Synthesis report on the R&D for the Horonobe Underground Research Laboratory; Project carried out during fiscal years 2015-2019

Nakayama, Masashi; Saiga, Atsushi; Kimura, Shun; Mochizuki, Akihito; Aoyagi, Kazuhei; Ono, Hirokazu; Miyakawa, Kazuya; Takeda, Masaki; Hayano, Akira; Matsuoka, Toshiyuki; et al.

JAEA-Research 2019-013, 276 Pages, 2020/03

JAEA-Research-2019-013.pdf:18.72MB

The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant disposal technologies for geological disposal of High-level Radioactive Waste through investigations of the deep geological environment within the host sedimentary rock at Horonobe Town in Hokkaido, north Japan. The investigations will be conducted in three phases, namely "Phase 1: Surface based investigations", "Phase 2: Construction phase" (investigations during construction of the underground facilities) and "Phase 3: Operation phase" (research in the underground facilities). According to the research plan described in the 3rd Mid- and Long- term Plan of JAEA, "Near-field performance study", "Demonstration of repository design option", and "Verification of crustal-movement buffering capacity of sedimentary rocks" are important issues of the Horonobe URL Project, and schedule of future research and backfill plans of the project will be decided by the end of 2019 Fiscal Year. The present report summarizes the research and development activities of these 3 important issues carried out during 3rd Medium to Long-term Research Phase.

Status of the JENDL project

Iwamoto, Osamu; Shibata, Keiichi; Iwamoto, Nobuyuki; Kunieda, Satoshi; Minato, Futoshi; Ichihara, Akira; Nakayama, Shinsuke

EPJ Web of Conferences, 146, p.02005_1 - 02005_6, 2017/09

https://doi.org/10.1051/epjconf/201714602005

Relationship between the material properties and pyroelectric-generating performance of PZTs

Yamanaka, Satoru*; Kim, J.*; Nakajima, Akira*; Kato, Takanori*; Kim, Y.*; Fukuda, Tatsuo; Yoshii, Kenji; Nishihata, Yasuo; Baba, Masaaki*; Yamada, Noboru*; et al.

Advanced Sustainable Systems (Internet), 1(3-4), p.1600020_1 - 1600020_6, 2017/04

http://doi.org/10.1002/adsu.201600020

no abstracts in English

Long-term immersion experiments of low alkaline cementitious materials

Seno, Yasuhiro*; Noguchi, Akira*; Nakayama, Masashi; Sugita, Yutaka; Suto, Shunkichi; Tanai, Kenji; Fujita, Tomoo; Sato, Haruo*

JAEA-Technology 2016-011, 20 Pages, 2016/07

JAEA-Technology-2016-011.pdf:7.56MB

Cementitious materials are expected to be used for the construction of an underground repository for the geological disposal of radioactive wastes. Ordinary Portland Cement(OPC) would conventionally be used in the fields of civil engineering and architecture, however, OPC has the potential to generate a highly alkaline plume (pH12.5), which will likely degrade the performance of other barriers in the repository such as the bentonite buffer and/or host rock. Low alkaline cementitious materials are therefore being developed that will mitigate the generation of a highly alkaline plume. JAEA has developed a High-volume Fly ash Silica fume Cement (HFSC) as a candidate low alkaline cementitious material. The workability of the HFSC shotcrete was confirmed by conducting In-situ full scale construction tests in the Horonobe underground research laboratory. This report summarizes the results of immersion tests to assess the long-term pH behavior of hardened HFSC cement pastes made with mix designs that are expected to be able to be used in the construction of an underground repository in Japan.

Decontamination of school facilities in Fukushima-city

Yoshikawa, Hideki; Iijima, Kazuki; Sasamoto, Hiroshi; Fujiwara, Kenso; Mitsui, Seiichiro; Kitamura, Akira; Kurikami, Hiroshi; Tokizawa, Takayuki; Yui, Mikazu; Nakayama, Shinichi

Materials Research Society Symposium Proceedings, Vol.1518, p.269 - 275, 2013/10

https://doi.org/10.1557/opl.2013.75

Following the release of radionuclides into the environment as a result of the accident at Fukushima Daiichi Nuclear Power Plant, Japan Atomic Energy Agency (JAEA) had to develop an immediate and effective method of reducing the dose rate received by students in school facilities. A demonstration of a reducing method was carried out by JAEA at a junior high school ground and kindergarten yard in the center of Fukushima-city. Dose rates of the released radionuclides are largely controlled by the ground level contamination and accumulation of mainly cesium-137 (Cs) and cesium-134 (Cs) in populated areas. An effective means of reducing dose rate was to remove the surface soil and to bury it on-site under fresh uncontaminated soil or soil collected under deep depth at the site for shielding. The dose rate at1 m above ground level was reduced from 2.5 Sv/h to 0.15 Sv/h.

Study on applicability of low alkaline cement in Horonobe Underground Research Laboratory Project, 3 (Contract research)

Nakayama, Masashi; Kobayashi, Yasushi; Noguchi, Akira; Miura, Norihiko*; Noda, Masaru*; Iriya, Keishiro*; Hitomi, Takashi*

JAEA-Research 2009-036, 49 Pages, 2009/11

JAEA-Research-2009-036.pdf:20.34MB

In Horonobe Underground Research Laboratory (Horonobe URL) Project, construction practicality test with HFSC (Highly Fly-ash contained Silica-fume Cement) is planned in a part of the gallery. It is necessary to validate that HFSC has performance under the actual construction, before HFSC is placed in the gallery. The main tasks in 2008 are follows; (1) suggestion of mix design for liner concrete of shaft in Horonobe URL, (2) investigation of long term pH changes in order to use for modeling, and (3) an experiment for interaction between HFSC and ground water around Horonobe URL. (1) 4 types of mix proportion are designed for ordinary concrete and high strength concrete which contains polypropylene fiber or not. As early age strength, 5N/mm is required because of concrete formwork. HFSC424 with low water binder ratio can fulfill this requirement in combination with super plasticizer. (2) pH and components of solid and liquid phase which were made in 2003, and stored in water were analyzed. And cement paste of shotcrete which are made in 2006 were also analyzed. In this pH of shotcrete is lower than other in situ concrete since accelerating agent may act as decreasing factor of pH. (3) An experiment which investigates dissolution of HFSC cement hydrates to ground water around Horonobe URL. According to the experiment, dissolving depth of HFSC is 4 times small comparing to Ordinary Portland Cement hydrates after 30th water exchange.

Determination of the solubility limiting solid of selenium in the presence of iron under anoxic conditions

Iida, Yoshihisa; Yamaguchi, Tetsuji; Tanaka, Tadao; Kitamura, Akira; Nakayama, Shinichi

Proceedings of International Workshop on Mobile Fission and Activation Products in Nuclear Waste Disposal, p.135 - 145, 2009/00

We performed dissolution experiments of iron-selenium compounds from both undersaturation and oversaturation directions to determine the solubility limiting solid of selenium in the presence of iron under anoxic conditions. The solid products was identified to be iron diselenide but the concentration of selenium was 9 orders of magnitude higher than the value calculated from the existing thermodynamic data of FeSe, therefore FeSe was not considered to be the solubility limiting solid. The pH and Eh dependencies of the concentration of selenium were best interpreted as the dissolution reaction of Se(cr), but the concentration of selenium was still 3 orders of magnitude higher than the value calculated from the existing thermodynamic data of Se(cr). Because any selenium compounds other than FeSe was not detected by XRD and the concentration of selenium was higher than the solubility of Se(cr), the solubility limiting solid was considered to be amorphous selenium.

path integral ring polymer molecular dynamics; Vibrational spectra of molecules

Shiga, Motoyuki; Nakayama, Akira*

Chemical Physics Letters, 451(4-6), p.175 - 181, 2008/01

https://doi.org/10.1016/j.cplett.2007.11.091

The path integral ring polymer molecular dynamics method is combined with "on-the-fly" electronic structure calculations and applied to vibrational spectra of small molecules, LiH and HO, at the room temperature. The results are compared with those of the numerically exact solution and path integral centroid molecular dynamics calculation. The peak positions in the calculated spectra are found to be reasonable, showing the red shift due to potential anharmonicity. This unification enables the investigation of real-time quantum dynamics of chemically complex molecular systems on the Born-Oppenheimer potential energy surface.

Study on thermal stratification in a compact reactor vessel; Effects of Richardson number and upper plenum geometries

Nakayama, Okatsu; Ogawa, Hiroshi*; Kimura, Nobuyuki; Hayashi, Kenji; Tobita, Akira; Kamide, Hideki

Proceedings of 15th International Conference on Nuclear Engineering (ICONE-15) (CD-ROM), 8 Pages, 2007/04

Water experiment using an 1/10th scaled upper plenum model was carried out to investigate thermal stratification after a scram in a compact reactor, which has high velocity local flow in the upper plenum. The experiments showed that the rising speed of the stratification interface was dependent on Richardson number and the temperature gradient of the stratification interface was also influenced by the temperature difference and fluctuation. Furthermore, the temperature gradient could be reduced greatly by changing position of structure in the upper plenum.

Water experiment on gas entrainment in reactor vessel using 1/1.8th scaled model, Gas entrainment in large scaled model

Kimura, Nobuyuki; Tobita, Akira; Kobayashi, Jun; Nakayama, Oukatsu; Ito, Masami*; Kamide, Hideki

JNC TN9400 2004-067, 48 Pages, 2004/05

JNC-TN9400-2004-067.pdf:19.55MB

An innovative sodium cooled fast reactor has been investigated in a frame work of the FBR feasibility study. A compact reactor vessel is designed to reduce the construction cost, where sodium flow velocity increases. One of the thermal hydraulic issues in this design is gas entrainment at free surface in the reactor vessel. Dipped plates (D/P) are set below the free surface in order to prevent the gas entrainment.We performed an 1/10th scaled model water experiment for the upper plenum of reactor vessel and flow optimization was done to reduce flow velocity near the free surface. However, previous studies showed that the gas entrainment depends on model scale. Then an 1/1.8th scaled model was also planned to confirm the phenomena in an enough large model. As a test section, 90 degree sector and region between the free surface and the D/P was modeled by 1/1.8th scale. Boundary conditions at D/P gaps and radial cross sections of sector ends were obtained by the 1/10th scaled full sector model. The gas entrainment was not observed in the model under the velocity condition of reactor full power operation at water levels higher than 4% of the normal height from the D/P. It is shown that the gas entrainment will be eliminated in the reactor vessel according to the current design approach.