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; Tobita, Yoshiharu; ; ; Ishida, Masayoshi; ;
JNC TN9400 2001-056, 64 Pages, 2001/03
JNC-TN9400-2001-056.pdf:2.66MB
The Phase I of the Feasibility Studies on Commercialized Fast Breeder Reactor Cycle System is being performed for two years from Fisca1 Year (FY) 1999. This report describes the results obtained in FY 1999 as an interim report of the Phase I from the viewpoint of reactor safety for various FBR plant condidates. The objectives of the study are to understand the safety charaeteristics of advanced fuel and to examine the fulfillment of the target level of reactor safety in each plant concept. The items studied are the recriticality characteristics of degraded core for various core concepts, investigation of the measures for avoiding recriticality event, safety analysis of sodium cooled MOX fueled cores, target of void worth in core design for sodium cooled reactors, and investigation of core disruptive accident sequences in various reactor concepts. The results of this study have been reflected properly to the core and plant design. In FY 2000, the study will be continued along with the progress of the plant design in order to prepare for the judgment of the candidates from the viewpoint of reactor safety.
Tobita, Yoshiharu; ; Fujita, Satoshi
JNC TN9400 2000-082, 24 Pages, 2000/07
JNC-TN9400-2000-082.pdf:0.92MB
The feasibility study for the commercialization of fast reactors is underway in Japan Nuclear Cycle Development Institute, aiming at the achievement of the economic competitiveness, making full use of the natural resources, reduction of the environmental impact and the assurance of the nuclear non-proliferation and safety. This report shows the results of the analysis of the core-disruptive accident in lead-cooled reactor, which was performed to clarify the safety aspects of the heavy metal cooled fast reactors. The analysis showed that the high boiling point and density of lead made the event progression in the core-disruptive accident genuine and mild and prohibited the energetic re-criticality. Therefore, the dedicated designs to avoid the energetic recriticality, such as the fuel sub-assembly with inner duct and/or the fuel sub-assembly with partial removal of axial blanket pellet are not necessary in the lead-cooled fast reactor. On the other hand, the importance of the integrity of the primary boundary, structures in the reactor vessel, and decay heat removal system against the high temperature lead was pointed out from the viewpoint of the in-vessel retention of the accident.
Cao, X.; Tobita, Yoshiharu
JNC TN9400 2000-100, 52 Pages, 2000/06
JNC-TN9400-2000-100.pdf:1.48MB
The QUEOS,an experiment of the premixing phase of fuel coolant interactions(FCls), in which several kilograms of solid molybdenum spheres with low temperature (Q-8 300K) and high temperature (Q-12 2300K) are released into water, are simulated to evaluate the drag correlations between the fuel and coolant liquid on the mixing region in FCls, by SIMMER-III code, in which lshii's drag correlations in dispersed two-Phase flow are employed. The calculated results suggest that the momentum exchange between the spheres and coolant liquid is overestimated in the hot sphere cases by employing the current drag conrrelations. The difference of the advancement of the sphere cloud between experiments and simulations induced by the drag coefficients is discussed through the change of the multiplier of the drag coefficients.
JNC TN9400 2000-038, 98 Pages, 2000/04
JNC-TN9400-2000-038.pdf:7.49MB
As an effort in the feasibility study on commercialized Fast Breeder Reactor cycle systems, an evaluation of the measures to prevent the energetic re-criticality in sodium-cooled large MOX core, which is one of the candidates for the commercialized reactor, has been performed. The core disruptive accident analysis of Demonstration FBR showed that the fuel compaction of the molten fuel by radial motion in a large molten core pool had a potential to drive the severe super-prompt re-criticality phenomena in ULOF sequence. ln order to prevent occurrence of the energetic re-criticality, a subassembly with an inner duct and the removal of a part of LAB are suggested based on CMR (Controlled Material Relocation) concept. The objective of this study is the comparison of the effectiveness of CMR among these measures by the analysis using SIMMER-III. The molten fuel in the subassembly with inner duct flows out faster than that from other measures. The subassembly with inner duct will work effectively in preventing energetic re-criticality. Though the molten fuel in the subassembly without a part of LAB flows out a little slower, it is still one of the promising measures. However, the UAB should be also removed from the same pin to prevent the fuel re-entries into the core region due to the pressurization by FCl below the core, unless it disturbs the core performance. The effect of the axial fuel length of the center pin to CMR behavior is small, compared to the effect of the existence of UAB.
JNC TN9400 2000-102, 40 Pages, 2000/03
JNC-TN9400-2000-102.pdf:1.03MB
There are many models for dryout in debiris beds and various conditions under which these models are applicable. For a reliable analysis of post-accident heat remova1 (PAHR), it is important that characteristics and applicability of each model should be made clear. ln this report formulation of the models for dryout and applicabilily of them are studied through comparing with experimental data. A new model for dryout prediction is also discussed here. lt is difficult to predict the dryout power especially for a relatively shallow bed using a conventional model for channeled beds. The new model, which is based on the one-dimensional model derived by Lipinski, has permeability of channels in the goveming equation, and enables us to predict the dryout power for relatively shallow beds. The following conclusions are derived from comparing the predicted dryout power with experimental data. (1)The model for series heat removal is applicable to a packed bed while the DEBRIS-MD underestimates the dryout power for it. (2)Either the original model assuming channel formation on the top of the bed or the modified model is applicable to a relatively deep bed with channels. (3)For a relatively shallow bed with channels, the dryout power predicted by the modified model agrees with the experimental data in comparison with other models.
; ; *;
JNC TN9400 2000-043, 23 Pages, 2000/03
ln the feasibility study on commercialized fast breeder reactor (FBR) cycle systems conducted in JNC, it is required for candidate FBR plants that the level of safety should be enhanced so as to assure: (1)Comparative or superior safety level to that of light water reactors (LWRs), and (2)releaf of the public from anxiety about potential nuclear hazard. Adopting Passive safety characteristics is one of the measures. To attain the above safety objective, we considered implication of the basic safety principles for nuclear power plants that were created by the international nuclear safety advisory group of IAEA. The way to relieve from the anxiety was also taken into account. Then a definite safety objective was set from the standpoint of prevention of core disruptive accident (CDA). Furthermore, as a definite safety goal relating to reactor coresafety, elimination of re-criticality issues under CDA was set by considering characteristics of FBR in comparison with those of LWR. To examine measures for elimination of re-criticality issues, we developed a quick method to estimate possibility of re-criticality under CDA, by drawing a map about criticality characteristics under CDA in various degraded cores. Then hopeful measures were proposed for elimination of re-criticality issues in sodium-cooled FBR with mixed-oxide fuel. Molten fuel discharge behavior of their measures was preliminarily analyzed. We concluded that discharge capability of "a subassembly with an internal duct" was effective, and that "partial removal of axial blanket" was also effective as one of the measures though it has small effect on core performance.