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JAEA Reports

Controlled release of radioactive krypton gas

Watanabe, Kazuki; Kimura, Norimichi*; Okada, Jumpei; Furuuchi, Yuta; Kuwana, Hideharu*; Otani, Takehisa; Yokota, Satoru; Nakamura, Yoshinobu

JAEA-Technology 2023-010, 29 Pages, 2023/06


The Krypton Recovery Development Facility reached an intended technical target (krypton purity of over 90% and recovery rate of over 90%) by separation and rectification of krypton gas from receiving off-gas produced by the shearing and the dissolution process in the spent fuel reprocessing at the Tokai Reprocessing Plant (TRP) between 1988 and 2001. In addition, the feasibility of the technology was confirmed through immobilization test with ion-implantation in a small test vessel from 2000 to 2002, using a part of recovered krypton gas. As there were no intentions to use the remaining radioactive krypton gas in the krypton storage cylinders, we planned to release this gas by controlling the release amount from the main stack, and conducted it from February 14 to April 26, 2022. In this work, all the radioactive krypton gas in the cylinders (about 7.1$$times$$10$$^{5}$$ GBq) was released at the rate of 50 GBq/min or less lower than the maximum release rate from the main stuck stipulated in safety regulations (3.7$$times$$10$$^{3}$$ GBq/min). Then, the equipment used in the controlled release of radioactive krypton gas and the main process (all systems, including branch pipes connected to the main process) were cleaned with nitrogen gas. Although there were delays due to weather, we were able to complete the controlled release of radioactive krypton gas by the end of April 2022, as originally targeted without any problems such as equipment failure.

JAEA Reports

Horonobe Underground Research Laboratory Project; Synthesis of Phase II (Construction Phase) investigations to a depth of 350m

Sato, Toshinori; Sasamoto, Hiroshi; Ishii, Eiichi; Matsuoka, Toshiyuki; Hayano, Akira; Miyakawa, Kazuya; Fujita, Tomoo*; Tanai, Kenji; Nakayama, Masashi; Takeda, Masaki; et al.

JAEA-Research 2016-025, 313 Pages, 2017/03


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 through investigations of the deep geological environment within the host sedimentary formations at Horonobe, northern Hokkaido. This report summarizes the results of the Phase II investigations carried out from April 2005 to June 2014 to a depth of 350m. Integration of work from different disciplines into a "geosynthesis" ensures that the Phase II goals have been successfully achieved and identifies key issues that need to made to be addressed in the Phase II investigations Efforts are made to summarize as many lessons learnt from the Phase II investigations and other technical achievements as possible to form a "knowledge base" that will reinforce the technical basis for both implementation and the formulation of safety regulations.

JAEA Reports

Long-term pore-pressure-monitoring using deep boreholes in the Horonobe Underground Research Project

Yoshino, Hiromitsu; Kishi, Atsuyasu*; Yokota, Hideharu

JAEA-Data/Code 2015-014, 42 Pages, 2015/09


Long-term pore-pressure-monitoring has been performed using HDB-1$$sim$$11 and PB-V01 boreholes in the Horonobe Underground Research Laboratory Project. This report summarizes the results obtained from the starting of monitoring to March 2015.

JAEA Reports

Synthesized research report in the second mid-term research phase; Mizunami Underground Research Laboratory Project, Horonobe Underground Research Laboratory Project and Geo-stability Project

Hama, Katsuhiro; Mizuno, Takashi; Sasao, Eiji; Iwatsuki, Teruki; Saegusa, Hiromitsu; Sato, Toshinori; Fujita, Tomoo; Sasamoto, Hiroshi; Matsuoka, Toshiyuki; Yokota, Hideharu; et al.

JAEA-Research 2015-007, 269 Pages, 2015/08


We have synthesised the research results from Mizunami/Horonobe URLs and geo-stability projects in the second mid-term research phase. It could be used as technical bases for NUMO/Regulator in each decision point from sitting to beginning of disposal (Principal Investigation to Detailed Investigation Phase). High quality construction techniques and field investigation methods have been developed and implemented and these will be directly applicable to the National Disposal Program (along with general assessments of hazardous natural events and processes). It will be crucial to acquire technical knowledge on decisions of partial backfilling and final closure by actual field experiments in Mizunami/Horonobe URLs as main themes for the next phases.

Journal Articles

Dipole tracer migration and diffusion tests in fractured sedimentary rock at Horonobe URL

Tanaka, Shingo*; Yokota, Hideharu; Ono, Hirokazu; Nakayama, Masashi; Fujita, Tomoo; Takiya, Hiroaki*; Watanabe, Naoko*; Kozaki, Tamotsu*

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

Journal Articles

Preliminary analysis of dipole tracer migration experiments in fractured sedimentary rock at Horonobe URL of Japan

Yokota, Hideharu; Tanaka, Shingo

Proceedings of 19th Pacific Basin Nuclear Conference (PBNC 2014) (USB Flash Drive), 10 Pages, 2014/08

For understanding mass transport mechanism in the rock as natural barrier, ${it in-situ}$ dipole tracer migration experiments were implemented for a fracture in mudstone of Wakkanai Formation at the G.L.-250m gallery of the Horonobe URL, northern Hokkaido, Japan. Results of its preliminary analysis by the analytical solution retrieved from one-dimensional advection-dispersion equation indicate that a fracture surface in mudstone has both reversible and irreversible sorption characteristics for Cs$$^{+}$$ and Sr$$^{2+}$$ but only irreversible that for Co$$^{2+}$$ and Eu$$^{3+}$$.

JAEA Reports

Applicability study of numerical analysis for coupled mechanical and hydrological processes by drift excavation (Contract research)

Yamamoto, Nobuyuki; Iwano, Keita*; Namikawa, Tadashi*; Morikawa, Seiji*; Seno, Shoji*; Tabei, Kazuto*; Toida, Masaru*; Yokota, Hideharu

JAEA-Research 2013-003, 252 Pages, 2013/06


This study reconsiders rock's mechanical and hydrological parameters based on additional ${it in-situ}$ data given in this year, and conducts the mechanical-hydrological analysis using the Micromechanics-Based Continuum (MBC) model which can consider the behavior of fracture. The acquired analysis results are compared with actual test data such as drift convergence and hydraulic pressure around the drift. Then, following knowledge is obtained.

JAEA Reports

Study on development of evaluation technique of in-situ tracer test in Horonobe Underground Research Laboratory Project (Contract research)

Yokota, Hideharu; Amano, Kenji; Maekawa, Keisuke; Kunimaru, Takanori; Naemura, Yumi*; Ijiri, Yuji*; Motoshima, Takayuki*; Suzuki, Shunichi*; Teshima, Kazufumi*

JAEA-Research 2013-002, 281 Pages, 2013/06


To evaluate permeable heterogeneity in a fracture and scale effects which are problems to be solved based on the ${it in-situ}$ mass transportation data of fractures in hostrock, a number of tracer tests are simulated in a fictitious single plate fracture generated on computer in this study. And the transport parameters, e.g. longitudinal dispersion length, true velocity and dilution rate, are identified by fitting one- and two-dimensional models to the breakthrough curves obtained from the simulations in order to investigate the applicability of these models to the evaluation of ${it in-situ}$ tracer test. As a result, one-dimensional model yields larger longitudinal dispersion length than two-dimensional model in the both cases of homogeneous and heterogeneous hydraulic conductivity fields of the fictitious fracture. And, the longitudinal dispersion length identified from a tracer test is smaller and/or larger than the macroscopic longitudinal dispersion length identified from whole fracture. It is clarified that these are occurred by shorter or longer distance between boreholes compare to the correlation length of geostatistical heterogeneity of fictitious fracture.

Journal Articles

Validation of surface-based hydrochemical investigation and the impact of underground facility construction at Horonobe URL

Amano, Yuki; Nanjo, Isao; Murakami, Hiroaki; Yabuuchi, Satoshi; Yokota, Hideharu; Sasaki, Yoshito; Iwatsuki, Teruki

Chikasui Gakkai-Shi, 54(4), p.207 - 228, 2012/11

We verified the surface-based hydrochemical investigation for deep underground at Horonobe Underground Research Laboratory (URL) at Horonobe, Hokkaido, Japan, and identified the hydrochemical changes during the URL construction. The evaluation of the relationship between the number of borehole and understanding of water chemistry suggests that three basic borehole investigations and additional borehole for high permeable geological structure (fault and fractured zone) are required to illustrate cross-sectional hydrochemical distribution including the uncertainty in kilometers scale survey line. The observation and numerical analysis of hydrochemical variation (salinity, pH, ORP) around URL indicate that the groundwater pressure and the salinity in the vicinity of high permeable geological zone are varying due to groundwater inflow into the drift. The variation was consistent with the prediction reported previously. These results are considered to be referred to the management during surface-based investigation and construction of underground facility at the other sedimentary rock area.

JAEA Reports

Horonobe Underground Research Laboratory Project; Investigation report for the 2011 fiscal year

Nakayama, Masashi; Amano, Kenji; Tokiwa, Tetsuya; Yamamoto, Yoichi; Oyama, Takuya; Amano, Yuki; Murakami, Hiroaki; Inagaki, Daisuke; Tsusaka, Kimikazu; Kondo, Keiji; et al.

JAEA-Review 2012-035, 63 Pages, 2012/09


The Horonobe Underground Research Laboratory Project is planned to extend over a period 20 years. 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). This report summarizes the results of the investigations for the 2011 fiscal year (2011/2012). The investigations, which are composed of "Geoscientific research" and "R&D on geological disposal technology", were carried out according to "Horonobe Underground Research Laboratory Project Investigation Program for the 2011 Fiscal year". The results of these investigations, along with the results which were obtained in other departments of Japan Atomic Energy Agency (JAEA), are properly offered to the implementations and the safety regulations. For the sake of this, JAEA has proceeded with the project in collaboration with experts from domestic and overseas research organisations.

Journal Articles

An Observational construction management in the Horonobe Underground Research Laboratory Project

Tsusaka, Kimikazu; Inagaki, Daisuke; Tokiwa, Tetsuya; Yokota, Hideharu; Nago, Makito*; Matsubara, Makoto*; Shigehiro, Michiko*

Proceedings of ITA-AITES World Tunnel Congress 2012 (WTC 2012)/38th General Assembly (CD-ROM), 8 Pages, 2012/05

In the Horonobe URL Project, three shafts are planned to be excavated up to the depth of 500 m in the Neogene sedimentary rocks. The host rock of the URL site is comprised of diatomaceous and siliceous mudstones, which are the Koetoi and Wakkanai Formations, respectively. Approximately 100 m thick fracture zone with high hydraulic conductivity develops above about 400 m in depth in the Wakkanai Formation. The shaft sinking through the fracture zone is the most challenging issue from the aspect of tunnel engineering in the project. In the fracture zone, there is high possibility of severe breakout and spalling in shaft wall because the shafts might be intersecting faults with the size greater than shaft diameter in addition to low intact rock strength at great depth. In practice, prior to the construction of the Ventilation Shaft through the fracture zone below a depth of 250 m, the three dimensional fault distribution were predicted by integrating borehole investigation results and geological response to pre-excavation grouting operation. The countermeasure was also designed against massive spalling. During the shaft sinking, fracture mapping of shaft wall was carried out in order to evaluate the prediction of fault distribution. Roughness of shaft wall was also measured by three dimensional laser scanner in order to investigate the shape and volume of spalling resulting from the excavation work. Consequently, the Ventilation Shaft has successfully been constructed through the fracture zone. This is because the prediction of fault distribution was accurate, and the countermeasure against concrete lining damage due to spalling was promptly applied.

JAEA Reports

Estimation of groundwater recharge rate and spatial distribution of hydrological quantities in surface hydrogeological investigation basin of Horonobe URL Project; From December 2004 to November 2009

Yamamoto, Yoichi; Maekawa, Keisuke; Yokota, Hideharu; Yamazaki, Masanori

JAEA-Research 2011-042, 97 Pages, 2012/02


The surface hydrogeological investigation has been carried out in and around the Horonobe Underground Research Laboratory area as a part of Horonobe URL project. Observations of meteorological, river flux, water quality, soil moisture and groundwater level have been continued in order to understand the groundwater recharge rate and groundwater flow in the shallow part, which are required for the setting of boundary and initial condition of the groundwater flow analysis. This report shows the summary of the surface hydrogeological investigation and results of recharge rates of investigation basins from December 2004 to November 2009 are calculated by using the water budget method. Spatial estimation of hydrological quantities for the groundwater recharge rate is demonstrated by the runoff analysis. As a result, average of the groundwater recharge rate of whole basins is estimated to 131mm/yr. Suggestive observations related to hydraulic properties of the geology and faults are obtained from consideration to the groundwater recharge rate for each basin.

JAEA Reports

Data of groundwater from boreholes, river water and precipitation for the Horonobe Underground Research Laboratory Project; 2001-2010

Amano, Yuki; Yamamoto, Yoichi; Nanjo, Isao; Murakami, Hiroaki; Yokota, Hideharu; Yamazaki, Masanori; Kunimaru, Takanori; Oyama, Takahiro*; Iwatsuki, Teruki

JAEA-Data/Code 2011-023, 312 Pages, 2012/02


In the Horonobe Underground Research Laboratory (URL) Project, ground water from boreholes, river water and precipitation have been analyzed for the environmental monitoring since the fiscal year 2001. This report shows the data set of water chemistry since the fiscal year 2001 to the fiscal year 2010.

Journal Articles

Observation of evapotranspiration using a lysimeter at Horonobe basin in Hokkaido

Yamamoto, Yoichi; Yokota, Hideharu

Doboku Gakkai Heisei-23-Nendo Zenkoku Taikai Dai-66-Kai Nenji Gakujutsu Koenkai Koen Gaiyoshu (DVD-ROM), p.385 - 386, 2011/09

no abstracts in English

JAEA Reports

Horonobe Underground Research Laboratory Project; Research and development plan (H22-H26)

Iwatsuki, Teruki; Sato, Haruo; Nohara, Tsuyoshi; Tanai, Kenji; Sugita, Yutaka; Amano, Kenji; Yabuuchi, Satoshi; Oyama, Takuya; Amano, Yuki; Yokota, Hideharu; et al.

JAEA-Research 2011-009, 73 Pages, 2011/06


The research and development plan in Horonobe Underground Research Laboratory are summarized according to the 2nd Midterm Plan till 2014 fiscal year of JAEA. In this midterm, galleries and the infrastructures for the research and development up to the depth of 350 m are constructed by Private Financial Initiative (PFI). Additionally Phase 3: Operation phase at the galleries begins in parallel to Phase 2: Construction phase. In these phases various research and development including collaboration with other institutes are conducted at the galleries. Generallic applicable techniques on the subject of the investigation of geological environment, facility construction in deep underground and the reliability of geological deposal are developed during the phase. The feasibility and reliance of various technologies concerning geological disposal is demonstrated by widely opening the outcome to the public in the society.

Journal Articles

A Study of shallow groundwater flow based on groundwater level and geological structures in the Horonobe area, Hokkaido

Yokota, Hideharu; Yamamoto, Yoichi; Maekawa, Keisuke

Chikasui Gakkai-Shi, 53(2), p.193 - 206, 2011/05

It is important for assessing the safety of geological disposal of high-level radioactive waste to understand shallow to deep groundwater flow as the driving force of mass transport. JAEA has been carrying out the surface hydrological investigation in the Horonobe area, Hokkaido. Results of groundwater-level observations, and relationship between distributions of groundwater-level and geological structures suggest that constructions of underground facilities have no effect on shallow groundwater-level fluctuations, and that water infiltrate from ground surface into shallow underground in the snow covered season, and that water infiltrate into deeper underground along faults. In the future, it is necessary to quantitatively assess the water infiltration and recharge based on directly and/or indirectly observed data of evapotranspiration and soil moisture content by weighing lysimeter and ADR method soil moisture meter, and tensiometer.

Journal Articles

Spatial estimation of hydrological quantities at Horonobe basin in Hokkaido

Yamamoto, Yoichi; Maekawa, Keisuke; Yabuuchi, Satoshi; Yokota, Hideharu

Nihon Chikasui Gakkai 2010-Nen Shuki Koenkai Koen Yoshi, p.166 - 171, 2010/11

no abstracts in English

Journal Articles

Estimation of groundwater recharge rate by water balance method in Horonobe area, Hokkaido, Japan; Dec. 2004 $$sim$$ Nov. 2009

Yokota, Hideharu; Yamamoto, Yoichi; Yamazaki, Masanori; Maekawa, Keisuke

Nihon Chikasui Gakkai 2010-Nen Shuki Koenkai Koen Yoshi, p.160 - 165, 2010/11

no abstracts in English

Journal Articles

Relationship between hypocentral distribution and geological structure in the Horonobe area, northern Hokkaido, Japan

Tokiwa, Tetsuya; Asamori, Koichi; Hiraga, Naoto*; Yamada, Osamu; Moriya, Hirokazu*; Hotta, Hikaru*; Kitamura, Itaru*; Yokota, Hideharu

Proceedings of 13th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2010) (CD-ROM), p.117 - 122, 2010/10

In this paper, we discuss the relationship between the accurate hypocentral distribution and 3-D geological structure in and around the Horonobe area, Japan. We carried out multiplet-clustering analysis by using data of the 421 micro-earthquakes which occurred from 1st September, 2003 to 30th September, 2007. The 3-D geological structure model was mainly constructed from previous seismic reflection profiles and drilling data. As a result of this analysis, although there are some differences in depth between them, the hypocenters are distributed in NNW-SSE direction and become deeper from the west toward the east. The distributed pattern of the hypocenters is similar to the one of the geological structure. These results indicate that the hypocentral distribution may represent existence of active zone related to the geological structure, and provide effective information which can contribute to establishing methods for estimating the future evolution of the geological environment.

Journal Articles

A Study on groundwater infiltration in the Horonobe area, northern Hokkaido, Japan

Yokota, Hideharu; Yamamoto, Yoichi; Maekawa, Keisuke; Hara, Minoru*

Proceedings of 13th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2010) (CD-ROM), p.81 - 86, 2010/10

It is important for assessing the safety of geological disposal of high-level radioactive waste to understand groundwater flow as the driving force of mass transport. In the groundwater-flow simulation, hydraulic boundary conditions are required, including groundwater recharge rates. However, infiltration of water from the surface is difficult to clarify in detail because water near the surface is sensitive to external influence such as climatic variations. In the Horonobe area of northern Hokkaido, the Japan Atomic Energy Agency has been carrying out various hydrological observations to estimate the recharge rate. In the Horonobe area, subsurface temperature and soil moisture content have been observed at HGW-1 site and Hokushin Meteorological Station. These results have revealed the groundwater infiltration and recharge occurring throughout year, the shallow groundwater-infiltration velocity depending on the depth, and the position of Zero Flux Plane. In the future, it is necessary to quantitatively assess the shallow groundwater infiltration and recharge rate, the intermediate runoff, and the evapotranspiration based on the observed data of the weighing lysimeter, the tensiometer, and so on.

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