Design of the Concrete Used for Sub-surface LLW Disposal Facility

Niwase, Kazuhito; Hironaga, Michihiko; Tsuji, Yukikazu

doi:10.3151/coj1975.44.2_3

Cited by 7 publications

(3 citation statements)

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“…However, the pH will decrease to a lower level in the third stage because the calcium leaching depth from cementitious materials after 50 000 years is in the range 60-160 mm. 7 As the initial residual oxygen in the system is consumed by corrosion, the redox environment gradually changes from oxidising to reducing. Therefore, the dominant corrosion mechanism in the first stage is regarded as an oxygen–consumption type; however, this changes to a hydrogen–evolution type in the second and third stages.…”

Section: Resultsmentioning

confidence: 99%

Corrosion properties of carbon steel for performance assessment of sub-surface disposal systems

Kumagai¹,

Niwase²,

Edamatsu³

et al. 2014

Corrosion Engineering, Science and Technology

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Sub-surface disposal systems are expected to contain a large amount of carbon steel as containers for radioactive waste or rebar of concrete pits. Corrosion expansion of the steel can cause cracking or expansion of cementitious materials and deteriorate the performance of low diffusivity of the systems. This study evaluated available literature with regard to the corrosion rate and corrosion expansion of the steel, with the aim of determining the most likely parameter values that are requested for performing safety assessment of the likely scenario by the former Japanese regulatory body. Furthermore, polarisation, electrolytic corrosion, and hydraulic tests considering the disposal conditions were conducted to verify the validity of some of the values.

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Section: Resultsmentioning

confidence: 99%

Corrosion properties of carbon steel for performance assessment of sub-surface disposal systems

Kumagai¹,

Niwase²,

Edamatsu³

et al. 2014

Corrosion Engineering, Science and Technology

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“…In the case of engineered barriers for nuclear waste disposal facilities in particular, long-term durability on the order of thousands of years is expected (Niwase et al 2006). The construction of engineered barriers at depths of less than one hundred meters below the surface is being planned.…”

Section: Introductionmentioning

confidence: 99%

Application of Electrical Treatment to Alteration of Cementitious Material due to Leaching

Hashimoto

Otsuki

Saito

et al. 2013

ACT

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Long-term durability against leaching is considered necessary and is currently treated as an important issue. Electrical treatment, which can accelerate deterioration due to ion migration, has been used to evaluate long-term durability against leaching. In the case of nuclear waste disposal and facilities, long-term performance for hundreds or thousands of years is expected. The purposes of this research were to investigate with electrical treatment 1) chemical alteration, such as decrease of Ca(OH) 2 and Ca/Si ratio of C-S-H, 2) physical alteration, such as increase of cumulative pore volume and threshold pore, 3) the feasibility of electrical treatment for the evaluation of diffusion coefficient alteration due to leaching with void ratio, and 4) the proposition of a simple and feasible method to evaluate the continuous pore structure after electrical treatment with MIP (Mercury Intrusion Porosimeter). This study yielded important data for understanding leaching alteration by electrical treatment and indicating the feasibility of applying electrical treatment. Moreover, it was revealed that the continuous pore structure, concerning the durability of cementitious materials, can be resolved by hysteresis curves under increased and decreased pressures in MIP.

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“…The service life is expected to exceed over 10,000 years, and the long-term stability of a radioactive waste repository is indispensable during the intended operation period. At present, for a subsurface low-level waste disposal facility in Japan, geological repository with a given engineered barrier system is planned for construction of 50-100 m underground with horizontal tunnels about 10 m in diameter (Niwase, Hironaga, & Tsuji, 2006). The barrier system consists of a multilayer system with compacted bentonite and cement-based materials (Sugiyama & Tsuji, 2008).…”

Section: Introductionmentioning

confidence: 99%

Nondestructive Integrated CT-XRD Method for Research on Hydrated Cement System

Sugiyama¹,

Hitomi²,

Kajiwara³

2014

Proceedings of the 4th International Conference on the Durability of Concrete Structures

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A nondestructive integrated CT-XRD method has been developed and used to study hydrated cement system. In this research, a beam line (BL) at the third-generation synchrotron radiation facility, SPring-8, in Japan, was used. First, X-ray computed tomography (CT) was employed to obtain three-dimensional (3D) images and select a region of interest (ROI) in a given plane section of the hardened cement paste. Then, X-ray diffraction analysis (XRD) was conducted on the specified region. These operations were implemented in situ without the removal of specimen from the stage inside the BL. The hardened cement paste was precracked and then leached by continuous water flow through the specimen, and the integrated CT-XRD method was conducted before and after the leaching test. In this way, the change in the hydrated cement system was characterized over time using the same specimen. CT observation provides the location of cracks and air voids as well as high and low density substances present in the hydrated cement system. ROI is arbitrarily determined at a set of coordinates at which one likes to evaluate the change in the cement system using XRD. This newly developed technique enables the evaluation of the presence of calcium hydroxide (portlandite) over time and space.

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Design of the Concrete Used for Sub-surface LLW Disposal Facility

Cited by 7 publications

References 0 publications

Corrosion properties of carbon steel for performance assessment of sub-surface disposal systems

Corrosion properties of carbon steel for performance assessment of sub-surface disposal systems

Application of Electrical Treatment to Alteration of Cementitious Material due to Leaching

Nondestructive Integrated CT-XRD Method for Research on Hydrated Cement System

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