Helium Engineering Demonstration Loop Research Articles

R&D on thermal hydraulics of core and core–bottom structure

Thermal hydraulic tests on the core and core–bottom structure of the high-temperature engineering test reactor (HTTR) were carried out with the helium engineering demonstration loop (HENDEL) under simulated reactor operating conditions. The HENDEL was composed of helium gas circulation loops, mother sections (M 1 and M 2) and adaptor section (A), and two test sections, i.e. the fuel stack test section ( T 1) and in-core structure test section ( T 2). In the T 1 test section simulating a fuel stack of the core, thermal and hydraulic performances of helium gas flowing through a fuel block were investigated for thermal design of the HTTR core. In the T 2 test section simulating the core–bottom structure, demonstration tests were performed to verify the structural integrity of graphite and metal components, seal performance against helium gas leakage among the graphite permanent blocks and thermal mixing performance of helium gas. The above test results in the T 1 and T 2 test sections were applied to the detailed design and licensing works of the HTTR and the HENDEL-loop was dismantled in 1999.

Fuel temperature analysis method for channel-blockage accident in HTTR

During operation of the High Temperature Engineering Test Reactor (HTTR), coolability must be maintained without core damage under all postulated accident conditions. Channel blockage of a fuel element was selected as one of the design-basis accidents in the safely evaluation of the reactor. The maximum fuel temperature for such a scenario has been evaluated in the safety analysis and is compared to the core damage limits. For the design of the HTTR, an in-core thermal and hydraulic analysis code Flownet/trump was developed. This code calculates fuel temperature distrubution, not only for a channel blockage accident but also for transient conditions. The validation of flownet/trump code was made by comparison of the analytical results with the results of thermal and hydraulic tests by the Helium Engineering Demonstration Loop (HENDEL) multi-channel test rig (T 1-M), which simulated one fuel column in the core. The analytical results agreed well with experiments in which the HTTR operating conditions were simulated. The maximum fuel temperature during a channel blockage accident is 1653°C. Therefore, it is confirmed that the integrity of the core is maintained during a channel blockage accident.

Cooling performance of helium-gas/water coolers in HENDEL

The helium engineering demonstration loop (HENDEL) has four helium-gas/water coolers where the cooling water flows in the tubes and helium gas on the shell side. Their cooling performance was studied using the operational data from 1982 to 1991. The heat transfer of helium gas on the shell was obtained for segmental and step-up baffle type coolers. Also, the change with operation time was investigated. The cooling performance was lowered by the graphite powder released from the graphite components for several thousand hours and thereafter recovered because the graphite powder from the components was reduced and the powder in the cooler shell was blown off during the operation.

Thermal-Hydraulic Characteristics of Coolant in the Core Bottom Structure of the High-Temperature Engineering Test Reactor

This paper discusses the high-temperature engineering test reactor (HTTR), a 30-MW (thermal) helium gas-cooled reactor being constructed by the Japan Atomic Energy Research Establishment. A thermal mixing study of the coolant in the core bottom structure (CBS) of the HTTR is conducted to clarify the thermal-hydraulic characteristics of the coolant and estimate the influence of a hot streak on the intermediate heat exchanger (IHX) and a pressurized water cooler (PWC) down-stream from the core. An experiment is carried out using an in-core structure test section (a full-scale simulation model of the (CBS) of the helium engineering demonstration loop (HENDEL), and a numerical analysis is made using a three-dimensional time-dependent flow and heat transfer code including a k-{epsilon} model of turbulence. It is confirmed that the coolant is mixed sufficiently in the CBS and the outlet gas duct of the HTTR, and the hot streak had little effect on the IHX and the PWC.

ＨＥＮＤＥＬによる高温工学試験研究炉用制御棒駆動装置の信頼性試験

Test on a control rod driving mechanism (CRDM) including a control rod (C/R) of the high temperature engineering test reactor (HTTR) has been performed to verify their reliability using the single-channel test rig of the fuel stack test section in the helium engineering demonstration loop (HENDEL) under the same operational conditions as the HTTR.The CRDM has been operated far more than the total driving number considered for 20 year HTTR operation. Then there has happened no situation being impossible to insert C/R into a simulated C/R channel at scrams as well as to insert or draw out C/R at normal operations. The CRDM could move C/R to any given position in the channel without error at normal operations. Overruns at scrams by disconnecting an electromagnetic clutch were short ranged 63-71mm. Pressure drop change in the channel with C/R movement was found to be so small as not to affect flow rate distribution of coolant in fuel stacks. After the test, components of the CRDM and C/R were disassembled and examined. The test results showed no failure of them.

高温ガス炉用高熱流束燃料棒の伝熱流動矩形突起による伝熱促進

Experimental studies on the heat transfer and fluid dynamics of a high heat fiux fuel rod for a very high temperature reactor (VHTR) were performed using a single channel test rig of a fuel stack test section (T1-S) installed in a helium engineering demonstration loop (HENDEL).The fuel rod has been developed in order to enhance the turbulent heat transfer coefficient than that of the standard fuel rod obtained by the previous experiment. Two-dimensional square ribs were settled on the outer surface of the fuel rod axially to improve the heat transfer. The configuration of a square rib is 0.5mm in width (ω), 0.5mm in height (h) and 5mm in pitch (p): p/h=10. The experiment were carried out under the helium gas conditions of high temperature and pressure simulated the VHTR operation. For the turbulent region of Reynolds number 2, 500-8, 000 of the VHTR core flow condition, it was found that the heat transfer coefficient of the fuel rod and the friction factor of the fuel channel became about 120-140% and 200-250% higher than those of the standard fuel rod for the turbulent region, respectively. The studies also derived the heat transfer correlation of the fuel rod and clarified the effect on square ribs contribution as the turbulence promoter to the heat transfer augmentation.

高温ガス実験炉燃料体の伝熱流動試験，（ＶＩ） ＨＥＮＤＥＬ多チャンネル試験装置によるクロス流れ試験結果

The multi-channel test rig (T1-M) of the fuel stack test section in a helium engineering demonstration loop (HENDEL) is a large-scale experimental facility which simulates one fuel column of the HTTR core.A crossflow test was carried out using the T1-M. The objective of this test is to investigate the thermal and hydraulic characteristics in the fuel stack under the conditions that produced the crossflow through a gap from the outside of the graphite blocks into twelve coolant channels. The crossflow was forcibily produced by a parallel gap situated between the third and fourth blocks from the top of those in the heated section mounted in the vertical direction.The crossflow was 43-56% of the total flow rate of helium gas in T1-M for heated flow and 5-37% for isothermal flow, and that became more in an outer channel of Nos. 7-12 channels than in an inner channel of Nos. 1-6 with decreasing the gap width. Also it was found that the crossflow affected a redistribution of flow rate flowing into the ch nnels and a temperature distribution of the fuel rod.

Estimation of Hot Streak in Core Bottom Structure of High-Temperature Gas-Cooled Reactor. Thermal Mixing Test of Coolant in Core Bottom Structure of HENDEL.

The high-temperature engineering test teactor (HTTR) is a gas-cooled reactor being developed in JAERI. A thermal mixing test of coolant in a core bottom structure (CBS) was conducted in order to estimate the influence of the hot streak on an intermediate heat exchanger (IHX) and a pressurized-water cooler (PWC) installed at a downstream location from the HTTR. An experimental study was carried out using an in-core structure test section (a full-scale simulation model of the CBS) of the helium engineering demonstration loop (HENDEL), and a numerical study was made using a three-dimensional time-dependent flow and heat transfer code and k-ε model of turbulence. It was confirmed that coolant was mixed sufficiently in the CBS and an outlet gas duct of the HTTR and a hot streak had little effect on the IHX and the PWC.

Thermal and hydraulic tests of test sections in the helium engineering demonstration loop

The helium engineering demonstration loop (HENDEL) has been constructed and operated to test the large-scale components of the high temperature engineering test reactor (HTTR) under simulated reactor operating conditions. The fuel stack test section (T 1) of HENDEL simulates the fuel stack of the HTTR core and is used to investigate thermal and hydraulic performance. Hot tests with 1000°C helium gas have been conducted using simulated fuel rods having uniform, exponential and cosine axial heat flux distributions. The test results agreed with previously proposed correlations, although the simulated fuel rods had various heat flux distributions and high heat flux rates. The in-core structure test section (T 2) also was installed in the HENDEL to verify the performance of the core bottom structure of the HTTR. The tests show that good performance was obtained. Examination of the thermal mixing characteristics indicated that mixing started at the location where the hot helium gas flowed into the hot plenum and that complete mixing was achieved during the downward flow in the outlet hot gas duct. The seal performance testing indicated no change of the leakage flow rate after 4000 hours of operation. The temperature of the metal portion of the structure was below 500°C and uniform around circumferential cross-sections due to the good performance of the thermal insulation blocks.

高温ガス実験炉燃料体の伝熱流動実験 Ｖ ＨＥＮＤＥＬ多チャンネル試験装置による高温試験結果

Experimental studies on thermal and hydraulic performance of fuel blocks of the very high-temperature gas-cooled reactor (VHTR) have been performed with a multi-channel test rig of fuel stack test section (T1-M) installed in a helium engineering demonstration loop (HENDEL).Present paper reports the experimental results obtained by a high temperature test that He gas was heated up to 1, 000°C in 12 T1-M. Under the conditions of uniform heating of 12 simulated fuel rods installed in the fuel block, it was found that a flow rate distribution of He gas in 12 fuel channels was almost uniform, radiant heat flux from the fuel rod was large considerably, and average heat transfer coeffcients agreed with the correlation reported previously. On the other hand, the temperature distribution in the horizontal cross section with power distributions of 12 fuel rods was calculated with a three dimensional thermal analysis code, and the temperature difference was found to be small.

Corrosion Behavior of Zirconia-Coated Hastelloy X in a High-Temperature Helium Environment

Abstract The corrosion behavior of Hastelloy X coated with (NiCrAl)/(ZrO2-CaC2) was examined, after serving as the liner tube of helium engineering demonstration loop (HENDEL) hot gas duct. The Has...

Thermal and hydraulic tests in hendel T 2 supporting the development of the core bottom structure of the High Temperature Engineering Test Reactor (HTTR)

The in-core structure test section (T 2) in the Helium Engineering Demonstration Loop (HENDEL) is a full scale simulation of a part of the core bottom structure of the High Temperature Engineering Test Reactor (HTTR) being planned by JAERL. In the T 2 test section, thermal and hydraulic tests for the core bottom structure were carried out to verify the following items under the same conditions as that of the HTTR: (1) sealing performance between permanent reflector blocks as related to their accuracy of fabrication, (2) insulation performance of the carbon blocks, (3) mixing characteristic of the hot plenum, and (4) structural integrity of the core bottom structure. Sealing performance is of prime importance to achieve the outlet coolant temperature of 950°C. If the gaps between the permanent reflector blocks around the core were wider than 0.2 mm, the outlet temperature would become lower than 950°C because of leaking cold coolant gas. Experimental results revealed that the leakage flow rate was about 20–30% of the design value because the as-fabricated gap was about 1 5 of the size of value allowed by design of 0.2 mm. The tests also showed that good insulation performance was obtained. While mixing characteristic measurements for helium flows showed for some cases incomplete mixing in the lower plenum. These data will be useful for licensing and design of the HTTR.

炉内構造物実証試験部（ＨＥＮＤＥＬ Ｔ２）の建設 ＩＩ 試験装置と開発試験

An in-core structure test section (T2) in Helium Engineering Demonstration Loop (HENDEL) simulates a part of the core bottom structure with the same scale as that of a High Temperature engineering Test Reactor (HTTR) designed in Japan Atomic Energy Research Institute.Testing devices, such as an inner vessel, flow regulators, region heaters and flow rate measurement blocks, were fabricated so that T2 test section could be tested under the same conditions as those of HTTR. Design problems were solved by element tests of the devices during their fabrications. Testing devices were finally confirmed to have required performances in helium gas conditions of 4.0 MPa and 1, 000°C through preliminary test of HENDEL operation.

炉内構造物実証試験部（ＨＥＮＤＥＬ Ｔ２）の建設 Ｉ 試験部の概要と試験体

An In-core Structure Test Section (T2) in Helium Engineering Demonstration Loop (HENDEL) simulates a part of the core bottom structure with the same scale as that of a high temperature engineering test reactor (HTTR) designed in Japan Atomic Energy Research Institute. The design and construction of T2 test section were started in March 1983, and completed in June 1986. The main objectives of the T2 test section are to verify thermal-hydraulic performance and integrity of the core bottom structure.The report describes the general outline of T2 test section, and experience gained from construction and preliminary test with regard to the simulated core bottom structure.

ＨＥＮＤＥＬにおけるカーボン輸送現象とヘリウムガス中の不純物濃度特性

In a high temperature gas cooled reactor (HTGR), high gaseous impurity levels could lead to carbon transport problem. The carbon transport process is based on two chemical reactions occurring in turn. One is the reaction of the impurity species water and/or CO2 with graphite in the core, and the other is that of produced CO and H2 to form C deposit at metal surface.Carbon deposition occurred on the inner surface of the pressure vessel of the T2 test section in Helium Engineering Demonstration Loop (HENDEL), where the 50t graphite is installed. From the analysis of the deposition, the C was not graphite but amorphous carbon. Chemical reaction should take place.The levels of H2 and CO in He gas remarkably increased just after increasing the temperature of He gas flowing into the graphite from 700°C to 930°C. The increase of the impurities can be regarded as the result of the reaction of graphite with water absorbed in the atmosphere and outgassing of the products.It has been shown that the effective method to reduce the C deposition is the He gas purification taking account of the impurity concentration ratios, H2/H2O and/or CO/CO2 based on the thermodynamical equilibrium state.

高温ガス実験炉燃料体の伝熱流動試験 ＩＶ ＨＥＮＤＥＬ１チャンネル試験装置による高温試験結果

Experimental studies on thermal and hydraulic performance of a fuel channel of the very high-temperature gas-cooled reactor (VHTR) have been performed with a single-channel test rig of a fuel stack test section (T1-s) installed in a helium engineering demonstration loop (HENDEL).Present paper reports the experimental results obtained by a high temperature test that helium gas was heated up to 1, 000°C in T1-s, using with a simulated fuel rod of which heat flux distribution was uniform in the axial direction and varied like an exponential function, respectively. In this test, friction factors of a fuel channel and heat transfer coefficients of a fuel rod were well correlated, respectively. Especially, it was showed that there was almost no difference of heat transfer coefficients between two types of the heat flux distribution.

Experimental studies on the thermal and hydraulic performance of the fuel stack of the VHTR: Part I. HENDEL single-channel tests with uniform heat flux

The Helium Engineering Demonstration Loop (HENDEL) was constructed for a large-scale component test of the very high temperature gas-cooled reactor (VHTR) under simulated reactor operating conditions. The fuel stack test section (T 1) of HENDEL simulates the fuel stack of the VHTR core to investigate thermal and hydraulic performance. Experimental results showed that the turbulent heat transfer characteristics were maintained down to a low Reynolds number of about 2000. Friction factors and heat transfer coefficients for the fuel rod were found to be higher than those in a concentric smooth annular channel.

Experimental studies on the thermal and hydraulic performance of the fuel stack of the VHTR: Part II. HENDEL multi-channel test rig with twelve fuel rods

Tests on heat transfer and fluid-dynamics of the mock-up fuel stack of the Very High Temperature Gas Cooled Reactor (VHTR) were performed by the multi-channel test rig (T 1 - M) of the Helium Engineering Demonstration Loop (HENDEL). The T 1 - M simulated one column of the fuel stack in the VHTR core and contained twelve simulated fuel rods. The heat generation rate of each fuel rod was varied to simulate the power distribution of the VHTR core in the horizontal plane. In parallel with this experiment, a three-dimensional thermal analysis code was developed in order to check the experimental temperature distribution of the fuel stack. Experimental results showed that the distribution of the helium gas flow rate was influenced by the temperature distortion in the mock-up fuel stack. The maximum deviation of the helium gas flow rate from the mean value was 10% in the case of an asymmetric power distribution test at a low Reynolds number. The variation of the calculated temperature distribution in the fuel stack was about 17-35°C in each case, indicating that the temperature distortion in the fuel stack was flattened by thermal conduction in the graphite block.

高温ガス実験炉燃料体の伝熱流動試験 ＩＩＩ ＨＥＮＤＥＬ多チャンネル試験装置による不均一発熱試験結果と解析

Experimental studies on heat transfer and fluid-dynamic characteristics of a mock-up fuel stack of the Very High Temperature Gas Cooled Reactor (VHTR) were carried out by the use of a multi-channel test rig of Helium Engineering Demonstration Loop (HENDEL). Heat generation rate of each simulated fuel rod was varied independently to simulate a power distribution of the VHTR core in a horizontal plane. In parallel with this experiment, a three-dimensional thermal analysis code was developed in order to check the experimental temperature distribution of the fuel stack.Experimental results showed that the distribution of coolant flow rate varied with the temperature distortion in the fuel stack. The variation of calculated temperature distribution in the fuel stack was about 20-35°C in each case, indicating that the temperature distortion in the fuel stack was flattened by thermal conduction through the graphite.

高温ガス実験炉燃料体の伝熱流動試験 ＩＩ ＨＥＮＤＥＬ多チャンネル試験装置による均一発熱試験結果

A fuel block composed of hexagonal prism-shaped graphite block and fuel rods is under development for the experimental very high-temperature gas-cooled reactor (VHTR) at the Japan Atomic Energy Research Institute (JAERI). Helium gas flows in an annular channel between a fuel hole and a fuel rod. In order to investigate the heat transfer and flow characteristics in the channels of the fuel block, the simulated fuel block test section called multi-channel test rig was set in the Helium Engineering Demonstration Loop (HENDEL) of JAERI. The present paper reports the experimental results obtained under the conditions of uniform heating of 12 fuel rods. It was found that the He gas flow rate was almost uniform in all of the fuel channels and that the temperature distribution in the horizontal cross section of the fuel block was also uniform. As for the heat transfer, the measured heat transfer coefficient was higher than the values predicted with heat transfer correlations of a smooth annular channel used as a design basis for VHTR.