High-temperature Gas-cooled Reactor Helium Research Articles

Research on the design method of highly loaded helium compressor based on the physical properties

ABSTRACTA highly loaded design method of helium compressor is presented in this paper. First, particular loss prediction models based on corrections of isentropic index and velocity triangle are deduced for highly loaded helium compressor. Then the influence of design parameters such as reaction, flow coefficient and load coefficient on aerodynamic loss of highly loaded helium compressor is analyzed in detail with the loss models. The design principles are also discussed. A highly loaded helium compressor design study is carried out based on a 300-MW high-temperature gas-cooled reactor (HTGR) helium multistage compressor to validate the method. The results indicate that the 16-stage helium low-pressure compressor of the 300-MW HTGR can be reduced to a 3-stage compressor by the proposed highly loaded design method at the same tip tangential velocity. The isentropic efficiency could be as high as 90% under design condition.

Development and primary verification of a transient analysis software for high temperature gas-cooled reactor helium turbine power system

The transient analysis software, HTR-GTsim, is developed to simulate transient characteristics of a high temperature gas-cooled reactor helium turbine power system (HTR-10GT) of INET in Tsinghua University, which is the secondary engineering project of HTR-10. The analysis models include point reactor neutron kinetics model, one-dimensional thermodynamic reactor model, rotor dynamic blower model, counter-current heat exchanger model, quasi-static helium turbine and pressure compressor model, and so on. HTR-GTsim is verified by 3 tests of a 10MW high temperature gas-cooled reactor (HTR-10), which are reactivity insertion test, helium flow change test and water flow change test. The simulation results of reactivity insertion test show that there is a strong self-adjusting ability for HTR-10 reactor power due to negative temperature feedback. The simulation results of helium flow change test are compared with those of the water flow change test. It is found that the disturbance induced in the latter test is significantly weaker than that in the former due to the huge heat capacity of the graphite in the core. The calculation results of HTR-GTsim are compared with the test data and simulation results of THERMIX program. Good agreement is obtained. Because of the limitation of validation, more work need to be done to verify the accuracy of HTR-GTsim to simulate a gas turbine device.

Long-Term Creep Properties of Hastelloy XR in Simulated High-Temperature Gas-Cooled Reactor Helium

Creep tests of Hastelloy XR (a modified version of the conventional Hastelloy X) were carried out in simulated high-temperature gas-cooled reactor (HTGR) helium at 800, 900 and 1,000°C. The test results up to about 50,000 h showed no significant degradation in creep properties. The creep-rupture strength obtained through long-term tests was above the level corresponding to the design allowable creep-rupture stress of the High-Temperature Engineering Test Reactor. The values of the stress exponent were 4.5 to 5.7 when the stress dependence of the steady-state creep rate was expressed in terms of the Norton equation. It is judged that dominant creep process is dislocation creep. Rupture lives could be estimated with sufficient accuracy using Larson- Miller parameter. Carburization during creep in simulated HTGR helium did not degrade creep properties of Hastelloy XR. Internally formed cracks were initiated at sites of precipitates at grain boundaries, growing nearly perpendicular to the stress axis. Two phases, Cr-rich carbide and Mo-rich carbide, co-existed in specimens after long-term creep tests.

Long-Term Creep Properties of Hastelloy XR in Simulated High-Temperature Gas-Cooled Reactor Helium.

Creep tests of Hastelloy XR (a modified version of the conventional Hastelloy X) were carried out in simulated high-temperature gas-cooled reactor (HTGR) helium at 800, 900 and 1,000°C. The test results up to about 50,000 h showed no significant degradation in creep properties. The creep-rupture strength obtained through long-term tests was above the level corresponding to the design allowable creep-rupture stress of the High-Temperature Engineering Test Reactor. The values of the stress exponent were 4.5 to 5.7 when the stress dependence of the steady-state creep rate was expressed in terms of the Norton equation. It is judged that dominant creep process is dislocation creep. Rupture lives could be estimated with sufficient accuracy using Larson- Miller parameter. Carburization during creep in simulated HTGR helium did not degrade creep properties of Hastelloy XR. Internally formed cracks were initiated at sites of precipitates at grain boundaries, growing nearly perpendicular to the stress axis. Two pha...

高温ガス炉近似ヘリウム雰囲気におけるハステロイＸＲのクリープおよび破断挙動

Creep and rupture tests were conducted on Hastelloy XR (a modified version of the conventional Hastelloy X) at 1, 073, 1, 173 and 1, 273K in simulated high-temperature gas-cooled reactor helium. The test section of creep testing machine was designed and constructed with special care for impurity chemistry in helium. A device for counting Moire patterns was developed for contamination-free creep strain measurement. The test results up to 10, 000h showed no significant degradation in creep properties. Comparing the data on the stresses to rupture, to cause 1% total strain and to the onset of tertiary creep, the stress to cause 1% total strain is judged to be the dominant factor for the allowable stress (St) in the ASME Code. Carbon analysis for ruptured specimen showed that caburization was limited to the region near the ruptured portion and slight carbon intrusion occurred only in the early stage of exposure. Surface cracks were not responsible for creep-rupture, because they were blunted at the depth of approximately 100μm from the specimen surface at 1, 173K and 200μm at 1, 273K. Internally formed cracks were initiated at the sites of carbide precipitation at grain boundary, growing nearly perpendicular to the stress axis. Recrystallization observed was localized at 1, 173K but became pronounced at 1, 273K. Creep deformation enhanced coasening of the grain boundary carbide under tensile stress.

Strain-time effects in low-cycle fatigue of nickel-base heat-resistant alloys at high temperature

A series of strain controlled low-cycle fatigue tests in the simulated high-temperature gas-cooled reactor (HTGR) helium environment were conducted at 900°C on Hastelloy X and its modified version, Hastelloy XR. In those tests the effects of strain rate and hold time on high-temperature low-cycle fatigue behavior were investigated. Decreasing the strain rate led to notable reductions in the fatigue life. In the tests with the trapezoidal strain waveform, the fatigue life was found to be reduced most effectively in tensile hold-time experiments. The tendency was interpreted through the feature of the crack morphology.

Corrosion of high temprature alloys in the primary circuit helium of high temperature gas cooled reactors. – Part I: Theoretical background

AbstractThe interaction of Ni and Fe‐Ni base alloys with the reactive impurities H2O, CO, H2 and CH4 in simulated cooling gas of the primary circuit of the High Temperature Gas Cooled Reactor (HTGR) causes corrosion effects that can significantly influence the mechanical properties. Apart from the formation of surface scales (oxides, carbides or mixed oxides/carbides), structural changes of the alloys are observed; depending on gas composition, gas supply rate and test temperature, carburization or decarburization can occur. In this report it is shown that an interpretation of the basic corrosion effects is possible on the basis of a modified stability diagram for chromium provided that‐ the kinetics of elementary gas metal reactions are incorporated in the expressions for carbon activity and oxygen partial pressure of the atmosphere and‐ the gradients of the potentials across the surface scales are taken into account.The interpretation allows the derivation of the corrosion behaviour of NiCr‐base alloys in different HTGR helium compositions and enables the limits for the formation of protective chromia surface scales to be given. The influence of alloying elements other than chromium can be explained qualitatively.The results can be transferred to other reactive gas mixtures, which are characterized by an oxygen partial pressure near to the dissociation pressure of the scale forming oxides.

The Effect of Gaseous Environment on the Low Cycle Fatigue Behavior of Ni-Cr-W Alloys for HTGR

Low cycle fatigue behavior of two Ni-Cr-W alloys (KSN and 113MA) was investigated at 1 273K in the simulated High Temperature Gas-cooled Reactor (HTGR) helium, He-2. Both alloys showed little cyclic hardening in fatigue tests and failed with a completely intergranular manner. Although the fatigue life (Nf) of 113MA was a little longer than that of KSN, observed intergranular fractures indicated that the fatigue properties of both alloys were severely influenced by impurities in He-2.As well as in He-2, fatigue tests of KSN and 113MA were carried out in pure He, air and vacuum. The results clearly showed that, regardless of the concentration of reactive gases, both alloys failed intergranularly with short Nfs in gas environments, as compared with the transgranular fracture with long Nf in vacuum. A minor effect of impurity contents was shown as an increase in Nf when substituting air by He-2 and then by pure He. It is considered from these behaviors that the fatigue fractures were affected by residual oxygen gas in the environments penetrating into the specimens along the grain boundaries.

Effects of thermal aging on the low cycle fatigue behavior of Ni-15%Cr-25%W alloy in the simulated HTGR helium.

The effects of thermal aging on the low cycle fatigue behavior of Ni-Cr-W alloys were investigated on KSN alloy (Ni-15wt%Cr-25wt%W) at 1 273K in the simulated helium (He-2) for High Temperature Gas-cooled Reactor (HTGR). Fully reversed strain control tests were made at a strain rate of 1×10-3 s-1 with holdtimes of 0, 6 and 60min. The thermal aging at 1 273K for 1 000hr initiated the precipitation of α2 phase (bcc-W) in the matrix and on grain boundaries of KSN.Although a degradation of fatigue lives was observed with increase of the period of holdtime for both solution annealed and aged KSN (KSN-SA and-AGE), the value of fatigue life was significantly longer for KSN-AGE than for KSN-SA. The morphology of intergranular fracture of two materials indicated that the existence of α2 particles at the grain boundaries increased both cycles to initiation and those to propagation of fatigue crack. The role of α2 precipitates was to reduce the weakening of grain boundaries and the oxidation rate by changing the corrosion products at a crack tip from Cr-oxides for KSN-SA to Ti/Al-oxides for KSN-AGE.

Thermodynamic and Kinetic Aspects of the Corrosion of High-Temperature Alloys in High-Temperature Gas-Cooled Reactor Helium

In corrosion tests with iron- and nickel-based alloys in simulated cooling gases of the primary circuit of high-temperature gas-cooled reactors (HTGR helium), different effects have been found. The...

Relationship of H2O and CH4 Supply Rates in HTGR Helium to the Carburization of Hastelloy-X and Alloy 800H

A detailed study of the carburization of Hastelloy-X and alloy 800H in high-temperature gas-cooled reactor helium was made to determine the cause of the wide variability of data generated in retorts. Data for 1000/sup 0/C and 2500-h exposure show that up to an order of magnitude difference in the carburization levels can be caused by changes in the flow rate of the test gas and/or the position of the corrosion specimen in the gas stream. The results are unambiguously explained by the parameters S(H/sub 2/O) and S(CH/sub 4/), the supply rates of water and methane, respectively.

Low-Cycle Fatigue of Heat-Resistant Alloys in High-Temperature Gas-Cooled Reactor Helium

Strain controlled low-cycle fatigue tests were conducted on four nickel-base heat-resistant alloys at 900/sup 0/C in simulated high-temperature gas-cooled reactor (HTGR) environments and high vacuums of about 10/sup -6/ Pa. The observed behaviors of the materials were different and divided into two groups when tests were made in simulated HTGR helium, while all materials behaved similarly in vacuums. The materials that have relatively high ductility and compatibility with impure helium at test temperature showed considerable resistance to the fatigue damage in impure helium. On the other hand, the alloys qualified with their high creep strength were seen to suffer from the adverse effects of impure helium and the trend of intergranular cracking as well. The results were analyzed in terms of their susceptibility to the environmentenhanced fatigue damage by examining the ratios of the performance in impure helium to in vacuum. The materials that showed rather unsatisfactory resistance were considered to be characterized by their limited ductility partly due to their coarse grain structure and susceptibility to intergranular oxidation. Moderate carburization was commonly noted in all materials, particularly at the cracked portions, indicating that carbon intrusion had occurred during the crack growth stage.

Behavior of Metallic Materials Between 550 and 870°C in High-Temperature Gas-Cooled Reactor Helium Under Pressures of 2 and 50 bar

In order to estimate the influence of the helium pressure on the corrosion of ferritic and austenitic materials, tests were carried out under 2 absolute bar in a circuit without helium recirculatio...

Effect of Carburizing Service Environments on the Mechanical Properties of High-Temperature Alloys

Carburization of high-temperature alloys has been frequently observed during exposure to dry high-temperature gas-cooled reactor (HTGR) helium compositions. Therefore, the influence of carburization on mechanical properties of alloys that may be used for HTGR high-temperature components has been studied.In creep rupture tests on high-temperature alloys for up to 20 000 h, the data in air and in various simulated HTGR heliums lie in the same scatterband irrespective of carburization that has been observed in the contaminated helium atmospheres. The dependence of room temperature tensile properties and the impact strength in the 20 to 800 °C range on the carburization level has been measured so that the maximum carbon level for a given room temperature ductility and impact strength could be specified. The results showed that the minimum room temperature elongation fell to below 5% when the carbon content exceeded 0.5 wt% for Incoloy-800H and 0.2 wt% for lnconel-617. At these carbon levels, the alloys have impact strengths (ISO V-notch specimens) of ∼50 J or above at temperatures in the 25 to 800°C range.

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Creep and Rupture Behavior of a Special Grade Hastelloy-X in Simulated HTGR Helium

Creep and rupture tests were conducted for Hastelloy-XR (a modified version of the conventional Hastelloy alloy X) at 800, 900, and 1000/sup 0/C in simulated high-temperature gas-cooled reactor helium. Creep testing machines with special control of helium chemistry were used. As a result, the scatter of creep-rupture data could be reduced, and the variability of creep-rupture behavior due to manufacturing history could be resolved. Results of metallography and carbon analysis of ruptured specimens showed that the material improved resistance to corrosion in the helium environment, and carbon intrusion during the steady-state creep stage was suppressed to a negligible level. Under refined test conditions combined with the quality controlled material, it was demonstrated that there was little significant difference between helium and air in the creep-rupture results obtained at 800 to 1000/sup 0/C up to about 10/sup 4/h. The importance of maintaining the protective function of the surface oxide film of alloys was stressed in securing reproducibility and predictability of long-time creep performance.

Creep Rupture Properties of Hastelloy-X and lncoloy-800H in a Simulated HTGR Helium Environment Containing High Levels of Moisture

Creep rupture tests on Incoloy-800H and Hastelloy-X have been carried out in a simulated steamcycle high-temperature gas-cooled reactor helium environment containing a high level of moisture. For the maximum test time of 16 000 h, the creep rupture behavior of Incoloy-800H in the helium environment was not significantly different from that in air. Hastelloy-X showed a slightly lower rupture life in helium in comparison with standard air tests. Surface cracks initiated at the grain boundaries penetrating surface and cavities formed at the grain boundary triple points have been identified as major fracture mechanisms in both environments. Oxidation was the only gas/metal interaction observed in the helium environment.

High-Cycle Fatigue Behavior of Incoloy Alloy 800H in a Simulated HTGR Helium Environment Containing High Moisture Levels

A study has been carried out to evaluate the highcycle fatigue strength of Incoloy alloy 800H in a high-temperature gas-cooled reactor helium environment containing significant quantities of moisture. As-heat-treated and thermally aged materials were tested to determine the effects of long-term oxidation in the helium test gas. Results from these tests were compared to those for a standard air environment. It was found that the mechanisms of fatigue failure were complex and involved recovery/recrystallization of the surface-ground layer on the specimens, sensitization, work hardening, oxide scale integrity, and oxidation at the tips of propagating cracks. For certain situations, a corrosion-fatigue process seems to be important. However, for the helium environment studied, the fatigue strength was nearly always higher than that for air.

The Development of High-Strength Alloys Resistant to Corrosion in Impure Helium

The three completed stages of an alloy development program aimed at defining a nickel chromiumbased alloy resistant to carburization in simulated high-temperature gas-cooled reactor (HTGR) helium with high-temperature strength similar to alloy Inconel-617 show that alloys based on nickel and 10% chromium with 10 to 16% tungsten and 1.1 to 3.2% titanium exhibit good corrosion resistance in dry simulated HTGR helium and have short-time creep properties similar to Inconel-617. The alloys are readily hot and cold workable and show potentially good structural stability.

Mechanical Properties of Heat-Resistant Alloys Exposed to Air and HTGR Helium at High Temperatures

The effect of a corroded surface layer on the tensile properties and the high-temperature low-cycle fatigue life was studied on Hastelloy-X and on Incoloy alloys 800 and 800H by comparing the properties between specimens exposed to air and high-temperature gas-cooled reactor helium at 1000/sup 0/C prior to testing and specimens aged under the same temperature/time conditions as those of exposed specimens. The ratio of the corroded surface layer to the total cross-sectional area was controlled at 1000/sup 0/C by environment, exposure time, and shape/size combinations of specimens. Tensile strength could be quantitatively expressed in terms of the intergranular oxidation, irrespective of the variation of materials and corrosive conditions. By comparing the low-cycle fatigue lives at 1000/sup 0/C between exposed and aged materials, it was clarified that lifetime was remarkably reduced by the formation of a corroded surface layer. However, fatigue life of aged material was less than that of solution-treated materials. These two opposing effects of corrosion and aging brought about a small difference in fatigue life between solution-treated and exposed materials.