Improvement of Temperature Evaluation Model of Biological Shielding Concrete for HTTR Test Simulating LOFC With VCS Inactive

2013 ◽  
Author(s):  
Shoji Takada ◽  
Shunki Yanagi ◽  
Kazuhiko Iigaki ◽  
Masanori Shinohara ◽  
Daisuke Tochio ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Thermal Radiation ◽  
Cooling System ◽  
Evaluation Model ◽  
Reactor Core ◽  
Reactor Power ◽  
Coolant Temperature ◽  
Water Cooling ◽  
Reactor Outlet

HTTR is a helium gas cooled graphite-moderated HTGR with the rated power 30 MWt and the maximum reactor outlet coolant temperature 950°C. The vessel cooling system (VCS), which is composed of thermal reflector plates, cooling panel composed of fins connected between adjacent water cooling tubes, removes decay heat from reactor core by heat transfer of thermal radiation, conduction and natural convection in case of loss of forced cooling (LOFC). The metallic supports are embedded in the biological shielding concrete to support the fins of VCS. To verify the inherent safety features of HTGR, the LOFC test is planned by using HTTR with the VCS inactive from an initial reactor power of 9 MWt under the condition of LOFC while the reactor shut-down system disabled. In this test, the temperature distribution in the biological shielding concrete is prospected locally higher around the support because of thermal conduction in the support. A 2-dimensional symmetrical model was improved to simulate the heat transfer to the concrete through the VCS support in addition to the heat transfer thermal radiation and natural convection. The model simulated the water cooling tubes setting horizontally at the same pitch with actual configuration. The numerical results were verified in comparison with the measured data acquired from the test, in which the RPV was heated up to around 110 °C without nuclear heating with the VCS inactive, to show that the temperature is locally high but kept sufficiently low around the support in the concrete due to sufficient thermal conductivity to the cold temperature region.

Loss of Core Cooling Test With One Cooling Line Inactive in Vessel Cooling System of High-Temperature Engineering Test Reactor

2017 ◽  
Vol 3 (4) ◽  
Author(s):  
Yusuke Fujiwara ◽  
Takahiro Nemoto ◽  
Daisuke Tochio ◽  
Masanori Shinohara ◽  
Masato Ono ◽  
...  
Keyword(s):  
Control System ◽  
High Temperature ◽  
Cooling System ◽  
Thermal Power ◽  
Reactor Power ◽  
Coolant Temperature ◽  
Water Cooling ◽  
Test Reactor ◽  
Core Cooling ◽  
Cooling Function

In the high-temperature engineering test reactor (HTTR), the vessel cooling system (VCS) which is arranged around the reactor pressure vessel (RPV) removes residual heat and decay heat from the reactor core when the forced core cooling is lost. The test of loss of forced cooling (LOFC) when one of two cooling lines in VCS lost its cooling function was carried out to simulate the partial loss of cooling function from the surface of RPV using the HTTR at the reactor thermal power of 9 MW, under the condition that the reactor power control system and the reactor inlet coolant temperature control system were isolated, and three helium gas circulators (HGCs) in the primary cooling system (PCS) were stopped. The test results showed that the reactor power immediately decreased to almost zero, which is caused by negative feedback effect of reactivity, and became stable as soon as HGCs were stopped. On the other hand, the temperature changes of permanent reflector block, RPV, and the biological shielding concrete were quite slow during the test. The temperature decrease of RPV was several degrees during the test. The numerical result showed a good agreement with the test result of temperature rise of biological shielding concrete around 1 °C by the numerical method that uses a calibrated thermal resistance by using the measured temperatures of RPV and the air outside of biological shielding concrete. The temperature increase of water cooling tube panel of VCS was calculated to be about 15 °C which is sufficiently small in the view point of property protection. It was confirmed that the sufficient cooling capacity of VCS can be maintained even in case that one of two water cooling lines of VCS loses its function.

On Efficient Passive Cooling of Control Rod Drivers

2013 ◽  
Author(s):  
A. N. Gershuni ◽  
A. P. Nishchik ◽  
V. G. Razumovskiy ◽  
I. L. Pioro
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
High Performance ◽  
Cooling System ◽  
Vertical Channel ◽  
Passive Cooling ◽  
Primary Circuit ◽  
Two Phase ◽  
Primary Coolant ◽  
Control Rod

Experimental research of natural convection and the ways of its suppression in an annular vertical channel to simulate the conditions of cooling the control rod drivers of the reactor protection system (RPS) in its so-called wet design, where the drivers are cooled by primary circuit water supplied due to the system that includes branched pipelines, valves, pump, heat exchanger, etc., is reported. Reliability of the drivers depends upon their temperature ensured by operation of an active multi-element cooling system. Its replacement by an available passive cooling system is possible only under significant suppression of natural convection in control rod channel filled with primary coolant. The methods of suppression of natural convection proposed in the work have demonstrated the possibility both of minimization of axial heat transfer and of almost complete elimination of temperature non-uniformity and oscillation inside the channel under the conditions of free travel of moving element (control rod) in it. The obtained results widen the possibilities of substitution of the active systems of cooling the RPS drivers by reliable passive systems, such as high-performance heat-transfer systems of evaporation-condensation type with heat pipes or two-phase thermosyphons as heat-transferring elements.

CFD-Assisted Optimization of Chimneylike Flows to Cool an Electronic Device

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Varghese Panthalookaran
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Energy Efficient ◽  
Electronic Device ◽  
Cooling System ◽  
Electronic Devices ◽  
Cost Effective ◽  
Transfer Rates ◽  
Slot Opening ◽  
Convection Cooling

Natural convection cooling provides a reliable, cost-effective, energy-efficient and noise-free method to cool electronic equipment. However, the heat transfer coefficient associated with natural convection mode is usually insufficient for electronic cooling and it requires enhancement. Chimneylike flows developed within the cabinets of electronic devices can provide better mass flow and heat transfer rates and can lead to greater cooling efficiency. Constraints in the design of natural convection cooling systems include efficiency of packing, aesthetics, and concerns of material reduction. In this paper, methods based on computational fluid dynamics are used to study the effects of parameters such as (1) vertical alignment of the slots, (2) horizontal alignment of slots, (3) area of slots, (4) differential slot opening, and (5) zonal variation in heat generation on natural convection cooling within such design constraints. Insights thus derived are found useful for designing an energy-efficient and ecofriendly cooling system for electronic devices.

Optimizing Laminar Natural Convection for a Heat Generating Cylinder in a Channel

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Corey E. Clifford ◽  
Mark L. Kimber
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Spent Nuclear Fuel ◽  
Reactor Core ◽  
Horizontal Cylinder ◽  
Cylinder Surface ◽  
Transfer Program ◽  
Wet Storage

Natural convection heat transfer from a horizontal cylinder is of importance in a large number of applications. Although the topic has a rich history for unconfined cylinders, maximizing the free convective cooling through the introduction of sidewalls and creation of a chimney effect is considerably less studied. In this investigation, a numerical model of a heated horizontal cylinder confined between two vertical adiabatic walls is employed to evaluate the natural convective heat transfer. Two different treatments of the cylinder surface are investigated: constant temperature (isothermal) and constant surface heat flux (isoflux). To quantify the effect of wall distance on the effective heat transfer from the cylinder surface, 18 different confinement ratios are selected in varying increments from 1.125 to 18.0. All of these geometrical configurations are evaluated at seven distinct Rayleigh numbers ranging from 102 to 105. Maximum values of the surface-averaged Nusselt number are observed at an optimum confinement ratio for each analyzed Rayleigh number. Relative to the “pseudo-unconfined” cylinder at the largest confinement ratio, a 74.2% improvement in the heat transfer from an isothermal cylinder surface is observed at the optimum wall spacing for the highest analyzed Rayleigh number. An analogous improvement of 60.9% is determined for the same conditions with a constant heat flux surface. Several correlations are proposed to evaluate the optimal confinement ratio and the effective rate of heat transfer at that optimal confinement level for both thermal boundary conditions. One of the main application targets for this work is spent nuclear fuel, which after removal from the reactor core is placed in wet storage and then later transferred to cylindrical dry storage canisters. In light of enhanced safety, many are proposing to decrease the amount of time the fuel spends in wet storage conditions. The current study helps to establish a fundamental understanding of the buoyancy-induced flows around these dry cask storage canisters to address the anticipated needs from an accelerated fuel transfer program.

scholarly journals Thermal Radiation Effect on Fully Developed Natural Convection Flow in a Vertical Micro-Channel

2021 ◽  
Vol 28 (2) ◽  
pp. 20-28
Author(s):  
B. Aina
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Thermal Radiation ◽  
Temperature Jump ◽  
Velocity Slip ◽  
Convection Flow ◽  
Physical Situation ◽  
Fluid Temperature ◽  
Micro Channel ◽  
Natural Convection Flow

The effect of thermal radiation on steady fully developed natural convection flow in a vertical micro-channel is presented in this article. Effects of velocity slip and temperature jump conditions are taken into account due to their counter effects on both the volume flow rate and the rate of heat transfer. Due to the presence of thermal radiation, the momentum and energy equations are coupled system of ordinary differential equations. Governing coupled nonlinear equations are solved analytically by employing the perturbation analysis method to obtain an expression for fluid temperature, fluid velocity, rate of heat transfer and skin friction on the microchannel walls. The effect of various parameters controlling the physical situation such as thermal radiation, temperature difference, Knudsen number, and fluid wall interaction are discussed with the aid of line graphs and Tables. Results indicate that both velocity and temperature enhanced with the increase of the thermal radiation parameter. Keywords: Thermal radiation, Natural convection, Micro-channel, Velocity slip, Temperature jump

Radiation Protection Experience in RA Heavy Water Research Reactor Important for Decommissioning

2003 ◽  
Author(s):  
Marko M. Ninkovic
Keyword(s):  
Heavy Water ◽  
Cooling System ◽  
Single Case ◽  
Reactor Core ◽  
Lessons Learned ◽  
Water Cooling ◽  
Element Failure ◽  
Fuel Elements ◽  
Water Cooling System ◽  
Radiological Characterization

The RA reactor has been in service since the end of 1959. The beginning of the eightieth using of the reactor was interrupted because of some irregular deposits on the fuel elements in the core. Since that time, for about 20 years, the reactor has not been in service and is now being prepared for decommissioning. There have been no serious accidents to the RA reactor during the operation period, but a few small accidents or incidents, which affected the reactor systems and higher exposure of personnel. These incidents were: contamination of the heavy water cooling system by 60Co; flooding of a few hundred liters of heavy water from the heavy water cooling system; the first and single case of fuel element failure in the reactor core. A specific accident called “phantom”; and finally, some irregular deposits on the fuel elements inside the reactor core that were registered. In this paper more detailed data is given on the above mentioned accidents or incidents, their consequences on the reactor systems and personnel and countermeasures taken for reducing danger radioactivity. According to the opinion of the author, these data and lessons learned would be very interesting in general, and especially, for radiological characterization, as one of the first steps in the process of reactor decommissioning.

Heat Transfer and Fluid Flow Characteristic of One Side Heated Vertical Rectangular Channel That Inserted Thin Metallic Wire

2020 ◽  
Author(s):  
Gota Suga ◽  
Tetsuaki Takeda
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
High Temperature ◽  
Natural Convection ◽  
Cooling System ◽  
Copper Wire ◽  
Rectangular Channel ◽  
Flow Characteristics ◽  
Experimental Apparatus ◽  
High Temperature Reactor

Abstract A Very High Temperature Reactor (VHTR) is one of the next generation nuclear systems. From a view point of safety characteristics, a passive cooling system should be designed as the best way of a reactor vessel cooling system (VCS) in the VHTR. Therefore, the gas cooling system with natural circulation is considered as a candidate for the VCS of the VHTR. Japan Atomic Energy Agency (JAEA) is advancing the technology development of the VHTR and is now pursuing design and development of commercial systems such as the 300MWe gas turbine high temperature reactor GTHTR300C (Gas Turbine High Temperature Reactor 300 for Cogeneration). In the VCS of the GTHTR300C, many rectangular flow channels are formed around the reactor pressure vessel (RPV), and a cooling panel utilizing natural convection of air has been proposed. In order to apply the proposed panel to the VCS of the GTHTR300C, it is necessary to clarify the heat transfer and flow characteristics of the proposed channel in the cooling panel. Thus, we carried out an experiment to investigate heat transfer and fluid flow characteristics by natural convection in a vertical rectangular channel heated on one side. Experiments were also carried out to investigate the heat transfer and fluid flow characteristics by natural convection when a porous material with high porosity is inserted into the channel. An experimental apparatus is a vertical rectangular flow channel with a square cross section in which one surface is heated by a rubber heater. Dimensions of the experimental apparatus is 600 mm in height and 50 mm on one side of the square cross section. Air was used as a working fluid and fine copper wire (diameter: 0.5 mm) was used as a porous material. The temperature of the wall surface and gas in the channel were measured by K type thermocouples. We measured the outlet flow rate by hot-wire anemometer which is an omnidirectional spherical probe of diameter 2.5mm. The experiment has been carried out under the condition that a copper wire with a scourer model and a cubic lattice model were inserting into the channel.

Sign in / Sign up

Export Citation Format

Share Document