bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbulent Characteristics in Lead-Bismuth Flows Flowing in Poor and Good Wettability Pipes
Authors: Ariyoshi Gen , Ito Daisuke , Saito Yasushi , Mishima Kaichiro
Published: October 2016

Lead-bismuth single-phase and two-phase upward flows in a round tube were measured by using an electro-magnetic probe and an electrical conductivity probe. Experiments were performed under adiabatic conditions by varying the superficial gas and liquid velocity from 0 to 0.04 m/s and 0.1 to 0.2 m/s respectively. From the experimental results, it was found that the local liquid velocity and the void fraction in the lead-bismuth two-phase flow take the maximum value near the wall region at low void fraction conditions. These results indicate bubbles would tend to flow along the wall surface due to the poor wettability of the test section to the lead-bismuth. To verify this hypothesis, the liquid velocity and void fraction were also measured by using a test tube with better wettability. In addition, the experimental results were compared with existing experimental results to evaluate the effect of surface wettability on flow structure of lead-bismuth.
Regimes of Formation of Bubbly Flows
Authors: Kashinsky O. N. , Vorobyev M. A. , Lobanov P. D. , Chinak A. V.
Published: October 2016

An experimental study of the process of bubble detachment from a single capillary was performed. Glycerin was used as a test liquid. To study the effect of physical properties of liquid on the process of bubble formation the experiments were conducted at different temperatures. The dependencies of mean bubble diameter on gas flow rate, liquid temperature and liquid velocity along with the size of capillary are presented. The data on the most typical regimes of bubbly mixture formation are obtained. The bubble coalescence near the capillary is shown to be the process which determines the shape of bubble size distribution in the flow.
Measurement of Flow Rate of Droplets and Liquid Film in Venturi Scrubber
Authors: Nakao Yasuhiro , Horiguchi Naoki , Yoshida Hiroyuki , Kanagawa Tetsuya , Kaneko Akiko , Abe Yutaka
Published: October 2016

As one of filtered venting systems which should be installed in light water reactors from viewpoint of protecting a containment vessel and suppressing the diffusion of radioactive materials, there is a system composed of venturi scrubbers. The radioactive materials in the contaminated gas are collected into liquid. By dispersed flow formed in the venturi scrubber, large interfacial area between liquid and gas was obtained, and large decontamination factor is realized. In evaluation for the decontamination performance of the venturi scrubber, interface of droplets and liquid film are important. However, there is a little knowledge about the interfacial area in the venturi scrubber for filtered venting. In this study, to obtain the interfacial area data, amount of the droplets and the liquid film in the venturi scrubber is evaluated by visualizing observation and sampling the liquid film at the outlet of the venturi scrubber.

In the venturi scrubber, a pressure drop occurs in the throat part by the inflow of air from the compressor. Water flows from the tank by a pressure difference between a suctioned hole with head pressure and a throat part. An annular spray flow is then formed in the venturi scrubber. Therefore, the liquid flow rate changes according to the gas phase flow rate. To discharge separately the droplets and the liquid film, a rectangular separator is installed at the venturi scrubber outlet. The superficial gas phase flow rate is 25.2–292.3 m/s in the throat.

As a result, the liquid film and the droplets through the wall were confirmed to be discharged separately by the separator. The ratio of the liquid film to the total amount of liquid is 80 to 95% and that of the droplets was estimated as 5 to 20%. However, the change of the liquid film thickness caused by the increase of gas phase flow rates was observed. When the liquid film thickness is large, it is possible that some liquid film flowing into the droplet side.
Evaluation of Liquid-Vapor Interphase Friction Models Based on Vertical Upflow Experiments
Authors: Clark Randy R. , Kornhauser Alan A.
Published: October 2016

A method was developed for calculating liquid-vapor interphase friction using data from vertical upflow experiments. This method was applied to data sets from six experimental setups. Results were compared with interphase friction correlations used in RELAP5/MOD3.3 and with RELAP5/MOD3.3 simulations of the experiments. There were large differences between the friction calculated from experimental data and that predicted by the code.
RELAP5-3D Simulation of Natural Circulation in Fast Reactors With Lead-Bismuth Eutectic Alloy Coolant
Authors: Matev Alex
Published: October 2016

Many researchers are investigating the potential of lead-bismuth cooled fast reactors for producing electricity, as well as for the safe transmutation of minor actinides and the nuclear incineration of long-lived fission products.

BelV is a Technical Support Organization to the Belgian Nuclear Regulator, FANC, and has begun a project with the goal to identify and analyze key technical issues in core neutronics, thermal-hydraulics, fuels, and materials associated with the development of a fast nuclear reactor with a lead-bismuth coolant.

The paper presents the results from simulating with the RELAP5-3D code of natural circulation in a generic design of a pool-type nuclear reactor with lead-bismuth eutectic alloy (LBEA) as a primary, and water/steam as a secondary coolant.

The simulation results provide valuable insights in the evolution of key reactor safety-relevant phenomena and support also the qualified use of system analysis codes as RELAP5-3D for the simulation of transients in pool-type reactor systems.
Investigations on RELAP5-3D to RELAP5-3D Coupling Methodology by PVMEXEC
Authors: Parrinello Valeria , Lanfredini Marco , Petruzzi Alessandro , Cherubini Marco
Published: October 2016

In the framework of a BEPU (Best Estimate Plus Uncertainty) approach within the licensing process of a nuclear power plant, the need to extend the resources of nuclear system thermal-hydraulics codes, such as RELAP5-3D, arises to allow more detailed simulations of the complex 3D reality of Nuclear Power Plants (NPPs), either under normal steady-state or during various accident scenarios.

Currently, it is not possible to achieve the same degree of detail for a whole nuclear system when it is simulated with RELAP5-3D and this is due to the inherent limitations in the number of components and volumes to be used for the analysis. For this reason, it is of extreme interest the use of tools for codes coupling that enable the use of different codes for the simulation of different portions of a system in a unified analysis.

In this paper the attention will be focused on the decomposition of the thermal-hydraulic domain of a system into subsystems to be simulated by different instances of the same code (e.g. RELAP5-3D) coupled together by means of PVMEXEC program and parallel virtual machine (PVM) technology. Explicit and semi-implicit solution algorithms were used for the analyses.

Among the analyzed cases, the following will be discussed in detail with the aim to provide additional guidelines for the use of the PVMEXEC tool: (i) the Edward’s pipe blowdown test, (ii) a simplified countercurrent heat exchanger, (iii) different hydraulics and heat structure coupling schemes for a shell-tube heat exchanger and (iv) a three-task coupled model of a simplified BWR model.
Cyber Attack Detection of I&C Systems in NPPS Based on Physical Process Data
Authors: Li Jianghai , Huang Xiaojin
Published: October 2016

The cyber security problem is posing new challenges to the current safety analysis of nuclear power plants. Historically, analogue control systems in the absence of interactive communications are immune to cyber-attacks; however, digital control systems with extensive interconnection of reprogrammable components are intensely vulnerable to cyber-attacks which shed light on the significance and urgency of the cyber security. The current cyber security approaches, which merely focus on information networks, have not given multi-faceted considerations to instrumentation and control (I&C) systems. The cyber-attack on I&C systems may lead to more severe consequences, including the abnormal change of parameters, the malfunction of equipment, and even the accident condition. The existing cyber security approaches for information networks, such as firewalls, encryption, can enhance the cyber security of I&C systems, but are often insufficient in addressing challenges associate with the I&C systems which link cyber space and physical systems. The defense approach based on physical information should be developed to meet the emerging challenges. In this paper, we propose the cyber-physical security (CPS) approach based on the physical process data for the cyber defense. This approach does not intend to replace current cyber defense mechanisms. It could be served as the last barrier for security defense. The goal of the CPS defense approach is to detect attacks at the beginning of the occurrence of physical process anomalies cause by cyber-attacks. A practical implementation of the CPS approach is proposed and its influence on the existing infrastructure is discussed. The statistical analysis techniques are utilized on physical process data for attack detection. The method of dynamic principal component analysis (dynamic PCA) is employed to characterize the correlation of multiple variables in the normal operational condition. In the abnormal operational occurrence, the chi-square detector is able to distinguish adversarial cyber-attacks from ordinary random failures.
Simulation of Direct Contact Condensation Using Large Scale Interface Multifluid Model
Authors: Gada Vinesh H. , Tandon Mohit P. , Elias Jebin , Splawski Andrew , Lo Simon
Published: October 2016

The Large Scale Interface (LSI) model of the Euler-Euler method in STAR-CCM+ is extended to simulate two-phase flow with phase change. This extended methodology is used to simulate direct contact condensation (DCC) of steam in a hot leg when cold water is injected by emergency core cooling system to remove the residual heat. The case corresponds an experimental study conducted at Hungarian Atomic Energy Research Institute KFKI using the PMK-2 device. Out of the several experiments reported for this scenario, the one experiment considered in this work corresponds to a case without the water hammer phenomena. It was found that the LSI model is able to capture core physics of direct contact condensation during steam-water counter-current flow in a pipe. The model could capture entrapment of steam between the interface and its subsequent rapid condensation. The role of the relaxation time-scale of the large interface drag and the turbulence damping at interface is also studied.
The Sensitivity of the Addition of Low-Low Pressurizer Pressure in Coincidence With High Containment Pressure on M310 Type Nuclear Power Plant
Authors: Yanfei Qiu
Published: October 2016

Due to the new security system that the operator intervention is assumed to occur in 20 minutes is not acceptable, for the current M310 type nuclear power plant. The loss of coolant accident with Intermediate breaks in primary loop is the only one of design basis accident which need operator action in 20 minutes. For certain size break, the consequences are very sensitive to the pump stop time. According to deterministic analysis that for a certain size break, if stop the pump in 20 minutes after accident, the peak cladding temperature will exceed the limit value of 1204°C. Therefore, it is necessary to add low-low pressurizer pressure in coincidence with high containment pressure signal to stop pump automatically on M310 type nuclear power plant.
Numerical Study on the Heat Transfer Characteristics of COPRA-L1 Melt Pool Based on the LES Method
Authors: Zhang Yapei , Zhang Luteng , Tian Wenxi , Qiu Suizheng , Su Guanghui
Published: October 2016

Natural convection in a volumetrically heated fluid is of significant importance related to the In-Vessel Retention (IVR) issue. The COPRA facility is designed to simulate the lower plenum of reactor vessel at 1:1 scale for the Chinese advanced PWR, which is a two-dimensional 1/4 circular slice structure with an inner radius of 2.2 m. Water was used as simulant in COPRA-L1 tests. Due to the full scale geometry, The Rayleigh numbers within the corium pools could reach to 1016, matching those in the prototypical situation during severe accident. Due to the high Rayleigh numbers and high turbulence in the melt pool, we choose the Large-Eddy Simulation (LES) method to do the numerical calculations. The LES method can better capture the heat transfer characteristic in a high-Rayleigh number volumetrically heated liquid pool. The numerical results of pool temperature and heat flux distribution were compared with those from COPRA-L1 tests.
VERA-CS Modeling and Simulation of PWR Main Steam Line Break Core Response to DNB
Authors: Kucukboyaci Vefa N. , Sung Yixing , Xu Yiban , Cao Liping , Salko Robert K.
Published: October 2016

The Virtual Environment for Reactor Applications core simulator (VERA-CS) being developed by the Consortium for Advanced Simulation of Light Water Reactors (CASL) includes coupled neutronics, thermal-hydraulics (T/H), and fuel temperature components with an isotopic depletion capability. The neutronics capability is based on the Michigan Parallel Characteristics Transport Code (MPACT), a three-dimensional whole-core transport code. The T/H and fuel temperature models are provided by the COBRA-TF (CTF) subchannel code. As part of the CASL development program, the VERA-CS (MPACT/CTF) code system was applied to model and simulate reactor core response with respect to the departure from nucleate boiling (DNB) ratio at the most limiting point of a postulated pressurized water reactor main steam line break event initiated at the hot zero power, either with offsite power available and the reactor coolant pumps in operation (high-flow case) or without offsite power, where the reactor core is cooled through natural circulation (low-flow case). The VERA-CS simulation was based on core boundary conditions from the RETRAN-02 system transient calculations and STAR-CCM+ computational fluid dynamics (CFD) core inlet distribution calculations. The evaluation indicated that the VERA-CS code system is capable of modeling and simulating quasi-steady-state reactor core response under the main steam line break accident condition, the results are insensitive to uncertainties in the inlet flow distributions from the CFD simulations, and the high-flow case is more DNB limiting than the low-flow case.
Use of FEA Software in Evaluating Pump Vibration and Potential Remedial Actions to Abate Resonance in Industrial Vertical Pump/Motor Combinations
Authors: Tompkins Michael , Stakenborghs Robert , Kramer Gregory
Published: October 2016

Reactor recirculation motor generator lube oil twin screw pumps are commonly found in nuclear power plants and throughout industry. In a vertical mounting configuration in which the electric motor is bolted atop the twin screw pump in an unsupported manner the natural frequency of the pump/motor structure can be quite low, resulting in damaging vibration. When a structure’s natural frequency coincides at or near the operating speed, or multiple thereof, a phenomena known as resonance can occur. Resonance can occur when a driving force, in this case minor imbalances in either the motor or pump, begins to vibrate and excite the structure resulting in greatly amplified levels of vibration.

In this paper, finite element analysis software is utilized to first calculate the natural frequency of the pump/motor structure, and then potential modifications are modeled to determine their impact on eliminating harmful resonance.
Post Small-Break LOCA Long Term Core Cooling Performance in ACME Test Facility
Authors: Qi Zhanfei , Zhu Sheng
Published: October 2016

CAP1400 Pressurized Water Reactor is developed by China’s State Nuclear Power Technology Corporation (SNPTC) based on the passive safety concept and advanced system design. The Advanced Core-cooling Mechanism Experiment (ACME) integral effect test facility, which was constructed at Tsinghua University, represents a 1/3-scale height of CAP1400 RCS and passive safety features. It is designed to simulate the performance of CAP1400 passive core cooling system in the small break loss of coolant accidents (SBLOCA) for design certification, safety review and safety analysis code development. The Long Term Core Cooling (LTCC) post-LOCA could be simulated by ACME as well. A series of test cases with various break sizes and locations with post-LOCA LTCC period were conducted in ACME facility. This paper describes the post-LOCA LTCC test conducted in ACME test facility. The LTCC phenomena in different cases are very similar. It’s found that the interval that switching from IRWST injection to sump recirculation has the least safety margin. However, it’s shown that the post-LOCA LTCC in ACME could be well maintained by passive core cooling system according to the test results even though the recirculation water level in ACME IRWST-2 is lower than the containment recircualtion level in CAP1400 conservatively.
Development of Hydrogen Treatment System in Severe Accident: Part 2 — Study on Reaction Characteristic of a Hydrogen Processing Unit
Authors: Iwaki Chikako , Kittaka Daigo , Yoshii Toshihiro , Yagyu Motoshige , Okamura Masato , Tanabe Masashi , Ishibashi Fumihiko
Published: October 2016

In the course of a severe accident, a large amount of hydrogen gas is generated by a metal-water reaction in a PCV (Primary Containment Vessel) of Light Water Reactors. Although the filter vent of gas mixture, which includes hydrogen and steam, is an effective method for the accident management of BWR that prevents the PCV overpressure, the filter vent at the early stage of severe accident may cause releasing radioactive material to environment. We have been developing the hydrogen treatment system to prevent excessive pressure without PCV vent and releasing radioactive material to environment.

We focus on the oxidation-reduction reaction of metal oxides with high reaction rates, for the hydrogen treatment system. Metal oxide material would be an effective device under low-oxygen conditions like PCV of BWR. The hydrogen treatment system mainly consists of a hydrogen processing unit, a blower and pipes. The hydrogen treatment unit has a lot of reaction pipes in which metal oxides are filled. Some fundamental chemical experiments which we have done have revealed that copper oxides (CuO) rapidly react with hydrogen to form cupper (Cu). Their results show that metal oxides are effective as hydrogen treatment elements. On the other hand, there are few evaluations for the characteristics of hydrogen treatment unit. The dependency of hydrogen treatment performance on gas temperature, hydrogen concentration and pressure is investigated in the present study.

We conducted experiments using a test section with one reaction pipe, which simulated a hydrogen processing unit. The processing materials granulated CuO, MnO2 and Co3O4 with 2mm diameter were used. Gradual increase of processing material temperature in the test section was observed along the gas streams caused by oxidation-reduction reaction after the mixing gases were supplied. Consequently, the hydrogen concentration at the outlet of the test section decreased with time. The increase of the hydrogen reaction rate was also observed with increase of gas temperature, hydrogen concentration and pressure. We have developed the thermal-chemical model of hydrogen processing unit from these experiment results, and confirmed that the model could predict the characteristics of a hydrogen processing unit qualitatively.
The Development of RELAP5 for Reactor System Analysis and Simulation Use of Visualized Modularization Software (RELAP-MV)
Authors: Yousif Eltayeb , Zhang Zhijian , Tian Zhaofei , Ju Haoran
Published: October 2016

The RELAP5 code, designed to predict the behavior of reactor systems during accident conditions, is used widespread over the world. This work aims to show and describe the RELAP-MV graphical software developed using computer language (XML) and Visualized Modularization software technology to recognized best estimated transient simulation program of Light water reactor, in combination with new options for improved modeling methods, advanced programming, computational simulation techniques and integrated graphics displays. RELAP5 code is complex and inconvenient for utilizing method of data cards and close logic relationship of data in input file. The main purpose of developing RELAP5-MV is to simplify progress and increase simulation efficiency.

Traditional modeling method and modular modeling method are supported with RELAP5-MV to achieve aims of device and system simulation. For traditional modeling method, all kinds of components are developed such as single volume, single junction, pipe, branch, time dependent volume, etc. For modular modeling method, the module library is established in the software. The library packages include the main system equipments of primary and secondary loops such as reactor core, U tube steam generator, once through steam generator, pump, pressurizer, steam turbine, condenser, heat exchanger, deaerator, etc. in a pressurized water reactor, which can be analyzed and modeled in details. From the library the capabilities are easy to select icons interface from the library packages. The analysis results show that the software can effectively simulate nuclear power system by RELAP5.

Plot and data binding function is supported for post-processing of calculation result. Personal computer interface of RELAP5-MV makes it more convenient, fast and visualized in simulation system establishing process. Performance Relap5 related analysis activities, such as creating and modifying input file, viewing component division figures and generating output files can be realized by RELAP5-MV. The interactive simulation interface feature allows the users to simulate specific reactor transients and accidents — such as LOCA, LOFA, scram, etc. Accuracy and reliability of RELAP5-MV have already been confirmed by simulating main coolant system of Pressurize Water Reactor (PWR) and modeling efficiency increases significantly by using RELAP5-MV.

Visualization modeling, analysis and computational simulation for thermal hydraulic analysis of nuclear reactor can not only lower the RELAP5 threshold but also improve the efficiency of nuclear science research greatly, and also promoting the development of related research in RELAP5 safety analysis.

RELAP5-MV can give an approach to build, verify and assess simulation design of reactor power system.
Development of Prevention Method for Air Ingress During a Depressurization Accident of the VHTR
Authors: Takeda Tetsuaki , Funatani Shumpei
Published: October 2016

A depressurization accident is a design-basis accidents of a very high temperature reactor. When a depressurization accident occurs, air is expected to enter the reactor pressure vessel from the breach and oxidize in-core graphite structures. Therefore, it is important to know a mixing process of different kind of gases in the stable and unstable stratified fluid layer. Especially, it is also important to examine an influence of localized natural convection and molecular diffusion on mixing process from a viewpoint of safety. In order to predict and analyze the phenomena of air ingress during a depressurization accident, therefore, it is important to develop the method for prevention of air ingress during the accident. We have carried out an experiment and a numerical analysis using three-dimensional computational fluid dynamics (3D CFD) to obtain the mixing process of two component gases and flow characteristics of the localized natural convection. This study is also to investigate a control method of natural circulation of air by injection of helium gas. The numerical model consists of a storage tank and a reverse U-shaped vertical slot. They are separated by a partition plate. One side of the left wall of the left side vertical slot is heated and the other side was cooled. The right side vertical slot is cooled. The procedure of the experiment and the numerical analysis is as follows. Firstly, the storage tank was filled with heavy gas and the reverse U-shaped vertical slot was filled with light gas. In the left side vertical slot, the localized natural convection was generated by the temperature difference between the vertical walls. The flow characteristics were obtained by the experiment and steady state analysis. The unsteady state experiment and analysis were started after the partition plate was opened. The result obtained in the experiment was simulated by the numerical analysis quantitatively. The gases were mixed by molecular diffusion and natural convection. After the time elapsed, natural circulation occurred. When the temperature difference of the left vertical fluid layer was set to 100K and the combination of the mixed gas was helium and nitrogen, natural circulation produced after 110 minutes elapsed.
Direct Numerical Simulation of a Turbulent Flow on an Oscillating Wall Using Cut-Cell Based Immersed Boundary Method
Authors: Kino Chiaki
Published: October 2016

The flow-induced vibration of a pipe is an important issue in various engineering fields, and this phenomenon is widely observed in nuclear power plants. Although turbulent structures play important roles in the velocity and pressure fields in a pipe, only a few studies have been conducted on the turbulent flow on an oscillating wall. In this study, direct numerical simulations were conducted to establish a large eddy simulation model for a turbulent flow on an oscillating wall and scrutinize the energy transfer between the grid scale (GS) and sub-grid scale (SGS). Although energy is generally transferred from the GS to SGS (forward scatter), it is likely that energy is transferred from the SGS to GS (backward scatter) under specific conditions. The present numerical results indicated that backward scatter exists in the production term in the case of a static wavy wall. On the other hand, such backward scatter could not be observed in the case of an oscillating wall. It is well known that separated flows and backward flows are generated behind the crest. Stronger backward flows accelerate the main flow and enhance the velocity gradients in a wide range behind the crest. In the case of an oscillating wall, the development of separated flow is immature because the shape of the wall is not fixed. Eventually, the backward scatter is deemed to be suppressed.
Thermal-Hydraulic Investigations to the Flow of Model Gases at a PWR Fuel Assembly Dummy and Overflow of Air Above the Top of the Dummy
Authors: Chahi H. , Kästner W. , Alt S.
Published: October 2016

The burnt fuel assemblies, which are unloaded from the reactor core, are storage in a water-cooled storage pool until radioactivity and heat decays to the authorized transportation value of dry storage containers.

With the incident in a storage pool fatal consequences can occur that depend on the initiating event (station blackout, loss of coolant, etc.). The integrity of the cladding tubes of the fuel assemblies is an important aspect in the nuclear safety.

Thermal-hydraulic phenomena were investigated, which occur during evaporation of the storage pool and overheating of the steam followed by an upwards flow in the fuel assembly boxes. According the principle of similarity, physical parameters of the steam upwards flow were simulated by not heated model gases.

The overflow of air above the fuel assembly storage boxes was experimentally investigated in a horizontal overflow channel. The conditions of the air overflow were vary by air conditioning (temperature, humidity). The interactions of density driven flow or diffusion (air / gas model) and the interaction (air / steam) with the overflow simulated the thermal-hydraulic phenomena during these processes.

The paper includes the presentation of the experimental facility and some results of the experiments.

This research project supported by the German Federal Ministry of Education and Research named SINABEL (Safety of spent fuel pools: Experimental analysis, modeling and validation of system and CFD codes) delivers with a combination of experiments and simulations, knowledge’s of the heat transfer processes for the case of a partially or completely evaporated spent fuel storage pool in light water reactor nuclear power plants both within the fuel rod bundle of a fuel assembly (FA) and in the spaces between the FA in order to be able to predict via the modeling and simulation the development of the axial and radial temperature profiles of rods by different accident scenarios.

SINABEL is a joint research project which three research institutions (TU-Dresden, HZDR and HSZG) work together.
Numerical and Theoretical Study on Parameter Selection of Acoustic Load Test of Steam Dryer
Authors: Zhong Jia , Wang Han , Wang Nan , Zhang Jinyi , Liu Yujia , Liu Wen , Zhang Kai
Published: October 2016

In recent years some reactors have experienced significant steam dryer cracking. The cause of the dryer’s failure was considered as flow-induced acoustic resonance at the stub pipes of the safety relief valves (SRVs) on the main steam lines (MSLs). A research program was started to investigate the acoustic resonance of the steam dryer. Most studies used scaled down method, while our research based on the full scale steam dryer of the prototype CAP1400 but with only one unit of the steam dryer. The purpose of our research program is to study the strength of the steam dryer under flow-induced acoustic resonance. This paper introduces the parameter selection of the main pipe and the stub pipe through numerical method and theoretical method.
Influencing Factors of the HTR-10 Core Dynamics in Reactivity Insertion ATWS Tests
Authors: Gou Feng , Chen Fubing , Dong Yujie
Published: October 2016

After the full power operation of the 10 MW High Temperature Gas-cooled Reactor-Test Module (HTR-10), several safety demonstration tests, representing the anticipated transient without scram (ATWS) conditions, were successfully performed on this reactor. Among these tests, two reactivity insertion ATWS tests were conducted by withdrawing a single control rod without reactor scram at 30% rated power.

In the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University, these two tests have been reanalyzed using the THERMIX code, and the code itself was strictly checked through the test data. According to the previous code benchmark activities utilizing the HTR-10 tests, the temperature coefficient of reactivity (TCR), the residual heat level (RHL) and the xenon poisoning effect (XPE) could be considered the most important influencing factors of the THERMIX simulation accuracy for the core dynamics. In this study, sensitivity analyses are performed on the basis of the assumed variations of TCR, RHL and XPE. The impacts of these concerned parameters on the reactor power transient are qualitatively identified.
An aqueous preoxidation method for monolithic perovskite electrocatalysts with enhanced water oxidation performance
Authors: Li Bo-Quan , Tang Cheng , Wang Hao-Fan , Zhu Xiao-Lin , Zhang Qiang
Published: October 2016

Aqueous preoxidation strategy for in situ hybridization of oxidative perovskite and reductive conductive frameworks.
Verifying Heisenberg’s error-disturbance relation using a single trapped ion
Authors: Zhou Fei , Yan Leilei , Gong Shijie , Ma Zhihao , He Jiuzhou , Xiong Taiping , Chen Liang , Yang Wanli , Feng Mang , Vedral Vlatko
Published: October 2016

A newly formulated uncertainty relation has been verified experimentally by a single ultracold ion.
Nonradiating and radiating modes excited by quantum emitters in open epsilon-near-zero cavities
Authors: Liberal Iñigo , Engheta Nader
Published: October 2016

Quantum emitters embedded in arbitrarily shaped epsilon-near-zero cavities can selectively excite both nonradiating and radiating modes.
Stabilizers as a design tool for new forms of the Lechner-Hauke-Zoller annealer
Authors: Rocchetto Andrea , Benjamin Simon C. , Li Ying
Published: October 2016

A new formalism to understand a novel class of quantum annealing devices and new designs obtained using the formalism.
Structure and mechanism of human PrimPol, a DNA polymerase with primase activity
Authors: Rechkoblit Olga , Gupta Yogesh K. , Malik Radhika , Rajashankar Kanagalaghatta R. , Johnson Robert E. , Prakash Louise , Prakash Satya , Aggarwal Aneel K.
Published: October 2016

Analysis of crystal structure elucidates the mechanism by which a human enzyme acts as both a primase and a DNA polymerase.
Entropy-driven structural transition and kinetic trapping in formamidinium lead iodide perovskite
Authors: Chen Tianran , Foley Benjamin J. , Park Changwon , Brown Craig M. , Harriger Leland W. , Lee Jooseop , Ruff Jacob , Yoon Mina , Choi Joshua J. , Lee Seung-Hun
Published: October 2016

In a photovoltaic perovskite, entropy-driven structural transition enables kinetic trapping of a desired photovoltaic phase.
Biochemical and Genetic Bases of Indole-3-Acetic Acid (Auxin Phytohormone) Degradation by the Plant-Growth-Promoting Rhizobacterium Paraburkholderia phytofirmans PsJN
Authors: Donoso Raúl , Leiva-Novoa Pablo , Zúñiga Ana , Timmermann Tania , Recabarren-Gajardo Gonzalo , González Bernardo
Published: October 2016

Several bacteria use the plant hormone indole-3-acetic acid (IAA) as a sole carbon and energy source. A cluster of genes (named
iac
) encoding IAA degradation has been reported in
Pseudomonas putida
1290, but the functions of these genes are not completely understood. The plant-growth-promoting rhizobacterium
Paraburkholderia phytofirmans
PsJN harbors
iac
gene homologues in its genome, but with a different gene organization and context than those of
P. putida
1290. The
iac
gene functions enable
P. phytofirmans
to use IAA as a sole carbon and energy source. Employing a heterologous expression system approach,
P. phytofirmans
iac
genes with previously undescribed functions were associated with specific biochemical steps. In addition, two uncharacterized genes, previously unreported in
P. putida
and found to be related to major facilitator and tautomerase superfamilies, are involved in removal of an IAA metabolite called dioxindole-3-acetate. Similar to the case in strain 1290, IAA degradation proceeds through catechol as intermediate, which is subsequently degraded by
ortho
-ring cleavage. A putative two-component regulatory system and a LysR-type regulator, which apparently respond to IAA and dioxindole-3-acetate, respectively, are involved in
iac
gene regulation in
P. phytofirmans
. These results provide new insights about unknown gene functions and complex regulatory mechanisms in IAA bacterial catabolism.

IMPORTANCE
This study describes indole-3-acetic acid (auxin phytohormone) degradation in the well-known betaproteobacterium
P. phytofirmans
PsJN and comprises a complete description of genes, some of them with previously unreported functions, and the general basis of their gene regulation. This work contributes to the understanding of how beneficial bacteria interact with plants, helping them to grow and/or to resist environmental stresses, through a complex set of molecular signals, in this case through degradation of a highly relevant plant hormone.
Metabolic Engineering of Raoultella ornithinolytica BF60 for Production of 2,5-Furandicarboxylic Acid from 5-Hydroxymethylfurfural
Authors: Hossain Gazi Sakir , Yuan Haibo , Li Jianghua , Shin Hyun-dong , Wang Miao , Du Guocheng , Chen Jian , Liu Long
Published: October 2016

2,5-Furandicarboxylic acid (FDCA) is an important renewable biotechnological building block because it serves as an environmentally friendly substitute for terephthalic acid in the production of polyesters. Currently, FDCA is produced mainly via chemical oxidation, which can cause severe environmental pollution. In this study, we developed an environmentally friendly process for the production of FDCA from 5-hydroxymethyl furfural (5-HMF) using a newly isolated strain,
Raoultella ornithinolytica
BF60. First,
R. ornithinolytica
BF60 was identified by screening and was isolated. Its maximal FDCA titer was 7.9 g/liter, and the maximal molar conversion ratio of 5-HMF to FDCA was 51.0% (mol/mol) under optimal conditions (100 mM 5-HMF, 45 g/liter whole-cell biocatalyst, 30°C, and 50 mM phosphate buffer [pH 8.0]). Next,
dcaD
, encoding dicarboxylic acid decarboxylase, was mutated to block FDCA degradation to furoic acid, thus increasing FDCA production to 9.2 g/liter. Subsequently,
aldR
, encoding aldehyde reductase, was mutated to prevent the catabolism of 5-HMF to HMF alcohol, further increasing the FDCA titer, to 11.3 g/liter. Finally, the gene encoding aldehyde dehydrogenase 1 was overexpressed. The FDCA titer increased to 13.9 g/liter, 1.7 times that of the wild-type strain, and the molar conversion ratio increased to 89.0%.

IMPORTANCE
In this work, we developed an ecofriendly bioprocess for green production of FDCA in engineered
R. ornithinolytica
. This report provides a starting point for further metabolic engineering aimed at a process for industrial production of FDCA using
R. ornithinolytica
.
Extended-Spectrum-Beta-Lactamase- and Plasmid-Encoded Cephamycinase-Producing Enterobacteria in the Broiler Hatchery as a Potential Mode of Pseudo-Vertical Transmission
Authors: Projahn Michaela , Daehre Katrin , Roesler Uwe , Friese Anika
Published: October 2016

Antimicrobial resistance through extended-spectrum beta-lactamases (ESBLs) and transferable (plasmid-encoded) cephamycinases (pAmpCs) represents an increasing problem in human and veterinary medicine. The presence of ESBL-/pAmpC-producing commensal enterobacteria in farm animals, such as broiler chickens, is considered one possible source of food contamination and could therefore also be relevant for human colonization. Studies on transmission routes along the broiler production chain showed that 1-day-old hatchlings are already affected. In this study, ESBL-/pAmpC-positive broiler parent flocks and their corresponding eggs, as well as various environmental and air samples from the hatchery, were analyzed. The eggs were investigated concerning ESBL-/pAmpC-producing enterobacteria on the outer eggshell surface (before/after disinfection), the inner eggshell surface, and the egg content. Isolates were analyzed concerning their species, their phylogroup in the case of
Escherichia coli
strains, the respective resistance genes, and the phenotypical antibiotic resistance. Of the tested eggs, 0.9% (
n
= 560) were contaminated on their outer shell surface. Further analyses using pulsed-field gel electrophoresis showed a relationship of these strains to those isolated from the corresponding parent flocks, which demonstrates a pseudo-vertical transfer of ESBL-/pAmpC-producing enterobacteria into the hatchery. Resistant enterobacteria were also found in environmental samples from the hatchery, such as dust or surfaces which could pose as a possible contamination source for the hatchlings. All 1-day-old chicks tested negative directly after hatching. The results show a possible entry of ESBL-/pAmpC-producing enterobacteria from the parent flocks into the hatchery; however, the impact of the hatchery on colonization of the hatchlings seems to be low.

IMPORTANCE
ESBL-/pAmpC-producing enterobacteria occur frequently in broiler-fattening farms. Recent studies investigated the prevalence and possible transmission route of these bacteria in the broiler production chain. It seemed very likely that the hatcheries play an important role in transmission and/or contamination events. There are only few data on transmission investigations from a grandparent or parent flock to their offspring. However, reliable data on direct or indirect vertical transmission events in the hatchery are not available. Therefore, we conducted our study and intensively investigated the broiler hatching eggs from ESBL-/pAmpC-positive broiler parent flocks as well as the hatchlings and the environment of the hatchery.
Allelochemicals Produced by Brown Macroalgae of the Lobophora Genus Are Active against Coral Larvae and Associated Bacteria, Supporting Pathogenic Shifts to Vibrio Dominance
Authors: Morrow Kathleen M. , Bromhall Katrina , Motti Cherie A. , Munn Colin B. , Bourne David G.
Published: October 2016

Pervasive environmental stressors on coral reefs are attributed with shifting the competitive balance in favor of alternative dominants, such as macroalgae. Previous studies have demonstrated that macroalgae compete with corals via a number of mechanisms, including the production of potent primary and secondary metabolites that can influence coral-associated microbial communities. The present study investigates the effects of the Pacific brown macroalga
Lobophora
sp. (due to the shifting nature of the
Lobophora
species complex, it will be referred to here as
Lobophora
sp.) on coral bacterial isolates, coral larvae, and the microbiome associated with the coral
Porites cylindrica.
Crude aqueous and organic macroalgal extracts were found to inhibit the growth of coral-associated bacteria. Extracts and fractions were also shown to inhibit coral larval settlement and cause mortality at concentrations lower (<0.3 mg · ml
−1
) than calculated natural concentrations (4.4 mg · ml
−1
). Microbial communities associated with coral tissues exposed to aqueous (e.g., hydrophilic) crude extracts demonstrated a significant shift to
Vibrio
dominance and a loss of sequences related to the putative coral bacterial symbiont,
Endozoicomonas
sp., based on 16S rRNA amplicon sequencing. This study contributes to growing evidence that macroalgal allelochemicals, dissolved organic material, and native macroalgal microbial assemblages all play a role in shifting the microbial equilibrium of the coral holobiont away from a beneficial state, contributing to a decline in coral fitness and a shift in ecosystem structure.

IMPORTANCE
Diverse microbial communities associate with coral tissues and mucus, providing important protective and nutritional services, but once disturbed, the microbial equilibrium may shift from a beneficial state to one that is detrimental or pathogenic. Macroalgae (e.g., seaweeds) can physically and chemically interact with corals, causing abrasion, bleaching, and overall stress. This study contributes to a growing body of evidence suggesting that macroalgae play a critical role in shifting the coral holobiont equilibrium, which may promote the invasion of opportunistic pathogens and cause coral mortality, facilitating additional macroalgal growth and invasion in the reef. Thus, macroalgae not only contribute to a decline in coral fitness but also influence coral reef ecosystem structure.
Glycerol Phosphate Cytidylyltransferase Stereospecificity Is Key to Understanding the Distinct Stereochemical Compositions of Glycerophosphoinositol in Bacteria and Archaea
Authors: Rodrigues Marta V. , Borges Nuno , Santos Helena
Published: October 2016

Glycerophosphoinositol (GPI) is a compatible solute present in a few hyperthermophiles. Interestingly, different GPI stereoisomers accumulate in
Bacteria
and
Archaea
, and the basis for this domain-dependent specificity was investigated herein. The archaeon
Archaeoglobus fulgidus
and the bacterium
Aquifex aeolicus
were used as model organisms. The synthesis of GPI involves glycerol phosphate cytidylyltransferase (GCT), which catalyzes the production of CDP-glycerol from CTP and glycerol phosphate, and di-
myo
-inositol phosphate-phosphate synthase (DIPPS), catalyzing the formation of phosphorylated GPI from CDP-glycerol and
l
-
myo
-inositol 1-phosphate. DIPPS of
A. fulgidus
recognized the two CDP-glycerol stereoisomers similarly. This feature and the ability of
31
P nuclear magnetic resonance (NMR) to distinguish the GPI diastereomers provided a means to study the stereospecificity of GCTs. The AF1418 gene and genes aq_185 and aq_1368 are annotated as putative GCT genes in the genomes of
A. fulgidus
and
Aq. aeolicus
, respectively. The functions of these genes were determined by assaying the activity of the respective recombinant proteins: AQ1368 and AQ185 are GCTs, while AF1418 has flavin adenine dinucleotide (FAD) synthetase activity. AQ185 is absolutely specific for
sn
-glycerol 3-phosphate, while AQ1368 recognizes the two enantiomers but has a 2:1 preference for
sn
-glycerol 3-phosphate. In contrast, the partially purified
A. fulgidus
GCT uses
sn
-glycerol 1-phosphate preferentially (4:1). Significantly, the predominant GPI stereoforms found in the bacterium and the archaeon reflect the distinct stereospecificities of the respective GCTs: i.e.,
A. fulgidu
s accumulates predominantly
sn
-glycero-1-phospho-3-
l
-
myo
-inositol, while
Aq. aeolicus
accumulates
sn
-glycero-3-phospho-3-l-
myo
-inositol.

IMPORTANCE
Compatible solutes of hyperthermophiles show high efficacy in thermal protection of proteins in comparison with solutes typical of mesophiles; therefore, they are potentially useful in several biotechnological applications. Glycerophosphoinositol (GPI) is synthesized from CDP-glycerol and
l
-
myo
-inositol 1-phosphate in a few hyperthermophiles. In this study, the molecular configuration of the GPI stereoisomers accumulated by members of the
Bacteria
and
Archaea
was established. The stereospecificity of glycerol phosphate cytidylyltransferase (GCT), the enzyme catalyzing the synthesis of CDP-glycerol, is crucial to the stereochemistry of GPI. However, the stereospecific properties of GCTs have not been investigated thus far. We devised a method to characterize GCT stereospecificity which does not require
sn
-glycerol 1-phosphate, a commercially unavailable substrate. This led us to understand the biochemical basis for the distinct GPI stereoisomer composition observed in archaea and bacteria.