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Konno, Shotaro; Fukuda, Seiji; ; Hazama, Taira; ; Hashimoto, Makoto
JNC TN9410 2002-015, 59 Pages, 2002/10
Deuterium critical assembly (DCA) is a critical facility with 1 kW maximum thermal output reached its initial criticality in 1969. DCA operations were stopped on 26
September 2001, then it has been planed to submit a legal application for decommissioning of DCA to MEXT and to shift to decommissioning phase. In this work, we have evaluated the calculation value of neutron flux by comparison with an actual measurement in biological shield and the amount of contaminated radioactive materials etc. to make a document on estimation of the inventories and the wastes quantity etc. in the legal application. Results are as follows. (1)Fast, epithermal and thermal neutron flux calculated have exceeded the measurement data at almost all location. Therefore concentration of activated materials calculated by neutron flux calculation value is estimated higher than actual that. (2)The amount of radioactive materials that contaminated by nuclides other than tritium is estimated about 3.0
10
Bq. The concentration of tritium-contaminated radioactive materials is estimated about 4.110
Bq/g at the maximum in concrete, about 7.6 10
Bq/g in the surface of aluminum plumbing. (3)Consequential waste quantity (solid waste) to radioactive waste generated in total process of dismantling is estimated about 30ton. As for Radioactive liquid waste quantity, moderator for specimen is estimated about 1.4m
, consequential liquid wastes is estimated about 300m. (4)The amount of Tritium generated in dismantling (radioactive gas waste) is estimated about 7.2510
Bq in dismantling of heavy water system facility, measurement control system facility and neutron reactor.
; Konno, Shotaro
JNC TN9410 2001-026, 106 Pages, 2002/01
JNC-TN9410-2001-026.pdf:4.53MB
Dismantling methods of contaminated liquid waste tanks have been developed for decommissioning of Joyo Waste Treatment Facility. In this report, we discussed a concept of dismantling system for the tanks using a water jet. Results are follows. (1)A water jet dismantling system is composed from dismantling work area, a water jet dismantling device, Waste tank moving device, Radioactive waste carrying device. (2)Evaporator room is appropriate for the dismantling work area. (3)A pressure intensifier with 400 MPa output pressure is choused for the dismantling device to decrease radioactive secondary wastes. (4)The waste tank moving device has a carrier used in a waste tank room and casters attached to the tanks when they are brought into the evaporator room to avoid cross contamination. (5)Radioactive waste carrying device is composed from a lifter, carrying containers, a green-house and a container-carrier. (6)2.5 tons of solid waste and 3.3 m of liquid waste will be the secondary waste. (7)At points of developing working efficiency and decreasing the secondary waste, it is appropriate to break the tanks into large fragments and put them in 1 m containers. (8)About 8 man*mSv is expected for whole dismantling works of the tanks. (9)Deliberate cutting of tanks will makes a filling ratio about 40%. (10)Introducing the water jet dismantling system, it is indispensable to decrease the secondary wastes including devices and introducing costs and to develop cost effectiveness much more.
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JNC TN9410 2001-029, 47 Pages, 2001/12
JNC-TN9410-2001-029.pdf:1.76MB
The decommissioning evaluation system that evaluated and optimizes the decommissioning scenario (total amount of men and days, period of works, exposure dose, abundance of waste, cost) has been developed. In this report, for test study of old JWTF decontamination using the decommissioning evaluation system, survey work of location and surface dose rate of machines and pipes in old JWTF, calculation using the decommissioning evaluation system, comparing a scenario carrying out a decontamination work and one which did not use the decontamination work were carried out. Results are as follows. (1)The DECMAN calculated that total amount of men and days was 4.510man day, period of works was 490 days, cost was 3.910
yen, abundance of waste was 1.410
ton (radioactive waste was 6.9ton). (2)Total amount of men and days of a scenario using decontamination (scenario A) was nearly 1.3 times as large as one of a scenario which did not use decontamination (scenario B). Cost of "A" was 2.0 times as large as that of "B". Exposure dose of "A" was l/4 times as low as that of "B". (3)The DECMAN overestimated exposed dose. The reason was thought as follows. The exposed dose from each equipments was estimated in 2 dimension. Distance between each equipments in the DECMAN was estimated short compared with actual distance. Workers were moving around the equipment in actual work, and averted stopping at high dose rate points. The system could not add the process in calculation.
; Fukui, Yasutaka; ; Tanimoto, Kenichi
JNC TN9410 2001-028, 62 Pages, 2001/12
JNC-TN9410-2001-028.pdf:6.96MB
On irradiating laser ray to surface of metal, the surface is rapidly heated, melted, and evaporated. Laser decontamination technique has been developed by using the transpire process to radionuclides contaminated machine surface. The decontamination experiments using normal pulse YAG laser and hot sample were carried out. In the experiments, it was understood that even if the surface is ground by 150
m or more, radioactivities could not be completely removed. 0n this account, for the purpose of study the depth where a radioactivities merges in the metal by the laser irradiation, surveys using the hot test specimen were per拓rmed. Results are as follows. (1) Observation of topographic profile suggested that the depth of irregularity by laser irradiation were from 200m to 500m, and there were crud on the surface, which seems reattached melting crud by laser irradiation. (2) Metallic composition analysis with fluorescent X-ray analysis device suggested that there was the segregation of Cr in the test specimen that used Air for the assistance gas, and there were not the segregation that used Ar for the assistance gas. (3) The radioactivity analysis of the test specimen that uses the imaging plate and the radio autograph could not clear the distribution of radioactivities. However, it could be confirmed that a radioactive nuclide exited in a range of 500 m or less. (4) Grounding the test specimen and measurement of the doses of radiation with Ge measuring tool suggested that there were radioactivities up to the depth of 300m in the test specimen which used Air for the assistance gas, and 120m in the test specimen which used Ar for the assistance gas.
; Konno, Shotaro; Tanimoto, Kenichi; Kondo, Hitoshi; Hazama, Taira;
JNC TN9410 2001-027, 136 Pages, 2001/12
Deuterium Critical Assembly (DCA) is a critical facility with 1 kW maximum themmal output used for development of an Advanced Thermal Reactor and a subcriticality measurement technique for criticality safety management of nuclear fuel facilities since its initial criticality in 1969. DCA operations were stopped on 26 September 2001, then it has been planed to submit a legal application for decommissioning of DCA and to shift to decommissioning phase. In this work, we have evaluated an amount of materials in all controlled areas, activated inventories and activated radioactive wastes to make a document on estimation of the inventories and the wastes et.al. in the legal application. Results are as follows. (1)Total amounts of materials in the controlled areas are 9,464 tons. An amount of concrete is 9,162 tons and greater than 97% of all materials in weight. (2)The radioactive inventories of metals et.al and a biological shield will be respectively l.39 10Bq and 4.9010
Bq in about 2008 when actual dismantling of components will be started. (3)We classified decommissioning materials according to clearance level that has been discussed to be legalized. An amount of low level radioactive wastes will be 36 tons. Amounts of clearanced or nonradioactive waste will be 9,428 ton and greater than 99% of all wastes in weight. 7,005 tons of concrete will be nonradioactive waste.
; Kondo, Hitoshi; ; Tanimoto, Kenichi
JNC TN9410 2001-011, 124 Pages, 2001/12
JNC-TN9410-2001-011.pdf:6.73MB
Deuterium Critical Assembly (DCA) is a critica facility with 1 kW maximum thermal output used for development of an Advanced Thermal Reactor and a subcriticality measurement technique for criticality safety management of nuclear fuel facilities since its initial criticality in 1969. It has been planed to stop DCA operation in 2001 and shift to decommissioning phase. In this study, we evaluated activated inventories being primary data for study of an amount of radioactive wastes, dismantling method and cost which are indispensable for a decommissioning plan and a draft of a legal application for decommissioning. The evaluation was carried out for components in Reactor room and a D
O handling room irradiated with neutron flux. Results are as follows. (1)Each amounts of components and a building related with Reactor room and D2O handling room are 108 tons and 6,039 tons respectively. They are classified into 28 tons of aluminum, 37 tons of stainless steel, 73 tons of carbon steel, 6,004 tons of concrete and 5 tons of the others. (2)The activated inventories are very little due to a low neutron flux in DCA. Thus, radioactive materials concentrations in most of matelials except 37 tons of stainless steel and 12 tons of carbon steel will be lower than that of proposed clearance level in 7 years after the end of operation. The inventories of the components and the shield will be respectively 4.2510Bq and l.7110
Bq.
; ; Kondo, Hitoshi; Tanimoto, Kenichi
JNC TN9410 2001-007, 105 Pages, 2000/12
JNC-TN9410-2001-007.pdf:7.42MB
Dismantling methods of liquid waste tanks lined with flammable natural rubber for decommissioning of Joyo Waste Treatment Facility. In this development, we researched common mechanical and heat cutting methods and chose appropriate one that was effective to decrease exposure and had no risk to fire the natural rubber lining. We next carried out dismantling tests using the chosen method with rubber lined mock-ups ofthe tanks to obtain cutting conditions and removal conditions of the lining to minimize secondary wastes. Results are follows. (1)We chose abrasive water jet that has an ablity to remove the rubber lining and to be controllable remotely with ease as a cutting method for the natural rubber lined tanks. (2)As a result of cutting tests under parameters of a cutting nozzle speed and a abrasive feed rate, cutting conditions minimizing secondary wastes are 0.4 kg/min abrasive feed rate and 300 mm/min nozzle speed. (3)As a result of a removing test under a parameter of a removing nozzle speed, a removing condition minimizing secondary wastes is 60 mm/min nozzle speed, thus removing speed is 3720 mm/min. (4)Improving the removing method, especially decreasing water feed, and general design of a dismantling system including treatment with secondly waste are required.
; ; Tanimoto, Kenichi
JNC TN9410 99-017, 117 Pages, 1999/08
Decontamination methods have been studied for decommissioning of Joyo Waste Treatment Facility whose operation has been stopped in 1994. In this study, we analyzed samples of its system piping, whose dose rate was relatively low, to determine conditions of contamination. We also study appropriate decontamination methods for them. Results are as follows. (1)The inner surfaces of piping were covered with a very thin clad that was less than 1 micrometer in thickness and had many vacancies, looked like particle detachment, that were about 20 micrometers in depth. Something like corrosion product was observed near the surface and it was 440 micrometers in depth. (2)Radioactive contamination was considered to settle on a lower part of the piping and to be buried in the clad. A kind of dominant contamination nuclide was 
Co. (3)Hot nitric acid process will be suitable for system decontamination to reduce dose rate before dismantling. But its feasibility tests are indispensable using samples of main system components that have high dose rate. Rubber lining tanks requires another methods because of its difficulty of decontamination. (4)Analyses and decontamination tests using main system are required to decide through decontamination methods according to the clearance level.