[en] The containment structures of the HTTR consist of the reactor containment vessel (CV), service area (SA) and emergency air purification system, which minimize the release of FPs in the postulated accidents with FP release from the reactor facilities. The CV is designed to withstand the temperature and pressure transients and to be leak-tight within the specified leakage limit even in the case of a rupture of the primary concentric hot gas duct. The pressure of inside of the SA should be maintained slightly lower than that of atmosphere by the emergency air purification system. The radioactive materials are released from the stack to environment via the emergency air purification system under the accident condition. Then the emergency air purification system should remove airborne radio-activities and should maintain proper pressure in the SA. We established the method to measure leak rate of the CV with closed reactor coolant pressure boundary although it is normally measured under opened reactor coolant pressure boundary as employed in LWRs. The CV leak rate test was carried out by the newly developed method and the expected performance was obtained. The SA and emergency air purification system were also confirmed by the performance test. We concluded that the reactor containment structures were fabricated to minimize the release of FPs in the postulated accidents with FP release from the reactor facilities. (author)

[en] The gas circulator is a one of the most important component in Gas-Cooled Reactor system. Being low density of the coolant helium gas of HTGR, multi-stage compression or high-speed driving are required for the coolant circulator to accomplish the required head. The gas circulators for the large scale HTGRs with mechanical and buffer-gas sealing in the shaft penetration had encountered troubles at the part more or less. On the other hand, smaller scale electric driven gas circulators with gas bearings as used for HENDEL and former DRAGON reactor enable fully encased construction and provide easier maintainability, however, those types of the circulator need highly precise machining, adjustment and superior operational techniques. Moreover, practical rotor weight seems to be limited up to around 150kg for the gas-bearing machinery. The fine dynamic mass-balancing of the rotor becomes extremely difficult in the large gas-bearing machine. The whirling phenomena of the journal tend to originate and to grow approaching the rotating frequency to the first bending natural frequency or the third critical speed of the rotor. Inspite of many efforts and works on instability of the gas-bearing system, concrete or practical condition and countermeasure to the instability have not clarified. Present report describes the experimental result on shaft vibration and bearing characteristics of typical gas circulators among the five machines which have gas-bearings and are largest class in those types. It is clarified through the experiments that the fine dynamic balancing of the rotor, dynamic response of the bearing pads and gas-film thickness in the bearing clearance are extremely important to suppress the instability. However, it is also found that too much difficulties make them impractical in these machines. So one might conclude that the countermeasure with fine sensing technique of the half-speed whirling must be practical and usefull. (author)

[en] The high-temperature engineering test reactor (HTTR), Japan's first high-temperature gas reactor, is being constructed at the Oarai Research Establishment of the Japan Atomic Energy Research Institute. The article reports on the electrical and instrumentation control equipment for the 30 MW helium-gas-cooled reactor, which is decelerated by graphite. (author)

[en] The bearing loads were measured and analyzed for the gas bearing type circulator of the Helium loop HENDEL. From results of the study, it was found that the static load acting to bearing pads in the journal bearing does not remain constant as expected and is not isogonal due to the external forces from momentum changes and pressure gradient of the working gas and from electromagnetic force in the driving motor. As to the dynamic load in the bearing, it was found to depend on the static load and was also found that the absolute value of its vector is not constant in a rotation of the shaft. It was predicted and reasoned that the divergent shaft vibration is caused by the vibrational dynamic load in absolute value and relatively low stiffness of the spring-pivot. To improve weak points of the gas bearing circulator, some new design criteria are offered and the substantial methods are also indicated to realize those criteria. (author)

[en] The High Temperature Engineering Test Reactor (HTTR) is a graphite moderated and He gas cooled high temperature reactor with a 30 MW thermal. The functional test of the HTTR consists of the component functional, system functional and overall system functional tests. At the beginning, the pressure test on all primary and secondary systems was initiated in March of 1996 by using nitrogen gas and have since been in progress in order of the planned their procedures successfully. This report presents the outline of the test results concerning helium gas circulators, the containment leak rate and loss of electrical power supply. Performance of primary and secondary helium gas circulators were confirmed to fulfill their specifications respectively. Concerning containment leakage, the obtained leakage levels less than 0.0178 %/day were satisfactory low comparing allowable leak rate of 0.09 %/day. In the transient event test, 'loss of electric power supply', it was confirmed that the reactor was scrammed, and emergency power feeder was started up to supply electricity to the reactor facility and then the auxiliary cooling system was energized automatically to remove the residual heat of the core by safety protection system safely. (H. Itami)

[en] The Japan Atomic Energy commission (JAEC) decided to construct the high-Temperature engineering Test Reactor (HTTR) in 1987 for establishing and upgrading the basic technologies for advanced HTGRs and serving an irradiation test facility for research in high temperature technologies. The HTTR is a graphite-moderated and helium-gas-cooled test reactor with thermal output of 30MW and inlet and maximum outlet coolant temperature of 395 C and 950 C respectively. Construction started in March 1991 at Oarai site of the Japan Atomic Energy Research Institute (JAERI), with its first criticality at the end of 1997 to be followed after a series of functional tests of half a year. Fabrication of reactor pressure vessel, an intermediate heat exchanger (IHX), gas circulators and other main cooling components has been finished in their factories and installed to the site in 1994. At present, the construction of HTTR reactor building and installation of containment vessel, main and auxiliary cooling systems, etc. are almost completed. This paper describes design of the HTTR reactor cooling system, control system and present status of the HTTR construction

[en] An examination and vibration measurements were conducted on the gas bearing type high speed helium gas circulator after the failure on April 1984 and the repairing on August 1984. The examination made clear that the cause of the failure and scratching of gas bearing pads and journal shaft was found. The vibrational spectra showed a clear difference between failed and repaired conditions, and a frequency analysis technique by means of fast Fourier transform and a small-scale computer is expected as a useful method of diagnosis for circulators. A conceptual scheme of gas circulator diagnostic system based on above principle is shown, and a basic process of diagnostic software is described. (author)

[en] During a preliminary no-nuclear heat-up test in the High Temperature Engineering Test Reactor (HTTR), temperature inside of stand pipes and a primary upper shield increased more than expected. Structures in stand pipes were modified and heat-up test was performed again. The modification decreased the temperatures significantly but not satisfactorily. Thus other countermeasures were considered, temporarily added and their performance was tested in another heat-up test. This paper describes the additional countermeasures, performance test result, analytical simulation of the test result, etc. Maximum temperature inside of the primary upper shield at full-power operation is estimated to be about 100degC by linear extrapolation of test result and about 85degC by analysis. We conclude from the estimation and measurement of percentage of total moisture content of mortar after being subjected to elevated temperatures that design requirement for radiation shielding performance of the primary upper shielding will be met at full-power operation. (author)