Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Kamiyama, Kenji; Isozaki, Mikio; Imahori, Shinji; Konishi, Kensuke; Matsuba, Kenichi; Sato, Ikken
JAEA-Research 2008-059, 33 Pages, 2008/07
JAEA-Research-2008-059.pdf:10.82MB
In CDA of LMFBR, molten core materials would discharge from the core region through the coolant paths. Rapid vaporization of the coolant by mixing of the molten core materials provides effective evacuation of the liquid coolant from the path and reduces significantly possibility of core-material freezing and blockage formation inside the paths. This characteristic enhances early discharge of molten-core materials and reduces possibility of severe re-criticality events. In this study, melt discharge experiments were conducted with a coolant channel simulating the discharge path with an enhanced length of the path compared with that of the realistic design structure. An alloy and water were used as simulant of the molten fuel and sodium respectively. This series of experiments showed that the discharge path can be entirely voided by vaporization of a part of the coolant at the initial melt discharge phase, followed by vapor expansion toward the end of the coolant channel. Furthermore, it was revealed that the condition where coolant void expansion started can be defined by melt-coolant sensible heats ratio and the heated height of the coolant. The heat balance evaluation during the coolant void expansion phase shows that the film condensation heat transfer should be considered. The coolant-void-expansion behavior in the discharge path of the realistic design condition was estimated based on an application of this knowledge to existing experiments with molten oxide and sodium.
Matsuba, Kenichi; Imahori, Shinji; Isozaki, Mikio
JNC TN9400 2004-051, 79 Pages, 2004/11
JNC-TN9400-2004-051.pdf:5.55MB
In a core disruptive accident of fast reactors, fuel escape from the reactor core is a key phenomenon for prevention of re-criticality with significant mechanical-energy release subsequent to formation of a large-scale fuel pool with high mobility. Therefore, it is effective to study possibility of early fuel escape through probable escape paths such as a control-rod-guide-tube space well before high-mobility-pool formation. The purpose of the present basic experimental study is to clarify the mechanism of fuel-escape under a condition expected in the reactor situation, in which some amount of coolant may be entrapped into the molten-fuel pool. The following results have been obtained through basic experiments in which molten Wood's metal (components: 60wt%Bi-20wt%Sn-20wt%In, density at the room temperature: 8700kg/m3, melting point: 78.8deg-C is ejected into an coolant channel filled with water. (1)In the course of melt ejection, a small quantity of coolant is forced to be entrapped into the melt pool as a result of thermal interactions leading to high-pressure rise within the coolant channel. (2)Melt ejection is accelerated by pressure build-up which results from vapor pressure of entrapped coolant within the melt pool. (3)Average melt-ejection rate tends to increase in lower coolant-subcooling conditions, in which pressure build-up within the melt pool is enhanced. These results indicate a probability of a phenomenon in which melt ejection is accelerated by entrapment of coolant within a melt pool. Through application of the mechanism of confirmed phenomenon into the reactor condition, it is suggested that fuel escape is enhanced by entrapment of coolant within a fuel pool.
Matsuba, Kenichi; Imahori, Shinji;
P.313(2004), 313 Pages, 2004/10
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.
Matsuba, Kenichi; Imahori, Shinji; Isozaki, Mikio
JNC TN9400 2003-001, 50 Pages, 2003/03
JNC-TN9400-2003-001.pdf:2.14MB
It is effective to demonstrate a rapid and massive relocation of molten fuel from the reactor core at an early stage of the core disruptive accident (CDA) in fast breeder reactors for elimination of the re-criticality issue in which meaningful mechanical energy release is concemed. The purpose of the present study is to clarify individual phenomena related to a fuel discharge behavior from the reactor core. In the present study, a series of experiments with simulant materials has been carried out. In the experiments, simulant of molten fuel (Wood's Metal: density
8500kg/m
, melting point 78.8
C) is injected into a coolant channel (water-filled) simulating the discharge path (e.g. control rod guide tube) from its side wall. In the previous report, it has been clarified that void development leading to enhanced fuel relocation is initiated by a sufficient reduction of coolant subcooling in the vicinity of the melt injection site, and that an early initiation of void development is highly probable under the reactor condition (MOX fuel/sodium coolant). In this report, dependency of void development behavior on related parameters to the reactor condition is analyzed from the experimental data. The following results have been obtained through the present experiments. (1)It was confirmed under a condition with high pressure loss at the upper part of a coolant channel that coolant void is forced to develop downward up to the lower plenum located under the coolant channel. The experimental fact indicates advantage of a reactor design with large pressure loss in the upper part of a fuel discharge path for enhanced fuel relocation. (2)The injection amount of melt enthalpy necessary to initiate void development tends to be constant, irrespective of its injection rate or melt/coolant mixing time. On the other hand, the injection amount of melt enthalpy strongly depends on coolant subcooling. This tendency suggests that initiation of void development ...
Kamiyama, Kenji; Isozaki, Mikio; Imahori, Shinji; Sato, Ikken
no journal, ,
no abstracts in English
Isozaki, Mikio; Imahori, Shinji; Kamiyama, Kenji; Sato, Ikken
no journal, ,
no abstracts in English