Contributing to the nuclear 3S's via a methodology aiming at enhancing the synergies between nuclear security and safety

Nuclear safety, nuclear security and nuclear safeguards regimes have not historically developed at the same pace and surely have not reached the same level of maturity. Nevertheless, these aspects are of special relevance in the current global nuclear energy context when considering the numerous countries that have and will have the legitimate ambition to start a nuclear energy production programme without any or scarce previous nuclear safety, security and safeguards cultures.The future development of nuclear energy exploitation will depend more and more on the convergence of decisions from governments, from the nuclear industry, from utilities, from private and institutional investors as well as from the level of acceptance by the public opinion.Following an in-depth state-of-the-art analysis and literature search, a methodological approach focussed on the safety and security connections is presented, as it seems a field where more commonalities and operational aspects could be possibly found and exploited.     

Multiple lines of evidence for performance of the canister and waste form in long-term nuclear waste disposal: Reviews

The time scales required for nuclear waste disposal are very large compared with those for other engineering endeavors. Because of this, there are many uncertainties associated with the quantitative performance assessment of canisters containing high-level radioactive waste in a waste form. Multiple lines of evidence can be helpful in building confidence in the long-term behavior (corrosion and dissolution) of the canister and waste form. These lines of evidence are derived from long-term supports and probabilistic models and developed based on shorter term tests, bounding and conservative approaches, and available observations on natural analogs. This paper presents the progress made for important lines of evidence considered in quantitatively assessing radionuclide release behavior from canisters and waste forms. This paper considers risk-significant issues for canisters and waste forms (i.e., risk informed approach) in the probabilistic performance assessment of the disposal system which has also other components such as geology and hydrology.     

Observed light yield of scintillation pixels: Extending the two-ray model

In this paper we propose an extended, two dimensional model describing the propagation of scintillation photons inside a cuboid crystal until they reach a PMT window. In the simplest approach the model considers two main reasons for light losses: standard absorption obeying the classical Lambert–Beer law and non-ideal reflectivity of the “mummy” covering formed by several layers of Teflon tape wrapping the sample. Results of the model calculations are juxtaposed with experimental data as well as with predictions of an earlier, one dimensional model.     

The decision making method of task arrangement based on analytic hierarchy process for nuclear safety in radiation field

Unstructured and multi-objective task arrangement in radiation field is a complicating problem decision-makers are most concerned about. Proper task arrangement is helpful to improve efficiency of engineering and reduce hazard. The goal of this work is to discuss some criteria of task, build task hierarchy structure model, and then propose a task analytic method in radiation field based on analytic hierarchy process (AHP). The proposed method is useful for selection of schemes to reduce hazard and increase efficiency of task. In addition, we use this proposed method solve a hypothetical case, which is utilized to explain how the method works and to prove the method effective.     

Determination of the anisotropic radiative properties of a porous material by radiative distribution function identification (RDFI)

The anisotropic extinction and absorption coefficients of a high porosity material with a semi-transparent solid phase are directly obtained from identification of the statistical cumulated distribution function of extinction distances in the material, linked to that of the chords, and the corresponding function in the equivalent semi transparent medium. The bidirectional phase function is then determined without any hypothesis. The model only requires the knowledge of the material morphology, given by a X-ray tomography and the phases local radiative properties.     

Thermogravimetric characteristics and kinetic of plastic and biomass blends co-pyrolysis

Co-pyrolytic behaviours of plastic/biomass mixtures were investigated using a thermogravimetric analyser under heating rate of 20 °C/min from room temperature to 650 °C. The biomass sample selected was Chinese pine wood sawdust, while high density polyethylene (HDPE), low density polyethylene (LDPE) and polypropylene were selected as plastic samples. Results obtained from this comprehensive investigation indicated that plastic was decomposed in the temperature range 438–521 °C, while the thermal degradation temperature of biomass is 292–480 °C. The difference of weight loss (ΔW) between experimental and theoretical ones, calculated as algebraic sums of those from each separated component, is about 6–12% at 530–650 °C. These experimental results indicate a significant synergistic effect during plastic and biomass co-pyrolysis at the high temperature region. In addition, a kinetic analysis was performed to fit thermogravimetric data, the global processes being considered as one to three consecutive first order reactions. A reasonable fit to the experimental data was obtained for all materials and their blends.     

Digital rebalance loop design for a dynamically tuned gyroscope using H2 methodology

Presented in this paper is a wide-bandwidth digital torquing rebalance loop for a dynamically tuned gyroscope (DTG) based on H₂ methodology. The role and the importance of a rebalance loop are explained first. The augmented plant model including gyroscope and integrator is composed. Next, an H₂-based controller is designed for the augmented plant model. Frequency analyses show that the proposed controller maintains a linear relationship between applied input rate and the output of the controller over a wide operating range and keeps the tilt angle small thereby reducing dynamic errors. To verify the performance of the controller in a real environment, a digital rebalance loop for a DTG is designed, fabricated, and examined. From simulation and experimental results, it is confirmed that the controller is robustly stable and has a wide bandwidth, significantly improving the performance of a DTG.     

The use of ferrites as highly active oxygen storage materials for chemical looping hydrogen production under intermediate temperature

Shifting chemical looping from high temperatures to intermediate temperatures could mitigate the materials from sintering and benefit for longer durability as well as process economy. However, oxygen carriers cannot perform sufficiently due to the degrading effect at lower temperatures, resulting in the decrease of hydrogen production ability. Although doping precious metals can improve the poor performance at intermediate temperatures, the high cost impeded their large-scale application. In this paper, a range of oxygen carrier materials consisted of earth abundant elements were prepared for chemical looping hydrogen production. The results indicated that CoFe₂O₄ exhibited the highest hydrogen yield of 11.9 mmol·g⁻¹ and hydrogen production rate of 0.051 mmol g⁻¹·s⁻¹ at 650 °C, which was 1.7 times higher than that of Fe₂O₃. A combined experimental and DFT calculation method was used to understand the mechanism behind the performance. The results indicated that the synergistic effect between Co and Fe increased the reactivity of the ferrite materials. The enhanced hydrogen production performance was attributed to the high reduction degree and reversible phase change. This study can be also extended to develop more active oxygen carrier for chemical looping processes at intermediate temperatures.