NMR study of C-A-S-H structures

Hanamachi, Yuji*; Walker, C.*; Sasamoto, Hiroshi; Mihara, Morihiro

NIMS Bisai Kozo Kaiseki Purattofuomu Riyo Hokokusho (Internet), 2 Pages, 2023/12

A High-volume Fly ash Silica fume Cement (HFSC) has been considered as the use of concrete support of drift in deep disposal of radioactive wastes. JAEA has been carried out experiments and modeling studies to evaluate chemical stability of C-A-S-H gel synthesized which would be believed as the dominant component of the HFSC. For the modeling purpose, it is necessary to evaluate the chemical composition both of C-A-S-H gel synthesized and accompanied minerals in the experiment. In the year of 2020, Al and Si NMR measurement were performed to identify Al and Si distribution in the sample and chemical composition of C-A-S-H gel was derived. However, it was impossible to derive the C-A-S-H gel composition having the expected Al/Si molar ratio since there were several accompanied minerals produced in the experiment due to the short term of immersion. This time similar approach to derive C-A-S-H gel composition is adopted using NMR measurement for the sample of longer time (6 months).

NMR study of C-A-S-H structures

Walker, C.*

NIMS Bisai Kozo Kaiseki Purattofuomu Riyo Hokokusho (Internet), 2 Pages, 2021/09

High content fly ash silica fume cement (HFSC) has been considering a candidate low alkali cements for the geological disposal of radioactive waste in Japan. JAEA has been currently performing many experiments and modeling studies relevant to validation for the long-term stability of the C-A-S-H gel which is a dominant component of the HFSC. For developing the C-A-S-H model of hydration and degradation, it is necessary to determine the composition of C-A-S-H gel and accompanied minerals when it reacts with water. In the present subject, the synthesized sample of C-A-S-H gels were analyzed by using the NMR spectra of Al and Si to determine the coordination of these element in the C-A-S-H gel.

Natural systems evidence for the effects of temperature and the activity of aqueous silica upon montmorillonite stability in clay barriers for the disposal of radioactive wastes

Savage, D.*; Wilson, J.*; Benbow, S.*; Sasamoto, Hiroshi; Oda, Chie; Walker, C.*; Kawama, Daisuke*; Tachi, Yukio

Applied Clay Science, 179, p.105146_1 - 105146_10, 2019/10

https://doi.org/10.1016/j.clay.2019.105146

Natural systems evidence for the effects of temperature and the activity of aqueous silica upon montmorillonite stability was evaluated. Thermodynamic modeling using three different TDBs shows that stability fields for montmorillonite exist from 0 to 140C, but at low values of silica activity, a stability field for illite replaces that for montmorillonite. Pore fluid chemical and mineralogical data for sediments from ODP sites from offshore Japan show a trend from montmorillonite + amorphous silica stability at temperatures up to 60C to that for illite + quartz at higher temperatures. However, even over very long timescales ( 1 Ma), smectite does not transform to illite under thermodynamically-favourable conditions at temperatures less than 80C.

Hydration and degradation of High content Fly ash Silica fume Cement (HFSC)

Anraku, Sohtaro; Walker, C.*; Oda, Chie; Mihara, Morihiro; Honda, Akira

Proceedings of 15th International Congress on the Chemistry of Cement (ICCC 2019) (Internet), 11 Pages, 2019/09

Calcium silicate hydrate (C-S-H) gel solubility data and a discrete solid phase model at 25C based on two binary non-ideal solid solutions

Walker, C.; Suto, Shunkichi; Oda, Chie; Mihara, Morihiro; Honda, Akira

Cement and Concrete Research, 79, p.1 - 30, 2016/01

https://doi.org/10.1016/j.cemconres.2015.07.006

Modeling the solubility behavior of calcium silicate hydrate (C-S-H) gel is important to make quantitative predictions of the degradation of hydrated ordinary Portland cement (OPC) based materials. Experimental C-S-H gel solubility data have been compiled from the literature, critically evaluated and supplemented with new data from the current study for molar Ca/Si ratios = 0.2-0.83. All these data have been used to derive a discrete solid phase (DSP) type C-S-H gel solubility model based on two binary non-ideal solid solutions in aqueous solution(SSAS). Features of the DSP type C-S-H gel solubility model include satisfactory predictions of pH values and Ca and Si concentrations for all molar Ca/Si ratios = 2.7 0 in the C-S-H system, portlandite (CH) for Ca/Si ratios 1.65, congruent dissolution at Ca/Si ratios = 0.85, and amorphous silica (SiO) for Ca/Si ratios 0.55 as identified in the current study by IR spectroscopy.

Port-based plasma diagnostic infrastructure on ITER

Pitcher, C. S.*; Barnsley, R.*; Bertalot, L.*; Encheva, A.*; Feder, R.*; Friconneau, J. P.*; Hu, Q.*; Levesy, B.*; Loesser, G. D.*; Lyublin, B.*; et al.

Fusion Science and Technology, 64(2), p.118 - 125, 2013/08

https://doi.org/10.13182/FST13-A18065

The port-based plasma diagnostic infrastructure on ITER is described, including the port plugs, the interspace support structure and port cell structure. These systems are modular in nature with standardized dimensions. The design of the equatorial and upper port plugs and their modules is discussed, as well as the dominant loading mechanisms. The port infrastructure design has now matured to the point that port plugs are now being populated with multiple diagnostics supplied by a number of ITER partners - two port plug examples are given.

Development of grouting technologies for HLW disposal in Japan, 1; Overall program and key engineering technologies

Fujita, Tomoo; Kawaguchi, Masanao; Walker, C.; Sasamoto, Hiroshi; Yui, Mikazu; Onishi, Yuzo*

Proceedings of 7th Asian Rock Mechanics Symposium (ARMS-7) (USB Flash Drive), p.675 - 681, 2012/10

The Japan Atomic Energy Agency started new grout project for geological disposal of high-level radioactive waste in 2007. This study presented the overall JAEA grout project program and an example of how to apply key engineering technologies to the construction and operation of an underground facility for the geological disposal of HLW.

Accelerated hydration of high silica cements

Walker, C.; Yui, Mikazu

NEA/RWM/R(2012)3/REV, p.159 - 163, 2012/03

https://www.oecd-nea.org/rwm/docs/2012/rwm-r2012-3.pdf#page=161

no abstracts in English

Electromagnetic studies of the ITER generic upper port plug

Sato, Kazuyoshi; Yaguchi, Eiji; Pitcher, C. S.*; Walker, C.*; Encheva, A.*; Kawano, Yasunori; Kusama, Yoshinori

Fusion Engineering and Design, 86(6-8), p.1264 - 1267, 2011/10

https://doi.org/10.1016/j.fusengdes.2011.02.020

no abstracts in English

Isomeric states observed in heavy neutron-rich nuclei populated in the fragmentation of a Pb beam

Steer, S. J.*; Podolyk, Z.*; Pietri, S.*; Grska, M.*; Grawe, H.*; Maier, K.*; Regan, P. H.*; Rudolph, D.*; Garnsworthy, A. B.*; Hoischen, R.*; et al.

Physical Review C, 84(4), p.044313_1 - 044313_22, 2011/10

https://doi.org/10.1103/PhysRevC.84.044313

Heavy neutron-rich nuclei were populated via the fragmentation of a E/A=1 GeV Pb beam. Secondary fragments were separated and identified and subsequently implanted in a passive stopper. By the detection of delayed rays, isomeric decays associated with these nuclei have been identified. A total of 49 isomers were detected, with the majority of them observed for the first time. Possible level schemes are constructed and the structure of the nuclei discussed. To aid the interpretation, shell-model as well as BCS calculations were performed.