Rapid interrogation of special nuclear materials by combining scattering and transmission nuclear resonance fluorescence spectroscopy

The smuggling of special nuclear materials(SNMs)across national borders is becoming a serious threat to nuclear nonproliferation.This paper presents a feasibility study on the rapid interrogation of concealed SNMs by combining scattering and transmission nuclear resonance fluorescence(s NRF and t NRF)spectroscopy.In s NRF spectroscopy,SNMs such as^(235,238)U are excited by a wide-band photon beam of appropriate energy and exhibit unique NRF signatures.Monte Carlo simulations show that one-dimensional scans can realize isotopic identification of concealed^(235,238)U when the detector array used for interrogation has sufficiently high energy resolution.The simulated isotopic ratio^(235U/238)U is in good agreement with the theoretical value when the SNMs are enclosed in relatively thin iron.This interrogation is followed by t NRF spectroscopy using a narrow-band photon beam with the goal of obtaining tomographic images of the concealed SNMs.The reconstructed image clearly reveals the position of the isotope^(235)U inside an iron rod.It is shown that the interrogation time of s NRF and t NRF spectroscopy is one order of magnitude lower than that when only t NRF spectroscopy is used and results in a missed-detection rate of 10^(-3).The proposed method can also be applied for isotopic imaging of other SNMs such as^(239,240)Pu and^(237)Np.

Current state and prospect on the development of advanced nuclear fuel system materials:A review

The intricate balance between reactor economics and safety necessitates the emergence of new and advanced nuclear systems and,very importantly,advanced materials,which can overcome current shortcomings and bring about more economic nuclear systems with designed-in inherent safety features.These advances will achieve greater safety and better nuclear reactor economics by reaching longer reactor lives with higher levels neutron irradiation,and by providing higher operation temperatures and resistance to more aggressive corrosive environments.This paper provides a review of the current state of research and development on innovative nuclear fuel materials design and development which have the potential of benefiting simultaneously reactor economics and safety.Our discussion focuses on three areas of research:Accident-tolerant Fuels(ATFs),Oxidation Dispersion Strengthened(ODS)steels and High Entropy Alloys(HEAs).The paper also gives a prospective description of future research activities on these materials.

ATOMIC AND NUCLEAR PROPERTIES OF MATERIALS

Table 6.1 Abridged from pdg. ibl.gov/AtomicNuclearProperties by D. E. Groom （2007）. See web pages for more detail about entries in this table including chemical formulae, and for several hundred other entries. Quantities in parentheses are for gases at 20℃ and 1 atm, and square brackets indicate evaluation at 0℃ and 1 atm. Boiling points are at 1 atm.

Preparation and properties of Ti_(3)SiC(2) -based corrosion mitigation coatings for SiC_(f) /SiC PWR accident tolerant fuel cladding

To enhance the resistance of SiC_(f)/SiC to hydrothermal corrosion in the pressurized water reactor(PWR)environment,structurally tunable Ti_(3)SiC(2)-based corrosion mitigation coatings for SiC_(f)/SiC were prepared using molten salt synthesis.The influence of various process parameters,such as Si/Ti molar ratio in raw materials,annealing time,and annealing temperature,on the phase composition and the structure of the coatings was explored.Through the process control,the fabricated coatings can be either Ti_(3)SiC(2) monolithic structure or TiC/Ti_(3)SiC(2) and TiC/Ti_(3)SiC(2)/Ti_(5)Si_(3)C_(x) multilayered structures.The coatings demonstrate strong bonding to the substrate due to in-situ reaction,exhibiting tensile and shear strength of at least 26.9 and 30.8 MPa,respectively.Incorporating TiC as a transition layer further enhances the tensile and shear strength to 41.3 and 51.4 MPa,respectively.Monolithic Ti_(3)SiC(2) coatings enhance the thermal conductivity of SiC_(f)/SiC by 10%–12%.Notably,Ti_(3)SiC(2) coatings effectively protect SiC_(f)/SiC from hydrothermal corrosion,demonstrating an 83%strength retention rate compared to 71%in the control group after corrosion.However,the Ti5Si3Cx layer exhibits unsatisfactory corrosion mitigation.The Ti_(3)SiC(2) monolithic coating has higher thermal conductivity,TiC/Ti_(3)SiC(2) multi-layered coating has higher bonding strength,and both have desirable resistance to the hydrothermal corrosion.

Current development of body-centered cubic high-entropy alloys for nuclear applications

High-entropy alloys greatly expand the alloy design range and offer new possibilities for improving material performance.Based on the worldwide research efforts in the last decade,the excellent mechanical properties and promising radiation and corrosion resistance of this group of materials have been demonstrated.High-entropy alloys with body-centered cubic(BCC)structures,especially refractory high-entropy alloys,are considered as promising materials for high-temperature applications in advanced nuclear reactors.However,the extreme reactor conditions including high temperature,high radiation damage,high stress,and complex corrosive environment require a comprehensive evaluation of the material properties for their actual service in nuclear reactors.This review summarizes the current progress on BCC high-entropy alloys from the aspects of neutron economy and activation,mechanical properties,high-temperature stability,radiation resistance,as well as corrosion resistance.Although the current development of BCC high-entropy alloys for nuclear applications is still at an early stage as the large design space of this group of alloys has not been fully explored,the current research findings provide a good basis for the understanding and prediction of material behaviors with different compositions and microstructures.Further in-depth understanding of the degradation mechanisms and characterization of material properties in response to conditions close to reactor environment are necessary.A critical down-selection of potential candidates is also crucial for further comprehensive evaluation and engineering validation.

Leakage of nuclear material powder from pressure container through a small orifice

Because of the radioactivity and toxic nature of nuclear materials, their containment within oxide matrices, encased in sealed containers, has been proposed as a suitable means for storage and transportation. However, container failures because of cracks or small orifices present a major leakage risk for nuclear materials, consequently posing a significant hazard to the environment and human beings. In this study, terbium oxide powder was used as a nuclear material representative to examine the leakage of nuclear material powder through orifices located at the base of a pressure container. The dependence of the orifice diameter, the powder layer thickness, and the internal pressure of the container on the leakage mechanism and amount was examined. A simplified model correlating the dependence of the above-mentioned parameters to determine the utmost leakage amount was also developed based on the present results. The leakage of the nuclear material powder was assessed by measuring its concentration using an optical particle counter. The diameter of the orifice determined the powder leakage mechanism, which in turn influenced the amount of leakage produced. Comparison studies showed that unlike the changes in the differential pressure, the volume of the container has little effect on the leakage amount. Under sufficiently high internal pressures, the oxide powder can be released as a fine aerosol. The work is not only crucial from the nuclear safety aspect, but is also beneficial for the safe application of powder and nanoparticles.

Radioanalytical chemistry for nuclear forensics in China:Progress and future perspective

A relatively new branch of science-nuclear forensics,aiming at providing the nature,origin,history and possible trafficking route of seized nuclear materials/devices,has been established and rapidly developed over decades to screen illicit nuclear activities.This highly interdisciplinary science is built upon a foundation of analytical chemistry,radiochemistry,nuclear physics,material sciences,geology,and other scientific disciplines,within which radiochemical methodologies and radioanalytical techniques play a key role.The present review provides a brief overview about the crucial aspects of nuclear forensics,including basic content,procedure,concerned elements,common separation,analytical method,and so on.The state of the art and recent progresses of nuclear forensics by research communities in China are reviewed,while selected examples and practical applications are emphasized.The challenges associated with this new area and on-going developments are highlighted and discussed.