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Journal Articles

Wide-range krypton gas monitor using a plastic scintillation detector operated in current mode with a gate circuit

Takasaki, Koji; Kobayashi, Hirohide; Suzuki, Hideki; Ushigome, Sadaharu*

Journal of Nuclear Science and Technology, 47(3), p.255 - 261, 2010/03

 Times Cited Count:1 Percentile:11(Nuclear Science & Technology)

The wide-range krypton-85 detector was developed for monitoring of krypton-85 gas, which was discharged from the stack of a nuclear fuel reprocessing plant and varied largely in concentration. The detector combined a current-mode-operated plastic scintillation counter with a gated photomultiplier. The discrimination voltage of gated photomultiplier was determined, and the effects of temperature and humidity were examined on the background measurement. The detector was calibrated by krypton-85 gas and the decision threshold was estimated. These examinations showed that the wide-range krypton-85 detector worked in the measurement range as wide as 10$$^{-3}$$-10$$^{2}$$ Bq/cm$$^{3}$$ in linearity and the decision threshold of krypton-85 concentration was 1.3$$times$$10$$^{-3}$$ Bq/cm$$^{3}$$ for 10-minute measurement. The parallel measurement was made between this detector and a GM counter in the reprocessing laboratory. Both concentrations showed a good agreement with each other.

Journal Articles

Monitoring methodologies and chronology of radioactive airborne releases from Tokai reprocessing plant

Koarashi, Jun; Mikami, Satoshi; Nakada, Akira; Akiyama, Kiyomitsu; Kobayashi, Hirohide; Fujita, Hiroki; Takeishi, Minoru

Journal of Nuclear Science and Technology, 45(Suppl.5), p.462 - 465, 2008/06

 Times Cited Count:6 Percentile:43.18(Nuclear Science & Technology)

Tokai reprocessing plant (TRP) has released radionuclides such as $$^{3}$$H, $$^{14}$$C, $$^{85}$$Kr and $$^{129}$$I into the atmosphere since the start of operation in 1977. We have established the monitoring methodologies for these nuclides, to realize an appropriate and continuous radioactive discharge control. The methodologies having various special technical considerations for matching the monitoring of reprocessing off-gas, were summarized in this paper. Briefly, $$^{3}$$H was collected by a cold-trap technique and the concentration was evaluated being independent of the water collection efficiency; $$^{14}$$C was collected by a monoethanolamine bubbler and then measured by liquid scintillation counting without any interferences from $$^{3}$$H and $$^{85}$$Kr; $$^{85}$$Kr was continuously measured by combination of two kinds of detectors to cover very wide range of the concentration; and $$^{129}$$I was collected by a charcoal filter and a charcoal cartridge in series with a relatively high collecting performance.

Journal Articles

Carbon-14 source, distribution and behavior around Tokai reprocessing plant

Koarashi, Jun; Takeishi, Minoru; Kobayashi, Hirohide

Proceedings of International Symposium on Environmental Modeling and Radioecology, p.223 - 230, 2007/03

no abstracts in English

Journal Articles

Selective detection using pulse time interval analysis for correlated events in Rn-progeny with a microsecond lifetime

Sanada, Yukihisa; Kobayashi, Hirohide; Furuta, Sadaaki; Nemoto, Kazuhiko*; Kawai, Keiichi*; Hashimoto, Tetsuo*

Radioisotopes, 55(12), p.727 - 734, 2006/12

The purpose of this study is to develop new measurement methods of radon progenies that discharged alpha-ray focused on pulse time interval. It is calculated that a delayed coincidence method, time-interval-analysis (TIA), has been applied to decay events on the microsecond time-scale (164microsecond). The measurement system with silicon detectors was produced and examined a basic performance of the system by using $$^{230}$$Th electrodeposited sources. This system was designed that it have shorter dead times. The results were as follows. (1) The theory of measurement $$^{214}$$Po using TIA methods was established. (2) Development of the system that measured $$^{214}$$Po. (3) Suggested that methods to examine a basic performance by using $$^{230}$$Th electrodeposited sources. It is scheduled to examine the method of subtracting the progenies of the thorium series, and to reflect this system in an actual work of radiation control in the future.

Journal Articles

Airborne radioiodine monitoring at Tokai reprocessing plant

Mikami, Satoshi; Koarashi, Jun; Miyauchi, Toru; Akiyama, Kiyomitsu; Kobayashi, Hirohide

Proceedings of 2nd Asian and Oceanic Congress Radiological Protection (AOCRP-2) (CD-ROM), p.308 - 312, 2006/10

As airborne radioiodine effluent monitoring in Tokai reprocessing plant (TRP), not only a weekly evaluation of exact discharged amount of radioiodine ($$^{129}$$I) for assessing environmental impact, but also continuous monitoring of radioiodine being discharged are performed for quick recognition of unexpected effluent tendency. Furthermore, to enhance effluent monitoring activity corresponding to features reprocessing plant, sequential radioiodine monitoring system without interference by the mingled $$^{85}$$Kr has been developed and effectively functioned as an assist during plant operation. The systematic configurations having these functions for airborne radioiodine monitoring corresponding to nuclear fuel reprocessing plant have been established.

Journal Articles

Development of dust monitor for rapid detection of plutonium with background compensation system

Sanada, Yukihisa; Kobayashi, Hirohide; Hashimoto, Tetsuo*

Proceedings of 2nd Asian and Oceanic Congress Radiological Protection (AOCRP-2) (CD-ROM), p.313 - 317, 2006/10

The dust monitor for rapid detection of artificial nuclides such as Plutonium with Rn-progeny background compensation system was developed to apply a time interval analysis (TIA). The TIA method was applied to beta and $$alpha$$ decay events with microsecond scale (half-life of $$^{214}$$Po: 164 microsecond). In actual experiments, dust sample on the filter (HE-40T pore size: 8micrometer) was collected in a workspace at the JAEA reprocessing facility to compensate $$^{214}$$Bi-$$^{214}$$Po correlated events. As a result, total alpha-ray counting rate except for $$^{214}$$Po was 0 $$pm$$ 0.05 cps. The small $$^{241}$$Am source with dust sampling was measured for simulation of unexpected additional $$alpha$$-ray emitted radionuclides. The increment for $$alpha$$-ray counting rate due to the $$^{241}$$Am source could be clearly detected. The present method will apply for on-line monitoring of $$alpha$$-ray measurement, because the method is able to detect artificial nuclides by compensating any changes of background due to Rn-progeny.

Journal Articles

A Simple and reliable monitoring system for $$^{3}$$H and $$^{14}$$C in radioactive airborne effluent

Koarashi, Jun; Mikami, Satoshi; Akiyama, Kiyomitsu; Kobayashi, Hirohide; Takeishi, Minoru

Journal of Radioanalytical and Nuclear Chemistry, 268(3), p.475 - 479, 2006/06

A simple and reliable sampling system for $$^{3}$$H and $$^{14}$$C in airborne release from nuclear facilities was designed. The sampling system can collect $$^{3}$$H and $$^{14}$$C simultaneously with a condensation technique using a commercially available cold trap equipment and a CO$$_{2}$$ absorption technique using an organic alkali solution monoethanolamine, respectively. In situ performance tests for the effluent from a reprocessing plant showed that the system has the high and stable efficiencies for collecting $$^{3}$$H and $$^{14}$$C for a one-week batch sampling at a sampling flow rate of 0.4 l min$$^{-1}$$. These collection techniques also provided a simple procedure of following sample preparations for activity measurement by liquid scintillation counting. The detectable concentrations of the proposed monitoring method were 3.0Bq/m$$^{3}$$ for $$^{3}$$H and 1.6Bq/m$$^{3}$$ for $$^{14}$$C, respectively. The sensitivity would be acceptable level for routine monitoring of airborne release at nuclear facilities.

JAEA Reports

Development of new $$alpha$$-ray measurement methods with radon suppression focused on pulse time interval

Sanada, Yukihisa; Nohara, Naofumi*; Adachi, Yasuyuki*; Nemoto, Kazuhiko*; Kawai, Keiichi*; Kobayashi, Hirohide; Hashimoto, Tetsuo*

JAEA-Technology 2005-009, 33 Pages, 2006/01

JAEA-Technology-2005-009.pdf:1.42MB

An $$alpha$$-ray measurement methods based on analyzing the time interval of pulses was newly developed. This method was developed aiming to suppress the background counts originated in progeny of uranium series. A delayed coincidence and time interval analysis (TIA) methods have been applied to measure a-b decay successive events (correlated events) on microsecond time-scale (164$$mu$$s). The measurement system have such functions with silicon detectors was developed intending to shorten the dead time. The basic performance of the system was examined by using $$^{230}$$Th electrodeposited sources. Follows were obtained in this work : The theory of measurement $$^{214}$$Po using TIA methods was established. Measurement system of $$^{214}$$Po was developed. Conformation methods of correlated events by using $$^{230}$$Th electrodeposited sources was suggested. The efficiency of correlated events in aerosol samples was estimated. The methods to measure correlated events was indicated by addition of $$^{230}$$Th. The method of subtracting the progenies of the thorium series are to examine.

Journal Articles

A Practical method for monitoring $$^{129}$$I concentration in airborne release

Koarashi, Jun; Akiyama, Kiyomitsu; Asano, Tomohiro; Kobayashi, Hirohide

Journal of Radioanalytical and Nuclear Chemistry, 267(1), p.155 - 159, 2006/01

 Times Cited Count:2 Percentile:18.81(Chemistry, Analytical)

To establish a practical method for monitoring$$^{129}$$I concentration in airborne release from the Tokai reprocessing plant,$$^{129}$$I collecting performance of sampling media used in the method was tested by in situ experiments. The results indicated that the combinational use of an activated charcoal-impregnated filter paper and an activated charcoal cartridge gives the collection efficiency of more than 90% for one-week sampling of real airborne effluent at sampling flow rates of 40.6-75.0 l min-1. The sampling and measurement conditions suitable for a routine-based monitoring were demonstrated taking into account the findings.

Journal Articles

Study on evaluation method of radionuclides discharged in criticality accident using stack gas monitor

Sanada, Yukihisa; Mikami, Satoshi; Kobayashi, Hirohide; Kurimata, Tomoyuki*; Fukazawa, Satoshi*

JAERI-Conf 2005-007, p.321 - 325, 2005/08

It researched concerning the method of evaluating the radionuclide discharged by using the gas monitor at a criticality accident. The measurement condition was set from the evaluation result of the $$gamma$$-ray spectrum at a criticality accident of the use of the calculation code. The measurement system was developed in consideration of those conditions. The evaluation after three hours is possible at a criticality accident according to this system. The evaluation before three hours was examined about the method of doing the detector pulse by high-speed processing by digital oscilloscope.

JAEA Reports

Re-Evaluation of a Method for Monitoring Airborne$$^{14}$$C Discharge and its Contribution to Development of an Advanced Method

Koarashi, Jun; Isaka, Keisuke*; Yokota, Tomokazu*; Kozawa, Tomoyasu*; Mikami, Satoshi; Akiyama, Kiyomitsu; Kobayashi, Hirohide

JNC TN8410 2005-005, 55 Pages, 2005/05

JNC-TN8410-2005-005.pdf:2.0MB

Some investigations were made for re-evaluating collection and measurement techniques in an airborne $$^{14}$$C discharge monitoring at the Tokai reprocessing plant (TRP), which include (1)collection efficiency of CO$$_{2}$$ in a carbon sampler using monoethanolamine as CO$$_{2}$$ absorbent;(2)affect of incorporating tritiated water into the carbon sampler on quantitative estimation of $$^{14}$$C activity in airborne effluent; (3)affect of leakage in air sampling on evaluating airborne $$^{14}$$C discharge; and (4)determination of chemical forms of $$^{14}$$C in airborne release from the TRP. The results presented not only the validity of the TRP's monitoring method, but also the technical aspects required for establishing a more reliable and effective monitoring method.

JAEA Reports

Re-Evaluation of a Method for Monitoring Airborne$$^{3}$$H Discharge and its Contribution to Development of an Advanced Method

Koarashi, Jun; Yokota, Tomokazu*; Kozawa, Tomoyasu*; Isaka, Keisuke*; Mikami, Satoshi; Akiyama, Kiyomitsu; Kobayashi, Hirohide

JNC TN8410 2005-004, 73 Pages, 2005/05

JNC-TN8410-2005-004.pdf:2.48MB

Some investigations were made for re-evaluating collection and measurement techniques in an airborn $$^{3}$$H discharge monitoring at the Tokai reprocessing plant (TRP), which include (1)collection efficiency of water in a tritium sampler; (2)quench correction in $$^{3}$$H activity measurement by liquid scintillation counting; (3)affect of leakage in air sampling on evaluating airborne $$^{3}$$H discharge; and (4)determination of chemical forms of $$^{3}$$H in airborne release from the TRP. The results presented not only the validity of the TRP's monitoring method, but also the technical aspects required for establishing a more reliable and effective monitoring method.

Journal Articles

Study on evaluation method of radionuclides discharged in criticality accident using stack gas monitor

Sanada, Yukihisa; Mikami, Satoshi; Kobayashi, Hirohide; Kurimata, Tomoyuki*; Fukazawa, Satoshi*

Program and abstracts, p.77, P. 77, 2005/02

It researched concerning the method of evaluating the radionuclide discharged by using the gas monitor at a criticality accident. The measurement condition was set from the evaluation result of the $$gamma$$-ray spectrum at a criticality accident of the use of the calculation code. The measurement system was developed in consideration of those conditions. The evaluation after three hours is possible at a criticality accident according to this system. The evaluation before three hours was examined about the method of doing the detector pulse by high-speed processing by digital oscilloscope.

Journal Articles

Chemical Composition of$$^{14}$$C in Airborne Release from the Tokai Reprocessing Plant, Japan

Koarashi, Jun; Akiyama, Kiyomitsu; Asano, Tomohiro; Kobayashi, Hirohide

Radiation Protection Dosimetry, 114(4), p.551 - 555, 2005/00

 Times Cited Count:18 Percentile:77(Environmental Sciences)

Fuel reprocessing plant is one of the most important sources of anthropogenic$$^{14}$$C in the environment. A method was developed to determine the amount and chemical composition of airborne $$^{14}$$C release from the Tokai reprocessing plant, Japan. Effluent monitoring using the method showed most of the $$^{14}$$C is released in CO$$_{2}$$ form and the ratio of $$^{14}$$C in hydrocarbons to the total is less than 3%, not depending on the type of fuel reprocessed. This evaluation would provide improved information on dynamical behavior of $$^{14}$$C in the environment and assessment of radioecological impact from nuclear fuel cycle.

JAEA Reports

Discharge Monitoring by the Wide Range Radioactive Krypton Detector

Morita, Suguru; Tanizawa, Teruaki*; Masayuki, Morifuji,; Takasaki, Koji; Suzuki, Hideki*; Suzuki, Kazunori; Kobayashi, Hirohide

JNC TN8410 2004-011, 83 Pages, 2004/07

JNC-TN8410-2004-011.pdf:5.88MB

In the Chemical Processing Facility (CPF), after reconstruction was completed, the examination for advanced hydrometallurgy reprocessing was carried out from December 2002 to March 2004. In this examination,$$^{85}$$Kr were discharged from the stack. Discharge of$$^{85}$$Kr was measured and estimated by the wide range radioactive Krypton detector.GM Gas monitor of the CPF stack monitor was exchanged for the wide range radioactive Krypton detector in fiscal 1994. In discharge monitoring of this examination for advanced hydrometallurgy reprocessing,$$^{85}$$Kr gas were detected for the first time by the wide range radioactive Krypton detector of CPF. In this examination, the temporary gas monitor of the conventional GM detector was installed, and the result of measurement and inventory were compared.In this report the discharge of$$^{85}$$Kr is indicated by the wide range radioactive Krypton detector. As a result of comparative evaluation, it was confirmed that the discharge monitoring by the wide range radioactive Krypton detector was appropriate.

JAEA Reports

Use Career of the Radioisotope in the Ridge According to Safety Control

Kamoshida, Tsuyoshi; Kobayashi, Hirohide

JNC TN8410 2004-006, 130 Pages, 2004/06

JNC-TN8410-2004-006.pdf:9.3MB

The use career of the radioisotope from 1972 to 2001 which obitained permission on the ridge according to safety control was summarized

JAEA Reports

Development of the Self Moving Survey System

Ishikawa, Hisashi; Nemoto, Norio; Izaki, Kenji; Kobayashi, Hirohide; Tanizawa, Teruaki*; Kanazawa, Yoshito*

JNC TN8400 2004-008, 124 Pages, 2004/05

JNC-TN8400-2004-008.pdf:58.81MB

In order to strengthen the functions of the self moving survey system, the design of the truck and the data transmission system, the investigation of the handling function and the durability test assumed under the disaster environment were executed.As the basic performance of the self moving survey system, it was demanded to have the functions in order to run on the bumpy road, go up and down the stairs and open and shut of the door. And the remote control by the PHS line or the SS wireless is adopted as an operational method. Moreover, as the function that can monitor the disaster situation in the facility, it was assumed the design that make modular the measurement equipments, which mainly measure alpha ray, gamma ray and neutron, and installed it.In consideration of the radiation monitoring under the environment that assumes the critical accident and a fire and the explosion etc. heat test, humidity test, radiation test, and aerosol (smoke) test for monitoring equipments were executed. As a result of the tests, it was confirmed that all equipment except the semiconductor detector operated normally.

JAEA Reports

The Support Activities of JNC against the JCO Criticality Accident

Kanamori, Masashi; Kawata, Tomio; Hitoshi, Watanabe,; Tobita, Yoshiharu; Sugiyama, Toshihide; Miyabe, Kenjiro; Kobayashi, Hirohide

JNC TN8450 2003-009, 506 Pages, 2004/03

JNC-TN8450-2003-009.pdf:14.21MB

This paper describes all the activities that were executed by JNC related to JCO criticality accident on September 30,1999. During the JCO accident, the activities of radiation monitoring, environmental monitoring, criticality termination operation, computer simulation of criticality accident, whole body exposure measurements by WBC about 24-Na, back up of local government like consultation of residents near by were performed by JNC. After the accident Japanese government and Nuclear Safety Commission establishes the investigation committee of JCO accident. JNC has also back up this activity. For example, investigation of the causes, accident scenario, estimation of the doses of the workers and personnel for deserter, counter measure operation. This paper summarizes all the important activity executed by JNC in the meantime.

JAEA Reports

Annual Report on Activities of Radiation Protection Division at JNC Tokai Works in Fiscal Year of 2002

Shinohara, Kunihiko; Asano, Tomohiro; Momose, Takumaro; Takeishi, Minoru; Kobayashi, Hirohide; Oka, Tsutomu; Takasaki, Koji

JNC TN8440 2003-020, 125 Pages, 2003/09

JNC-TN8440-2003-020.pdf:11.14MB

This annual report summarizes the activities of the Radiation Protection Division at JNC Tokai Works in fiscal 2002.The Tokai Works undertakes various research and development for the reprocessing of spent fuel, plutonium fuel fabrication, fast reactor fuel recycling technology, and radioactive waste treatment and disposal, all of which are done under strict safety management.The major radiation facilities in the Tokai Works are the Tokai Reprocessing Plant (TRP), which has been in operation since 1977, three MOX fuel fabrication facilities, the first of which has been in operation since 1965, the Chemical Processing Facility (CPF) where fast reactor (FR) reprocessing technologies are being developed, and various other radioisotope and uranium research laboratories.The Radiation Protection Division is responsible for radiation control in and around these facilities, including personnel monitoring, workplace monitoring, consultation on radiological work planning and evaluation, monitoring of gas and liquid waste effluents, environmental monitoring, instrumentation, calibration, quality assurance, and safety research. The Division also provides technical support and cooperation to other international and domestic institutes in the radiation protection field.In fiscal 2002, the results of radiological monitoring showed the situation to be normal, and no radiological incident or accident occurred. The maximum annual effective dose to radiation workers was 6.5 mSv and the mean annual effective dose was 0.1 mSv. Individual doses were kept within the annual dose limit specified in the safety regulations. The estimated effective dose caused by gas and liquid effluents from the TRP to members of the public around the Tokai Works was 4.2 * 10$$^{-4}$$mSv. Environmental monitoring and effluent control were performed appropriately in compliance with safety regulation and standards.

JAEA Reports

Report on long range alpha detector (LRAD) performance tests

Kobayashi, Hirohide; ; ; ; Ebana, Minoru*

JNC TN8410 2002-011, 24 Pages, 2002/10

JNC-TN8410-2002-011.pdf:4.36MB

At present, alpha contamination measurement on objects is conducted with ZnS scintillation survey meter (direct method) and smear test (indirect method). But it is difficult to measure large and complicated objects by direct method. Long Range Alpha Detector (LRAD) was produced as a solution for this problem. We carried out performance tests of this LRAD. As a result of the performance tests, we confirmed the linear relation between the measurement values of LRAD and alpha-radioactivity on the surface of objects.

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