bluuebunny/crossref_metadata_2025 huggingface dataset:
Critical Heat Flux Enhancement in Water-Based Nanofluid With Honeycomb Porous Plate on Large Heated Surface
Authors: Mt Aznam Suazlan , Mori Shoji , Okuyama Kunito
Published: October 2016

Heat removal through pool boiling is limited by the phenomena of critical heat flux (CHF). CHF enhancement is vitally important in order to satisfy demand for the cooling technology with high heat flux in In Vessel Retention (IVR). Various surface modifications of the boiling surface, e.g., integrated surface structures and coating of a micro-porous have been proven to effectively enhance the CHF in saturated pool boiling. We have been proposed a novel method of attaching a honeycomb structured porous plate on a considerably large heater surface. Previous results, by the authors in [1] reported that CHF has been enhanced experimentally up to more than approximately twice that of a plain surface (approximately 2.0 to 2.5 MW/m2) with a diameter of 30 mm heated surface. However, it is necessary to demonstrate the method together with infinite heater surface within laboratory scale. It is important that cooling techniques for IVR could be applicable to a large heated surface as well as remove high heat flux. Objective of this study is to investigate the CHF of honeycomb porous plate and metal solid structure in nanofluid boiling or water boiling on a large heated surface. Water-based nanofluid offers good wettability and capillarity. While metal solid structure is installed on honeycomb porous plate to increase the number of vapor jet. Experimental results of honeycomb porous plate and combination of honeycomb porous plate and metal solid structure in water-based nanofluid boiling shows that CHF is increased up to twice [2] and thrice, respectively compared to plain surface in water boiling. To the best of the author’s knowledge, the highest value (3.1 MW/m2) was obtained for a large heated surface having a diameter of 50 mm which is regarded as infinite heated surface. This demonstrates potential for general applicability to have more safety margin in IVR method.
Confirmation of Seismic Integrity of HTTR Against 2011 Great East Japan Earthquake
Authors: Ono Masato , Iigaki Kazuhiko , Shimazaki Yosuke , Shimizu Atsushi , Inoi Hiroyuki , Tochio Daisuke , Hamamoto Shimpei , Nishihara Tetsuo , Takada Shoji , Sawa Kazuhiro , Kondo Toshinari , Kojima Keidai
Published: October 2016

Japan Atomic Energy Agency (JAEA) has carried out research and development to establish the technical basis of High Temperature Gas-cooled Reactor (HTGR) by using High Temperature engineering Test Reactor (HTTR). On March 11th, 2011, the Great East Japan Earthquake of magnitude 9.0 occurred. When the great earthquake occurred, the HTTR had been stopped under the periodic inspection and maintenance of equipment and instrument. In the great earthquake, the maximum seismic acceleration observed at the HTTR exceeded the maximum value in seismic design. The visual inspection of HTTR facility was carried out for the seismic integrity conformation of HTTR. The seismic analysis was also carried out using the observed earthquake motion at HTTR site to confirm the integrity of HTTR.

The concept of comprehensive integrity evaluation for the HTTR facility is divided into two parts. One is the “inspection of equipment and instrument”. The other is the “seismic response analysis” for the building structure, equipment and instrument using the observed earthquake. For the basic inspections of equipment and instrument were performed for all them related to the operation of reactor. The integrity of the facilities is confirmed by comparing the inspection results or the numerical results with their evaluation criteria.

As the result of inspection of equipment and instrument and seismic response analysis, it was judged that there was no problem to operate the reactor, because there was no damage and performance deterioration, which affects the reactor operation. The integrity of HTTR was also supported by the several operations without reactor power in cold conditions of HTTR in 2011, 2013 and 2015.
Mechanism Study and Numerical Simulation on Blistering of Plate-Type Fuel
Authors: Deng Yangbin , Zhang Dalin , Lu Qing , Wu Yingwei , Tian Wenxi , Qiu Suizheng , Su G. H.
Published: October 2016

In this paper, the occurrence mechanism of blistering was studied and development processes of blistering were summarized. In addition, a thermal-mechanic-material coupling analysis code, named FROBA-PLATEs (Fuel Rod Behavior Analysis for PLATEs), was developed for plate-type fuel with the consideration of burnup effect. FROBA-PLATEs code was applied to perform the behavior analysis of a dispersion-plate-type fuel. Significant phenomena, including fission gas release and matrix damage, were simulated and key parameters, such as temperature profile, stress and strain profile, were obtained. Most important of all, the starting time of blistering was gained according to the deformation of cladding. The result indicates that: blistering happened at high burnup stage; power density and thickness of cladding are sensitive parameters for blistering. Reducing the power density or enlarge the thickness of cladding can delay or prevent blistering. Furthermore, the influence of blistering on thermal-hydraulic performance was preliminarily investigated by CFD simulation. The simulation result indicates that blistering results in deterioration of heat conduction in the fuel plate.
Vented Explosion Phenomena: Hydrogen Combustion Benchmark on Confined Vessel Experiments
Authors: Manzini Giovanni , Kljenak Ivo , Povilaitis Mantas
Published: October 2016

Confined vented explosion is a very complex topic as many parameters affect the phenomena, mainly because the flame front develops from an ignition source and travels through a medium which may involve complex boundary conditions and obstructions of various geometries.

Therefore, in the plant safety assessing step, it is important to provide correct estimates of the flame spreading rates as well as overpressures which may result from various explosion initiation scenarios. This will help designers for plant layout optimisation with the aim to minimize the risk associated with those events.

Although hydrogen explosion in unvented compartments was often simulated in the past, there were not many opportunities, so far, to simulate explosion in a vented room. With this purpose, a benchmark exercise was organized, based on simple hydrogen combustion experiments, performed in a vented compartment (Chamber for View of Explosion – CVE) at the Scalbatraio laboratory of University of Pisa (Italy). In that activity, many tests were performed by varying the initial hydrogen concentration and the obstacles inside the compartment.

The numerical codes used in the benchmark were lumped-parameter (LP) ones (ECART, ASTEC), which remain, for the time being, the customary tools for simulating hydrogen combustion accidents in current NPPs, because of their fast-running calculation capabilities also for large-scale scenarios.
Establishing a Construction Method of an Automatic Fire Suppression System for Cable Tray Fires
Authors: Shirai Koji , Iwata Mikimasa , Goda Yutaka , Miyagi Tsukasa
Published: October 2016

Among the countermeasures to reduce the impacts of cable fires, installing automatic fire detection and suppression equipment may be applicable for cable trays due to the overcurrent incident considering a single failure of the circuit breaker. To establish a method to construct such systems effectively, we applied two types of automatic fire suppression systems using gaseous and bubble foam agents. For cable tray fire suppression tests, we used the overcurrent test equipment installed in the high power short-circuit testing facility in the CRIEPI (Central Research Institute of Electric Power Industry) in Japan. Several series of tests subjected to 2kA-class overcurrent of six times the allowable current were performed using FR (Flame Retardant)/ Non-FR high-/low-voltage power cables. During these tests, to reproduce the cable fire, one target cable was continuously energized by ring transformers, which confirmed the reliable fire suppression capability of the cooling and suffocation.
Study on Power Transmission Plan of the Nuclear Power Base in Shandong Peninsula
Authors: Yin Chengzhu , Wang Miao
Published: October 2016

The nuclear power site resource is very rich in Jiaodong Peninsula of Shandong Province. It is suitable for construction of the large nuclear power base. The transmission scope and direction of Jiaodong Peninsula nuclear power base is analyzed, and optional transmission plans of Plant 1, Plant 2, Plant 3 and Plant 4 are proposed. The transmission plans are recommended based on technical and economic comparison, which provide good references for construction of the large-scale nuclear power base and power grid development planning.

Jiaodong Peninsula nuclear power base is planned to be built in the year of 2016–2030, planning capacity of which is 30500MW. The site of nuclear power base is 100∼400km away from the power load center. The nuclear power will use AC transmission and mainly meet the demand of local power load. The early 15500MW gensets will be accessed to the power grid at 500kV, as the following 15000MW gensets will be accessed at 1000kV UHV (Ultra-high voltage) grid. As the accessing of many large-capacity gensets will produce huge impact to the short-circuit current, sectionalized double-bus configuration is recommended in the 500kV main electrical wiring to reduce the short-circuit current of 500kV bus of nuclear power plant. Double bus section cross wire connection is presented to make sure that every two generators on each bus will be connected to different substations on two transmission lines which are set up on different poles and in different paths, to improve the reliability of the power plant. Through analysis and provement, the construction of large nuclear power base must be based on large and stronge power grid, especially the UHV (Ultra-high voltage) AC grid, to meet the demand of huge nuclear power transmission, and to improve the ability of power exchange and ensure the safety of regional power supply.

Also, as the nuclear power plant should better be in base-load operation, the construction of large-scale nuclear power base, would make the system load-control demands increase, which leads to more prominent problems. In order to avoid adding additional depth of peaking power operation and reducing the overall economic operation of power system, power grid should have the necessary means to load-control. Namely the construction of peaking units, such as pumped storage units or gas-fired units at about 5000MW.

By analyzing and demonstration, large-scale nuclear power base must rely on large-scale power grid, particularly the support of UHV power grid in order to meet the demond of large-scale power transmission and electricity exchange, and also to ensure regional security of electricity supply.
Numerical Analysis of Hydrogen Risk Related Severe Accident Scenario in Chinese PWR
Authors: Fan Yang , Kudriakov Sergey , Etienne Studer , Zhiqiang Zou , Yu Hongxing
Published: October 2016

Based on the fact that the pressure loads generated in hydrogen combustion process may jeopardize the integrity of the containment during severe accident, and the changing rate as well as the maximum value of the pressure loads are governed by the flame propagation process, it is important to simulate the hydrogen combustion process with proper methodology. Due to the insufficiency understanding of the turbulent combustion and the difficulties of hydrogen combustion simulation in large scale and complex geometry, explosion safety applications are always based on simplified combustion model, for which the validation work and specified conservative parameter is required. In this study, an methodology combining CFD analysis and model validation based on large scale combustion experiments (HDR E12 and HYCOM01/02) is built up. And domestic hydrogen combustion process in the containment during severe accident is simulated. This study provides solid basis for structure design and integrity analysis of the containment.
Seismic Qualification of Equipment: A PRA-Consistent Framework
Authors: Chatterjee Payel , Gupta Abhinav
Published: October 2016

The seismic probabilistic risk assessment (SPRA) for a nuclear power plant involves the estimation of fragility curves for plant equipment. The seismic qualification of an equipment based on testing requires the equipment to continue to function when subjected to a specific test response spectrum (TRS). Broad banded ground motions have been found to cause more damage to equipment than the filtered narrow banded excitations. As a result, the definition of acceleration capacity used in the fragility models use clipped response spectra for both test response spectrum (TRS) and required response spectrum (RRS). The main purpose of the clipping factors is to convert a narrow banded response spectrum to a broad banded spectrum. The broadband correction factor and the modal interaction correction factors together contribute to the definition of clipping factor. The current study involves reconciliation with previous research by generating the mean response factor for different waveforms and subsequently the root-mean-square (RMS) severity ratio as a function of bandwidth. This ratio can be estimated for real earthquakes from their peak-to-rms values and the peak spectral values. In addition it can be shown that in case of real narrow banded earthquakes, this ratio is even lower and therefore the clipping would be greater. The modal interaction correction factor which considers the effect of interaction between different modes in case of broad banded time histories has also been investigated. The primary objective of this work is to study the existing Conservative Deterministic Failure Margin (CDFM) and Probabilistic approaches for estimating these factors as per the guidelines of EPRI [2] and apply the same to real life ground motions. It has been observed that the recommended practices are based on studying the behavior of random ground motions generated artificially for different bandwidths and center frequencies. The present study aims towards a more realistic fragility estimation of equipment by studying the spectral response of equipment based on actual ground motions. The purpose is to evaluate clipping factors that are consistent with Seismic Probabilistic Risk Assessment.
Air Ingress Experiments Within High Temperature Graphite Flow Channels
Authors: Gould Dan , Bindra Hitesh , Schlaikjer Eric , Liu Hanwen
Published: October 2016

The graphite-fuel matrix in the core region of HTGRs can come into direct contact with air at high temperature during air ingress accident. Nuclear grade graphite has been shown to undergo oxidation when subjected to oxidizing flow at high temperatures. There is, however, no agreement on the relative importance of the numerous factors that can contribute to the overall rate of oxidation. Examples of some of these potential factors include graphite temperature, fluid temperature, fluid composition, graphite composition, and graphite surface conditions. Separate effects experiments have, in general, not been able to fully capture these complex interactions.

In this work, a new experimental apparatus was designed to conduct mixed-effect experiments to understand the complicated interactions that would influence the oxidation rate and heat removal rate of graphite exposed to a high temperature air ingress. Utilizing thermographic methods, experiments detailing the local temperature response of a representative graphite flow channel were conducted at high temperatures (1173 K) in both oxidizing and inert gaseous environments.
Vibration Effects on Bubbly Flow Structure in an Annulus
Authors: Xiao Xiu , Zhu Qingzi , Wang Guanyi , Chen Shao-Wen , Ishii Mamoru , Zhang Yajun
Published: October 2016

In order to investigate the seismic vibration effect on two-phase flow structure, experiments were performed for upwards bubbly flow in an annulus channel with and without externally-induced vibration. The inner and outer diameters of the annulus are 19.1 mm and 38.1 mm respectively, and the total height of the test section is 2.32 m. To simulate seismic vibrations, the test section is attached to an eccentric cam vibration module with an eccentricity of 9.5 mm. The eccentric cam rotation speed can reach up to 210 rpm. Local two-phase flow parameters were measured along radial direction within the annulus gap using miniaturized four-sensor conductivity probe at axial location of z/Dh = 77. The semi-instantaneous local parameters at different vibration angles were analyzed by tracing the quasi-sinusoidal acceleration signal under vibration conditions. The results showed that the seismic vibration can significantly affect the local parameters in bubbly flow regime. Void fraction can increase by 10% compared with non-vibration condition. During the vibration cycle, the void fraction also changed greatly, especially in the near wall region. The interfacial area concentration (IAC) and Sauter mean diameter displayed the same behavior as the respective void fraction profiles.
Temperature Measurements of Thermal Stratification and Turbulent Mixing in Nuclear Systems With a Single Heated Jet
Authors: Carasik Lane B. , Lee Saya , Cabral Arturo A. , Hassan Yassin A.
Published: October 2016

Large volumes or enclosures are utilized in nuclear systems such as the sodium fast reactor (SFR) upper plenum, spent fuel pools, and containment structures seen in common nuclear reactor designs. These volumes may be quiescent or turbulent the injection of a hotter or cooler jet of fluid. This can lead to turbulent mixing of the entire volume or thermal stratification of a hotter layer of fluid. Due to the large thermal gradients experienced by the structures due to a stratified volume, the structures can experience degradation which can lead to severe consequences such as a loss of coolant accident. In order to prevent or mitigate these consequences, computational fluid dynamics (CFD) codes can be utilized to predict the occurrence of turbulent mixing and thermal stratification. This data can be used in conjunction with structural analysis codes to determine the severity of phenomena occurrence on structures. Unfortunately, the validity of CFD codes to predict this type of behavior is limited due to the lack of experimental data to validate the predicted behavior. In response, the twin jet water facility (TJWF) created by the University of Tennessee was repurposed to create data sets of temperature using thermocouples and particle image velocimetry (PIV) for this effort. The temperature data collected using the thermocouples is similar to previous experiments conducted within an older version of the facility with a different geometric configuration. The most recently collected data was created by conducting several runs of each each set of experiment conditions and ensemble averaged. This was done to confirm the observed behavior is due to the physical processes and not due to noise or random happenstance. The spectral frequency responses of the temperature data were determined to observe frequencies or spectral behavior corresponding to turbulent mixing and stratification. The temperature and frequencies are reported to compare the experiments to simulations being conducted in conjunction with this study.
Corrosion of 9% Cr Ferritic/Martensitic Steels in Flowing Pb-Bi Eutectic With 10−7 Mass% Dissolved Oxygen at 450 and 550 °C
Authors: Tsisar Valentyn , Schroer Carsten , Wedemeyer Olaf , Skrypnik Aleksandr , Konys Jürgen
Published: October 2016

Corrosion behavior of 9 %Cr ferritic/martensitic (F/M) P92, E911 and EUROFER steels was investigated in flowing (2 m/s) Pb-Bi with 10−7 mass%O at 450 and 550 °C for up to 8766 and 2011 h, respectively. The steels show mixed corrosion modes simultaneously revealing protective scaling, accelerated oxidation and solution-based attack. At 450 °C, the accelerated oxidation resulted in a metal recession averaging 6 μm (± 2 μm) after ∼8766 h while local solution-based corrosion attack ranged from ∼40 to 350 μm. At 550 °C, the accelerated oxidation resulted in a metal recession of about 10 μm (± 2 μm) after ∼2011 h. Solution-based corrosion attack appears more regularly at 550 °C, with a maximum depth ranged from ∼90 to 1000 μm. Incubation time for solution based attack is 500–2000 h for 450 °C and < 300 h for 550 °C. The EUROFER steel showed more severe metal recession via both oxidation and solution-based corrosion in comparison with P92 and E911 steels. The possible effect of alloying and structure on the corrosion response of 9 %Cr F/M steels is discussed.
Experimental Activity for the Investigation of Mixing and Thermal Stratification Phenomena in the CIRCE Pool Facility
Authors: Martelli D. , Tarantino M. , Di Piazza I.
Published: October 2016

Since the Lead-cooled Fast Reactor (LFR) has been conceptualized in the frame of GEN IV International Forum (GIF), ENEA is strongly involved in the HLM technology development.

In particular, several experimental campaign employing HLM loop and pool facilities (CIRCE [1], NACIE [2], HELENA [3], HERO [4]) are carried out in order to support HLM technologies development.

In this frame, suitable experiments were carried out on the CIRCE pool facility refurbished with the Integral Circulation Experiment (ICE) test section in order to investigate the thermal hydraulics and the heat transfer in grid spaced Fuel Pin Bundle cooled by liquid metal providing, among the others aim, experimental data in support of codes validation for the European fast reactor development.

The study of thermal stratification in large pool reactor is relevant in the design of HLM nuclear reactor especially for safety issue. Thermal stratification should induce thermomechanical stresses on the structures and in accidental scenario conditions, could opposes to the establishment of natural circulation which is a fundamental aspect for the achievements of safety goals required in the GEN-IV roadmap.

In the present work, a Protected Loss of Heat Sink with Loss Of Flow (PLOHS+LOF) scenario is experimentally simulated and the mixed convection with thermal stratification phenomena is investigated during the simulated transient, as foreseen in the frame of Horizon 2020 SESAME project [5].

A full characterization of thermal stratification inside the pool is presented, and the main results gained during the run are reported.

The two tests named A (20 h) and B (6 h) here reported, essentially differs for the power supplied to the fuel bundle during the full power run (800 kW and 600 kW respectively). After the transition to natural circulation conditions, the power supplied to the bundle is decreased to about 30 kW simulating the decay heat.

Finally the Nusselt number for the central subchannel of the fuel bundle simulator (FPS) is evaluated and compared with values obtained from Ushakov and Mikityuk correlations [6–7].
Design of a Two-Stage Centrifugal Pump for Nuclear Systems
Authors: Shi Qian , Ye Ping , Zhao Gang
Published: October 2016

The drain pump is an essential part in the conventional island of a nuclear power plant. It affects the condensing efficiency of the condenser and the residual heat removal rate of the secondary loop. Multi-stage centrifugal pumps are used in nuclear drain pumps, of which pumps using magnetic bearings technology are innovations with extensive discussions. A design of a two-stage centrifugal pump with the magnetic bearings was presented. The stage number, the inner structure and the size of the blades came from the hydraulic calculation. Numerical simulation was employed to get the flow field. A guide vane was designed to alter the flow direction. Results indicated that an even-distributed pressure field and a fairly low turbulent kinetic energy field in the new design.
Implementation of Reliability Evaluation Into JSME Fast Reactor Codes: 1 — Current Status and Path Forward
Authors: Asayama Tai , Takaya Shigeru
Published: October 2016

This paper describes the current status and path forward of the ongoing activities in the Japan Society of Mechanical Engineers to implement reliability evaluation methodologies into the fast reactor codes and standards. The activities are going on on two aspects; design and inservice inspection. For design, methodologies are being developed to implement a reliability-based method for the evaluation of buckling of vessels using the Load and Resistance Factor Design method. With regards inservice inspection, in order to establish a methodology that takes account of the reliability of components when setting inspection requirements, evaluations are being performed on major passive components of fast reactors. To support the process, guidelines for reliability evaluation are being developed. The efforts to standardize reliability evaluation methodologies will be continued. One of the most important remaining issues is establishing a framework on which target reliabilities could be determined by the consensus of stakeholders.
The Deposition Behavior of Fine Glass Particle of PCVD
Authors: Song Xuefu , Peng Wei , Sun Yuancheng , Zhang Tianqi , Yu Suyuan
Published: October 2016

In the present study, the CFD method was used to investigate the flow field and temperature field distribution in the glass deposition furnace. Combined with the DPM model, the motion of fine glass particle inside the furnace are also studied. The results shows that there exists a large temperature gradient in the furnace and glass sedimentary basement. The glass particles with larger diameter are easier to deposit on the sedimentary basement. Meanwhile, the larger particles are easier to deposit on the left side of furnace wall, while the smaller particles are easier to deposit on the thin pipe entrance. Both the larger and smaller particle can deposit on the right side of the furnace. The injection angle of plasma has a great effect on the temperature and flow field.
A Strategy of DNBR On-Line Monitoring and Protection in PWR
Authors: Liu Yu , Ren Chunming
Published: October 2016

Based on the measured parameters, including core power distribution, system pressure, inlet coolant temperature and flow, departure from nucleate boiling ratio (DNBR) can be calculated on-line. This paper presents a strategy to develop the DNBR online monitoring and protection system for PWR nuclear power plant (NPP). The main functions are to provide core DNBR status to operator and to replace the delta-T protection in conventional PWR NPPs. The system structure consists of two different levels respectively for monitoring and protection. There are four cabinets in each level to insure the reliability. DNBR on-line algorithm is on the basis of a modified single channel thermal-hydraulic model. A computer program was developed and verified through comparison with the sub-channel code.
Investigation of Liquid Metal Embrittlement of AISI 316L Steels
Authors: Stefanini L. , Lo Frano Rosa , Stergar Erich
Published: October 2016

To support the feasibility and the deployment of LFRs one of the main issues to be solved is the reliability of structural materials to be exposed to liquid metal coolant.

Particularly the Liquid Metal Embrittlement (LME) of steels is of interest for nuclear reactors and spallation sources projects because structural materials for these systems are selected according to their corrosion resistance, irradiation embrittlement and compatibility with the coolant.

This study was performed in the framework of MYRRHA project, a new-generation sub-critical reactor (based on the Accelerator Driving System concept) that uses Lead-Bismuth Eutectic (LBE) as coolant.

LME phenomenon has been investigated by performing theoretical and experimental activity profiting and basing on the results obtained for the T91 m/f steel in contact with LBE.

This paper first reviews the model of Kamdar: weak points and contradictions are highlighted.

From an experimental point of view to verify the occurrence of LME, Slow Strain Rate Tensile tests were performed on the AISI 316L in LBE environment at SCK-CEN laboratories.

Besides, a fracture surface analysis was carried out together with a microstructural analysis by using that Scanning Electron Microscopy. This was done in order to confirm the results obtained by the mechanical tests and to look for impurities in the metallic matrix. These impurities are an interesting feature in case of high scatter in the results.

Indeed one of the difficulties was the opacity and conductivity of the medium.

The methodological approach and the procedure are also duly described along with preliminary results.
Physical and Numerical Investigations for the Development of a New Experimental Facility for Studying Blowdown Phenomena
Authors: De Lorenzo Marco , Lafon Philippe , Bartosiewicz Yann , Seynhaeve Jean-Marie
Published: October 2016

Electricité de France (EDF), with the scientific cooperation of Université Catholique de Louvain (UCL), is starting new investigations about the blowdown phenomena. For these purposes, EDF is considering to build a new experimental installation called BRECHE. In this article, the main features of the design of the test rig are presented together with the numerical simulation carried out with EUROPLEXUS code for the hydraulic and mechanical design of BRECHE.
Development of High Efficiency Containment Venting System by Using AgX
Authors: Narabayashi Tadashi , Sugano Yuuhei , Imaeda Hiroki , Chiba Go , Sato Nobuaki , Endo Koji , Kobayashi Toshiki
Published: October 2016

Fukushima Daiichi NPP accident would be terminated, if sufficient accident countermeasures, such as water proof door, mobile power, etc [1, 2]. In case of Europe, it had already installed the heat removal system and filtered containment venting system (FCVS) from the lessons of TMI and Chernobyl Accidents. The new regulatory standard in Japan, the filtered vent system (FCVS) should be installed, and prevent the radioactive material in case of the severe accident and the overpressure breakage prevention of a primary containment vessel (PCV) and also the robustization of the FCVS.

The authors examined the severe accident process in the 2nd unit of Fukushima Daiichi NPS, and found the vent by FCVS should be done before water injection into the core. The PCV spray and water injection into the pedestal basement should be also the countermeasures to the severe accident. Countermeasures for an intentional aircraft collision should be installed too.

Upon occurrence of a severe accident (SA), vent gas with radioactive fission products is blown out to a scrubbing pool through numerous venturi nozzles. Mist in steam moves upward to a metal fiber filter through a multi-hole baffle plate. After the mist is removed by that filter, radioactive methyl iodine (CH3I) is captured on the surface of a molecular sieve or AgX, made from zeolite particles with silver coating.

A FCVS visualized test facility was installed at Hokkaido University. An AgX filter is used down-stream of the scrubbing pool and metal fiver filter. Thickness of AgX filter is very important parameter to obtain enough decontamination factor (DF). The DF for the radioactive iodine exceeds 10,000 at bed depth (AgX filter thickness) greater than 75mm.
Numerical Analysis of the Corium Behavior Within the Fuel Support Piece by MPS
Authors: Chen Ronghua , Chen Lie , Tian Wenxi , Su Guanghui , Qiu Suizheng
Published: October 2016

In the typical boiling water reactor (BWR), each control rod guide tube supports four fuel assemblies via an orificed fuel support piece in which a channel is designed to be a potential corium relocation path from the core region to the lower head under severe accident conditions. In this study, the improved Moving Particle Semi-implicit (MPS) method was adopted to analyze the melt flow and ablation behavior in this region during a severe accident of BWR. A three-dimensional particle configuration was constructed for analyzing the melt flow behavior within the fuel support piece. Considering the symmetry of the fuel support piece, only one fourth of the fuel support was simulated. The eutectic reaction between Zr (the material of the corium) and stainless steel (the material of the fuel support piece) was taken into consideration. The typical melt flow and freezing behaviors within the fuel support piece were successfully reproduced by MPS method. In all the simulation cases, the melt discharged from the hole of the fuel support piece instead of plugging the fuel support piece. The results indicate that MPS method has the capacity to analyze the melt flow and solidification behavior in the fuel support piece.
Dynamic Simulation Studies of Performed Additional Tests During FAT for Emergency Diesel Generators at Nuclear Power Plant
Authors: Kanaan Salah K. , Omanovic Amer
Published: October 2016

In 2004, a decision was made to perform a modernization and a new power uprate of unit 2 at Oskarshamn nuclear power plant in Sweden. Among the most important reasons for this decision were new safety regulations from Swedish Radiation Safety Authority and ageing of important components. A project was established and became the largest nuclear power modernization in the world.

The modernization led to the need of analysing the auxiliary power system to ensure that it could supply the unit after the uprate, given tolerances on current, voltage and frequency. During the process of developing models for the diesel generator sets, it turned out that the suppliers could not deliver enough satisfactory material for modelling the diesel engines, the speed controllers and the magnetization systems. Therefore, Oskarshamn nuclear power plant with the help of the manufacturers of the diesel generator sets carried out additional measurements in order to collect data for modelling.

Based on electric circuit diagrams provided by the manufacturers, block diagrams of the magnetization systems were made. For the speed controllers, no information was available at all so it was assumed that the controller was of PI-type. The parameters of the magnetization systems and the speed controllers were then tuned using the measurement results.

Finally, a comparison between simulated results and the measurement results were made, showing good agreement. This is especially true in the most commonly used operating interval of the diesel generator sets.
Evaluation of Sodium Pool Fire and Thermal Consequence in Two-Cell Configuration
Authors: Ohno Shuji , Takata Takashi , Tajima Yuji
Published: October 2016

Evaluation of accidental sodium leak, combustion, and its thermal consequence is one of the important issues to be assessed in the field of sodium-cooled fast reactor (SFR) since the liquid sodium is chemically active and might give thermal load to plant building structure due to its exothermic reaction with oxygen in air atmosphere. Therefore, many experimental investigations and numerical simulation tools development have been and still now are being carried out to understand the details of sodium fire behaviors and to contribute to the investigation and preparation of appropriate mitigation measures in the plant design.

From various kinds of sodium fire situations, the present paper treats the sodium pool fire and subsequent heat transfer behavior in air atmosphere two-cell geometry both experimentally and analytically because such two-cell configuration is considered as the typical one to possess important characteristic of multi-compartment system seen in an actual plant. Main description of this paper consists of a sodium pool fire experiment that was performed in a rectangular-shaped two-cell system with an opening between the cells, and the discussion of the experimental results. Inner volume of the experimental cells is about 70 m3. The amount of used sodium and the prepared pool surface area in the experiment are about 55 kg and 2.25 m2, respectively. The experiment has provided the temperature data measured in more than 100 positions for atmospheric gas and structures other than the data of oxygen concentration and suspended sodium aerosols concentration in the cells. The analyses of the measured data clarify the basic characteristics of sodium pool combustion and consequential heat and mass transfer in the cells, for instance, suggesting several features of multidimensional thermal-hydraulic behaviors such as thermal stratification near the opening between the two cells. In the discussion, numerical analysis using a lumped-parameter based zonal model safety analysis code ‘SPHINCS’ and the comparison of its results with the experimental data are also carried out to investigate the validity and applicability of the code to this type of sodium fire situation.
A Three-Dimensional Flux Expansion Nodal Method for Hexagonal Geometry Application
Authors: Cai Yun , Peng Xingjie , Li Qing , Wang Kan , Sun Wei , Gong Zhaohu
Published: October 2016

In this paper, a new flux expansion nodal method for hexagonal-z geometry is presented to solve multi-group neutron diffusion equations. In each three dimensional node and each group, the intra-nodal flux is approximated by the linear combination of exponential functions and orthogonal polynomials up to the second order. The coefficients are obtained by the weighted residual methods and the coupling conditions of the nodes, which satisfy the continuity of both the zero- and first-order moments of fluxes and currents across the nodal surfaces. A series of benchmark problems including the three dimensional cases are used to test this method. The numerical results verify that it is a rather accurate and efficient for the estimation of the eigenvalue and power distribution.
Gas uptake of 3D printed acrylonitrile butadiene styrene using a vacuum apparatus designed for absorption and desorption studies
Authors: Sefa Makfir , Ahmed Zeeshan , Fedchak James A. , Scherschligt Julia , Klimov Nikolai
Published: October 2016

The authors describe a vacuum apparatus for determining the outgassing rate into vacuum, the diffusion coefficient, and the amount of gas absorbed for various materials. The diffusion coefficient is determined from a model applied to time-dependent desorption data taken using a throughput method. The authors used this method to determine the diffusion coefficient, D, for H2O in three dimensional printed acrylonitrile butadiene styrene (ABS). They found DH2O = 8.3 × 10−8 cm2/s ± 1.3 × 10−8 cm2/s (k = 1; 67% confidence interval) at 23.2 °C. This result was compared to the diffusion coefficient determined another by a gravimetric method, in which the sample weight was monitored as it absorbed gas from the atmosphere. The two methods agreed to within 3%, which is well within the uncertainty of the measurement. The authors also found that at least 80% of the atmospheric gas (air) absorbed by the ABS is water. The total amount of all atmospheric gas absorbed by ABS was about 0.35% by weight when exposed to ambient air in the laboratory, which was at a pressure of 101 kPa with a relative humidity of 57% at 22.2 °C.
Baby genome screening needs more time to gestate
Authors: Kaiser Jocelyn
Published: October 2016

Unenthused parents and missed diseases mar pilot efforts.
Climate scientists open up their black boxes to scrutiny
Authors: Voosen Paul
Published: October 2016

Modelers becoming less hush-hush about tuning, the “secret sauce” that controls fine-scale processes.
After the fall
Authors: Mervis Jeffrey
Published: October 2016

Some scientists debarred for research misconduct remain on the faculty. How that happens may surprise you.
Direct frequency comb measurement of OD + CO → DOCO kinetics
Authors: Bjork B. J. , Bui T. Q. , Heckl O. H. , Changala P. B. , Spaun B. , Heu P. , Follman D. , Deutsch C. , Cole G. D. , Aspelmeyer M. , Okumura M. , Ye J.
Published: October 2016

Combing through CO oxidation kinetics

Carbon monoxide reacts with OH radicals to produce CO
2
. This process is central to combustion and atmospheric oxidation chemistry. The reaction sequence is widely assumed to involve the intermediacy of a HOCO adduct that has eluded direct monitoring under thermal conditions. Bjork
et al.
successfully observed the formation of the deuterated analog of this intermediate, DOCO, while simultaneously monitoring OD by using a multifrequency infrared comb. The results confirm the termolecular nature of the formation mechanism and its sensitivity to the ambient bath gas.

Science
, this issue p.
444
Chimpanzee genomic diversity reveals ancient admixture with bonobos
Authors: de Manuel Marc , Kuhlwilm Martin , Frandsen Peter , Sousa Vitor C. , Desai Tariq , Prado-Martinez Javier , Hernandez-Rodriguez Jessica , Dupanloup Isabelle , Lao Oscar , Hallast Pille , Schmidt Joshua M. , Heredia-Genestar José María , Benazzo Andrea , Barbujani Guido , Peter Benjamin M. , Kuderna Lukas F. K. , Casals Ferran , Angedakin Samuel , Arandjelovic Mimi , Boesch Christophe , Kühl Hjalmar , Vigilant Linda , Langergraber Kevin , Novembre John , Gut Marta , Gut Ivo , Navarro Arcadi , Carlsen Frands , Andrés Aida M. , Siegismund Hans. R. , Scally Aylwyn , Excoffier Laurent , Tyler-Smith Chris , Castellano Sergi , Xue Yali , Hvilsom Christina , Marques-Bonet Tomas
Published: October 2016

Of chimpanzees and bonobos

Modern non-African human genomes contain genomic remnants that suggest that there was interbreeding between ancient humans and archaic hominoid lineages. Now, de Manuel
et al.
show similar ancestral interbreeding between the ancestors of today's chimpanzees and bonobos (see the Perspective by Hoelzel). The study also provides population-specific genetic markers that may be valuable for conservation efforts.

Science
, this issue p.
477
; see also p.
414
Climate change: The 2015 Paris Agreement thresholds and Mediterranean basin ecosystems
Authors: Guiot Joel , Cramer Wolfgang
Published: October 2016

A warming limit for the Mediterranean basin

Pollen cores from sediments provide rich detail on the history of vegetation and climate in the Mediterranean during the Holocene (the most recent ~10,000 years). Guiot and Cramer used this information as a baseline against which to compare predictions of future climate and vegetation under different climate-change scenarios. Vegetation and land-use systems observed in the Holocene records may persist under a 1.5°C warming above preindustrial temperature levels. A 2°C warming, however, is likely over the next century to produce ecosystems in the Mediterranean basin that have no analog in the past 10,000 years.

Science
, this issue p.
465
Is anyone out there?
The Aliens Are Coming! The Extraordinary Science Behind Our Search for Life in the Universe
Ben Miller
The Experiment, 2016, 304 pp.
Authors: Huerta Marcos
Published: October 2016

A witty romp through the cosmos explores the scientific search for intelligent alien life
Kinase inhibitors that block bromodomain interactions
Authors: Mushegian Alexandra A.
Published: October 2016

Interference with protein interactions may be the mechanism of the anti-inflammatory and antiproliferative activity of dual-function ERK5 inhibitors.
Molecular Bases Determining Daptomycin Resistance-Mediated Resensitization to β-Lactams (Seesaw Effect) in Methicillin-Resistant Staphylococcus aureus
Authors: Renzoni Adriana , Kelley William L. , Rosato Roberto R. , Martinez Maria P. , Roch Melanie , Fatouraei Maryam , Haeusser Daniel P. , Margolin William , Fenn Samuel , Turner Robert D. , Foster Simon J. , Rosato Adriana E.
Published: October 2016

Antimicrobial resistance is recognized as one of the principal threats to public health worldwide, yet the problem is increasing. Infections caused by methicillin-resistant
Staphylococcus aureus
(MRSA) strains are among the most difficult to treat in clinical settings due to the resistance of MRSA to nearly all available antibiotics. The cyclic anionic lipopeptide antibiotic daptomycin (DAP) is the clinical mainstay of anti-MRSA therapy. The decreased susceptibility to DAP (DAP resistance [DAP
r
]) reported in MRSA is frequently accompanied by a paradoxical decrease in β-lactam resistance, a process known as the “seesaw effect.” Despite the observed discordance in resistance phenotypes, the combination of DAP and β-lactams has been proven to be clinically effective for the prevention and treatment of infections due to DAP
r
MRSA strains. However, the mechanisms underlying the interactions between DAP and β-lactams are largely unknown. In the study described here, we studied the role of
mprF
with DAP-induced mutations in β-lactam sensitization and its involvement in the effective killing by the DAP-oxacillin (OXA) combination. DAP-OXA-mediated effects resulted in cell wall perturbations, including changes in peptidoglycan insertion, penicillin-binding protein 2 (PBP 2) delocalization, and reduced membrane amounts of PBP 2a, despite the increased transcription of
mecA
through
mec
regulatory elements. We have found that the VraSR sensor-regulator is a key component of DAP resistance, triggering mutated
mprF
-mediated cell membrane (CM) modifications that result in impairment of PrsA location and chaperone functions, both of which are essential for PBP 2a maturation, the key determinant of β-lactam resistance. These observations provide for the first time evidence that synergistic effects between DAP and β-lactams involve PrsA posttranscriptional regulation of CM-associated PBP 2a.
Active-Site Protonation States in an Acyl-Enzyme Intermediate of a Class A β-Lactamase with a Monobactam Substrate
Authors: Vandavasi Venu Gopal , Langan Patricia S. , Weiss Kevin L. , Parks Jerry M. , Cooper Jonathan B. , Ginell Stephan L. , Coates Leighton
Published: October 2016

The monobactam antibiotic aztreonam is used to treat cystic fibrosis patients with chronic pulmonary infections colonized by
Pseudomonas aeruginosa
strains expressing CTX-M extended-spectrum β-lactamases. The protonation states of active-site residues that are responsible for hydrolysis have been determined previously for the apo form of a CTX-M β-lactamase but not for a monobactam acyl-enzyme intermediate. Here we used neutron and high-resolution X-ray crystallography to probe the mechanism by which CTX-M extended-spectrum β-lactamases hydrolyze monobactam antibiotics. In these first reported structures of a class A β-lactamase in an acyl-enzyme complex with aztreonam, we directly observed most of the hydrogen atoms (as deuterium) within the active site. Although Lys 234 is fully protonated in the acyl intermediate, we found that Lys 73 is neutral. These findings are consistent with Lys 73 being able to serve as a general base during the acylation part of the catalytic mechanism, as previously proposed.
Congenital Cytomegalovirus: a “Now” Problem—No Really, Now
Authors: Bernstein David I.
Published: October 2016

Despite the clear need, progress toward a vaccine for congenital cytomegalovirus (CMV) has been slow. However, recent events have provided new interest, and several vaccine candidates are either in clinical trials or the trials are close to starting. In this issue of
Clinical and Vaccine Immunology
, Schleiss and colleagues show that a nonreplicating lymphocytic choriomeningitis virus (rLCMV)-vectored vaccine expressing CMV glycoprotein B (gB) and/or pp65 induces B and T cells and improves pup survival in a guinea pig model of congenital CMV infection (Clin Vaccine Immunol 24:e00300-16, 2017,
https://doi.org/10.1128/CVI.00300-16
). The combination vaccine appeared to be the most effective.