Study on a unified criterion for preventing plastic strain accumulation due to long distance travel of temperature distribution

Okajima, Satoshi; Wakai, Takashi; Kawasaki, Nobuchika

Mechanical Engineering Journal (Internet), 4(5), p.16-00641_1 - 16-00641_11, 2017/10

http://doi.org/10.1299/mej.16-00641

Development of seismic isolation systems for sodium-cooled fast reactors in Japan

Kawasaki, Nobuchika; Watakabe, Tomoyoshi; Wakai, Takashi; Yamamoto, Tomohiko; Fukasawa, Tsuyoshi*; Okamura, Shigeki*

Proceedings of 2016 ASME Pressure Vessels and Piping Conference (PVP 2016) (Internet), 8 Pages, 2016/07

http://doi.org/10.1115/PVP2016-63437

Sodium-cooled Fast Reactors (SFRs) have components with thinner walls as compared with light water reactors, although Japan is an earthquake-prone country. Thus, seismic isolation systems have been conventionally employed in SFR system design to reduce seismic forces on the systems in Japan. Implementation of seismic design in the reactor core and buckling design in the reactor vessel requires 8 Hz (or less) vertical frequency's isolation system being applied. This paper introduces three isolation concepts to achieve the frequency. The isolation systems, which enable vertical 8 Hz natural frequency, comprise thicker laminated rubber bearings (TRBs). By combining coned disk springs with TRBs, vertical natural frequency is in a range from roughly 3 Hz to 5 Hz. Combining pneumatic springs to RBs and adding the rocking suppression system, vertical natural frequency becomes under 1 Hz. All isolation systems need horizontal damping like oil dampers. A vertical 8 Hz isolation system with TRBs and oil dampers is under development in Japan as a principal isolation concept. The reasons of choosing this system are its simplicity and the number of developing issues. Since TRBs and oil dampers are basic isolation elements, they can be applied to other isolation systems. The response acceleration of 5 Hz vertical isolation is 50% of that of 8 Hz based on the analytical survey. A series of static tests of coned disk springs was carried out to confirm design equations. Based on these knowledge, 5 Hz vertical isolation system with TRBs and the coned disk springs can be designed. The response acceleration of 1 Hz vertical isolation is 10% of that of 8 Hz. A rocking suppression system was studied in the past, and the further simplification of this system is the largest challenge for this concept. These three isolation concepts are isolation candidates for SFRs in Japan. To obtain enough seismic margins for each plant site, these isolation systems need to be developed.

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.

Development on rubber bearings for sodium-cooled fast reactor, 2; Fundamental characteristics of half-scale rubber bearings based on static test

Fukasawa, Tsuyoshi*; Okamura, Shigeki*; Yamamoto, Tomohiko; Kawasaki, Nobuchika; Somaki, Takahiro*; Sakurai, Yu*; Masaki, Nobuo*

Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 10 Pages, 2015/07

This paper described the results of static loading tests using a half-scale rubber bearing model to investigate the fundamental characteristics such as restoring force of a rubber bearing applied to a Sodium-Cooled-Fast-Reactor (SFR). Since the SFR has thin-walled structures, a seismic isolation system is employed to mitigate the seismic force. The static loading tests were performed using the half-scale rubber bearing with a diameter of 800 mm in the range which exceeds a linear limit of horizontal direction and a yield stress of vertical direction to investigate the horizontal and vertical of each stiffness and damping ratio. The fundamental characteristic of rubber bearing employed to the SFR and the validity of a design formula became clear through the static tests.

JSFR design progress related to development of safety design criteria for generation IV sodium-cooled fast reactors, 3; Progress of component design

Enuma, Yasuhiro; Kawasaki, Nobuchika; Orita, Junichi*; Eto, Masao*; Miyagawa, Takayuki*

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

In the frame work of generation IV international forum, safety design criteria and safety design guideline for the generation IV sodium-cooled fast reactors have been developing. JAEA, JAPC, MFBR have been investigating design study for JSFR to satisfy SDC. In addition to the safety measures, maintainability, reparability and manufacturability are taken into account in the JSFR design study. This paper describes the design of main components. Enlargement of the access route for the inspection devices and addition of the access routes were carried out for the reactor structure. The pump-integrated IHX was modified for the primary heat exchanger, which was installed for the decay heat removal in the IHX at the upper plenum, to be removable for improved repair and maintenance. For the steam generator, protective wall tube type design is under investigation as an option with less R&D risks.

Development of constitutive models for fast reactor design

Tsukimori, Kazuyuki; Iwata, Koji*; Kawasaki, Nobuchika*; Okajima, Satoshi; Yada, Hiroki; Kasahara, Naoto*

Nuclear Engineering and Design, 269, p.23 - 32, 2014/04

https://doi.org/10.1016/j.nucengdes.2013.08.001

R&D to enable a practical fast breeder reactor plant is proceeding in Japan, which is called "FaCT" (Fast reactor Cycle Technology development). One of the key issues of R&D is to realize a reasonably compact reactor vessel by eliminating the wall protection equipment which is installed inside the vessel in order to reduce thermal loading in the conventional design. Most important concern is the amount of the inelastic strain of the vessel accumulated around the liquid sodium surface which moves upward and downward cyclically with start-up and shut-down. The aim of this study is to develop rational constitutive models that enable prediction of this kind of complex inelastic behaviors precisely and to prepare the design guide based on inelastic analysis. We developed a high accuracy plasticity model and a simplified plasticity model and valuated them by organized experiments.

Verification of the estimation methods of strain range in notched specimens made of Mod.9Cr-1Mo steel

Ando, Masanori; Hirose, Yuichi*; Date, Shingo*; Watanabe, Sota*; Enuma, Yasuhiro*; Kawasaki, Nobuchika

Journal of Pressure Vessel Technology, 134(6), p.061403_1 - 061403_12, 2012/12

https://doi.org/10.1115/1.4006902

To verify the methods of estimating strain range for discontinues structures, low cycle fatigue tests were carried out with notched specimens. All the specimens were made of Mod.9Cr-1Mo. Displacement control fatigue tests and thermal fatigue tests were performed by ordinary uni-axial push pull test machine and equipment generating the thermal gradient in the notched plate by induction heating. Elastic and inelastic finite element analysis were also performed to estimate strain range for predicting fatigue life. Then these predictions were compared with the test results. Several methods such as stress reduction locus (SRL) method, simple elastic follow-up (SEF) method, Neuber's law and the procedures employed by elevated temperature design codes were applied. Through these comparisons, the applicability and conservativeness of these strain range estimation methods are discussed.

Limitation study for cyclic hardening recovery for 316FR stainless steel derived from long-term holding with elevated temperature

Okajima, Satoshi; Kawasaki, Nobuchika*; Fukahori, Takuya*; Kikuchi, Koichi*; Kasahara, Naoto

Dai-49-Kai Koon Kyodo Shimpojiumu Koen Rombunshu, p.85 - 89, 2011/11

no abstracts in English

Conceptual design study for the demonstration reactor of JSFR, 4; Structural design of reactor vessel

Kawasaki, Nobuchika; Okamura, Shigeki*; Sawa, Naoki*; Sakamoto, Yoshihiko; Negishi, Kazuo

Proceedings of 19th International Conference on Nuclear Engineering (ICONE-19) (CD-ROM), 7 Pages, 2011/10

Japan Sodium-Cooled Fast Reactor adopts an compacted hot reactor vessel concept. From the point of structural designs to ensure both seismic design and elevated temperature design is important. In this study, based on a common conservative seismic loading condition considered with the Niigata-ken Chuetsu-oki Earthquake, seismic evaluations were carried out, the thicknesses of reactor vessels of 750 MWe and 500 MWe output plants were determined. For both plants 50 mm was selected as the thickness, and ensured buckling evaluation margins were more than 2.4. From the point of seismic design, the difference of plant output was negligible. With the condition of 50 mm thickness of reactor vessel, thermal integrities were evaluated. For three plant start-up conditions which were 2.2, 3.2, and 4.3 days, thermal ratcheting and creep-fatigue damage were evaluated. As a result plant start-up period needed more than 3.2 days for both 750 MWe and 500 MWe output plants. Caused thermal stress were the nearly same for both plants, therefore from the point of thermal design, the difference of plant output was negligible.

An Evaluation method for plastic buckling of cantilever type pipes controlled by displacement loads, 1; Proposal of the estimation method and the criterion

Ando, Masanori; Tezuka, Taiji*; Nakamura, Toshio*; Okawa, Tomohiro*; Enuma, Yasuhiro*; Kawasaki, Nobuchika; Tsukimori, Kazuyuki

Proceedings of 2011 ASME Pressure Vessels and Piping Conference (PVP 2011) (CD-ROM), 9 Pages, 2011/07