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Experimental investigations of piping phenomena in bentonite-based buffer materials for an HLW repository

Published online by Cambridge University Press:  09 July 2018

K. Suzuki ,
H. Asano ,
R. Yahagi ,
I. Kobayashi ,
P. Sellin ,
C. Svemar  and
M. Holmqvist
K. Suzuki*
Affiliation:
Radioactive Waste Management Funding and Reasearch Center 1-15-7, Tsukishima, Chuo-ku, Tokyo 104-0052, Japan
H. Asano
Affiliation:
Radioactive Waste Management Funding and Reasearch Center 1-15-7, Tsukishima, Chuo-ku, Tokyo 104-0052, Japan
R. Yahagi
Affiliation:
Radioactive Waste Management Funding and Reasearch Center 1-15-7, Tsukishima, Chuo-ku, Tokyo 104-0052, Japan
I. Kobayashi
Affiliation:
Kajima Corporation 2-19-1, Tobitakyu, Chofu-City, Tokyo 182-0036, Japan
P. Sellin
Affiliation:
Swedish Nuclear Fuel and Waste Management Co., Box250, SE-101 24 Stockholm, Sweden
C. Svemar
Affiliation:
SKB International, Box1091, SE-101 39 Stockholm, Sweden
M. Holmqvist
Affiliation:
SKB International, Box1091, SE-101 39 Stockholm, Sweden
*
*E-mail: k-suzuki@rwmc.or.jp
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Abstract

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During the installation of the buffer in a deposition hole of an HLW repository, it is necessary to control water flow from the fractured rock into the deposition hole. Water flow with inflow rate greater than 0.001 l/min may cause piping and erosion of the buffer, and may trigger mass redistribution of the buffer, sedimentation and material separation of bentonite materials. This paper describes the condition of parameters which cause piping and erosion; revised conditions which keep advection, inflow rate, buffer component, gap between buffer materials, gap between outside wall and buffer block, and type of water. The results from the experiment show the condition of the self-sealing function of bentonite materials, formation of piping, allowable limit of inflow rate in the case of an Na type bentonite block of 70 wt.% Kunigel V1 and 30 wt.% silica sand, or a pellet of 100 wt.% Kunigel V1. Piping and erosion continue until the engineered barrier (EB) is filled with water, and then the hydraulic gradient becomes small. Piping may lead to erosion and redistribution of material which needs to be taken into account in the long-term performance assessment.

Keywords

bentonite buffergeomechanicspipingerosionself-sealingwater inflow
Type
Research Article
Information
Clay Minerals , Volume 48 , Issue 2 , May 2013 , pp. 363 - 382
Creative Commons
Creative Common License - CCCreative Common License - BY
Copyright © The Mineralogical Society of Great Britain and Ireland 2013 This is an Open Access article, distributed under the terms of the Creative Commons Attribution license. (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2013

References

JNC (2000) Project to establish technical basis for HLW disposal in Japan. Supporting report 1 geological environment in Japan III-30III-34.Google Scholar
SKB TR-11-01 (2011) Long-term safety for the final repository for spent nuclear fuel at Forsmark. Main report of the SR-Site project Volume 1, 159 pp. Svensk Kärnbränslehantering AB.Google Scholar