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Journal Articles

An Experimental study on the fragmentation and accompanying cooling behaviors of a simulated molten oxide fuel penetrating into a sodium pool

Matsuba, Kenichi; Kamiyama, Kenji; Toyoka, Junichi; Zuev, V. A.*; Kolodeshnikov, A. A.*

Proceedings of 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17) (USB Flash Drive), 11 Pages, 2017/09

To clarify jet fragmentation and accompanying cooling behaviors of molten core materials discharged into sodium, results of the out-of-pile experiments with a simulant material (Al$$_{2}$$O$$_{3}$$) were analyzed. The results clarified that while Al$$_{2}$$O$$_{3}$$ jets were entirely fragmented into smaller particles during their penetration to several tenths of a meter in depth of sodium, an additional significant distance was needed to cool down the particles to the degree that thermal loading on the steel structures could be neglected. Based on the results, it is concluded that in terms of the reduction of thermal load on the lower structures in the reactor vessels, the cooling distance after fragmentation should be treated.

Journal Articles

Improvements to the simmer code model for steel wall failure based on EAGLE-1 test results

Toyoka, Junichi; Kamiyama, Kenji; Tobita, Yoshiharu; Suzuki, Toru

Proceedings of 10th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-10) (USB Flash Drive), 7 Pages, 2016/11

Journal Articles

A Recent experimental program to evidence in-vessel retention by controlled material relocation during core disruptive accidents of sodium-cooled fast reactors

Matsuba, Kenichi; Kamiyama, Kenji; Toyoka, Junichi; Zuev, V. A.*; Ganovichev, D. A.*; Kolodeshnikov, A. A.*

Proceedings of 10th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-10) (USB Flash Drive), 5 Pages, 2016/11

Molten fuel discharge through control rod guide tubes (CRGTs) is a key process that dominates the termination of core disruptive accidents of sodium-cooled fast reactors, since fuel dispersion from the core contributes to the achievement of both deeper subcriticality in the degraded core and formation of coolable debris bed. Within a framework of a collaborative research program between Japan Atomic Energy Agency and National Nuclear Center of the Republic of Kazakhstan, called EAGLE program, a new experimental program has been started with out-of-pile experiments to clarify the fuel discharge through CRGTs. This paper presents the status of the new program, including experimental results obtained so far.

Journal Articles

Experimental discussion on fragmentation mechanism of molten oxide discharged into a sodium pool

Matsuba, Kenichi; Kamiyama, Kenji; Toyoka, Junichi; Tobita, Yoshiharu; Zuyev, V. A.*; Kolodeshnikov, A. A.*; Vassiliev, Y. S.*

Mechanical Engineering Journal (Internet), 3(3), p.15-00595_1 - 15-00595_8, 2016/06

To develop a method for evaluating the distance for fragmentation of molten core material discharged into sodium, the particle size distribution of alumina debris obtained in the FR tests was analyzed. The mass median diameters of solidified alumina particles were around 0.3 mm, which are comparable to particle sizes predicted by hydrodynamic instability theories such as Kelvin-Helmholtz instability. However, even though hydrodynamic instability theories predict that particle size decreases with an increase of Weber number, such the dependence of particle size on We was not observed in the FR tests. It can be interpreted that this tendency of measured mass median suggests that before hydrodynamic instabilities sufficiently grow to induce fragmentation, thermal phenomena such as local coolant vaporization and resultant vapor expansion accelerate fragmentation.

Journal Articles

Experimental discussion on fragmentation mechanism of molten oxide discharged into a sodium pool

Matsuba, Kenichi; Kamiyama, Kenji; Toyoka, Junichi; Tobita, Yoshiharu; Zuev, V. A.*; Kolodeshnikov, A. A.*; Vasilyev, Y. S.*

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05

To develop a method for evaluating the distance for fragmentation of molten core material discharged into sodium, the particle size distribution of alumina debris obtained in the FR tests was analyzed. The mass median diameters of solidified alumina particles were around 0.4 mm, which are comparable to particle sizes predicted by hydrodynamic instability theories such as Kelvin-Helmholtz instability. However, even though hydrodynamic instability theories predict that particle size decreases with an increase of Weber number, such the dependence of particle size on We was not observed in the FR tests. It can be interpreted that the tendency of measured mass median diameters (i.e., non-dependence on Weber number) suggests that before hydrodynamic instabilities sufficiently grow to induce fragmentation, thermal phenomena such as local coolant vaporization and resultant vapor expansion accelerate fragmentation.

Journal Articles

An Experimental study on heat transfer from a mixture of solid-fuel and liquid-steel during core disruptive accidents in Sodium-Cooled Fast Reactors

Kamiyama, Kenji; Konishi, Kensuke; Sato, Ikken; Toyoka, Junichi; Matsuba, Kenichi; Suzuki, Toru; Tobita, Yoshiharu; Pakhnits, A. V.*; Vityuk, V. A.*; Vurim, A. D.*; et al.

Proceedings of 10th International Topical Meeting on Nuclear Thermal Hydraulics, Operation and Safety (NUTHOS-10) (USB Flash Drive), 8 Pages, 2014/12

Journal Articles

Experimental studies on the upward fuel discharge for elimination of severe recriticality during core-disruptive accidents in sodium-cooled fast reactors

Kamiyama, Kenji; Konishi, Kensuke; Sato, Ikken; Toyoka, Junichi; Matsuba, Kenichi; Zuyev, V. A.*; Pakhnits, A. V.*; Vityuk, V. A.*; Vurim, A. D.*; Gaidaichuk, V. A.*; et al.

Journal of Nuclear Science and Technology, 51(9), p.1114 - 1124, 2014/09

AA2013-0469.pdf:1.18MB

 Times Cited Count:9 Percentile:62.74(Nuclear Science & Technology)

Journal Articles

Study on mechanism of inner duct wall failure within fuel subassembly during core disruptive accidents in an LMFBR; Results of parametric analyses for heat transfer

Toyoka, Junichi; Endo, Hiroshi*; Tobita, Yoshiharu; Takahashi, Minoru*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 13(2), p.35 - 50, 2014/05

In the design of future sodium-cooled fast reactor, a design measure to prevent severe re-criticality events even in case of core disruptive accidents is considered. This design adopts inner duct within the fuel sub-assembly that should allow molten fuel ejection out of the core region. The effectiveness of this design is dependent on failure time of the duct and it depends significantly on heat transfer from the melting core materials to the duct. In the previous study by the authors, heat transfer from molten fuel/steel mixture to the inner duct was evaluated with a computer model simulation for an in-pile experiment performed in IGR (Impulse Graphite Reactor) focusing on demonstration of the design effectiveness. In the present study, possible uncertainties in the assumption and model parameters in the previous study were evaluated so that validity of the main conclusion of the previous study could be confirmed and re-enforced. This confirmation consisted of evaluation of necessary fuel-to-steel heat transfer area, effect of hydrodynamic fragmentation of steel droplets, steel-vapor condensation heat transfer onto the duct surface and fuel crust formation. Furthermore, possible effect of variation in fuel designs and transient scenarios to the heat transfer was evaluated changing steel volume fraction as the initial boundary conditions. It was concluded that the previous study was appropriate in representing the realistic situation and the conclusions in the previous study were enforced. An additional set of analysis showed that possible under-estimation of heat transfer from fuel/steel mixture to the duct could be enhanced with a condition where steel volume fraction is less. Future model improvement is preferable for this characteristic.

Journal Articles

A Study on mechanism of early failure of inner duct wall within fuel subassembly with high heat flux from molten core materials based on analysis of an EAGLE experiment simulating core disruptive accidents in an LMFBR

Toyoka, Junichi; Endo, Hiroshi*; Tobita, Yoshiharu; Ninokata, Hisashi*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 12(1), p.50 - 66, 2013/03

In the design of JSFR (Japan Sodium-cooled Fast Reactor), a design measure (FAIDUS: Fuel sub-Assembly with an Inner DUct Structure) is considered to prevent severe re-criticality events even in case of core disruptive accidents by molten fuel ejection out of the core region through the duct equipped within the fuel subassembly. Confirming principle effectiveness of such design measure is important. In this study, systematic heat transfer behavior of the ID1 test, which was conducted in IGR (Impulse Graphite Reactor) in Republic of Kazakhstan, was evaluated applying a heat conduction code TAC2D and a reactor safety analysis code SIMMER-III focusing on the clarification of heat transfer from high-temperature mixture of molten fuel and steel to the duct. As a result, the duct failure by high heat flux from the mixture was identified as one of an important mechanism of early duct failure in FAIDUS. It was also suggested from this study that the high heat flux from the mixture is caused by the direct contact of molten steel without the presence of fuel crust on the duct wall. Based on these findings, it is judged that the mechanism of early duct failure with high heat flux obtained in the ID1 test satisfies the required condition to FAIDUS, i.e., the inner duct of FAIDUS should fail at an early phase of core disruptive accident in advance to wrapper tube failure so that produced molten fuel can escape from the core region, and it supports feasibility of the FAIDUS concept.

Journal Articles

Experimental studies on upward fuel discharge during core disruptive accident in sodium-cooled fast reactors

Kamiyama, Kenji; Konishi, Kensuke; Sato, Ikken; Toyoka, Junichi; Matsuba, Kenichi; Zuyev, V. A.*; Pakhnits, A. V.*; Vurim, A. D.*; Gaidaichuk, V. A.*; Kolodeshnikov, A. A.*; et al.

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

In order to eliminate energetics potential in the case of postulated core disruptive accidents (CDAs) of sodium-cooled fast reactors, introduction of a fuel subassembly with an inner duct structure has been considered. Recently, a design option which leads molten fuel to discharge upward is considered to minimize developmental efforts for the fuel subassembly fabrication. In this paper, a series of out-of-pile tests and one in-pile test were presented. The out-of-pile tests were conducted to investigate the effects of driving pressures on upward discharge, and the in-pile test was conducted to demonstrate a sequence of upward discharge behavior of molten-fuel. Based on these experimental results, it is concluded that the most of molten-fuel is expected to complete discharging upward before core melting progression, and thereby, introduction of the fuel subassembly with the upward discharge duct has the sufficient potential to eliminate energetics events.

Journal Articles

Experimental study on material relocation during core disruptive accident in sodium-cooled fast reactors; Results of a series of fragmentation tests for molten oxide discharged into a sodium pool

Matsuba, Kenichi; Kamiyama, Kenji; Konishi, Kensuke; Toyoka, Junichi; Sato, Ikken; Zuev, V. A.*; Kolodeshnikov, A. A.*; Vasilyev, Y. S.*

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

A series of fragmentation tests (FR tests) for molten oxide was conducted to obtain experimental knowledge on the distance for fragmentation of molten core material discharged into the lower sodium plenum. Approx. 7$$sim$$14 kg of molten alumina was discharged into a sodium pool (depth: 1.3 m, diameter: 0.4 m, temperature: approx. 673 K) through a duct (inner diameter: 40$$sim$$63 mm). The test results showed that the molten alumina was fragmented into particles within 1 m from the surface of the sodium pool. The estimated distances for fragmentation in the FR tests were roughly 60$$sim$$70% lower than the predictions by the existing representative correlation. The experimental knowledge confirms the possibility that the distance for fragmentation of the molten core material can be significantly reduced due to thermal interactions in the lower sodium plenum.

Journal Articles

Safety strategy of JSFR eliminating severe recriticality events and establishing in-vessel retention in the core disruptive accident

Sato, Ikken; Tobita, Yoshiharu; Konishi, Kensuke; Kamiyama, Kenji; Toyoka, Junichi; Nakai, Ryodai; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vassiliev, Y. S.*; et al.

Journal of Nuclear Science and Technology, 48(4), p.556 - 566, 2011/03

In the JSFR design, elimination of severe recriticality events in the Core Disruptive Accident (CDA) is intended as an effective measure to assure retention of the core materials within the reactor vessel. The design strategy is to control the potential of excessive void reactivity insertion in the Initiating Phase selecting appropriate design parameters such as maximum void reactivity on one hand, and to exclude core-wide molten-fuel-pool formation, which has been the main issue of CDA, with introduction of Inner Duct on the other hand. The effectiveness of these measures are reviewed based on existing experimental data and evaluations performed with validated analysis tools. It is judged that the present JSFR design can exlude severe power burst events.

Journal Articles

SIMMER-III analysis of eagle-1 in-pile tests focusing on heat transfer from molten core material to steel-wall structure

Toyoka, Junichi; Kamiyama, Kenji; Konishi, Kensuke*; Tobita, Yoshiharu; Sato, Ikken

Proceedings of 7th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-7) (CD-ROM), 7 Pages, 2010/11

In this study, the heat flux from the molten core materials to the outer surface of the inner duct (the pool-to-duct heat flux) was evaluated based on all the EAGLE-1 in-pile experiments available. Through the evaluation, it was understood that the pool-to-duct heat flux was so high in all the in-pile experiments that the duct wall failed without coolant boiling in its behind. It was also indicated that the presence of steel in the molten core mixture played a key role in this high heat flux. Application of the SIMMER-III code for these tests suggested that some model improvements were necessary to simulate pool-to-duct heat transfer behavior in a mechanistic way.

Journal Articles

The Result of a wall failure in-pile experiment under the EAGLE project

Konishi, Kensuke; Toyoka, Junichi; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vurim, A. D.*; Gaidaichuk, V. A.*; Pakhnits, A. V.*; et al.

Nuclear Engineering and Design, 237(22), p.2165 - 2174, 2007/11

 Times Cited Count:39 Percentile:92.6(Nuclear Science & Technology)

The WF (Wall Failure) test of the EAGLE program, in which $$sim$$2kg of uranium dioxide fuel-pins were melted by nuclear heating, was successfully conducted in the IGR of NNC/Kazakhstan. In this test, a 3mm-thick stainless steel (SS) wall structure was placed between fuel pins and a 10mm-thick sodium-filled channel (sodium gap). During the transient, fuel pins were heated, which led to the formation of a fuel-steel mixture pool. Under the transient nuclear heating condition, the SS wall was strongly heated by the molten pool, leading to wall failure. The time needed for fuel penetration into the sodium-filled gap was very short (less than 1 second after the pool formation). The result suggests that molten core materials formed in hypothetical LMFBR core disruptive accidents have a certain potential to destroy SS-wall boundaries early in the accident phase, thereby providing fuel escape paths from the core region. The early establishment of such fuel escape paths is regarded as a favorable characteristic in eliminating the possibility of severe re-criticality events.

Journal Articles

The Eagle project to eliminate the recriticality issue of fast reactors; Progress and results of in-pile tests

Konishi, Kensuke; Kubo, Shigenobu*; Sato, Ikken; Koyama, Kazuya*; Toyoka, Junichi; Kamiyama, Kenji; Kotake, Shoji*; Vurim, A. D.*; Gaidaichuk, V. A.*; Pakhnits, A. V.*; et al.

Proceedings of 5th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-5), p.465 - 471, 2006/11

no abstracts in English

Journal Articles

The Result of medium scale in-pile experiment conducted under the EAGLE-project

Konishi, Kensuke; Toyoka, Junichi; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vurim, A. D.*; Gaidaichuk, V. A.*; Pakhnits, A. V.*; et al.

Proceedings of Technical Meeting on Severe Accident and Accident Management (CD-ROM), 16 Pages, 2006/03

no abstracts in English

JAEA Reports

Pre-calculation of the Middle-Scale In-Pile Test in the EAGLE Project; 3-D Evaluation using the SIMMER-IV code

Toyoka, Junichi

JNC TN9400 2005-036, 73 Pages, 2005/08

JNC-TN9400-2005-036.pdf:1.76MB

In the in-pile part of this project, establishment of the test technique has been conducted along with the progress of the test program leading to the final step tests. Before the final step tests(three tests) with about 8kg of fuel melt formation, a middle-scale test (WF test) with about 2kg of fuel melt has been planned.The WF test aims at confirmation of techniques to form fuel melt with a scale of 1/4 that of the final step ones, to collect measurement data and acquisition of basic data related to initiation of the melt discharge from the core.In order to confirm appropriateness of the selected test condition on one hand, and to provide useful information for preliminary interpretation of the test results on the other hand, predictive evaluation using an analytical tool has been conducted. Through this study, following points were confirmed:- Through SIMMER-IV-code application representing appropriately the complicated three-dimensional test-section geometry, it was concluded that the selected test conditions were appropriate.- Through this study reflecting the knowledge obtained from the small-scale tests of the EAGLE project, it was concluded that the rather early steel melting and resultant steel segregation from fuel, which had been regarded as a possible concern, would be avoided.- Present study suggested that SS wall cooled by sodium from its behind could be strongly cooled by oscillatory movement of sodium leading to significantly delayed wall failure.- Test data such as failure time and location of both the SS wall facing the sodium channel and the adiabatic SS wall with heat transfer from the molten fuel pool, and cover gas pressure, it is expected that one can get useful knowledge on heat transfer within the pool and wall failure mechanism.

Oral presentation

EAGLE project; Experimental study on elimination of the Re-criticality issue during CDAs, 12; The Prompt result of in-pile large scale dry test

Konishi, Kensuke; Toyoka, Junichi; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vurim, A. D.*; Pakhnits, A. V.*; Gaidaichuk, V. A.*; et al.

no journal, , 

no abstracts in English

Oral presentation

EAGLE project; Experimental study on elimination of the Re-criticality issue during CDAs, 14; The Result and interpretation of in-pile middle scale test

Toyoka, Junichi; Konishi, Kensuke; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vurim, A. D.*; Pakhnits, A. V.*; Gaidaichuk, V. A.*; et al.

no journal, , 

no abstracts in English

Oral presentation

EAGLE project: Experimental study on elimination of re-criticality issue during CDAs, 15; The Result of the first in-pile integral test

Konishi, Kensuke; Toyoka, Junichi; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vurim, A. D.*; Gaidaichuk, V. A.*; Pakhnits, A. V.*; et al.

no journal, , 

no abstracts in English

34 (Records 1-20 displayed on this page)