Fission Of 235U Research Articles

Accurate measurements of delayed neutron data for reactor applications: methodology and application to 235U(nth,f)

Large inconsistencies still exist in nuclear data libraries regarding the kinetic parameters of delayed neutron (DN) precursors. As an example, there is a 17% gap between ENDF-B/VIII.0 and JEFF-3.3 on the average lifetime T1/2 of DN precursors from thermal fission of 235U. This parameter is of major importance for reactivity predictions of nuclear reactors in nominal or accidental configurations. In this context, CEA is actively participating to the ALDEN project (Average number and Lifetime of DElayed Neutrons) which aims at providing the nuclear data community with new data sets of DN from thermal and fast neutron induced fission of various actinides. A dedicated experimental setup was designed and optimized for that purpose and is presented in this paper. It consists of a “long counter” detector containing 16 proportional counters filled with 3He, embedded in a high density polyethylene matrix. The detector surrounds a fissile target prepared in the form of a miniature fission chamber, containing a few hundreds of micro-grams of fissile material. This set-up is connected to fast and efficient neutron shutters that can produce step-irradiations of variable durations. The equations driving the DN counting following step-irradiations of the fissile target are established and discussed in the perspective of DN yield or group parameter measurement. A comprehensive analysis of the different steps of data reduction is detailed: dead time characterization, Region of Interest (ROI) determination, absolute and relative efficiency calibration, fission rate estimation, irradiation time and background determination, DN decay curve production and physical parameter fitting. Following a prototype experiment performed in 2018 at the PF1b cold neutron beam line of Institute Laue Langevin (ILL, Grenoble, France), we discuss here the analysis of two campaigns occurring in 2019 and 2021 in which significant improvements were achieved in terms of background minimization, counting statistics and fission rate determination. The achievements of this work are the measurement of the delayed neutron emission per fission for the thermal neutron induced fission of 235U, estimated at (1.625 ± 0.010) % and the group parameters leading to an estimated lifetime of T1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{1/2}$$\\end{document} = (8.87 ± 0.10) s. Those results are consistent with the values recommended by the IAEA/CRP work and they come with reduced uncertainties compared with previously published results.

Independent isomeric yield ratios of fission products in the epi-cadmium neutron induced fission of 235U

In the epi-cadmium neutron induced fission of 235U, independent isomeric yield ratios (IR) of fission products 130,132Sb, 131,133Te, 134,136I, 135Xe and 138Cs have been measured by using an off-line gamma-ray spectrometric technique. The average neutron energy of the epi-cadmium reactor neutron spectrum is 1.9 MeV. From the IR values, the root mean square fragment angular momenta (JRMS) were deduced by using spin dependent statistical model analysis. The IR and JRMS values of considered fission products in the epi-cadmium neutron induced fission of 235U were compared with the literature data in the thermal neutron induced fission of 235U to examine the influence of excitation energy on nuclear structure effect.

Investigation of uranium analysis using 140Ba/140La induced from 235U fission reaction

Investigation of uranium analysis using 140Ba/140La induced from 235U fission reaction

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 235U

Cumulative and independent yields of various fission products within the mass ranges of 78 to 117 and 123 to 155 have been measured in the epi-cadmium reactor neutron-induced fission of 235U by using an off-line gamma-ray spectrometric technique. The average neutron energy <En> of the epi-cadmium reactor spectrum is 1.9 MeV. From the cumulative yields, post-neutron mass chain yields were obtained by applying the charge distribution correction. In the mass yield distribution, values of the full-width at tenth-maximum of light and heavy mass wings, average light mass <AL> and heavy mass <AH>, and average number of neutrons <ν> were obtained. The peak-to-valley ratio in the epi-cadmium neutron-induced fission of 235U was obtained for the first time. The present data in the 235U(n,f) reaction were compared with the literature data in the 235U(nth,f) reaction to examine the role of excitation energy on the mass yield distribution parameters and nuclear structure effect. The role of the standard I and standard II asymmetric modes of fission was also discussed.

Studies of beam ion confinement to enhance plasma performance on EAST

Abstract A key physics issue for achieving steady-state high-performance plasmas on EAST tokamak is to decrease beam-ion losses to improve plasma confinement during neutral beam injections (NBIs). To decrease the beam losses, previous counter-Ip NBI injections are upgraded to co-Ip injections. Analysis shows that due to the reversed direction of drift across the flux surfaces caused by the pitch angle, the beam prompt loss fraction decreases from about 49% to 3% after the upgrade. Moreover, because of the change of entire beam path, beam shine-through (ST) loss fraction for counter-Ip tangential and counter-Ip perpendicular injections is reversed to co-Ip tangential and co-Ip perpendicular injections, respectively. Due to change in the initial trapped-confined beam ion fraction caused by the peaked pitch profiles, the losses induced by toroidal ripple field are also reversed after the upgrade. To further improve the beam-ion confinement under the present NBI layout, the amplitudes of toroidal field are increased from 1.75 to 2.20 T. Result shows that, due to the smaller orbit width and peaked pitch angle profile, the beam prompt loss power is lower with higher toroidal field. Due to the synergy of higher initial trapped-confined beam ion fraction and narrower Goldston-White-Boozer (GWB) boundary, the loss induced by ripple diffusion is higher with higher toroidal field. The combined effect of beam ST loss, prompt loss, and ripple loss, contributes to the increase in beam ion density. The decrease in beam loss power enhances beam heating efficiency, especially the fraction of beam heating ions. Finally, comparison between simulation and measurement by 235U fission chamber (FC) indicates that the increase in neutron rate are mainly contributed by improvement of beam-ion confinement. This study can provide potential support for beam operation and high-Ti experiment on EAST tokamak.

Prompt neutron emission calculations for the photon induced reactions of 238U and 232Th in the giant dipole resonance energy region

Prompt emission calculations for the photon induced fission of 238U and 232Th in the GDR energy region were performed by using (a) a systematic of input parameters for the most probable fragmentation approach (obtained on the basis of only spontaneous and neutron induced fission of actinides) and (b) photo-fission cross section ratios (expressing the fission probabilities at incident energies where multiple fission chances are involved) provided by nuclear reaction calculations performed with the EMPIRE code. The prompt neutron emission results describe well the experimental data recently measured at the laser Compton-scattering γ-ray source of the NewSUBARU facility, validating the use of this input parameter systematic for photon induced fission, too. The modelings and procedures described in this paper can constitute an useful tool for the prediction of prompt neutron emission data in photon induced reactions without any experimental information.

Total excitation energy distribution for neutron-induced fission and photo-fission of uranium isotopes

The fission fragment total excitation energy, TXE(A), is investigated for neutron-induced fission of uranium isotopes using three different methods. Different methods for calculations of the TXE(A) produced by the decay of low excited systems are analyzed and their results are compared with the available TXE values. The calculated TXE values have been compared with the results of other studies for the neutron induced fission of 233U, 235U as well as the photo-fission of 238U. The scission point method for evaluating TXE has been modified by comparing the available and calculated results. TXE(A) is evaluated for other uranium isotopes using three methods. It is found that TXE values in the neutron induced fission of 233U, 235U and the photo-fission of 238U are greater than the calculated TXE values of other uranium isotopes. The TXE values of light uranium isotopes decrease with increasing their mass numbers, while the TXE values of heavy uranium isotopes increase as their mass numbers increase. Also, the calculated TXE values for all isotopes increase sharply near the symmetric region, which is due to the formation of unstable fission fragment. On the other hand, a slight increase in neutron multiplicity and TXE values can be observed in heavy fission fragments (Ah>155), which could be due to the neutron excess. However, the sharp increase in neutron multiplicity and TXE values in some studies for the heavy fission fragments (Ah>155) is due to a missing correction in the data analysis.

Mesoporous manganese oxide/multiwalled carbon nanotubes as a base material for the 99mTc/99Mo generator: Development, characterization, and implementation study

The uptake capacity of Mo on the active MnO2 nanoparticles was determined in a previous study, and it was found to be 7 mg/g. This value is appropriate for 99Mo, which is more complex to separate due to its production using the 235U fission reaction with a high specific activity. Currently, multiwall carbon nanotubes (MWCNTs) linked to mesoporous MnO2 are being prepared and studied as a novel sorbent for the 99Mo produced with a low specific activity by thermal neutron activation of natural molybdenum consisting of 92M0, 94Mo, 95Mo, 96Mo, 97Mo, 98Mo, and 100Mo, based on the 98Mo(n,γ) reaction to prepare the 99Mo/99mTc generator with a high uptake capacity for Mo. FTIR spectroscopy, EDX-mapping, XRD, particle size analysis, FESEM, and TEM analysis were used to characterize the novel mesoporous MnO2/MWCNT sorbent with a large total pore area 193.3 m2/g and porosity about 52%. Several factors influencing the sorption of 99Mo and 99mTc onto the mesoporous MnO2/MWCNTs were studied, including the distribution coefficient (Kd), contact time, temperature, and sorbent/solute ratio, etc. The Mo uptake capacities on the novel sorbent were 133 and 115 mg Mo/g, respectively. A preliminary study on the prepared new sorbent for the 99Mo/99mTc generator was performed, and the elution yield of 99mTc was found to be 82.55% with low 99Mo breakthrough. The radiochemical, radionuclide, and chemical purity of the eluted 99mTc were checked to ensure that it was free of impurities.

Charge distribution studies in the epi-cadmium neutron induced fission of 233U

Charge distributions have been carried out in the epi-cadmium neutron induced fission of 233U for the first time by measuring the fractional cumulative yields (FCY) and independent yields (IY) of various fission products. The method of an off-line γ-ray spectrometric technique was used for the measurement. From the FCY values, the isobaric width parameter (σZ), most probable charge (ZP) and the charge polarization (ΔΖEXPT) as a function of fragment mass were obtained. Similarly, from the IY values, isotopic width parameter (σA), the most probable mass (AP) and the elemental yields (YZ) of Sn, Sb, Te, I, Xe, Cs, Ba, La, Ce and Pr were determined by using a non-linear fit. From the YZ values, the proton even-odd effect (δp) was obtained for the first time. The present data were compared with the similar data in the thermal neutron induced fission of 233U and other actinides to examine the role of excitation energy on charge distribution parameters.

Probability Density Functions with Correlations of Experimental and Evaluated 235U(nth,f) Fission Yields and Their Impacts on Reactivity Loss with Burnup

The study of fission yields has a major impact on the characterization and understanding of the fission process and its applications. For the latter, it is crucial to provide fission yields with their associated correlation matrix in order to estimate precisely the uncertainties of crucial quantities, such as the reactivity loss. In the last decade, different works have been proposed to estimate the correlations of the independent fission yields satisfying the consistency of the cumulative yield evaluations. In these previous works, only model parameters and conservation laws have driven the correlations. The novelty of the present work consists of new complete and consistent evaluations of 235U(nth,f) independent and cumulative yields and their correlation matrices, starting from experimental data. The characterization of the probability density functions of fission yields validates the multivariate Gaussian assumption and constitutes a major issue in the validation of the uncertainty propagation tools of the applications. In addition, the new 235U(nth,f) fission yield covariance data have resulted in a decrease in nuclear data related to uncertainty in associated burnup calculations.

Calculation of the energy dependence of fission fragments yields and kinetic energy distributions for neutron-induced 235U fission* *Supported by the National Natural Science Foundation of China (12075105), the NSFC-Nuclear Technology Innovation Joint Fund (U2167203), the Major Science and Technology Projects of Gansu Province (22ZD6GB020), the Fundamental Research Funds for the Central Universities of China (lzujbky-2022-ey14, lzujbky-2022- kb07)

Fission fragments yields and average total kinetic energy are fundamental nuclear data for nuclear energy applications and the study of nuclear devices. Certain fission products, such as 95Zr, 99Mo, 140Ba, 144Ce, and 147Nd, serve as burnup monitors, assessing the number of fissions induced by neutrons on 235U. However, current experimental data for these fission products worldwide are inconsistent, introducing significant uncertainty into related scientific research. In this study, we employed the Potential-driving Model to calculate the independent yields of 235U and evaluate its advantages in such calculations. Additionally, we investigated the energy dependence of independent yields to select important products. Furthermore, we calculated the cumulative yields of 95Zr, 99Mo, 140Ba, 144Ce, and 147Nd, and compared them with existing literature data to explore the energy dependence of fission products for 235U. Given the lack of fission product yield data above 14.8 MeV, we extended our calculated incident neutron energy to 20 MeV, aiming to support future scientific research. The Geant4 physical model does not consider the influence of incident neutron energy on the average total kinetic energy of fission fragments; thus, we introduced the excitation function of the total kinetic energy of fission fragments recommended by Madland et al., which effectively describes the experimental data of the average total kinetic energy of fragments formed in 235U fission. In this paper, we comprehensively discuss the energy dependence of fission product yields and average total kinetic energy.

Experience in the production of 99Mo from low enriched uranium at the VVR-ts research nuclear facility

The key industrial method for producing 99Mo is production of the radionuclide as one of the 235U fission fragments. 235U is irradiated with neutrons in a nuclear reactor (both heterogeneous and homogeneous nuclear reactors can be used) and then processed in radiochemical laboratories, where 99Mo is chemically extracted from fission products. Both highly enriched uranium (HEU) and low enriched uranium (LEU) can be used to produce 99Mo by the fragmentation method. To date, almost all world producers, with the exception of Russia, are either in the final stages of transferring production from highly enriched uranium to low enriched uranium, or are already producing 99Mo using LEU. This is due to the problems of non-proliferation of nuclear materials and the prevention of the likelihood of terrorist threats. A number of experimental studies have been carried out on the basis of the VVR-ts research reactor. Experimental studies included the study of the effect of LEU targets on the reactivity reserve of the VVR-ts reactor, irradiation of these targets in experimental channels and separation of 99Mo from them. The paper presents the results of producing and separating 99Mo from targets with LEU material. It is shown that it is necessary to improve the processing technology to increase the production of fragmented 99Mo from LEU.

Independent isomeric yield ratios of fission products in the epi-cadmium neutron induced fission of 233U

The independent isomeric yield ratios (IR) of 128,130,132Sb, 131,133Te, 132,134,136I, 135Xe and 138Cs have been measured in the epi-cadmium neutron induced fission of 233U by using an off-line gamma-ray spectrometric technique. The average neutron energy of the epi-cadmium reactor neutron spectrum is 1.9 MeV. The root mean square fragment angular momenta (JRMS) were deduced from the IR values by using spin dependent statistical model analysis. The IR and JRMS values of considered fission products in the epi-cadmium neutron induced fission of 233U were compared with the literature data in the thermal neutron induced fission of 233U to examine the influence of excitation energy on nuclear structure effect.

Interpreting and reporting fission-track chronological data

Abstract Fission-track dating is based on the analysis of tracks—linear damage trails—produced by the spontaneous fission of 238U in a range of natural accessory minerals and glasses. The retention of tracks is sensitive to elevated temperatures, and the data serve principally as a tool for recording thermal histories of rocks, potentially over the range of ~20–350 °C, depending on the specific minerals studied. As such, in most cases, fission-track data generally bear little or no direct relationship to the original formation age of the material studied. The age range of fission-track dating is related to the product of age and uranium content, and ages from several tens of years to older than 1 Ga are reported. Fission-track analysis led to the development of powerful modeling techniques. When used with appropriate geological constraints, these modeling techniques allow important geological processes to be addressed in a broad range of upper crustal settings. Since early attempts to standardize the treatment of fission-track data and system calibration over more than 30 years ago, major advancements were made in the methodology, necessitating the development of new, updated data reporting requirements. Inconsistencies in reporting impede public data transparency, accessibility and reuse, Big Data regional syntheses, and interlaboratory analytical comparisons. This paper briefly reviews the fundamentals of fission-track dating and applications to provide context for recommended guidelines for reporting and supporting essential meta fission-track data for publication and methodological archiving in structured formats that conform with FAIR (Findable, Accessible, Interoperable, and Reusable) data principles. Adopting such practices will ensure that data can be readily accessed, interrogated, and reused, allowing for further integration with other numerical geoscience techniques.

Calculation And Uncertainty Analysis of Core Parameters of ALMANAR Reactor Using New Nuclear Data Libraries

Abstract A small modular lead-cooled fast spectrum core concept called ALMANAR designed to produce 45 MWth power for 22 years operating without refuelling was proposed in a previous study. The neutronics investigation showed its excellent inherent safety features. It could be considered as a candidate for future electricity source for the near future. It is noteworthy that the target accuracy for eigenvalue calculation for keff regardless of spectrum is set to 300 pcm. However, findings in this analysis revealed that the keff uncertainty was larger for the recently released nuclear data libraries (about 800 pcm), mostly from 235U capture cross section (624 pcm) in the case of ENDF/B-VIII.0 and 238U inelastic scattering cross section (437 pcm) in the case of JENDL-5. Selected kinetic parameters of the ALMANAR core and their uncertainty were also evaluated and analysed. No major impact on the total ßeff, leffeff and λeff simulation results was found. In order to improve the reliability of criticality calculations of the lead-cooled small fast reactor, the accuracy of capture and fission cross section of 235,238U, the capture cross section of 10B and the elastic scattering cross section of 208Pb at the fast energy range of ENDF/B-VIII.0 should be improved. Furthermore, the inelastic scattering and capture cross section of 238U, fission and capture cross section of 235U and the capture cross section of 10B of JENDL-5 should also be improved.

Comments on the Frisch-Peierls Estimate of the Critical Mass of a Uranium Fission Bomb

The Frisch-Peierls memorandum of March 1940 opened the way to nuclear weapons through its conclusion that the critical mass for an explosive chain reaction in 235U could be as small as 0.6 kg. This gross underestimate was based on the conjecture that the cross section for the fission of 235U with fast neutrons was 10 barns. Though this value turned out to be far too high, it is argued here that the choice made was not unreasonable at the time.

Determination of the absolute intensity of the 1205 keV [formula omitted]-ray emission from 91Y

A radiochemically pure solution of 91Y was produced by the thermal neutron fission of 235U followed by successive chemical separations to remove fission product impurities. The gamma emission rate of the 91Y 1205 keV gamma was measured using multiple high purity germanium gamma spectrometers previously calibrated for counting efficiency using a certificated mixed nuclide gamma standard. The activity concentration of the 91Y was subsequently standardised by liquid scintillation counting. From the combination the activity concentration and gamma emission intensity, the absolute intensity of the 1205 keV gamma emission was derived as 0.2297(39)%. This data agrees within the quoted uncertainties with the absolute intensity of 0.26(4)% published in nuclear data sheets A=91 (Baglin, 2013), but reduces the uncertainty by an order of magnitude.

Excitation energy dependency of the low-energy fission dynamics: Probing through prompt gamma-ray spectroscopy

Fission Fragment Spectroscopy (FFS) technique has been utilized to make simultaneous measurements of both the relative charge and mass yield distributions of even-even fission fragments produced from the fission of 236U at two different excitation energies, Eex. The necessary analysis has been carried out on the measured yield distributions by employing the Multimodal Random Neck Rupture Model (MM-RNRM). The relative contribution of two different types of asymmetric mode of fission – Standard I and Standard II has been extracted at Eex = 6.5 and 21.5 MeV. An attempt has been made to study the evolution of these two asymmetric fission modes with respect to the values of Eex of the concerned fissioning system at low-excitation regime. The probable evidence, although at the primitive stage, for an oscillatory behavior of the relative contributions of different low-energy fission modes with increasing values of Eex has been presented.

Energy-Dependent Fission-Product Yields in the Region of Second-Chance Fission

The energy dependence of high-yield fission products has been measured using quasi-monoenergetic neutron beams at energies between 5.5 and 11.0 MeV. The absolute number of fissions during the irradiation period was determined via dual-fission ionization chambers, while the fission products were measured via direct g-ray spectroscopy. This paper presents absolute fission product yields from neutron-induced fission of 235U, 238U, and 239Pu isotopes for five incident energies in the second chance fission region.

Prompt-fission observable and fission yield calculations for actinides by TALYS

The nuclear reaction code TALYS adopts the Hauser-Feshbach statistical decay theory, to de-excite fission fragments. This involves for instance the evaporation of prompt fission neutrons and γ-rays. TALYS incorporates databases of primary fission fragment distribution which consists of primary fission fragment yield and data for excitation energy distribution of fission fragments. We conducted a sensitivity study on three parameters in TALYS and fitted them in order to reproduce experimental and evaluated data, in thermal neutron-induced fission of 235U. Moreover, we demonstrate a large-scale calculation of average prompt neutron and γ-ray multiplicities for 243 selected actinide isotopes.