Development of remote sensing technique using radiation resistant optical fibers under high-radiation environment

Ito, Chikara; Naito, Hiroyuki; Ishikawa, Takashi; Ito, Keisuke; Wakaida, Ikuo

JPS Conference Proceedings (Internet), 24, p.011038_1 - 011038_6, 2019/01

https://doi.org/10.7566/JPSCP.24.011038

A high-radiation resistant optical fiber has been developed in order to investigate the interiors of the reactor pressure vessels and the primary containment vessels at the Fukushima Daiichi Nuclear Power Station. The tentative dose rate in the reactor pressure vessels is assumed to be up to 1 kGy/h. We developed a radiation resistant optical fiber consisting of a 1000 ppm hydroxyl doped pure silica core and 4 % fluorine doped pure silica cladding. We attempted to apply the optical fiber to remote imaging technique by means of fiberscope. The number of core image fibers was increased from 2000 to 22000 for practical use. The transmissive rate of infrared images was not affected after irradiation of 1 MGy. No change in the spatial resolution of the view scope by means of image fiber was noted between pre- and post-irradiation. We confirmed the applicability of the probing system, which consists of a view scope using radiation-resistant optical fibers.

Development of crack evaluation models for probabilistic fracture mechanics analyses of Japanese reactor pressure vessels

Lu, K.; Masaki, Koichi; Katsuyama, Jinya; Li, Y.

Proceedings of 2018 ASME Pressure Vessels and Piping Conference (PVP 2018), 8 Pages, 2018/07

Confirmation tests for Warm Pre-stress (WPS) effect in reactor pressure vessel steel (Contract research)

Chimi, Yasuhiro; Iwata, Keiko; Tobita, Toru; Otsu, Takuyo; Takamizawa, Hisashi; Yoshimoto, Kentaro*; Murakami, Takeshi*; Hanawa, Satoshi; Nishiyama, Yutaka

JAEA-Research 2017-018, 122 Pages, 2018/03

JAEA-Research-2017-018.pdf:44.03MB

Warm pre-stress (WPS) effect is a phenomenon that after applying a load at a high temperature fracture does not occur in unloading during cooling, and then the fracture toughness in reloading at a lower temperature increases effectively. Engineering evaluation models to predict an apparent fracture toughness in reloading are established using experimental data with linear elasticity. However, there is a lack of data on the WPS effect for the effects of specimen size and surface crack in elastic-plastic regime. In this study, fracture toughness tests were performed after applying load-temperature histories which simulate pressurized thermal shock transients to confirm the WPS effect. The experimental results of an apparent fracture toughness tend to be lower than the predictive results using the engineering evaluation models in the case of a high degree of plastic deformation in preloading. Considering the plastic component of preloading can refine the engineering evaluation models.

Probabilistic fracture mechanics analysis models for Japanese reactor pressure vessels

Lu, K.; Katsuyama, Jinya; Uno, Shumpei; Li, Y.

Proceedings of 2017 ASME Pressure Vessels and Piping Conference (PVP 2017) (CD-ROM), 8 Pages, 2017/07

Development of Stress intensity factor coefficients database for a surface crack of an RPV considering the stress discontinuity between cladding and base metal

Onizawa, Kunio; Shibata, Katsuyuki*; Suzuki, Masahide

Proceedings of 2005 ASME/JSME Pressure Vessels and Piping Division Conference (PVP 2005), 12 Pages, 2005/07

Under a transient loading like pressurized thermal shock (PTS), the stress discontinuity near the interface between cladding and base metal of a reactor pressure vessel (RPV) is caused by the difference in their thermal expansion factors. So the stress intensity factor (SIF) of a surface crack which the deepest point exceeds the interface should be calculated by taking account of the stress discontinuity. Many SIF calculations are performed in Monte Carlo simulation of the probabilistic fracture mechanics (PFM) analysis. To avoid the time consuming process from the SIF calculation in the PFM analysis, the non-dimensional SIF coefficients corresponding to the stress distributions in the cladding and base metal were developed. The non-dimensional SIF coefficients database were obtained from 3D FEM analyses. The SIF value at the surface was determined by linear extrapolation of SIF value near the surface. Using the SIF coefficients database, the SIF values at both surface and deepest points of a surface crack can be evaluated precisely and in a reasonable time.

Importance of fracture criterion and crack tip material characterization in probabilistic fracture mechanics analysis of an RPV under a pressurized thermal shock

Shibata, Katsuyuki; Onizawa, Kunio; Li, Y.*; Kato, Daisuke*

International Journal of Pressure Vessels and Piping, 81(9), p.749 - 756, 2004/09

http://dx.doi.org/10.1016/j.ijpvp.2004.05.003

The paper describes the procedure to evaluate the ductile crack extension, where an increase in fracture resistance by a ductile crack extension is considered. Two standard -resistance curves are prepared for applying the elasto-plastic fracture criterion. Case studies concerning the effect of elasto-plastic fracture criterion were carried out using a severe PTS transient. The introduction of the elasto-plastic fracture criterion significantly contributes to remove the over-conservatism in applying the linear elastic fracture criterion. It was also found that the algorithm of the re-evaluation of crack tip characterization also has a significant effect on the failure probability.

Correlation between cleavage fracture toughness and charpy impact properties in the transition temperature range of reactor pressure vessel steels

Onizawa, Kunio; Suzuki, Masahide

JSME International Journal, Series A, 47(3), p.479 - 485, 2004/07

In the structural integrity assessment of reactor pressure vessel, fracture toughness values are estimated by assuming that the radiation effect on fracture toughness is equivalent to that on Charpy properties. Therefore, it is necessary to establish the correlation between both properties especially on irradiation embrittlement. In this paper, we present the fracture toughness data obtained by applying the master curve approach that was adopted recently in the ASTM test method. Materials used in this study are five ASTM A533B class 1 steels and one weld metal. Neutron irradiation for Charpy-size specimens as well as standard Charpy-v specimens was carried out at the Japan Materials Testing Reactor. The shifts of the reference temperature on fracture toughness due to neutron irradiation are evaluated. Correlation between the fracture toughness reference temperature and Charpy transition temperature is established. Based on the correlation, the optimum test temperature for fracture toughness testing and the method to determine a lower bound fracture toughness curve are discussed.

Embedded crack treatments and fracture toughness evaluation methods in probabilistic fracture mechanics analysis code for the PTS analysis of RPV

Onizawa, Kunio; Shibata, Katsuyuki; Suzuki, Masahide; Kato, Daisuke*; Li, Y.*

RPV Integrity and Fracture Mechanics (PVP-Vol.481), p.11 - 17, 2004/07

At JAERI, the prpbabilistic fracture mechanics analysis code PASCAL has been developed. Using the PASCAL, the treatment methods of an embedded crack and the fracture toughness evaluation methods were studied on the probability of crack initiation and fracture of a RPV. For calculating the stress intensity factor (SIF) of an embedded crack, the ASME and CRIEPI procedures were introduced into PASCAL. Under a severe pressurized thermal shock condition, the crack growth analysis models with different SIF calculation points and crack growth directions are compared. The results showed that the crack tip at the inner side was most important to the fracture probability. The conditional fracture probability for an embedded crack when the same crack size distribution is assumed is approximately one order of magnitude lower than that of a surface crack. Fracture toughness curves based on Weibull distribution were incorporated into PASCAL. The comparison between these new curves and the current curves showed little effect on the conditional fracture probability of a RPV.

Probabilistic fracture mechanics analyses of RPV under some PTS transients

Onizawa, Kunio; Shibata, Katsuyuki; Kato, Daisuke*; Li, Y.*

Proceedings of 11th International Conference on Nuclear Engineering (ICONE-11) (CD-ROM), 8 Pages, 2003/04

Probabilistic Fracture Mechanics (PFM) has been used in the fields of reliability analysis for important structural components. At JAERI, the PFM analysis code PASCAL has been developed. This code evaluates the conditional probabilities of crack initiation and fracture of a reactor pressure vessel (RPV) under transient conditions such as pressurized thermal shock (PTS). Four cases of PTS transients were selected based on the severity for a typical 3-loop PWR. Based on thermal stress analyses, PFM analyses were performed by using PASCAL code focusing on some important variables on the RPV fracture probability. The results showed that non-destructive examination methods had a significant effect on the fracture probability by more than three orders of magnitude. The comparisons of the results using fracture toughness estimation methods between in Japan and USA, and crack geometries between a semi-elliptical surface crack and an infinite surface crack are also made.

Design study on Gas Turbine High Temperature Reactor (GTHTR300) in FY2001

Kunitomi, Kazuhiko; Katanishi, Shoji; Takada, Shoji; Takizuka, Takakazu; Yan, X.; Nakata, Tetsuo; Takei, Masanobu; Kosugiyama, Shinichi; Shiozawa, Shusaku

Nippon Kikai Gakkai Dai-8-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu, p.181 - 184, 2002/00

no abstracts in English