Development of failure mitigation technologies for improving resilience of nuclear structures, 1; Failure mitigation by passive safety structures without catastrophic failure

Kasahara, Naoto*; Yamano, Hidemasa; Nakamura, Izumi*; Demachi, Kazuyuki*; Sato, Takuya*; Ichimiya, Masakazu*

Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 8 Pages, 2024/03

In this study, we propose failure mitigation methods by application of passive safety structures. The idea of the passive safety structures was applied to next generation fast reactors under high temperature conditions and excessive earthquake conditions.

Parametric design study about seismic isolation system for fast reactor JSFR

Kawasaki, Nobuchika; Yamamoto, Tomohiko; Fukasawa, Tsuyoshi*; Okamura, Shigeki*

Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 9 Pages, 2015/07

Japanese seismic conditions are getting severer and natural frequencies of components are getting lower due to the enlargements of components' size, therefore response accelerations and buckling margins of reactor vessels were parametrically surveyed with attention to thicknesses, diameters, and isolation frequencies for reviewing necessary isolation specification. RV installed floor responses and buckling margins were calculated based on this seismic condition. Expansion characteristic of isolation system was evaluated by parametric acceleration response analyses. Japanese seismic design condition may become severer than present one, and a natural frequency of main component may decrease. However based on the buckling margin with present plant specifications and the expansion characteristic of isolation system, the advanced isolation system with 8Hz vertical natural frequency was selected as the isolation system of JSFR at still present occasion.

Optimization study on the normal conducting center post for the low aspect ratio tokamak reactor

Song, Y.*; Nishio, Satoshi

Fusion Engineering and Design, 72(4), p.345 - 362, 2005/01

https://doi.org/10.1016/j.fusengdes.2004.08.002

This paper presents detailed optimization results and design windows for the engineering design of normal conducting (NC) center post based on the analysis of thermal-hydraulic, static stress and critical buckling. At the same time a method to reduce the stress in the center post have been proposed, which can be applied to enhance the possibility of normal conducting center post in the future power plants. When the method of improvement for reducing the stress is applied in the system of the center post, the maximum magnet field can be improved from 8.6T to 15T.

Development and the results for the control rods in MK-II core of experimental fast reactor JOYO

Miyakawa, Shunichi; ; Soga, Tomonori

PNC TN9410 97-068, 113 Pages, 1997/07

PNC-TN9410-97-068.pdf:3.97MB

Since the first control rod design for the Joyo Mk-II core (about twenty years ago), there have been several challenging improvements; for example, a helium venting mechanism and a flow induced vibration prevention mechanism. Forty-four control rods with these various modifications have been fabricated. To date, thirty-four have been irradiated and the sixteen have been examined, This experience and effort has produced fruitful results: (1)Efficiency and reliability of the diving-bell type Helium venting mechanism (2)Efficiency of the flow induced vibration prevention mechanism (3)Efficiency of the improvement for scram damping mechanism (4)Clarification of absorvber-pellet-cladding-mechanical-interaction (ACMI)phenomena and preventive methods The fourth result listed above has been a subject of investigation for fifteen years in several countries, that is a main phenomena to dominate control rod life time. The results of this investigation of ACMI in absorber elements are summarized below: (a)In five of Joyo Mk-II control rods, cladding cracks were found in fifteen of the elements. These cracks were caused by a acceleration ACMI, due to BC fragments relocation. They occurred over a wide burnup range from 5E+26 Cap./m to 45E+26Cap./m in a nearly typical provability distribution. The cladding cracked because of its low ductility (approximately 1/4 lower than the uniform elongation of usual tensile testing for irradiated 316SS cladding) due to neutron irradiation and the ultra slow ACMI induced strain rate. (b)In this case the crack growth rate is extremely slow and the ACMI induced cracking in absorber elements do not influence either the reactor or plant operations. It is on this basis that a strict limitation to avoid the cladding crack is not necessary. According1y, it is suggested that a realistic design standard should consider the ACMI phenomena and the burnup limit be based on the nominal base calculation for average plastic strain use ...

Estimation of creep buckling deformation under external pressure at elevated temperature

Kaji, Yoshiyuki; Ioka, Ikuo; ; *

J. Pressure Vessel Technol., 118(2), p.194 - 197, 1996/05

https://doi.org/10.1115/1.2842180

no abstracts in English

Analytical evaluation of the effect of interaction between shear and bending on the buckling strength of cylindrical shells under shear/bending load

Tsukimori, Kazuyuki

PNC TN9410 95-042, 313 Pages, 1995/02

PNC-TN9410-95-042.pdf:15.49MB

Prevention of the buckling under seismic loading is an important issue, since vessels and piping components of Fast Breeder Reactor(FBR) plants are generally thin wall structures. A research and development on the shear/bending buckling of thin-walled cylindrical shells as the basic structure models has been proceeded since 1987-FY in order to rationalize the safety margin in the structural design of FBR components and to realize the sophistication of design. As the result, an analytical evaluation method of the buckling strength of cylindrical shells under shear loading, which is avalable within a wide range of dimensions and for various materials, has been proposed. Present study is located on the extension of this R&D and is focused on the effect of the interaction between shear and bending loading which is not considered in the previous buckling strength evaluation method. The examination of the interaction effects are implemented from the following three points of view. (1)The maximum values of stress indeces such as the difference between two principal stresses and their location. (2)The investigation of the interaction effects in the transition region between shear mode dominant buckling and bending mode dominant one based on the elastic buckling eigen-value analysis. (3)Development of an analytical evaluation method of the shear-bending interaction due to the propagation of plasticity, based on the idea that the shear stress and the axial stress are not dependent each other in the elastic-plastic region.Obtained results are followings. (1)No changes are found in the maximum values of the principal stress difference or the equivalent stress and their locations between the pure shear or the pure bending case and the shear and bending combined case. (2)Though a little effect due to the interaction between shear and bending loads is observed from elastic eigen value analyses, the effect of the interaction due to plasticity is dominant in the inelastic ...

None

Nogami, Yoshitaka; ; Tobita, Noriyuki; Obata, Shinichi; ;

PNC TN8410 93-228, 66 Pages, 1993/07

PNC-TN8410-93-228.pdf:2.3MB

None

Dynamic buckling analysis of liquid-filled shells with imperfections

Tsukimori, Kazuyuki

PNC TN9410 91-393, 152 Pages, 1992/12

PNC-TN9410-91-393.pdf:2.47MB

There can be some imperfections in actual shell structures. In order to achievehighuality in manufacturing structures, the imperfections should be restricted within reonable tolerance ranges through design or examinations. In this paper, the governingquations to solve the dynamic buckling problems of shell structures, which consider namic fluid-structure interaction, model coupling in both axial and circumferential rections, and circumferential imperfections,are derived by using Variationl PrinciplApplying finite element method (FEM) to these equations, the matrix equation of motiois formulated to apply to computer analyses. Therough the implementation of some exames, the influence of the amplitude and pattern of imperfections on the buckling streth is descussed. Also, the validity and applicability of this method to the design ofhell structures is discussed.

Finite element dynamic bifurcation buckling analysis of torispherical head of BWR containment vessel subjected to internal pressure

*; *; *; *; Soda, Kunihisa

Transactions of the 11th Int. Conf. on Structural Mechanics in Reactor Technology, Vol. J, p.153 - 158, 1991/08

no abstracts in English

Torsional buckling analysis of bellows

Tsukimori, Kazuyuki*; Iwata, Koji; *; *

PNC TN9410 88-136, 69 Pages, 1988/08

PNC-TN9410-88-136.pdf:3.54MB

PNC has proceeded the feasibility study in respect of the bellows expansion joint for FBR pipings because the expansion point is an effective measure to rationaliz evarious piping systems. Essencially bellows should be designed not to be subjected to torsional loads and usually bellows is protected by hardware not to move in the direction of torsion. Actually, however, there are some sources of torsional deformation, e.g. the clearance of bearing structure, the deformation of hardware etc. Therefore it must be available to limit the torsional displacement of bellows clearly in view of improvement of reliability in design and fabrication. The torsional buckling behavior of bellows was investigated with both theory and numerical analysis. The new element, 3-mode axisy㎜etric shell harmonic series element (NAXSHEL3) which was developed in the FINAS fimite element computer progran, was used for the buckling eigen valve analysis. The numerical solutions corresponded to the theory very well in a wide range of dimensions and number of convolutions. Besed on these results the framework of the design rule related to the torsion of bellows was drawn.