Development of Inherently Safe Technologies for Large Scale BWRs: (4) Hydrogen Explosion Prevention System Using SiC Fuel Claddings

2014 ◽  
Author(s):  
Ryo Ishibashi ◽  
Tomohiko Ikegawa ◽  
Kenji Noshita ◽  
Kazuaki Kitou ◽  
Mamoru Kamoshida
Keyword(s):  
High Temperature ◽  
Hydrogen Generation ◽  
Cooling System ◽  
Hydrogen Gas ◽  
Metallic Layer ◽  
Normal Operation ◽  
Air Cooling ◽  
Composite Substrate ◽  
Prevention System ◽  
High Temperature Steam

In the aftermath of the lessons learned from the Fukushima Daiichi nuclear accident, we have been developing the following various safe technologies for boiling water reactors (BWRs), including a passive water-cooling system, an infinite-time air-cooling system, a hydrogen explosion prevention system, and an operation support system for reactor accidents. One of inherently safe technologies currently under development is a system to prevent hydrogen explosion during severe accidents (SAs). This hydrogen explosion prevention system consists of a high-temperature resistant fuel cladding of silicon carbide (SiC), and a passive autocatalytic recombiner (PAR). Replacing the zircaloy (Zry) claddings currently used in LWRs with the SiC claddings decreases the hydrogen generation and thus decreases the risk of hydrogen leakage from a primary containment vessel (PCV) to a reactor building (R/B) such as an operation floor. The PAR recombines the leaked hydrogen gas so as to maintain the hydrogen concentration at less than the explosion limit of 4 % in the R/B. The advantages of using SiC claddings in the system were examined through experiments and SA analysis. Results of steam oxidation tests confirmed that SiC was estimated to show 2 to 3 orders of magnitude lower hydrogen generation rates during oxidation in a high temperature steam environment than Zry. Results of SA analysis showed that the total amount of hydrogen generation from fuels was reduced to one fifth or less. Calculation also showed that the lower heat of the oxidation reaction of SiC moderated the steep generation with the temperature increase. We expected this moderated steep generation to reduce the pressure increase in the PCV as well as prevent excess amounts of leaked hydrogen from hydrogen disposal rate capacity using PARs. The SiC cladding under consideration consists of an inner metallic layer, a SiC/SiC composite substrate, and an outer environment barrier coating (EBC). A thin inner metallic layer in combination with a SiC/SiC composite substrate functions as a barrier for fission products. EBC is introduced to have both corrosion resistance in high temperature water environments during normal operation and oxidation resistance in high temperature steam environments during SA. Further reduction of the hydrogen generation rate in high temperature steam by improving the EBC is expected to decrease the total amount of hydrogen generation even more.

Performance Evaluation of DRACS System for FHTR and Time Assessment of Operation Procedure

2013 ◽  
Author(s):  
Junya Nakata ◽  
Mikihiro Wakui ◽  
Michitsugu Mori ◽  
Hiroto Sakashita ◽  
Charles Forsberg
Keyword(s):  
Performance Evaluation ◽  
High Temperature ◽  
Cooling System ◽  
Heat Removal ◽  
Severe Accident ◽  
Air Cooling ◽  
Fluoride Salt ◽  
Nuclear Power Reactor ◽  
Decay Heat ◽  
Operation Procedure

The Fluoride-salt-cooled High-temperature Reactor (FHR) is a new concept of nuclear power reactor being investigated mainly in U.S. and China. The coolant is a liquid salt with a melting point of about 460°C and a boiling point of over 1400°C. As the baseline decay heat removal system, a passive Direct Reactor Air Cooling System (DRACS) is utilized. Though DRACS system has been developed in Sodium Fast reactors (SFR), there are some differences between both. For example, the system in FHR must decrease heat removal when temperatures are low to avoid freezing of the salt and blocking the flow of liquid. Therefore, considering its characteristics, a numerical investigation of DRACS system is needed to evaluate whether FHR has proper ability to remove decay heat and to be robust for a long-time cooling operation after even a severe accident. Furthermore, in addition to its performance evaluation, it is required to make up the operation plan of FHR considering features of this system. It is highly important, with the view of avoiding severe accident, to determine by when the system should be started up. In both countries mentioned above, Fluoride-salt-cooled High-temperature Test Reactor (FHTR) is currently in progress to build. Reviewing its design and system is a crucial step needed to develop the FHR technology. In this research, a performance of DRACS system under some thermal-hydraulic basic events was evaluated by numerical simulation. This paper also suggested the adequate operation procedure suitable for FHTR to avoid a severe accident.

scholarly journals Comparative response on the accumulation of inorganic phosphate in leaf of Basella alba to low and high temperature

2014 ◽  
Vol 20 ◽  
pp. 83-90
Author(s):  
Md Shahidul Haque ◽  
Md Monirul Islam ◽  
Tanzima Yeasmin
Keyword(s):  
High Temperature ◽  
Inorganic Phosphate ◽  
Metabolic Regulation ◽  
Room Temperature ◽  
Prolonged Exposure ◽  
Cooling System ◽  
Air Cooling ◽  
Water Control ◽  
Basella Alba ◽  
Short Term Exposure

Context: Basella alba is a green vegetable and grows in both winter and summer; however the temperature sensitivity on metabolic regulation in this species is not clarified. Objective: To find the role of low and high temperature induced regulation of metabolic functions particularly alteration and accumulation of inorganic phosphate in leaf. Materials and Methods: Plants grown in pot were exposed to cold (8°C) for 24h, 48h and 72h periods and the respective controls were kept in ambient room temperature for the above mentioned time. For high temperature induced plants, they were exposed to 45°C with full aeration along with sufficient water. Control pot was used similarly in room temperature; however, the temperature was maintained 30°C by using air cooling system (AC). Results: Low temperature causes the higher inorganic phosphate level in leaf and was increased by 33.6%, 34.7% and 62.8% respectively when compared to the respective controls. Therefore, it is assumed that short term exposure has mild effect on phosphate accumulation in leaf; conversely as the time extended, the synthesis assumed to be higher and increased time dependently. Similarly, the inorganic phosphate concentrations were increased by 27.8%, 37.5% and 74.9% respectively whenever the plants were exposed to high temperature (45°C). Taken together, a faster increase in accumulation of phosphate in leaf was mediated by high temperature for prolonged exposure. Conclusion: The plants exposed to both abiotic stresses cause the release of inorganic phosphate which may participate in the survival of the species in the adverse environment DOI: http://dx.doi.org/10.3329/jbs.v20i0.17719 J. bio-sci.  20:  83-90, 2012

High Temperature Intrinsically Safe Nuclear Reactor

2015 ◽  
Author(s):  
Robin J. McDaniel
Keyword(s):  
High Temperature ◽  
Alternative Energy ◽  
Nuclear Reactor ◽  
Cooling System ◽  
Clean Energy ◽  
Normal Operation ◽  
The Core ◽  
Small Modular Reactor ◽  
Loss Of Coolant ◽  
Minimum Number

Small Modular Reactor (SMR) technologies have been recently included by the DOE as clean energy, a low carbondioxide emitting “alternative energy” source. The objective of this paper is to further the discussion of intrinsically safe nuclear reactors in the context of passive safety design principles and introduction of a novel conceptual reactor design. After a multiple year research study of past fast neutron reactor designs and recent reactor proposals, the following design is the result of analysis of the best concepts discovered. An improved fast reactor of the liquid metal cooled type including a core configuration allowing for only two operational states, “Power” or “Rest”. The flow of the primary cooling fluid suspends the core in the “Power” state, with sufficient flow to remove the heat to an intermediate heat exchanger during normal operation. This design utilizes the force of gravity to shut down the reactor after any loss of coolant flow, either a controlled reactor shut down or a Loss of Coolant Accident (LOCA) event, as the core is controlled via dispersion of fuel elements. Electromagnetic pumps incorporating automatic safety electrical cut-offs are employed to shutdown the primary cooling system to disassemble the core to the “Rest” configuration due to a loss of secondary coolant or loss of ultimate heat sink. This design is a hybrid pool-loop pressurized high-temperature reactor unique in its use of a minimum number of components, utilizing no moving mechanical parts, no rotating seals, and no control rods. This defines an elegantly simple Gen IV intrinsically safe nuclear reactor. [Advanced Small Modular Reactor (aSMR)]

Review on Water Radiolysis in the Fukushima Daiichi Accident: Potential Cause of Hydrogen Generation and Explosion

2014 ◽  
Author(s):  
Genn Saji
Keyword(s):  
Hydrogen Generation ◽  
Hydrogen Gas ◽  
Severe Accident ◽  
Normal Operation ◽  
Water Radiolysis ◽  
Chain Reactions ◽  
Decay Heat ◽  
Severe Accidents ◽  
Heat Curve ◽  
Fukushima Daiichi

Although the water radiolysis, decomposition of water by radiation, is a well-known phenomenon the exact mechanism is not well characterized especially for severe accidents. The author first reviewed the water radiolysis phenomena in LWRs during normal operation to severe accidents (e.g., TMI- and Chernobyl accidents) and performed a scoping estimation of the amount of radiological hydrogen generation, accumulation and release for the Fukushima Daiichi accident. The estimation incorporates the decay heat curve after a reactor trip combined with G-values. As much as 450 cubic meters-STP of accumulated hydrogen gas is estimated to be located inside the PCV just prior to the hydrogen explosion which occurred a day after the reactor trip in Unit 1. When a set of radiological chain reactions are incorporated the resultant reverse reactions substantially reduce the hydrogen generation, even when removal of molecular products (i.e., oxygen and hydrogen) is assumed stripped rapidly from boiling water through bubbles. Even in the most favorable configuration a typical amount of hydrogen gas reduces to only several tens of cubic meters. Finally, the author tested a new mechanism, “radiation-induced electrolysis,” which had been applied to his corrosion studies for last several years. His theory has been verified with the published in-pile test data, although he has never tried to apply this to his severe accident study. The predicted results indicated that the total inventory of hydrogen gas inside RPV may reach as much as 1000 cubic meters in just 3 hours during the SBO due to a high decay heat soon after the reactor trip through this process.

Study on the Installed Position Determination Method of the Air Condensers in High Temperature Mine

2014 ◽  
Vol 1065-1069 ◽  
pp. 2129-2132
Author(s):  
Ping Chen ◽  
Fang Fang Li ◽  
Yu Tian Li
Keyword(s):  
High Temperature ◽  
High Efficiency ◽  
Cooling System ◽  
Great Influence ◽  
Air Cooling ◽  
Determination Method ◽  
Coal Face ◽  
Position Determination ◽  
Efficiency And Effectiveness ◽  
The Ideal

Mine cooling system plays an important role in the high temperature mine. The installed position of the air condensers in the intake airway has great influence on the cooling efficiency and effectiveness of coal face. According to the concept of the air cooling length, we mainly study the effective installation position of the mine air condensers in the intake airway and put forward the installed position determination method of more groups of air condensers. Through the average calculation method, the ideal installed position of the air condensers is determined. Thus the efficiency of the mine cooling system is improved, and the safety and high efficiency of the mine production is ensured.

Numerical Simulation and Experiment of the Fire Protecting System of the Manipulator in High Temperature Environment

2019 ◽  
Author(s):  
Byeong Cheon Kim ◽  
Kyoungsik Chang
Keyword(s):  
Numerical Simulation ◽  
High Temperature ◽  
Fire Protection ◽  
Cooling System ◽  
Normal Operation ◽  
Hydraulic Pressure ◽  
Flexible Pipe ◽  
Ansys Fluent ◽  
Temperature Environment ◽  
High Temperature Environment

Abstract In the present work, the strategy for cooling the manipulator in high temperature environment is studied using both numerical and experimental methods. Since the manipulator is designed to operate in the environment with the maximum 250 °C temperature, fire protection system and the cooling system should be installed for normal operation of the manipulator. The para-aramid-filament with the thickness of 0.5 mm and Graphite felt with the thickness of 5.5mm is considered for fire protection suit and air blowing technique is applied for cooling the electronic circuit and hydraulic pressure cylinders. For numerical simulation, ANSYS Fluent V18.2 is adopted to simulate the convective heat transfer flows and the radiation with the model, S2S (Surface to surface). Two types of blowing techniques are considered, global blowing and local one. Even though the global blowing at the inlet is most effective for cooling system, so much amount of compressed air is required, which means that extra big compression system should be added in the system. The local blowing is applied to the component with small holes of the flexible pipe and the magnitude of the local blowing mass flow rate is 0.0166kg/s. The technique of local blowing is more effective than the global blowing for cooling the system. To validate numerical simulation, the model is tested within the hot temperature chamber whose mean temperature is approximately 250 °C.

Dynamic Analysis of Hybrid Cooling Data Centers Subjects to the Failure of CRAC Units

2013 ◽  
Author(s):  
Tianyi Gao ◽  
Emad Samadiani ◽  
Roger Schmidt ◽  
Bahgat Sammakia
Keyword(s):  
Data Center ◽  
Heat Exchangers ◽  
Data Centers ◽  
Cooling System ◽  
Normal Operation ◽  
Air Cooling ◽  
Rear Door ◽  
Hybrid Cooling ◽  
Air Cooling System ◽  
The Impact

Thermal management of high power data centers poses challenges due to the high operational cost which is made worse due to the many inefficiencies that arise in them. Additional challenges arise due to the dynamic behaviors that occur during normal operation, and also during emergencies such as power outages or failure of some or all of the cooling equipment. Water and hybrid air plus water cooled data centers are an alternate cooling solution combining liquid cooling systems, such as rear door heat exchangers located within the racks themselves, in addition to the traditional raised floor cold aisle air cooling system. Such a solution may be used when some of the equipment in a data center is upgraded to higher end and higher power equipment which may not be manageable with the existing air cooling system. For a data center with a hybrid cooling system, the cold air supply and the cold water supply should increase in case of an emergency, such as a CRAC (Computer Room Air Conditioner) units’ failure. In this paper, a detailed computational study is conducted to investigate the dynamic response of the impact of a CRAC failure on both water side and air side in a representative hybrid cooling room. The room studied is an air cooled data center using the common cold aisle approach, with rear door heat exchangers installed on all of the racks. CRAC failure is investigated in a hybrid cooling room. The variation and fluctuation in an average rack inlet temperature, and inlet temperatures at different detail locations are presented in plots, showing the dynamic performance of a hybrid cooling data center subjected to the different CRAC failure scenarios. Different response time studies are also presented in this paper.

Development of Inherently Safe Technologies for Large Scale BWRs: (1) Plant System

2014 ◽  
Author(s):  
Kazuaki Kitou ◽  
Naoyuki Ishida ◽  
Akinori Tamura ◽  
Ryou Ishibashi ◽  
Masaki Kanada ◽  
...  
Keyword(s):  
Support System ◽  
Large Scale ◽  
Cooling System ◽  
Hydrogen Gas ◽  
Air Cooling ◽  
Water Cooling ◽  
Infinite Time ◽  
Operation Support System ◽  
Air Cooling System ◽  
Water Cooling System

The Fukushima Daiichi nuclear accident and their consequences have led to some rethinking about the safety technologies used in boiling water reactors (BWRs). We have been developing the following various safe technologies: a passive water-cooling system, an infinite-time air-cooling system, a hydrogen explosion prevention system, and an operation support system to better deal with reactor accidents. The above mentioned technologies are referred to as “inherently safe technologies”. The passive water-cooling system and infinite-time air-cooling system achieve core cooling without electricity. These systems are intended to cope with a long-term station black out (SBO), such as that which occurred at the Fukushima facility. Both these cooling systems remove relatively high decay heat for the initial 10 days after an accident, and then the infinite-time air-cooling system is used alone to remove attenuated decay heat after 10 days. The hydrogen explosion prevention system consists of a high-temperature resistant fuel cladding made of silicon-carbide (SiC cladding) and a passive autocatalytic recombiner (PAR). Since the SiC cladding generates less hydrogen gas than the current zircaloy fuel cladding when core damage occurs, the risk of hydrogen leakage from a primary containment vessel (PCV) to a reactor building (R/B), such as an operating floor, can be reduced because the pressure in the PCV can be kept lower with less hydrogen gas generation. The leaked hydrogen gas is recombined by the PAR. When a large-scale natural disaster occurs, fast event diagnosis and recognition of damaged equipment are necessary. Therefore, the operation support system consists of event identification and progress prediction functions to reduce the occurrence of false recognitions and human errors. This paper describes the following items: the targeted plant system; the heat exchange tests conducted for both water-cooling and air-cooling systems; the air-cooling enhancing technology for air-cooling in a 4700 MW thermal power class reactor; hydrogen generation tests for SiC material; and the concept of the operation support system.

ANALYSIS OF COMPETING VARIANTS OF AIR CONDITIONING SYSTEMS WITHOUT AIR EXTRACTION FROM ENGINES AT THE STAGE OF PASSENGER AIRCRAFT ONBOARD SYSTEMS CONCEPTUAL DESIGN

2019 ◽  
Vol 6 (3) ◽  
pp. 80-85
Author(s):  
Denis Igorevich Smagin ◽  
Konstantin Igorevich Starostin ◽  
Roman Sergeevich Savelyev ◽  
Anatoly Anatolyevich Satin ◽  
Anastasiya Romanovna Neveshkina ◽  
...  
Keyword(s):  
Conceptual Design ◽  
Air Conditioning ◽  
Research University ◽  
Cooling System ◽  
Fuel Efficiency ◽  
Air Cooling ◽  
Moscow Aviation Institute ◽  
Air Conditioning System ◽  
Low Efficiency ◽  
Air Conditioning Systems

One of the ways to achieve safety and comfort is to improve on-board air conditioning systems.The use of air cooling machine determines the air pressure high level at the point of selection from the aircraft engine compressor. Because of the aircraft operation in different modes and especially in the modes of small gas engines, deliberately high stages of selection have to be used for ensuring proper operation of the refrigeration machine in the modes of the aircraft small gas engines. Into force of this, most modes of aircraft operation have to throttle the pressure of the selected stage of selection, which, together with the low efficiency of the air cycle cooling system, makes the currently used air conditioning systems energy inefficient.A key feature of the architecture without air extraction from the main engines compressors is the use of electric drive compressors as a source of compressed air.A comparative analysis of competing variants of on-board air conditioning system without air extraction from engines for longrange aircraft projects was performed at the Moscow Aviation Institute (National Research University).The article deals with the main approaches to the decision-making process on the appearance of a promising aircraft on-board air conditioning system at the stage of its conceptual design and formulated the basic requirements for the structure of a complex criterion at different life cycle stages.The level of technical and technological risk, together with a larger installation weight, will require significant costs for development, testing, debugging and subsequent implementation, but at the same time on-board air conditioning system scheme without air extraction from the engines will achieve a significant increase in fuel efficiency at the level of the entire aircraft.

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