Decrease in air dose rate after decontamination relating to difference in the ground surface properties

Nakama, Shigeo; Yoshimura, Kazuya; Fujiwara, Kenso; Ishikawa, Hiroyasu; Iijima, Kazuki

KEK Proceedings 2018-7, p.154 - 158, 2018/11

https://lib-extopc.kek.jp/preprints/PDF/2018/1825/1825007.pdf

Decrease in air dose rate in decontaminated area is essential information to estimate external exposure and to facilitate return of local residents, but the factors to control the decrease rate have not been cleared wholly. To clarify the effect of ground surface type (i.e. paved and soil surfaces) on the decrease in air dose rate at 1 m above the ground, surface dose rate at 1 cm above the ground and the air dose rate were monitored for four years since decontamination in 2011, and their decrease rates were compared relating to the ground surface type. Decrease in the air dose rate and the surface dose rate on the asphalt pavement showed faster rates than those on the soil surface. Ratio of decrease in the air dose rate and surface dose rate (decrease rate ratio) was distributed between 0.8 and 1.2 on open place not affected by surrounding environment. Therefore, decrease in the air dose rate was in agreement with the decrease of the surface dose rate, which is greatly affected by the ground surface. It became clear that the decrease rate constant of the air dose rate differs depending on the difference in the ground surface. Furthermore, it was also confirmed that the local soil erosion and sedimentation of the ground surface does not affect the decrease rate of the air dose rate.

Conceptual design study for the demonstration reactor of JSFR, 5; Reactor cooling system design

Kisohara, Naoyuki; Ishikawa, Hiroyasu; Futagami, Satoshi; Xu, Y.*; Shimoji, Kuniyuki*; Kawamura, Masaya*

Proceedings of 19th International Conference on Nuclear Engineering (ICONE-19) (CD-ROM), 9 Pages, 2011/10

The cooling system of the JSFR adopts an integrated primary sodium pump/intermediate heat exchanger (IHX), dual structure straight tube steam generator (SG) and short elbow sodium piping layout. Since, however, this is the first experience applying these technologies to SFRs in Japan, design approaches have been evaluated and R&D has been undertaken. This paper addresses the design study of the cooling system of the demonstration reactor JSFR in terms of thermal-hydraulic and structural integrity. Recent studies have shown that these new technologies have potential to be applied to the JSFR.

Experimental results of the -ray imaging capability with a Si/CdTe semiconductor Compton camera

Takeda, Shinichiro*; Aono, Hiroyuki*; Okuyama, Sho*; Ishikawa, Shinnosuke*; Odaka, Hirokazu*; Watanabe, Shin*; Kokubun, Motohide*; Takahashi, Tadayuki*; Nakazawa, Kazuhiro*; Tajima, Hiroyasu*; et al.

IEEE Transactions on Nuclear Science, 56(3), p.783 - 790, 2009/06

https://doi.org/10.1109/TNS.2008.2012059

Experimental study of sodium/carbon dioxide reaction

Ishikawa, Hiroyasu; Miyahara, Shinya; Yoshizawa, Yoshio*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 7(4), p.452 - 461, 2008/12

https://doi.org/10.3327/taesj.J07.054

Supercritical CO is being investigated as a material for a secondary cooling system of Na-cooled fast reactor in to avoid Na/water reaction. In this type of reactor, however, it is necessary to consider the consequences of Na/CO reaction, which might occur in the case of tube rupture in a heat exchanger between primary and secondary systems. Experiments were carried out with test equipment for the Na/CO reaction, which can handle 1-5 g order of Na. The solid products of the Na/CO reaction sampled from the equipment were analyzed by XRD and chemical analysis. From these experimental results, we proved that the reaction proceeded between liquid Na and CO. The Na/CO reaction stopped only the pool surface reaction with a small quantity of aerosol emission when the temperature was lower than 570C. On the other hand, the reaction continuously proceeded with on orange-colored flame and aerosol release when the temperature was higher than 580C.

Experimental Study of Sodium - Carbon Dioxide Reaction

Ishikawa, Hiroyasu; Miyahara, Shinya; Yoshizawa, Yoshio*

Proceedings of 2005 International Congress on Advances in Nuclear Power Plants (ICAPP '05) (CD-ROM), P. 5688, 2005/05

Focusing on the cover layer materials (as the Radon Barrier Materials), which could have the effect to restrain the radon from scattering into the air and the effect of the radiation shielding, we produced the radon barrier materials with crude bentonite on an experimental basis, using the rotary type comprehensive unit for grinding and mixing, through which we carried out the evaluation of the characteristics thereof.

Tritium release behavior from the graphite tiles used at the dome unit of the W-shaped divertor region in JT-60U

Katayama, Kazunari*; Takeishi, Toshiharu*; Manabe, Yusuke*; Nagase, Hiroyasu*; Nishikawa, Masabumi*; Miya, Naoyuki

Journal of Nuclear Materials, 340(1), p.83 - 92, 2005/04

https://doi.org/10.1016/j.jnucmat.2004.11.005

no abstracts in English

Conclusive Experimental Study of Prevention Measures Against Sodium Combustion Residuum Reignition; Run-F9-1, Run-F9-2

Ishikawa, Hiroyasu; Ohno, Shuji; Miyahara, Shinya

JNC TN9400 2004-038, 84 Pages, 2004/04

JNC-TN9400-2004-038.pdf:10.3MB

Nitrogen gas can be an extinguisher or a mitigating material in the case of sodium leak and fire accident in an air atmosphere, which may occur at a liquid metal cooled nuclear power plant. However, sodium combustion residuum sometimes reignites in the air atmosphere even at room temperature when it was produced by nitrogen gas injection to the burning sodium. Then, in this study we executed conclusive experiments of prevention measures against sodium combustion residuum reignition by a mixture of carbon-dioxide (C0 sub2) gas, humidity and nitrogen gas. The experiments were carried out with the FRAT-1 test equipment; the humidity conditions were changed in air which were used to sodium combustion atmosphere and exposure air for confirmation of prevented combustion residue reignition. First of all, the sodium of about 2.5kg was leaked in air atmosphere, and next, the sodium combustion was stopped by nitrogen gas injection. Next, the combustion residuum was cooled in the nitrogen atmosphere, and then the combustion residuum was exposed to atmosphere of carbon-dioxide (4%); humidity (6000vppm); oxygen (3%)-nitrogen (based gas) mixture. It was confirmed that the combustion residuum was not reignition even if exposed to the air atmosphere again at the end of experiment. We had confirmed that the prevention measures against sodium combustion residuum reignition to establish by this research were effective.

Evidence for a narrow = +1 Baryon resonance in photoproduction from the neutron

Nakano, Takashi*; Ahn, D. S.*; Ahn, J. K.*; Akimune, Hidetoshi*; Asano, Yoshihiro; Chang, W. C.*; Date, S.*; Ejiri, Hiroyasu*; Fujimura, Hisako*; Fujiwara, Mamoru; et al.

Physical Review Letters, 91(1), p.012002_1 - 012002_4, 2003/07

https://doi.org/10.1103/PhysRevLett.91.012002

no abstracts in English

Experimental Study of Prevention Measures against Sodium Combustion Residuum Reignition

Ishikawa, Hiroyasu; Ohno, Shuji; Miyahara, Shinya

Nihon Nensho Gakkai-Shi, 45(134), 248 Pages, 2003/00

Nitrogen gas can be an extinguisher or a mitigating in the case of sodium leak and fire accident in an air atmonphere, which may occur at a liquid metal cooled nuclear power plant. However sodium combustion residuum sometimes reignites in the air atmosphere even at room temperature when it was produced by nitrogen gas injection to the burning sodium. In this study we have been investigating the cause of reignition and prevention measures. Experiments were carried out with small type test equipment, which can handle 1g order sodium fire and extinguishment. Sodium combustion residua, which were made by our equipment and sampled, were analyzed by X-ray diffraction and chemical analyses. The chemical analysis of reignitable residua showed that the residuum contained metallic sodium of about 40Wt-%(61mol-%)to 60-wt %(76mol-%) and most of the rest was sodium-monoxide (Na2O).Sodium-peroxide (Na2O2) was also included in less than 1wt-% of the residuu. Sodium or Na2O cannot ignite by itself in the air atmosphere at room temperature in a few minutes. Therefore the reignition seems to be due to increase in the local temperature that is caused by oxidizing heat of Na and by adiabatic effect of Na2O. It is important to deactivate this dispersed sodium on oxygen for prevention of the residuum reigntion, hence it is considered as a rational measure to change the sodium to sodium-carbonate. Our experments showed that the dispersed sodium on the exterior of residuum could be changed to carbonate by a mixture by a mixture of carbon-dioxide(CO2) gas (2 to 8vol-%),humidity (0.6 to 3vol-%) and mitrogen gas. The deactivated residuum did not reignite in the air atmospherebe bwlow 473K.

Sodium pool combustion test Run-F7; Interim report

Futagami, Satoshi; Nishimura, Masahiro; Kawata, Koji; Ishikawa, Hiroyasu; Miyahara, Shinya

PNC TN9410 98-074, 154 Pages, 1998/08

PNC-TN9410-98-074.pdf:4.94MB

Supposing sodium leak accident from a IHTS pipe in FBR, sodium pool combusion test Run-F7 series is under way to know liner peak temperature and to study sodium pool growth and combustion behavior in the case of small-scale sodium leaks (0.01ton/hr) in an air atmosphere. This report consists of a result of Run-F7-1 (Feb,17,1998) and Run-F7-2 (Apr, 21, 1998) : In these tests, sodium temperature and sodium leak rates are the same (about 0.01ton/hr), but the height of leak point was changed. The test was performed using FRAT-1 (Fission Product and Radioactive Aerosol Release Test Rig . volume : 3m) of SAPFIRE (Safety Phenomenology Tests on Sodium Leak, Fire and Aerosols) facility. A burning pan (diameter : about 1000 mm, thickness : 6 mm) made of carbon steel (SM400B) to simulate floor steal liner was installed in FRAT-1. a 5kg of sodium was leaked at the leak rate of 0.01ton/hr under the temperature of 507C from the height of 0.1m and 1.5m (Run-F7-1 and Run-F7-2, respectively) during 30minutes when air was continued to feed into the cell. From the results, the following conclusion were drawn concerning the liner peak temperature, and sodium pool growth and combustion behavior, in the small-scale (0.01ton/hr) sodium leak: (1)In this case (1eak rate 0.01ton/hr), burning pan thermocouple measured 616C at approximately 33minutes in Run-F7-1, and 675C at 33minutes in Run-F7-2. therefore, the height of leak point has an effect on liner peak temperature. (2)Post test observation clarified that the deposits covered an area of about 0.3m in both tests. Sodium pool growth velocity during experiments were also similar. therefore, the height of leak point doesn't have a notable effect on sodium pool growth. (3)In both tests, burning rate of a unit area was 16kg-Na/mhr. (4)Analysis of the chemical composition of the deposits on the burning pan revealed that the main compounds were sodium oxides, but sodium dioxide and ...