Resilient design in nuclear energy: Critical lessons from a cross-disciplinary analysis of the Fukushima Dai-ichi nuclear accident

This paper presents a multidisciplinary analysis of the Fukushima Dai-ichi Nuclear Power Plant accident. Along with the latest observations and simulation studies, we synthesize the time-series and event progressions during the accident across multiple disciplines, including in-plant physics and engineering systems, operators' actions, emergency responses, meteorology, radionuclide release and transport, land contamination, and health impacts. We identify three key factors that exacerbated the consequences of the accident: (1) the failure of Unit 2 containment venting, (2) the insufficient integration of radiation measurements and meteorology data in the evacuation strategy, and (3) the limited risk assessment and emergency preparedness. We conclude with new research and development directions to improve the resilience of nuclear energy systems and communities, including (1) meteorology-informed proactive venting, (2) machine learning-enabled adaptive evacuation zones, and (3) comprehensive risk-informed emergency planning while leveraging the experience from responses to other disasters.

Synthesizing nuclear power plant fouling with fractal characteristics enables an in-depth study of concerned nuclear safety issues

Fouling deposit on nuclear fuel cladding causes wick boiling and boron hideout, resulting in localized corrosion and power shift with great potential security and economic risks. Herein, a cost-effective time-saving adjustable reproduction method combining sol-gel with ceramic sintering is presented to enable wide coverage of fouling's morphologies and microstructures. Based on fractal analysis, structurally self-similar fouling deposits from different reactors conform to proposed porosity-fractal dimension law under 3% relative error. Wick boiling and boron hideout numerical simulation based on fractal dimension is implemented to treat different morphologies and structures in a unified way. Cladding surface underneath fouling deposit has a maximum 9.243 K temperature increasement due to thermal resistance, and H3BO3 is concentrated 11.274 times by mean of wick boiling, causing Li2B4O7 precipitation under extreme conditions with low porosity and high heat flux. The insights in this study provide a precise approach for quantitative evaluation of localized corrosion and power shift.

Assessment of environmental radioactive surface contamination from a hypothetical nuclear research reactor accident

The environmental surface contamination by radioactive elements following a nuclear research reactor hypothetical accident is evaluated employing the hotspot code, IAEA safety guide, and NRC guidelines. Gaussian plume depositions of radioactive contaminants are calculated under very conservative assumptions for a worst-case accident scenario, and site most probable wind speed and metrological conditions. Results reveal that the contamination strongly decreases with distance, dropping seven orders of magnitude from 2.2E+09 kBq/m² at the reactor site to 9.5E+2 kBq/m² 60 km from the reactor at the plume centerline. In rainy weather, the wet deposition is depleted to 6.0E+2 kBq/m² after 50 km, limiting the spread of contaminants to a much smaller area. Although the results of this work tend to overestimate the surface deposition of radionuclides, they present a clear insight into the radiological consequences of nuclear accident worst-case scenario. Thus, it assists with the development of a comprehensive emergency preparedness program by identifying all areas with potential risk to contamination.

Fusion breeding for mid-century, sustainable, carbon free power

Fusion has often been billed as the ultimate 21st century sustainable energy source. However, not only is the pace of the program glacially slow, it seems to recede further and further into the future. One way to speed up the delivery of economical fusion could be to change the objective from pure fusion, that is the use of the 14 MeV fusion neutron's kinetic energy to boil water; to fusion breeding, that is the former, but also making use of the neutrons 'potential energy' to breed ten times its energy in the form of nuclear fuel to be burned in separate reactors. The requirements of a fusion breeder are greatly relaxed from the requirements for a pure fusion reactor. For instance, ITER, the large tokamak being built by an international consortium in France, could well be the basis of an economical fusion breeder, but would have to clear many more scientific and technical hurdles before it could become the basis for a pure fusion reactor; hurdles it may or may not be able to clear. Even if it clears them, ITER is unlikely to evolve into an economical pure fusion power supply this century. A fusion breeder as could be alternate approach to speed the delivery of economical of fusion power.

Design, qualification & manufacture of ITER gravity supports

As one of the key components to support all the magnet coils, the GS faces engineering challenge to its operational safety throughout the design, qualification and manufacturing process as a result of extreme loading condition. The structural safety of GS was confirmed by both the FEM analysis and the semi-prototype engineering test after a long time of design, qualification, manufacture and assembly. Welding the cooling pipe to the flexible plate without obvious deformation as well as tightening uniformly and precisely all the tie rods to clamp the plates were carried out successfully during manufacturing. The result of final vacuum leakage test indicates that the GS can not only meet the ITER vacuum requirement but also have no slow out-gassing. The first set of GS which has passed the ITER acceptance test is to be delivered to ITER construction site soon.

Measurement of natural radioactivity in several sandy-loamy soil samples from Sijua, Dhanbad, India

The activity concentrations of natural radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K in soil samples collected from Sijua Dhanbad, India were measured by using a gamma-ray spectrometer with a NaI(Tl) detector. The average activity concentration of ²²⁶Ra, ²³²Th, and ⁴⁰K was found as 60.3, 64.5 and 481.0 Bq. kg−1, respectively. Average radium equivalent activity, absorbed dose rate, outdoor dose, external hazard index and internal hazard index for the area under study is determined as 189.5 Bq. kg−1, 87.2 nGy h−1, 0.4, 0.5 and 0.6 mSv. y−1, respectively. The annual effective dose to the general public is found 0.4 mSv. y−1. This value lies well below the limit of 1 mSv. y−1. Measured values have found safe for the environment and public health of the study area.

Nanometre to micrometre length-scale techniques for characterising environmentally-assisted cracking: An appraisal

The appraisal is strongly focussed on challenges associated with the nuclear sector, however these are representative of what is generally encountered by a range of engineering applications. Ensuring structural integrity of key nuclear plant components is essential for both safe and economic operation. Structural integrity assessments require knowledge of the mechanical and physical properties of materials, together with an understanding of mechanisms that can limit the overall operating life. With improved mechanistic understanding comes the ability to develop predictive models of the service life of components. Such models often require parameters which can be provided only by characterisation of processes occurring in situ over a range of scales, with the sub-micrometre-scale being particularly important, but also challenging. This appraisal reviews the techniques currently available to characterise microstructural features at the nanometre to micrometre length-scale that can be used to elucidate mechanisms that lead to the early stages of environmentally-assisted crack formation and subsequent growth. Following an appraisal of the techniques and their application, there is a short discussion and consideration for future opportunities.

Estimation of optimized timely system matrix with improved image quality in iterative reconstruction algorithm: A simulation study

The system matrix (SM) being a main part of statistical image reconstruction algorithms establishes relationship between the object and projection space. The aim was to determine it in a short duration time, towards obtaining the best quality of contrast images. In this study, a new analytical method based on Cavalieri's principle as subdividing common regions has been proposed in which the precision of the amounts of estimated areas was improved by increasing the number of divisions (NOD), and consequently the total SM's time was increased. An important issue is the tradeoff between the NODs and computational time. For this purpose, a Monte Carlo simulated Jaszczak phantom study was performed by the Monte Carlo N-Particle transport code version 5 (MCNP5) in which the tomographic images of resolution and contrast phantoms were reconstructed by maximum likelihood expectation maximization (MLEM) algorithm, and the influence of NODs variations was investigated. The results show that the lowest and best quality have been obtained at the NODs of 0 and 8, respectively and in the optimum case, the SM's total time at NOD of 8 was 925 s, which was much lower than those of the conventional Monte Carlo simulations and experimental test.

Experimental study of consistency degradation of different greases in mixed neutron and gamma radiation

Many of the moving components in accelerator and target environments require lubrication. Lubricants in such environments are exposed to high fluxes of secondary radiation, which originates from beam interactions with the target and from beam losses. The secondary radiation is a mix of components, which can include significant fractions of neutrons. Lubricants are radiation-sensitive polymeric materials. The radiation-induced modifications of their structure reduce their service lifetime and impose additional facility maintenance, which is complicated by the environmental radioactivity. The study of the lubricants radiation resistance is therefore necessary for the construction of new generation accelerators and target systems. Nevertheless, data collected in mixed radiation fields are scarce. Nine commercial greases were irradiated at a TRIGA Mark II Research Reactor to serve for the construction of new accelerator projects like the European Spallation Source (ESS) at Lund (Sweden) and Selective Production of Exotic Species (SPES) at Legnaro, (Italy). Mixed neutron and gamma doses ranging from 0.1 MGy to 9.0 MGy were delivered to the greases. For an experimental quantification of their degradation, consistency was measured. Two of the greases remained stable, while the others became fluid. Post-irradiation examinations evidence the cleavage of the polymeric structure as the dominant radiation effect. Dose and fluence limits for the use of each product are presented. Apart from the scientific significance, the results represent an original and useful reference in selecting radiation resistant greases for accelerator and target applications.

Assessment of heat transfer correlations in the sub-channels of proposed rod bundle geometry for supercritical water reactor

There are heat transfer correlations for heat transfer analysis in single tube geometries after several experimental and theoretical heat transfer studies in these single tube geometries. This is not the case for heat transfer analysis in rod bundle geometry with regard to proposed square fuel assembly of the Supercritical-Water-Cooled Reactor (SCWR) European Atomic Energy (EURATOM) design. Thus limited heat transfer studies exist on rod bundle geometry at supercritical pressures. Heat transfer correlations with accurate prediction capabilities of coolant and wall temperatures will be helpful in carrying out heat transfer studies at supercritical pressures. This paper presents the performance of twelve selected heat transfer correlations assessed on the 1/8^th bare square fuel assembly of the SCWR EURATOM design using Simulation of Turbulent flow in Arbitrary Regions Computational Continuum Mechanics C ++ based code (STAR-CCM + CFD code). The obtained numerical results were compared with the results obtained by Waata numerical experimentation. Overall, the Cheng et al. correlation provided the most satisfying prediction for the wall temperatures in all the sub-channels and captured closely Wataa's Numerical data. The maximum wall temperature was obtained in sub-channel 9, the hottest sub-channel and exceeded the design limit 620 °C by 60 °C for the Cheng correlation. The difference in temperature between the hottest and coldest sub-channels 9 and 1 respectively was approximately 80 °C. It was found that Cheng correlation is best suited for heat transfer prediction in rod bundle geometry at supercritical pressures with regard to the proposed square fuel assembly of the SCWR EURATOM design. It was also found that the different numerical tools adopted for this study and Waata study were able to capture the trends of normal, enhanced and deteriorated heat transfer regimes normally observed at supercritical pressures. Nevertheless, experimental investigations involving rod bundles adopted in this study should be conducted to validate the results obtained numerically and address the inconsistency of the conclusions drawn when compared with Waata data and other similar studies.

EXABCal: A program for calculating photon exposure and energy absorption buildup factors

This research presents a new Windows compatible program (EXABCal) for photon exposure and energy absorption buildup factors for standard energy grid from 0.015- 15 MeV for elements, mixtures and compound. This program was written using Python programming language and the calculation of buildup factors was based on the well-known Geometric Progression (GP) fitting procedure. The equivalent atomic numbers and GP fitting parameters of mixtures and compounds can also be evaluated using this program. The program has been used to evaluate the photon exposure and energy absorption buildup factors for standard energy grid from 0.015- 15 MeV for water, air and concrete, compared with values from the American Nuclear Society (ANS) standard reference data (ANSI-6.4.3) and found to be of high accurate with minimal errors. The program is fast and easy to use and will be of valuable interest to medical Physicist, radiation Physicists, Radiation shielding design engineers, students, teachers and researchers and other experts working in areas where nuclear radiation is applied.

Synthesis of sandwich-like Mn3O4@reduced graphene oxide nano-composites via modified Hummers' method and its application as uranyl adsorbents

Efficient and sustainable remediation technologies for uranium have recently been gaining more and more interest. Adsorption techniques are facile, effective and universal for kinds of heavy metal ions. In this paper, sandwich-like Mn₃O₄@reduced graphene oxide (Mn₃O₄@G) nano-composites were prepared facilely and greenly by adding NaOH solution into crude graphite oxide suspension prepared via the Hummers' method to modify the pH. The Mn₃O₄@G nanocomposites possess a reasonable maximum equilibrium adsorption quantity 195.6 mg [U] g^-1. Moreover, the magnetism of Mn₃O₄@G makes it easy to remove Mn₃O₄@G from water by strong magnet field.

Synthesis and radiation shielding properties of polyimide/Bi2O3 composites

Radiation shielding composites based on polyimide and Bi₂O₃ were synthesized. Surface and physical-mechanical properties of polyimide/Bi₂O₃ composites were studied. Bi₂O₃ particles were modified by polymethylphenylsiloxane for the uniform distribution of filler in composites. This paper presents data on the production of composites in two ways: hot- and cold-pressing. The hot-pressing method for the synthesis of composites is preferable compared to the cold-pressing method (the density increases by 10-12%, and the Vickers microhardness by 10-20%). The results show that the introduction of Bi₂O₃ significantly increases the thermal stability of the composites. At 680 °C, a polymer composite containing 10 wt% Bi₂O₃ retains 9.7% of its mass, and at 60 wt% Bi₂O₃, retains 58.4%. The radiation-protective characteristics of the composites with respect to gamma radiation were evaluated by experimental and theoretical methods. High radiation-protective characteristics of the composites have been established in the gamma-quanta energy range of 0.1-1 MeV.

Three-dimensional model of DEMO-FNS facility considering neutronics and radiation shield problems

Recent neutronics studies of blankets for tokamak-based demonstration fusion neutron source (DEMO-FNS) showed a crucial influence of coolant composition on the transmutation rate of transuranic elements and tritium breeding in the system. The coolant choice varies with the neutron spectrum and shielding properties of the blanket. This paper presents a three-dimensional model developed for the Monte Carlo calculations of DEMO-FNS neutronics. The model was used for estimating the capability of the radiation shield to protect the superconducting electromagnetic system (EMS) from neutrons and gamma radiation for two types of coolants, namely water and supercritical carbon dioxide. The neutron balance, neutron energy spectra, and energy release of the neutrons and gamma radiation were evaluated in the shield, case, and superconductor at the inner and outer contours of the EMS. In comparison with the closed shielding option, the radiation heating power at the case and superconductor of the outer contour located between the injection port (IP) and the blanket maintenance port was 10 times higher than that in the area facing the injector. Thus, further improvement of the local shield design near the IP is needed.

A comparative investigation on structure evolution of ZrN and CrN coatings against ion irradiation

Binary ZrN and CrN nanostructured coatings deposited by magnetron sputtering were irradiated with 600 keV Kr³⁺ at room temperature. The ion irradiation fluences varied from 0 to 1×10¹⁷ Kr³⁺/cm⁻². The results indicate the microstructure of the CrN illustrates higher stability during the Kr³⁺ ion irradiation compared to that of the ZrN. The ion irradiation produces surface etching of the CrN coating. However, the etching transfers to recrystallization and grain coarsening on the ZrN coating surface as the Kr³⁺ fluence increases.

Determination of the degree of grain refinement in irradiated U-Mo fuels

A simple, repeatable method for determination of the degree of grain refinement in irradiated Uranium-Molybdenum fuels has been developed. This method involves mechanical potting and polishing of samples along with examination using a scanning electron microscope located outside of a hot cell. The commercially available software package Mathematica was used to determine the degree of grain refinement by way of a built-in iterative active contour method of image segmentation. Baseline methods for degree of grain refinement assessment are suggested for consideration and further development.

Stand-alone containment analysis of Phébus FPT tests with ASTEC and MELCOR codes: the FPT-2 test

During the last 40 years, many studies have been carried out to investigate the different phenomena occurring during a Severe Accident (SA) in a Nuclear Power Plant (NPP). Such efforts have been supported by the execution of different experimental campaigns, and the integral Phébus FP tests were probably some of the most important experiments in this field. In these tests, the degradation of a Pressurized Water Reactor (PWR) fuel bundle was investigated employing different control rod materials and burn-up levels in strongly or weakly oxidizing conditions. From the findings on these and previous tests, numerical codes such as ASTEC and MELCOR have been developed to analyze the evolution of a SA in real NPPs. After the termination of the Phébus FP campaign, these two codes have been furthermore improved to implement the more recent findings coming from different experimental campaigns. Therefore, continuous verification and validation is still necessary to check that the new improvements introduced in such codes allow also a better prediction of these Phébus tests. The aim of the present work is to re-analyze the Phébus FPT-2 test employing the updated ASTEC and MELCOR code versions. The analysis focuses on the stand-alone containment aspects of this test, and three different spatial nodalizations of the containment vessel (CV) have been developed. The paper summarizes the main thermal-hydraulic results and presents different sensitivity analyses carried out on the aerosols and fission products (FP) behavior. When possible, a comparison among the results obtained during this work and by different authors in previous work is also performed. This paper is part of a series of publications covering the four Phébus FP tests using a PWR fuel bundle: FPT-0, FPT-1, FPT-2, and FPT-3, excluding the FPT-4 one, related to the study of the release of low-volatility FP and transuranic elements from a debris bed and a pool of melted fuel.

95gTc and 96gTc as alternatives to medical radioisotope 99mTc

We studied 95gTc and 96gTc as alternatives to the medical radioisotope 99mTc. 96gTc (95gTc) can be produced by (p, n) reactions on an enriched 96Mo (95Mo) target with a proton beam provided by a compact accelerator such as a medical cyclotron that generate radioisotopes for positron emission tomography (PET). The γ-rays are measured with an electron-tracking Compton camera (ETCC). We calculated the relative intensities of the γ-rays from 95gTc and 96gTc. The calculated γ-ray intensity of a 96gTc (95gTc) nucleus is as high as 63% (70%) of that of a 99mTc nucleus. We also calculated the patient radiation doses of 95gTc and 96gTc, which were larger than that of 99mTc by a factor of 2-3 based on the applied assumptions. A medical PET cyclotron which can provide proton beams with energies of 11-12 MeV and a current of 100 μA can produce 12 GBq (39 GBq) of 96gTc (95gTc) for operation time of 8 h, which can be used for 240 (200) diagnostic scans.

Numerical investigation of heat transfer in parallel channels with water at supercritical pressure

Thermal phenomena such as heat transfer enhancement, heat transfer deterioration, and flow instability observed at supercritical pressures as a result of fluid property variations have the potential to affect the safety of design and operation of Supercritical Water-cooled Reactor SCWR, and also challenge the capabilities of both heat transfer correlations and Computational Fluid Dynamics CFD physical models. These phenomena observed at supercritical pressures need to be thoroughly investigated.

An experimental study was carried out by Xi to investigate flow instability in parallel channels at supercritical pressures under different mass flow rates, pressures, and axial power shapes. Experimental data on flow instability at inlet of the heated channels were obtained but no heat transfer data along the axial length was obtained. This numerical study used 3D numerical tool STAR-CCM+ to investigate heat transfer at supercritical pressures along the axial lengths of the parallel channels with water ahead of experimental data. Homogeneous axial power shape HAPS was adopted and the heating powers adopted in this work were below the experimental threshold heating powers obtained for HAPS by Xi. The results show that the Fluid Centre-line Temperature FCLT increased linearly below and above the PCT region, but flattened at the PCT region for all the system parameters considered. The inlet temperature, heating power, pressure, gravity and mass flow rate have effects on WT (wall temperature) values in the NHT (normal heat transfer), EHT (enhanced heat transfer), DHT (deteriorated heat transfer) and recovery from DHT regions. While variation of all other system parameters in the EHT and PCT regions showed no significant difference in the WT and FCLT values respectively, the WT and FCLT values respectively increased with pressure in these regions. For most of the system parameters considered, the FCLT and WT values obtained in the two channels were nearly the same. The numerical study was not quantitatively compared with experimental data along the axial lengths of the parallel channels, but it was observed that the numerical tool STAR-CCM+ adopted was able to capture the trends for NHT, EHT, DHT and recovery from DHT regions. The heating powers used for the various simulations were below the experimentally observed threshold heating powers, but heat transfer deterioration HTD was observed, confirming the previous finding that HTD could occur before the occurrence of unstable behavior at supercritical pressures. For purposes of comparing the results of numerical simulations with experimental data, the heat transfer data on temperature oscillations obtained at the outlet of the heated channels and instability boundary results obtained at the inlet of the heated channels were compared. The numerical results obtained quite well agree with the experimental data. This work calls for provision of experimental data on heat transfer in parallel channels at supercritical pressures for validation of similar numerical studies.

Heteroepitaxial diamond growth on 4H-SiC using microwave plasma chemical vapor deposition

Deposition of heteroepitaxial diamond via microwave chemical vapor deposition has been performed on a 4H-SiC substrate using bias enhanced nucleation followed by a growth step. In future work, the diamond film will serve as a protective layer for an alpha particle sensor designed to function in an electrorefiner during pyroprocessing of spent fuel. The diamond deposition on the 4H-SiC substrate was carried out using a methane-hydrogen gas mixture with varying gas flow rates. The nucleation step was conducted for 30 minutes and provided sufficient nucleation sites to grow a diamond film on various locations on the substrate. The resulting diamond film was characterized using Raman spectroscopy exhibiting the strong Raman peak at 1332 cm⁻¹. Scanning electron microscopy was used to observe the surface morphology and the average grain size of the diamond film was observed to be on the order of ∼2–3 μm.