long-lived fission products was also considered.

The Transmutation of Long-Lived Fission Products by Neutron Irradiation

A general physical approach and simplified algorithm have been developed that allow utilities to choose their strategy for treatment of the most dangerous long-lived fission products (either to incinerate under neutron flux or to store in underground repository) as well as to assess the overall neutron consumption needed for their incineration in a fast neutron spectrum. It has been demonstrated that if nuclear power can solve transuranic (TRU) waste transmutation problems and be able to incinerate the most toxic long-lived nuclides, such as Tc, I, and Cs (it demands ~0.15 n/fission for all these nuclides without isotopic separation), then the long-term radiotoxicity in the underground repository will not exceed the initial radiotoxicity of uranium fuel. This is one of the most important criteria of the radiologically clean nuclear power concept. Hence, apart from TRU transmutation problems, the emphasis is now on long-lived fission product incineration.

Transmutation of long-lived fission products with use of available excess neutrons in BWR core

Feasibility of transmutation of long-lived Fps in BWR is studied from the view point of neuron balance. Pointing out the equilibrium mass amount of LLFP such as 129I, 99Tc, and 126Sn in BWR core, the neutron balance analysis shows that the available neutrons produced by the current BWR core modification is satisfactory to the required amount of neutrons for LLFP transmutation. Core performance of the LLFP-recycled BWR is then analyzed and the result shows satisfactory results for the present core design criteria. The results confirm the potential of the transmutation of LLFP in BWR and that the eventual radioactive hazard of the radwaste coming form the LLFP recycled BWR can be reduced well below the hazard level of the burned uranium.