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Journal Articles

Study on multi-dimensional core cooling behavior of sodium-cooled fast reactors under DRACS operating conditions

Ezure, Toshiki; Onojima, Takamitsu; Tanaka, Masaaki; Kobayashi, Jun; Kurihara, Akikazu; Kameyama, Yuri*

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.3355 - 3363, 2019/08

Steady-state sodium experiments under the operating conditions of a decay heat removal system (DHRS) were carried out as part of the safety enhancement of sodium-cooled fast reactors using the PLANDTL 2 facility, which has 30 heated channels with electric heaters and 25 no-heated channels as the simulated core. In the experiments, a direct reactor auxiliary cooling system (DRACS) with a dipped type direct heat exchanger (DHX) in the upper plenum was used as the DHRS. This paper reports on the preliminary experimental results of the PLANDTL 2 experiments under the DRACS operating conditions without flow in the primary circuit, including the thermal hydraulic interactions between the upper plenum and the core under the DHX operating conditions and the resulting core cooling behavior from the outside of the multiple rows of the fuel assemblies

Journal Articles

Upgrade and Replacement of Plant Dynamics Test Loop (PLANDTL)

Uchiyama, Naoki*; Ozawa, Tatsuya*; Sato, Koji*; Kobayashi, Jun; Onojima, Takamitsu; Tanaka, Masaaki

FAPIG, (194), p.12 - 18, 2018/02

no abstracts in English

Journal Articles

A Study on the thermal-hydraulics in the damaged subassemblies under the operation of decay heat removal system

Ono, Ayako; Onojima, Takamitsu; Doda, Norihiro; Miyake, Yasuhiro*; Kamide, Hideki

Proceedings of 2016 International Congress on Advances in Nuclear Power Plants (ICAPP 2016) (CD-ROM), p.2183 - 2192, 2016/04

Some auxiliary cooling systems to remove the decay heat of the core are under consideration for a sodium-cooled fast reactor, and two of the typical systems are primary reactor auxiliary cooling system (PRACS) and direct reactor auxiliary cooling system (DRACS). In this study, sodium experiments were conducted in order to confirm the applicability of the PRACS and DRACS under a situation assuming the severe accidents with core melting. The plant dynamics test loop was used for these experiments, which contains a simulated core, the PRACS and DRACS. The core melt situation is simulated by shutting off the inlet of subassemblies (S/A). The experimental results revealed the cooling process of the partially/completely inactive S/A and confirmed the long-term heat removal by the PRACS/DRACS.

Journal Articles

Investigation on thermal striping phenomena in Five Jets Modelled Water Test (FIWAT) simulating Sodium-cooled Fast Reactor

Aizawa, Kosuke; Kobayashi, Jun; Onojima, Takamitsu; Tanaka, Masaaki; Ohno, Shuji; Kamide, Hideki; Nagasawa, Kazuyoshi*

Proceedings of 10th International Topical Meeting on Nuclear Thermal Hydraulics, Operation and Safety (NUTHOS-10) (USB Flash Drive), 13 Pages, 2014/12

Thermal striping phenomenon is one of the most important issues in an advanced loop type sodium cooled reactor JSFR. Temperature fluctuation caused by mixing of fluids at different temperature from the control rod channels and the core fuel assemblies may touch the Core Instrument Plane (CIP) at bottom of the Upper Internal Structure (UIS) and cause high cycle thermal fatigue there. In JAEA, the 1/3-scaled Five Jets Water Test (FIWAT) has been performed in order to investigate thermal striping phenomena around the CIP. In the FIWAT, the test section was simulating a control rod channel, adjacent four fuel subassemblies and a part of the CIP. The flow rate ratio and the absolute velocity of hot jets as the reference experimental condition were equal to that of the JSFR and a third of JSFR, respectively. In the experiment, it was shown that the fluid temperature fluctuation characteristics around the structure depended on the flow rate ratio. The temperature fluctuation which showed sudden decrease and recovery like a spike form was intermittently observed in the fluid near the structure. The amplitude of such spike-like temperature fluctuation in the fluid was much mitigated on the structure surface.

JAEA Reports

Experimental study on thermal stratification phenomena in compact reactor vessel of sodium cooled fast reactor; Evaluation on stratification interface behavior under natural circulation condition

Hagiwara, Hiroyuki; Kimura, Nobuyuki*; Onojima, Takamitsu; Nagasawa, Kazuyoshi*; Kamide, Hideki; Tanaka, Masaaki

JAEA-Research 2014-014, 178 Pages, 2014/09

JAEA-Research-2014-014.pdf:53.12MB

Thermal stratification in the upper plenum is one of the most important issues of a reactor vessel in sodium cooled fast reactor. The steep temperature gradient across the stratification interface may cause the thermal load against the reactor vessel wall. In this study, the water experiment was carried out using the 1/11 scale upper plenum model of the Japan sodium-cooled fast reactor (JSFR) in order to evaluate the thermal stratification under the natural circulation condition and a direct heat exchanger (DHX) operation condition. The temperature gradient under the natural circulation condition was approximately 1/3 times smaller than that under the forced circulation condition. In the DHX operation case, the steep temperature gradient occurred in the lower region of upper plenum due to the cold fluid from the outlet of DHX.

Journal Articles

Effects of fluid viscosity on occurrence behavior of vortex cavitation; Vortex structures and occurrence condition

Ezure, Toshiki; Ito, Kei; Kimura, Nobuyuki; Onojima, Takamitsu; Kamide, Hideki; Kameyama, Yuri*

Proceedings of 15th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-15) (USB Flash Drive), 12 Pages, 2013/05

An experimental study on vortex cavitation was carried out in a cylindrical water tank to clarify how the viscosity of fluid influences on vortex cavitation occurrences. Vertical and horizontal velocity distributions were obtained under several experimental conditions, where the kinematic viscosity of water and the velocity of suction flow were varied as parameters. As the results, the flow patterns and the vortex structures, such as the circulation around the vortex, were grasped. And also, the acceleration behavior of vortex from the bottom of tank towards the intake of suction nozzle was clarified. Then, the occurrence map of vortex cavitation was also improved by using the present experimental data.

Journal Articles

Fundamental behavior of vortex cavitation in a 1/22 scaled upper plenum model of sodium-cooled fast reactor; Influences of kinematic viscosity and system pressure

Ezure, Toshiki; Ito, Kei; Onojima, Takamitsu; Kimura, Nobuyuki; Kamide, Hideki

Proceedings of 8th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-8) (USB Flash Drive), 7 Pages, 2012/12

In this study, water experiments were performed in the 1/22 scaled upper plenum model of JSFR. Occurrence behavior of vortex cavitation was grasped quantitatively by means of the visualization and image analyses under several conditions of kinematic viscosity $$nu$$) and pressure ($$P$$). The experimental results showed that the vortex cavitation has dependence on the variation of $$nu$$ and P. The increase of $$nu$$ at least in the present small model, leaded to the restriction of cavitation as assumed by Burgers model. And also, the restriction level of vortex cavitation according to the increase $$P$$ was smaller than the evaluation using cavitation factor.

Journal Articles

Experimental study on influence of fluid viscosity on occurrences of cavitation due to sub-surface vortex

Ezure, Toshiki; Ito, Kei; Kimura, Nobuyuki; Onojima, Takamitsu; Kamide, Hideki

Kyabiteshon Ni Kansuru Shimpojiumu (Dai-16-Kai) Koen Rombunshu (USB Flash Drive), 6 Pages, 2012/11

A fundamental water experiment was performed in the cylindrical tank geometry to clarify the influences of fluid viscosity on the vortex cavitation. The fluid temperature was varied from 10 $$^{circ}$$C to 80 $$^{circ}$$C to control the kinetic viscosity $$nu$$ of fluid from 1.3$$times$$10$$^{-6}$$ to 3.7$$times$$10$$^{-7}$$ m$$^{2}$$/s. The occurrences of vortex cavitation were detected by the visualization measurement and image analysis. The experimental results showed that the influence of $$nu$$ was obvious under the large $$nu$$ conditions, while the influence became smaller according to the decrease of $$nu$$. Then, the normalized circulation, $$Gamma$$$$^{*}$$ was installed as an evaluation parameter based on the Burgers Model. As the results, it was observed that occurrences of vortex cavitation in the present geometry could be marshaled on a map by employing $$Gamma$$$$^{*}$$ and cavitation factor.

Journal Articles

Experimental study on thermal stratification in a reactor vessel of innovative sodium cooled fast reactor; Characteristics of stratification interface under natural circulation operation

Kimura, Nobuyuki; Onojima, Takamitsu; Kamide, Hideki

Proceedings of 9th International Topical Meeting on Nuclear Thermal-Hydraulics, Operation and Safety (NUTHOS-9) (CD-ROM), 12 Pages, 2012/09

In the Japan Sodium-cooled Fast Reactor, thermal stratification phenomena occur in the reactor vessel during scram transient. In the study, the characteristics of stratification interface were investigated under the natural circulation operation during the scram transient using the 1/11th scale upper plenum model. The experimental results showed that the temperature gradient under the natural circulation operation was reduced to 1/2.6-1/6.2 in comparison with that under the forced circulation operation.

Journal Articles

The Sodium oxidation reaction and suppression effect of sodium with suspended nanoparticles; Growth behavior of dendritic oxide during oxidation

Nishimura, Masahiro; Nagai, Keiichi; Onojima, Takamitsu; Saito, Junichi; Ara, Kuniaki; Sugiyama, Kenichiro*

Journal of Nuclear Science and Technology, 49(1), p.71 - 77, 2012/01

 Times Cited Count:3 Percentile:69.44(Nuclear Science & Technology)

Oxidation in the early stage of sodium combustion is especially important regarding the aspect of reaction continuity. The purpose of this study is to understand the sodium reaction precisely in order to apply the knowledge of the sodium reaction to promoting further safety of FRs.

JAEA Reports

Development of sodium small leak detection technique Preliminary experimental study on sodium aerosol detection sensitivity using laser induced breakdown spectroscopy

Nagai, Keiichi; Nagai, Keiichi; Otaka, Masahiko; Miyakoshi, Hiroyuki; Onojima, Takamitsu

JNC-TN9400 2003-058, 35 Pages, 2003/05

JNC-TN9400-2003-058.pdf:1.15MB

A preliminary examination was carried out for evaluation of the detection sensitivity of Laser Sodium Leak Detector (LLD) based on a principle of Laser Induced Breakdown Spectroscopy (LIBS). Evaluation criteria and examination conditions were planned based on the results of preliminary experiments.The main results are as follows:(1) Signal intensity of LLD was obtained with parameter of sodium concentration in combustion aerosols. The signal intensity in the combustion aerosols was nearly equivalent to that in case of sodium mist using carrier gas of nitrogen. It was shown that LLD was effective to detect sodium in the combustion aerosols.(2) Diameter or chemical component of sodium aerosols are one of significant factors for the detection sensitivity of LLD. Preliminary experiments were carried out with parameters of humidity, oxygen concentration, and pressure of carrier gas. The obtained experimental data of a few cases showed that influence of these parameters was limited on the detection sensitivity of LLD.3) Based on the preliminary experimental results, main conditions of a sensitivity evaluation test plan were decided for LLD.

JAEA Reports

Dismantling and sodium removal of the intermediate heat exchanger(IHX) at the 50MW steam generator test facility

Gunji, Minoru; Yamamoto, Shimpei; Onojima, Takamitsu

PNC-TN9450 98-009, 150 Pages, 1998/06

PNC-TN9450-98-009.pdf:12.01MB

None

Oral presentation

Study on chemical reactivity control of liquid sodium, 5; Properties of nano-fluid

Saito, Junichi; Ara, Kuniaki; Nagai, Keiichi; Nishimura, Masahiro; Onojima, Takamitsu; Sugiyama, Kenichiro*; Zhang, Z.*; Kitagawa, Hiroshi*; Nakano, Haruyuki*; Oka, Nobuki*; et al.

no journal, , 

no abstracts in English

Oral presentation

Oral presentation

Study on chemical reactivity control of liquid sodium, 8; Characteristic of fundamental reaction, 1

Nagai, Keiichi; Onojima, Takamitsu; Nishimura, Masahiro; Saito, Junichi; Ara, Kuniaki

no journal, , 

no abstracts in English

Oral presentation

Study chemical reactivity control of liquid sodium, 10; Evaluation of fundamental property

Onojima, Takamitsu; Nagai, Keiichi; Nishimura, Masahiro; Saito, Junichi; Ara, Kuniaki; Sugiyama, Kenichiro*

no journal, , 

no abstracts in English

Oral presentation

Study on chemical reactivity control of liquid sodium, 9; Characteristic of fundamental reaction, 2

Nishimura, Masahiro; Nagai, Keiichi; Onojima, Takamitsu; Saito, Junichi; Ara, Kuniaki

no journal, , 

no abstracts in English

Oral presentation

Characterization of liquid sodium suspending nano-particles, 2; Investigation of fundamental property

Onojima, Takamitsu; Nagai, Keiichi; Nishimura, Masahiro; Saito, Junichi; Ara, Kuniaki

no journal, , 

no abstracts in English

Oral presentation

Characterization of liquid sodium suspending nanoparticles, 1; Investigation of chemical reactivity

Nagai, Keiichi; Onojima, Takamitsu; Nishimura, Masahiro; Saito, Junichi; Ara, Kuniaki

no journal, , 

no abstracts in English

Oral presentation

Study on chemical reactivity control of liquid sodium, 13; Changes of fundamental property based on atomic interaction

Onojima, Takamitsu; Nagai, Keiichi; Nishimura, Masahiro; Saito, Junichi; Ara, Kuniaki; Sugiyama, Kenichiro*

no journal, , 

no abstracts in English

35 (Records 1-20 displayed on this page)