Integration of CATHENA Thermal-Hydraulic Model with CANDU 6 Analytical Simulator Controller

This paper introduces a powerful design and analysis tool named SIMCAT, that is developed to support applications to license a CANDU nuclear reactor, refurbish projects, and support the existing CANDU stations. It consists of the CATHENA （Canadian Algorithm for Thermo-Hydraulic Network Analysis）, the control logics from C6SIM （CANDU 6 Analytical Simulator）, and a communication protocol, PVM （parallel virtual machine）. This is the first time that CATHENA has been successfully coupled directly with a program written in another language. The independence of CATHENA and the C6SIM controllers allows the development of both CATHENA and C6SIM controller to proceed independently.     

蒸汽发生器实时动态仿真

主要针对ＣＡＮＤＵ９型蒸汽发生器,建立了模块化的蒸汽发生器模型,并用图形化的仿真语言ＬａｂＶＩＥＷ编制了蒸汽发生器仿真程序,通过对ＣＡＮＤＵ ９型ＳＧ满功率运行工况的计算,表明本仿真程序的稳态计算结果与ＡＥＣＬ的实际结果比较吻合,对于引入单参数的阶跃扰动,该文对ＣＡＮＤＵ ９型ＳＧ的动态响应作了仿真计算,计算结果与实际分析完全一致,另外,单机计算的过程和结果具有实时性。     

Demonstrating leak-before-break for CANDU heat transport piping

The leak-before-break approach is being used for Ontario Hydro's Darlington nuclear generating station as an alternative to the provision of pipe-whip restraints on large diameter primary heat transport system piping. These technological developments have been used by Ontario Hydro as the nucleus of an approach for demonstrating that CANDU Class 1 carbon steel piping will not break catastrophically; at worst it would leak at a detectable rate and corrective action would be taken well before catastrophic rupture could occur. The present paper describes how the need for a leak-before-break approach evolved, considerations given to developing an approach, and how it is being applied. Finally, the paper updates the status of this program and discusses future plans in this area.     

A leak-before-break strategy for CANDU primary piping systems

Recent advances in elastic-plastic fracture mechanics have made it possible to assess the stability of cracks in ductile piping systems. These technological developments have been used by Ontario Hydro as the nucleus of an approach for demonstrating that CANDU primary heat transport piping systems will not break catastrophically; at worst they would leak at a detectable rate. This leak-before-break approach has been taken on the Darlington nuclear generating station as a design stage alternative to the provision of pipe whip restraints on large diameter, primary heat transport system piping. Positive conclusions reached via this approach are considered sufficient to exclude the requirement to provide protective devices, such as pipe whip restraints.

In arriving at the proposed leak-before-break approach a review of current and proposed leak-before-break licensing positions of other jurisdictions (particularly those in the United States and the Federal Republic of Germany) was carried out. The approach presented makes use of recent American developments in the area of elastic-plastic fracture mechanics. It also gives consideration to aspects which are unique to the pressurized heavy water (CANDU) reactors used by Ontario Hydro.

The present paper describes the proposed leak-before-break approach and illustrates its use by applying it to the Darlington generating station primary heat transport system pump suction piping.     

A probabilistic approach to leak-before-break in CANDU pressure tubes

In the ^R reactor, the coolant passes through the core in zirconium alloy pressure tubes. A few of these pressure tubes have leaked at cracks near the rolled joint where the pressure tube is attached to the end fitting.

A probabilistic methodology, and associated computer code (called ), has been developed to calculate the time from first leakage to unstable fracture in a probabilistic format. The methodology explicitly uses material property distributions, and allows the risk associated with leak-before-break to be estimated. A model of the leak detection system is included to calculate the time between leak detection and unstable fracture. The sensitivity of the risk to changing reactor conditions allows the optimization of reactor management after leak detection.

Preliminary material property distributions show the probability of unstable fracture is very low, and that ample time is available to shut down the unit and locate the leaking tube.     

Robust hydrogen detection system with a thermoelectric hydrogen sensor for hydrogen station application

A prototype hydrogen detection system using the micro-thermoelectric hydrogen sensor (micro-THS) was developed for the safety of hydrogen infrastructure systems, such as hydrogen stations. We have designed a detection part with a pressure proof enclosure adoptable for the international standard of Exd II CT3, and carried out an explosion strength test, explosion and fire hazard tests, and an impact test. The hydrogen sensing performance of the detection part of this prototype system showed a good linear relationship between the sensing signal and hydrogen concentrations in air, for a wide range of hydrogen concentrations from 10 ppm to 40,000 ppm (4 vol.%). This prototype detection system was installed in the outdoor field of the hydrogen station and the response for H₂ gas in air of 100 ppm, 1000 ppm, and 10000 ppm was tested monthly for 1 year.     

Synthesis of hydrogen network with hydrogen header of intermediate purity

In order to simplify the network configuration and enhance the expandability and flexibility of the hydrogen network, one or two hydrogen utility headers are typically set with the consideration of requirement of hydrogen consumers. This paper proposed a superstructure-based mathematical programming model for the synthesis of hydrogen network with intermediate hydrogen header. The comprehensive superstructure is embedded with hydrogen utility, internal hydrogen sources and sinks, hydrogen headers, fuel system, compressors, purifiers and all the feasible interconnections between them. Two case studies are utilized to illustrate the feasibility and applicability of the proposed approach. The results show that the optimal flow rate of hydrogen utility will be decreased with the increase of the total number of connections as well as the increase of the number of hydrogen headers. The minimum flow rate of hydrogen utility for direct reuse/recycle without any intermediate hydrogen header can be achieved with the emplacement of two intermediate hydrogen headers. Besides, there is no direct connection among the hydrogen sources and hydrogen sinks. The Pareto front is made for the comparison on the flowrate of hydrogen utility and number of connections. The purification reuse/recycle scheme is investigated with the installation of purifier and the flowrate of hydrogen utility is reduced further.     

Recovery of hydrogen from hydrogen sulfide with metals or metal sulfides

The following two types of reactions were investigated for the recovery of hydrogen from hydrogen sulfide: Type 1 H₂S → H₂ + S⁰, Type 2 H₂S + O₂ → H₂ + SO₂ Each type of reaction is constructed by a two-step cycle, in which H₂S is reacted with metal or metal sulfide and then the resulting sulfide undergoes thermal decomposition or oxidation. Ag₂S, FeS, Co₉S₈, Ni₃S₂, and the double sulfide CuFeS₂ were examined in the former type of reaction, while Ag, Cu, Ni, liquid Pb, and liquid BiAg alloy were used as an intermediate in the latter.     

Thermochemical production of hydrogen from hydrogen sulfide with iodine thermochemical cycles

With the goal of eventually developing a replacement for the Claus process that also produces $H_2$, we have explored the possibility of decomposing hydrogen sulfide through a thermochemical cycle involving iodine. The thermochemical cycle under investigation leverages differences in temperature and reaction conditions to accomplish the unfavorable hydrogen sulfide decomposition to $H_2$ and elemental sulfur over two reaction steps, creating and then decomposing hydroiodic acid. This proposed process is similar to ideas put forth in the 1980s and 1990s by Kalina, Chakma, and Oosawa, but makes use of thermochemical hydrogen iodide decomposition methods and catalysts rather than electrochemical or photoelectrochemical methods.Process models describing a potential implementation of this thermochemical cycle were created. Motivated by the process model results, experimentation showed the possibility of using alternative solvents to dramatically decrease the energy requirements for the process. Further process modeling incorporated these alternative solvents and suggests that this theoretical hydrogen sulfide processing unit has favorable economic and environmental properties.     

The role of leak-before-break in assessments of flaws detected in CANDU pressure tubes

This paper reviews the role of the Leak-Before-Break (LBB) concept in the Fitness for Service Guidelines being developed for cold worked (cw) Zr-2·5Nb pressure tubes in a CANDU reactor. The guidelines complement the rules of Section XI of the ASME Code and the requirements of Canadian Standards Association (CSA) CAN 3-N285.4-M83.

The evaluation procedures in the guidelines consist of a flaw growth analysis to determine the maximum size of the flaw at the end of the evaluation period. It must then be demonstrated that the flaw is stable with adequate margins of safety for the various loading conditions.

For the delayed hydride cracking failure mode LBB is used as defense in depth against unstable rupture. First the flaw must be shown to be non-susceptible to propagation by delayed hydride cracking during normal operating conditions. In addition, it must then be demonstrated that, if the flaw were to penetrate the tube wall, the leaking coolant would be detected and the reactor shutdown before the postulated crack became unstable.

The Guidelines contain criteria for performing both deterministic and probabilistic LBB analyses.     

An onboard hydrogen generator for hydrogen enhanced combustion with internal combustion engine

Hydrogen enhanced combustion (HEC) for internal combustion engine is known to be a simple mean for improving engine efficiency in fuel saving and cleaner exhaust. An onboard compact and high efficient methanol steam reformer is made and installed in the tailpipe of a vehicle to produce hydrogen continuously onboard by using the waste heat of the engine for heating up the reformer; this provides a practical device for the HEC to become a reality. This use of waste heat from engine enables an extremely high process efficiency of 113% to convert methanol (8.68 MJ) for 1.0 NM of hydrogen (9.83 MJ) and low cost of using hydrogen as an enhancer or as a fuel itself. The test results of HEC from the onboard hydrogen production are presented with 2 gasoline engine vehicles and 2 diesel engines; the results indicate a hike of engine efficiency in 15–25% fuel saving and a 40–50% pollutants reduction including 70% reduction of exhaust smoke. The use of hydrogen as an enhancer brings about 2–3 fold of net reductions in energy, carbon dioxide emission and fuel cost expense over the input of methanol feed for hydrogen production.     

Smart energy solutions with hydrogen options

We are in an era where everything is now requested to be smart. Here are some examples, such as smart materials smart devices, smartphones, smart grid, and smart metering. In regard to energy portfolio, we need to make it in line with these under smart energy solutions. With the developed cutting-edge technologies and artificial intelligence applications, we need to change the course of action in dealing with energy matters by covering the entire energy spectrum under five categories, namely, energy fundamentals and concepts, energy materials, energy production, energy conversion, and energy management. It is important to highlight the importance of a recent event. On 17 January 2017 a total of thirteen leading energy, transport and industry companies in the World Economic Forum in Davos (Switzerland) have launched a global initiative, so-called: Hydrogen Council, to voice a united vision and long-term ambition for hydrogen to foster the energy transition. It has aimed to join the global efforts in promoting hydrogen to help meet climate goals. This is a clear indication that smart solutions are not possible without hydrogen options. This study focuses on introducing and highlighting smart energy solutions under the portfolio pertaining to exergization, greenization, renewabilization, hydrogenization, integration, multigeneration, storagization, and intelligization. Each one of these plays a critical role within the smart energy portfolio and becomes key for a more sustainable future. This study also focuses on the newly developed smart energy systems by combining both renewable energy sources and hydrogen energy systems to provide more efficient, more cost-effective, more environmentally benign and more sustainable solutions for implementation. Furthermore, a wide range of integrated systems is presented to illustrate the feasibility and importance such a coupling to overcome several technical issues. Moreover, numerous studies from the recent literature are presented to highlight the importance of sustainable hydrogen production methods for a carbon-free economy.     

Simulation of Moderator Flow and Temperature Inside Calandria of CANDU Reactor Using Artificial Compressibility Method

Numerical computations of moderator flows inside calandria of the typical CANDU-6 reactor are presented here. The numerical model is based on incompressible Navier–Stokes equations in artificial compressibility formulation with dual time-stepping approach for time-accurate computations. A high-resolution unstructured finite-volume scheme, based on the HLLC-AC Riemann solver for convective fluxes and central differencing type discretization for viscous fluxes, is used here. In order to simulate more realistic flow, the calandria tube matrix is considered directly, in contrast with the usual practice of indirect accounting of tube bundles through porosity modeling. The moderator flows are computed for different operating conditions. The nature of computed flow is found to be dependent on the relative balance between momentum and buoyancy forces as observed by Carlucci. A parametric study is also carried out to investigate the effect of moderator inlet diffuser location, moderator inlet flow velocity, and angle of moderator inlet diffuser. The inlet flow velocity and inlet diffuser location are found to have significant effect on flow features inside the calandria.     

环境低负荷制氢技术及集成制氢系统

讨论了各种环境低负荷的制氢技术。SPE电解水制氢技术成熟,将成为未来主要制氢方法之一。生物化学制氢和半导体光解水制氢仅以太阳能为能源,前景广阔。生物质制氢清洁、节能,值得推广。环境低负荷集成制氢系统综合多种技术,是制氢技术发展的一个趋势。     

Life cycle assessment of hydrogen supply chain with special attention on hydrogen refuelling stations

The controversial and highly emotional discussion about biofuels in recent years has shown that greenhouse gas² (GHG) emissions can only be evaluated in an acceptable way by carrying out a full life cycle assessment (LCA) taking the overall life cycle including all necessary pre-chains into consideration. Against this background, the goal of this paper is it to analyse the overall life cycle of a hydrogen production and provision. A state of the art hydrogen refuelling station in Hamburg/Germany opened in February 2012 is therefore taken into consideration. Here at least 50% hydrogen from renewable sources of energy is produced on-site by water electrolysis based on surplus electricity from wind (mainly offshore wind parks) and water. The remaining other 50% of hydrogen to be sold by this station mainly to hydrogen-fuelled buses is provided by trucks from a large-scale production plant where hydrogen is produced from methane or glycerol as a by-product of the biodiesel production. These two pathways are compared within the following explanations with hydrogen production from biomass and from coal. The results show that – with the goal of reducing GHG emissions on a life cycle perspective – hydrogen production based on a water electrolysis fed by electricity from the German electricity mix should be avoided. Steam methane reforming is more promising in terms of GHG reduction but it is still based on a finite fossil fuel. For a climatic sound provision of hydrogen as a fuel electricity from renewable sources of energy like wind or biomass should be used.     

Comparison of hydrogen hydrates with existing hydrogen storage technologies: Energetic and economic evaluations

With the development of the hydrogen economy and FCV (fuel cell vehicles), the manner of storing and delivering large quantities of hydrogen arises as a major problem, and increasing research efforts are being targeted to solve this technological issue. Nowadays several hydrogen storage methodologies are available. Technologies are being developed and/or engineered other than the classical compression and liquefaction of hydrogen, which are based on the chemical (metal hydrides, ammonia) and physical (e.g., carbon nanotubes) adsorption of H₂. Also, a novel technology is in progress, which is based on clathrate hydrates of hydrogen. The object of the present work is to evaluate the features and performances of those storing systems with the aim to determine the best available technology throughout the “hydrogen chain”. For each one of the storage solutions presented, we have compared key parameters such as: interaction energy between hydrogen and support, storage capacity, specific energy consumption (SEC). By this work, it is demonstrated that a technology based on clathrate hydrates of hydrogen, while far from being optimized, may be competitive with the other approaches.     

Characteristics of hydrogen-fueled gas turbine cycle with intercooler,hydrogen turbine and hydrogen heater

The performances of a hydrogen-fueled gas turbine cycle equipped with an intercooler, regenerator, hydrogen turbine and recuperative hydrogen heater are analyzed. The intercooler is very effective to prevent the condensation and freezing of water vapor in cooling the suction air. The operation of hydrogen turbine in low-temperature range can also be prevented by adopting hydrogen heater. Thermodynamic analysis has revealed that the thermal efficiency and the specific output are considerably improved compared to those of the simple gas turbine cycle.     

Mg-based nanocomposites with improved hydrogen storage performances

MgH₂ is one of the most attractive candidates for on-board H₂ storage. However, the practical application of MgH₂ has not been achieved due to its slow hydrogenation/dehydrogenation kinetics and high thermodynamic stability. Many strategies have been adopted to improve the hydrogen storage properties of Mg-based materials, including modifying microstructure by ball milling, alloying with other elements, doping with catalysts, and nanosizing. To further improve the hydrogen storage properties, the nanostructured Mg is combined with other materials to form nanocomposite. Herein, we review the recent development of the Mg-based nanocomposites produced by hydrogen plasma-metal reaction (HPMR), rapid solidification (RS) technique, and other approaches. These nanocomposites effectively enhance the sorption kinetics of Mg by facilitating hydrogen dissociation and diffusion, and prevent particle sintering and grain growth of Mg during hydrogenation/dehydrogenation process.     

Water splitting for hydrogen production with ferrites

The water splitting reaction by a thermo-chemical cycle using ferrites was investigated for H₂ production. In the first step (activation step), ferrites were thermally reduced at 1200 °C to form an oxygen-deficient ferrite. In the second step (water splitting step), the activated ferrites were oxidized by water at 800 °C to produce hydrogen. Among the prepared ferrites, Ni-ferrite was found to be the most suitable for H₂ production. NiFe₂O₄ produced an average of 0.442 cm³/g cycle of H₂. The H₂ productivity of the Ni-ferrite was much higher than that of the other ferrites at the same temperature. XRD showed that the crystal structure of NiFe₂O₄ during the redox reaction was not changed during the repeated cycles, indicating that NiFe₂O₄ was an excellent material in terms of structural stability and durability.     

Vehicle refueling with liquid hydrogen thermal compression

We have modeled an approach for dispensing pressurized hydrogen to 350 and/or 700 bar vehicle vessels. Instead of relying on compressors, this concept stores liquid hydrogen in cryogenic pressure vessels where pressurization occurs through heat transfer, reducing the station energy footprint from 12 kW h/kgH₂ of energy from the US grid mix to 1.5–2 kW h/kgH₂ of heating. This thermal compression station presents capital cost and reliability advantages by avoiding the expense and maintenance of high-pressure hydrogen compressors, at the detriment of some evaporative losses. The total installed capital cost for a 475 kg/day thermal compression hydrogen refueling station is estimated at about $611,500, an almost 60% cost reduction over today's refueling station cost. The cost for 700 bar dispensing is $5.23/kg H₂ for a conventional station vs. $5.45/kg H₂ for a thermal compression station. If there is a demand for 350 bar H₂ in addition to 700 bar dispensing, the cost of dispensing from a thermal compression station drops to $4.81/kg H₂, which is similar to the cost of a conventional station that dispenses 350 bar H₂ only. Thermal compression also offers capacity flexibility (wide range of pressure, temperature, and station demand) that makes it appealing for early market applications.