Four-point-bend tests on high-burnup advanced fuel cladding tubes after exposure to simulated LOCA conditions

Narukawa, Takafumi; Amaya, Masaki

Journal of Nuclear Science and Technology, 57(7), p.782 - 791, 2020/07

https://doi.org/10.1080/00223131.2020.1724207

Method for groundwater monitoring on the disposal of radioactive waste

Murakami, Hiroaki; Iwatsuki, Teruki; Takeuchi, Ryuji; Nishiyama, Nariaki*

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 27(1), p.22 - 33, 2020/06

https://doi.org/10.3327/jnuce.27.1_22

Geological disposal of radioactive waste requires the large amounts of fundamental technical knowledge throughout the project. Monitoring is carried out to collect site-relevant information for the creation of an environmental database, to assist in the decision-making process, etc. We summarized the current technical level and problems of the groundwater monitoring in the world. Through the research and technology development so far, the technologies have been developed for drilling borehole in the geological environment survey prior to monitoring and the selection of the monitoring site. However, the following technical developments are remaining issues: long-term operation method of monitoring equipment, retrieving method of monitoring equipment after long-term operation, transport method of backfill material for borehole sealing, technical basis for the sealing performance when the borehole-protective casing and strainer tube are left.

Assessment model of radiation doses from external exposure to the public after the Fukushima Daiichi Nuclear Power Plant accident

Takahara, Shogo; Iijima, Masashi*; Watanabe, Masatoshi*

Health Physics, 118(6), p.664 - 677, 2020/06

https://doi.org/10.1097/HP.0000000000001176

Assessment model of radiation doses from external exposures was developed based on the actual measurement of individual doses and ambient dose equivalent rate inside and outside of a house in Fukushima city. The survey on behavioral pattern was also carried out under the same purpose. In addition to the actual measurement and survey by ourselves, we also took into account the latest insights from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Comparisons between the assessed results and the measured ones revealed that the time dependences of doses obtained using the developed models were in good agreement with the results of actual measurements. In addition, we were able to reproduce the distribution of doses for indoor and outdoor workers. Therefore, our probabilistic approach was validated. According to our assessment and actual measurement, no participants received 1 mSv/y or higher in Fukushima city in eight years after the FDNPP accident.

Influence evaluation of sampling methods of the nondestructive examination on failure probability of piping based on probabilistic fracture mechanics analysis

Mano, Akihiro; Katsuyama, Jinya; Li, Y.

Mechanical Engineering Journal (Internet), 7(3), p.19-00567_1 - 19-00567_11, 2020/06

https://doi.org/10.1299/mej.19-00567

Non-destructive examinations (NDEs) have an important role in assurance of the structural integrity of nuclear components including pipe lines. In Japanese nuclear power plants, NDEs are performed for welds in piping in accordance with the rules such as the Rules on Fitness-for-Service for Nuclear Power Plants of the Japan Society of Mechanical Engineers. For the welds where stress corrosion cracking (SCC) is not postulated, NDEs are performed in each 10-year interval. For each interval, the extent of examination is specified in the rules. In general, there are two kinds of sampling method for selecting welds to be examined in each interval considering the specified extent of examination. The first method is the fixed location sampling method, in which welds for NDEs are same as those examined in the last interval. The second method is the random location sampling method, in which welds for NDEs are selected from those not examined in the last interval. The selection of the sampling method is important to assure the structural integrity of piping. Probabilistic fracture mechanics (PFM) analysis which is one of rational structural integrity assessment methods can quantitatively calculate failure probability of welds in piping considering aging degradation mechanisms such as SCC and fatigue as well as crack detections and repair of cracked welds through NDE. In this study, to clarify the influence of the sampling methods on structural integrity of piping, we evaluated the failure probability of a typical nuclear piping considering NDEs based on the two sampling methods through PFM analysis. From the results, we clarified the quantitative influence of two sampling methods on failure probability of piping.

Impact simulations on local damage of reinforced concrete panel influenced by projectile nose shape

Kang, Z.; Nishida, Akemi; Okuda, Yukihiko; Tsubota, Haruji; Li, Y.

Mechanical Engineering Journal (Internet), 7(3), p.19-00566_1 - 19-00566_20, 2020/06

https://doi.org/10.1299/mej.19-00566

Most impact research has been presented on the basis of impact tests and numerical analysis performed by rigid projectile impact perpendicular to the target structure. On the other hand, there are only few reports on impacts at an oblique angle. To evaluate more realistic conditions regarding issues related to oblique impacts to reinforced concrete (RC) structures, we have proposed an analytical method to estimate the local damage to RC structures by an oblique impact and have validated the evaluation approach by comparison with experimental results. At present, we have finalized simulation analyses of oblique impact assessments on RC panels using rigid/soft projectiles with a flat nose shape utilizing the validated approach. Furthermore, in this study, we focus on impacts caused by rigid/soft projectiles with a hemispherical nose shape. The same analytical method is applied to simulate the structural damage caused by an RC panel due to a rigid/soft projectile with a hemispherical nose shape. Results on the penetration depth of the RC structure and the energy-contribution ratio are presented. By comparing the results of local damage to an RC structure caused by projectiles with flat and hemispherical nose shapes, the influence of the nose shape of the projectile on local damage of the RC panel has been investigated.

Expansion of high temperature creep test data for failure evaluation of BWR lower head in severe accident

Yamaguchi, Yoshihito; Katsuyama, Jinya; Kaji, Yoshiyuki; Osaka, Masahiko; Li, Y.

Mechanical Engineering Journal (Internet), 7(3), p.19-00560_1 - 19-00560_12, 2020/06

https://doi.org/10.1299/mej.19-00560

Since the Fukushima Daiichi nuclear power plant accident, we have been developing a failure evaluation method that considers creep damage mechanisms using detailed three-dimensional finite element analysis model of lower head including penetration, stub tubes, and weld parts, etc., for the early completion of the decommissioning of the nuclear power plants in Fukushima Daiichi. For the finite element analysis, we have been obtaining material properties for which no data are provided in existing databases or in the literature. In particular, creep data corresponding to the high temperature region near the melting point of materials is important in evaluating creep deformation under severe accident conditions. In this study, we obtained the uniaxial tensile and creep properties for low-alloy steel, stainless steel, and Ni-based alloy. In particular, creep test data with long rupture times at high temperatures are expanded using a tensile test machine that can measure the elongation of test specimens in a noncontact measurement system. The parameters related to the failure evaluation were improved on the basis of the expanded creep database.

Eye lens dosimetry for workers at Fukushima Daiichi Nuclear Power Plant, 2; Field study using humanoid phantoms

Tsujimura, Norio; Hoshi, Katsuya; Aoki, Katsunori; Yoshitomi, Hiroshi; Tanimura, Yoshihiko; Yokoyama, Sumi*

Radiation Measurements, 134, p.106305_1 - 106305_5, 2020/06

https://doi.org/10.1016/j.radmeas.2020.106305

The Effect of base irradiation on failure behaviors of UO and chromia-alumina additive fuels under simulated reactivity-initiated accidents; A Comparative analysis with FEMAXI-8

Udagawa, Yutaka; Mihara, Takeshi; Taniguchi, Yoshinori; Kakiuchi, Kazuo; Amaya, Masaki

Annals of Nuclear Energy, 139, p.107268_1 - 107268_9, 2020/05

https://doi.org/10.1016/j.anucene.2019.107268

Experimental and analytical investigation of formation and cooling phenomena in high temperature debris bed

Hotta, Akitoshi*; Akiba, Miyuki*; Morita, Akinobu*; Konovalenko, A.*; Vilanueva, W.*; Bechta, S.*; Komlev, A.*; Thakre, S.*; Hoseyni, S. M.*; Skld, P.*; et al.

Journal of Nuclear Science and Technology, 57(4), p.353 - 369, 2020/04

https://doi.org/10.1080/00223131.2019.1691078

Closed-form stress intensity factor solutions for surface cracks with large aspect ratios in plates

Azuma, Kisaburo*; Li, Y.; Xu, S.*

Journal of Pressure Vessel Technology, 142(2), p.021207_1 - 021207_10, 2020/04

https://doi.org/10.1115/1.4045029