The release of fission-recoiled xenon from Zr-2.5 wt% Nb alloy

The release of fission-recoiled ¹³³Xe from Zr-2.5 wt% Nb alloy was measured in the temperature range 640–1080 K. In the range 640–880 K, where purely phase exists, a linear relationship between log D versus 1/T is observed and can be represented by the equation: D(640–880 K) = 6.24 × 10⁻⁹exp(−142.7 kJmol/RT)m²/s. The release has been attributed to the non-volume diffusion process.

In the temperature range 930–1080 K where both and β phases coexist, the linearity in the plots of log D versus 1/T is violated.

The present values of the release parameters have been compared with the corresponding values for the release of fission-recoiled ¹³³Xe from Zircaloy-2. Alloying elements seem to have very small effect on the release kinetics. The results have been presented and discussed.     

Evaluation of recycle P&T treatment by using BWR to perform geologic disposal

Geologic disposal scenario combined with multiple-recycle P&T (partitioning and transmutation) treatment of MA (minor actinide) was thought to have an important potential merit to carry out the geologic disposal. P&T treatment was thought to have a role to avoid an uncertainty caused by geologic behavior, such as underground water migration rate, reductive and inorganic environment in a super-long time. Partitioning and grouping of LLRN (long-lived radionuclide), i.e. MA and LLFP (long-lived fission product), has an essential role to the transmutation treatment. B/T (burning and/or transmutation) treatment of MA, with R&P (reprocessing and partitioning) process, could be recycled and SLFP (short-lived fission product) was removed to immobilize in GSC (glass solidified canister). If R&P has a high performance, the multi-recycle system which combines B T-BWR (B/T boiling water reactor) and R&P can transmute of U&Pu, MA and LLFP etc. with small inventory. B/T fraction of MA is high in case of multi-recycle system, and then the remain of mass of MA or LLFP is recycled many times with low inventory. The B/T fraction of MA or LLFP could be high, if the flux is high, i.e. the time needed for high B/T fraction is relatively short in case of high flux BWR, or long in case of normal BWR. The optimum period for discharge of B/T fuel could be determined by the net difference between the reduced mass of MA burned and/or transmuted in the B/T fuel and the accumulated mass of MA in the normal fuel, and with the additional mass of MA accumulated by U&Pu, which was unrecovered in the reprocessing existed in B/T fuel.     

Analysis of the desorption of clusters of intact amino acid valine molecules induced by energetic monoatomic and cluster ions

The experiments on the desorption of intact valine molecules and (nM + H)⁺ clusters are analyzed and a ln(Y/S_e) − 1/S_e scaling is found where Y, and S_e are the sputtering yield and the electronic stopping power, respectively. The scaling can be derived with the assumption of a thermal activation mechanism. In the plots the desorption is a uniform process without threshold value of S_e, having different activation energies U in various charge states. The desorption of (nM + H)⁺ clusters proceeds in n steps with varying Coulomb contributions. Irradiation with C₁₀ and C₆₀ ions leads to higher Y, however, the increment is reduced with the increase of S_e.     

Aqueous corrosion of lanthanum aluminosilicate glasses: influence of inorganic anions

In order to confine specific long-life actinides, originating from high-level nuclear wastes, lanthanum aluminosilicate glasses are considered. The aqueous corrosion behavior of these glasses is studied under static conditions (T=96 °C, duration between one and six months, glass surface area/leachate volume, S/V=0.3, 50 and 500 cm⁻¹) by means of solution analysis (ICP-MS and spectrophotometry) and solid analysis (X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry). Tests performed at high S/V ratio lead to silicon releases of 10⁻³ mol l⁻¹ while lanthanum releases reach 10^−4.5 mol l⁻¹. Phosphate anions are found to modify the dissolution, as an amorphous lanthanide phosphate is evidenced at the glass surface after the corrosion experiment. The lanthanide releases decrease in presence of phosphate, but the matrix dissolution process is not reduced.     

Extraction efficiency of N(T1/2 = 9.96 min) atoms from a graphite target: comparison between off- and on-line obtained results

An off-line release study ¹³N(T1/2 = 9.96 min) produced by proton induced reaction on a graphite target (POCO-graphite EDM3, density = 1.84 g/cm³, grain size /t 3 μm) has been performed. The activation energy for the diffusion process is determined to be 6.15(16)×10⁵ J/mol. With this activation energy, extraction efficiencies for ¹³N are obtained at different temperatures and are compared to on-line measured extraction efficiencies.     

采用钙镁共沉淀和二氧化锰沉淀浓集进行大体积水中Pu的分析

采用沉淀浓集-离子交换方法对大体积水中Pu分析方法进行了实验研究。浓集过程采用了MnO₂沉淀、Ca-Mg共沉淀两种方案,水样体积为25 L时,两种沉淀法对钚分析的全程放化回收率均可达到70%左右,MnO₂沉淀法对于50 L以上水样回收率下降。Ca-Mg共沉淀法对100 L水样的全程放化回收率为63.5%~80.2%,平均值为(74.6±5.9)%(n=7),对^239+240Pu的最小可探测限为3.1 μBq/L(体积V=100 L,回收率Y=74.6%,测量时间t=72 h)。某实际淡水样品中^239+240Pu含量为9.32~15.6 μBq/L,取样体积为100 L时没有出现低于探测限的结果。     

Effect of electron excitation on radiation damage in fce metals

Defect production, radiation annealing and defect recovery are studied in several fcc metals (Al, Cu, Ni, Ag and Pt) irradiated with low-energy ( 1 MeV) and high-energy ( 100 MeV) ions. Irradiation of the metals with strong electron-lattice interaction (Al, Ni and Pt) by 100 MeV ions causes an anomalous reduction, or even a complete disappearance of stage-I recovery. This experimental result shows that the energy transferred from excited electrons to lattice atoms through the electron-lattice interaction contributes to the annihilation of single interstitials. This effect is also observed in Ni as a large cross section for radiation annealing, and a decrease of the damage efficiency. On the other hand, in Cu and Ag thin foils, we find that lattice defects are produced not only through elastic interactions, but also through a process strongly associated with electron excitation. In the latter process, the defect production cross section is proportional to S_e^1.7 in Cu and S_e^1.5 in Ag. The nearly quadratic dependence of the cross section on S_e suggests that the mutual Coulomb repulsion of ions positively charged by electron excitation causes the defect production.     

Primary creep of UO2 and the effect of amorphous grain boundary phases

Creep experiments were conducted on nearly stoichiometric UO₂ helical springs from 1000 to 1600°C and 2.1 to 80 MPa. Entirely transient behaviour was measured in all experiments with the plastic strain,ε = (Aσ/d^1.5) exp(−Q/RT)t^m, where A is a constant that depends on purity, d is the grain size, σ is the applied stress, Q is the apparent activation energy, t is the time, m is a constant, and the other terms have their usual meaning. At T > 1200°C, Q 100 kcal mol⁻¹, but at T < 1200°C, Q increased dramatically and became strain dependent. The value of m for most experiments was 0.8, but at σ > 48 MPa, m decreased, and for d < 10 μm, it increased. Amorphous or glassy grain boundary phases were observed by transmission electron microscopy in all specimens: specimens containing the largest concentrations of Fe and Si sometimes had anomalously high creep rates. The phases existed as discontinuous, lenticular bodies on grain faces and a continuous network along triple grain junctions. Some instances of precipitation of UO₂ from the phase were observed. At T > 1200°C, glassy phases may accelerate Coble creep by providing short circuit diffusion paths along the grain boundaries or may accelerate superplastic deformation by diffusion along the continuous glassy phase triple line junctions. At low temperatures the glassy phase appears to control grain-boundary sliding.     

Multi-recycling in the ENHS and the equilibrium core

This work investigates the effect of initial fuel composition, power density and number of recycles on the pitch-to-diameter (P/D) ratio and TRans-Uranium isotopes (TRU) loading required for attaining one of the most important design goals of the Encapsulated Nuclear Heat Source (ENHS) – nearly zero burnup reactivity swing over the 20 years of core life. It is found that the required P/D ratio is sensitive to, primarily, the initial concentration of the short-lived isotope ²⁴¹Pu in the fuel loaded into the first core and to the core power density. The longer is the cooling time of the TRU from LWR spent fuel the smaller becomes the relative ²⁴¹Pu concentration and the smaller becomes the fraction of ²⁴¹Pu lost via radioactive decay and, hence, the smaller needs be the conversion ratio required for nearly zero burnup reactivity swing and the larger can be the P/D ratio. Likewise, the higher is the ENHS power density, the smaller becomes the fraction of ²⁴¹Pu lost via radioactive decay and the larger becomes the P/D required for the first core. The optimal P/D ratio tends to increase with the number of times the fuel is recycled from one ENHS core to the next one. The optimal P/D ratio for the equilibrium composition core is in between 1.53 and 1.59. For a given discharge burnup it tends to somewhat increase with the equilibrium core power density. However, if structural materials will be developed to enable a 20 years core life at elevated power densities, the higher the power density the smaller is the required equilibrium P/D ratio.     

Double plasmon excitation in an electron gas

A many-body perturbation-theoretic calculation of the double-plasmon excitation in an electron gas is presented, using Feynman diagrams. The low-q limit of the inverse mean free path for this second order process is evaluated in the random-phase-approximation, and it is compared to previous theoretical and experimental estimations.     

The solubility of aluminium in Pb-17Li

The saturation solubility of aluminium in Pb-17Li has been measured over the temperature range envisaged for a Pb-17Li tritium breeder/coolant blanket for use in a fusion reactor. The solubility is given by the equation log¹⁰S(wppm) = 6.249 – 2784.9/T(K) for T = 525 – 813 K.The results are compared to literature values for the solubility of aluminium in pure lead and show good agreement. A value for the enthalpy of solution of + 55.8 kJ mol^-1 has been calculated.     

Fault monitoring of nuclear power plant sensors and field devices

Existing and new generation of nuclear power plants have economic and reliability concerns as addressed by overall plant performance, unscheduled downtime and the long-term management of critical assets. The key to achieving these needs is to develop an integrated approach for monitoring, control, fault detection and diagnosis of plant components such as sensors, actuators, control devices and other equipment. Both single and multiple fault cases have been considered. This paper presents the following approach for achieving this goal: 1. Development of data-driven system models using Group Method of Data Handling (GMDH), Principal Component Analysis (PCA) and Adaptive Network-based Fuzzy Inference System (ANFIS), 2. Fault detection by tracking model residuals of selected process variables and control functions, and 3. Fault isolation using a rule-based technique and/or a pattern classification technique. This approach is illustrated for a nuclear plant steam generator. Fault detection and isolation (FDI) of sensors and field devices is an important step towards the implementation of an automated and intelligent process control strategy, especially for Generation-IV reactors.     

Application of lattice constant measurements for stoichiometry determination in irradiated U-Pu mixed oxide fuels

A method is proposed for determining the oxygen/ metal ratio in mixed irradiated uranium-plutonium oxides. The method is based on a measurement of the lattice constants and on a standard thermal treatment which is used to obtain a tetravalent state of uranium and plutonium. The effects of irradiation and of the solution of solid fission products in the matrix, the variation in plutonium concentration, and influence of these factors on stoichiometry are discussed on the basis of the results of simulated experiments in which the state after irradiation of oxide fuels is computed, together with the concentrations of the fission products.

For a given burn-up τ the oxygen/metal ratio of the matrix O/U + Pu + FP, which has a considerable influence on the physical properties of the fuel, is obtained by direct measurement of the ratio O/U + Pu and correcting this value for the effect of soluble fission products using the equation: O/U + Pu + F.P. = 3/(3− τ) [(1− τ)O/U + Pu] + [2/3 τ·1.75].     

Use of reference samples for more accurate RBS analyses

While one of the primary assets of RBS analysis is that it is quantitative without use of reference samples, for certain types of analyses the precision of the method can be improved by measuring RBS spectra of unknowns relative to the RBS spectra of a similar known sample. The advantage of such an approach is that one can reduce (or eliminate) the uncertainties that arise from error in the detector solid angle, beam current integration efficiency, scattering cross-section, and stopping powers. We have used this approach extensively to determine the composition (x) of homogeneous thin films of TaN_x using as reference samples films of pure Ta. Our approach is to measure R=(Tacount)_unknown/(Tacount)_standard and use RUMP to determine the function x(R). Once the function x(R) has been determined, this approach makes it easy to analyze many samples quickly. Other analyses for which this approach has proved useful are determination of the composition (x) of WN_x, SiO_xH_y and SiN_xH_y, using W, SiO₂ and amorphous Si as reference samples, respectively.     

Heat transfer in LMFBR fuel elements Part II: Effects of fuel pellet cracks, granular fuel structure and azimuthally non-uniform heat transfer from cladding to bulk coolant

The single long-time method of observation for transmission experiments across boiling channels produces a indecisive value for the mean of the void fraction , and can be correctly interpreted for conditions of low noise level only. The finite interval method is employed in an attempt to determine with much greater accuracy; however, the problem arises that, since the value of (f) over the nth time interval t_n t t_n +δt is assumed approximately constant at _n, this finite period, δt, should be as small s possible whereas reducing δt increases the statistical counting errors. The systematic error introduced by the finiteness of δt is examined and a method is suggested for planning the experiment in such a manner as to minimize statistical counting errors. This method is based on achieving those conditions that ensure the expected variance of an experimentally estimated form of is so small that the estimated form of may be confidently assumed to be very close to its expected mean value.     

Mass spectrometric investigation of the vaporization of li2tio3(s)

The vaporization of Li₂TiO₃(s) has been investigated by the mass spectrometric Knudsen effusion method. Partial pressures of Li(g), LiO(g), Li₂O(g), Li₃O(g) and O₂(g) over Li₂TiO₃(s) have been obtained in the temperature range 1180–1628 K. When the vaporization of Li₂TiO₃(s) proceeds, the content of Li₂O in the Li₂TiO₃(s) sample decreases. The phase of the sample is a disordered Li₂TiO₃ solid solution above 1486 K. The enthalpies of formation and the atomization energies for LiO(g) and Li₃O(g) have been evaluated from the partial pressures to be ΔH^o_f0(LiO, g) = 65.4 ± 17.4 kJ/mol, ΔH^o_f0(Li₃O, g) = − 207.5 ± 56.6 kJ/mol, D^o₀(LiO) = 340.5 ± 17.4 kJ/mol and D^o₀(Li₃O) = 931.6 ± 56.6 kJ/mol, respectively.     

Mean excitation energy for the stopping power of light elements

We have evaluated the mean excitation energy or I value for Coulomb excitations by swift charged particles passing through carbon, aluminum and silicon. A self-consistent Kramers–Kronig analysis was used to treat X-ray optical spectra now available from synchrotron light sources allowing us to carry out Bethe’s original program of evaluating I from the observed dielectric response. We find that the K and L shell are the dominant contributors to I in these light elements and that the contribution of valence electrons is relatively small, primarily because of their low binding energy. The optical data indicate that Si and Al have nearly equal I values, in contrast to Bloch’s Thomas–Fermi result, I ∝ Z. The optically based I values for C and Al are in excellent agreement with experiment. However, the dielectric-response I value for Si is 164 ± 2 eV, at variance with the commonly quoted value of 173 ± 3 eV derived from stopping-power measurements.     

Effects induced by high electronic excitations in pure metals: A detailed study in iron

Although high electronic excitations were neglected for a long time in radiation effect studies of metallic targets, it is now well established that they can play a dominant role in the damaging processes of some metals. Iron is especially interesting in so far as, according to the rate of energy deposition in electronic excitations (dE/dx)_e, various behaviours are observed. Below (dE/dx)_e ≈ 40 keV/nm, due to electronic excitations, the amount of damage introduced in the sample is smaller than that expected from the sole elastic collisions. On the contrary, at very high (dE/dx)_e levels, a strong enhancement of the damage occurs. After describing the experimental results obtained during low temperature irradiations with a few 10 MeV/nucleon heavy (oxygen to uranium) ions, a phenomenological model which accounts for this intricate behaviour will be presented. Finally, a microscopic mechanism will be proposed to explain how the energy given to the electronic system can play a role in damage processes involving atomic motion. Molecular dynamics simulations validate this approach.     

Energy loss calculations for fast light ions in celluloid including charge-exchange processes

A method is proposed to calculate the charge-exchange energy loss (−dE/dx)_ex and electronic energy loss (−dE/dx)_el on the basis of the electron capture and loss cross-sections, extracted from the experimental data. The experimental and calculated results are presented for energy loss of projectile ions Be, B, N and O with 0.35 MeV/nucleon, passing through celluloid films. The dependence of energy loss on the initial charge of projectile ions and target thickness in nonequilibrium conditions is examined.     

Influence of dynamic strain aging on the ductile tearing of C–Mn steels: modelling by a local approach method

C–Mn steels and associated welds can be susceptible to dynamic strain aging (DSA). In this case, fracture toughness passes through a minimum when the temperature increases from 20 to 300 °C. Since Charpy V-Notch data are not affected by the DSA phenomenon, the method for predicting the evolution of J_0.2 and dJ/da in the temperature domain where DSA occurs is still an open question. The purpose of the present study is the assessment of this decrease in fracture toughness using a local approach method. The results of J–R tearing resistance tests, characterized by crack initiation resistance J_0.2 and tearing modulus dJ/da relative to a base metal (A48 French standard steel) and manual metal arc deposited metals are presented and discussed. The local approach determination of J_0.2 was performed using the Rice and Tracey model. Comparisons between experimental results and the results of local approach modelling indicate that both J_0.2 and dJ/da decreases with DSA can be correctly predicted.