The 13th International Conference on Environmental ... - Events

Abstracts
conditions in siliceous mudstones at the URL. <strong>The</strong> objective of this work is to establish a strategy for an in situ stress
measurement program for geological disposal and to develop an understanding of the in situ stress conditions in the deep
underground formed by the sedimentary rocks. <strong>The</strong> application of several stress measurement methods to the Horonobe
siliceous mudstones carried out during the surface-based investigations and the investigations during construction of the
underground facilities, as well as information on the initial stress state around the Horonobe URL are described in this
paper. During the surface-based investigations, determination of deep in situ stress was done using hydraulic fracturing
(HF), borehole breakout information in deep boreholes and core-based methods such as AE and DSCA. Subsurface
investigations during construction of the underground facilities utilized, the Compact Conical Ended Borehole
Overcoring (CCBO) method and hydraulic testing of pre-existing fractures (HTPF) were conducted in order to validate
results from initial stress measurements in the surface-based investigations. HF results indicate that horizontal maximum
and minimum principal stresses increase linearly with depth. <strong>The</strong> minimum principal stress is almost equivalent to
overburden pressure. <strong>The</strong> maximum principal stress estimated from the HF and borehole breakout data is almost E-W.
This is similar to the tectonic movement direction in the vicinity of the Horonobe URL. Due to tectonic movement,
horizontal maximum stress is almost 1.5 times larger than the horizontal minimum stress. Vertical stress determined from
HTPF during construction of the underground facilities is almost equal to the overburden pressure.
5) 40038 – Low alkaline Cement Used in the Construction of a Gallery in the Horonobe Underground Research
Laboratory
Masashi Nakayama, Haruo Sato, Yutaka Sugita, Seiji ITO, JAEA (Japan);
Masashi Minamide, Yoshito Kitagawa, Taisei Cooperation (Japan)
In Japan, any high level radioactive waste repository is to be constructed at over 300m depth below surface. Tunnel
support is used for safety during the construction and operation, and shotcrete and concrete lining are used as the tunnel
support. Concrete is a composite material comprised of aggregate, cement and various additives. Low alkaline cement
has been developed for the long term stability of the barrier systems whose performance could be negatively affected by
highly alkaline conditions arising due to cement used in a repository. Japan Atomic Energy Agency (JAEA) has
developed a low alkaline cement, named as HFSC (High fly-ash silicafume cement), containing over 60wt% of
silica-fume (SF) and coal ash (FA). JAEA are presently constructing an underground research laboratory (URL) at
Horonobe for research and development in the geosciences and repository engineering technology. HFSC was used
experimentally as the shotcrete material in construction of part of the 140m deep gallery in Horonobe URL. <strong>The</strong>
objective of this experiment was to assess the performance of HFSC shotcrete in terms of mechanics, workability,
durability, and so on. HFSC used in this experiment is composed of 40wt% OPC (Ordinary Portland Cement), 20wt% SF,
and 40wt% FA. This composition was determined based on mechanical testing of various mixes of the above
components. Because of the low OPC content, the strength of HFSC tends to be lower than that of OPC in normal
concrete. <strong>The</strong> total length of tunnel using HFSC shotcrete is about 73m and about 500m3 of HFSC was used. This
experimental construction confirmed the workability of HFSC shotcrete. Although several in-situ experiments using low
alkaline cement as shotcrete have been performed at a small scale, this application of HFSC at the Horonobe URL is the
first full scale application of low alkaline cement in the construction of a URL in the world. In the paper, we present
detailed results of the in-situ construction test and the future works.
6) 40040 – Effects of Nitrate on Nuclide Solubility for Co-location Disposal of TRU Waste and HLW
Gento Kamei, Morihiro Mihara, JAEA (Japan); Toshiyuki Nakazawa,
Norikazu Yamada, Mitsubishi Materials Corp. (Japan)
TRU wastes are generated by reprocessing spent fuel from nuclear power plants and by fabricating MOX fuel in
Japan. Some of the TRU wastes are expected to be disposed of deep underground to isolate it from the biosphere in the
long-term. To optimize the disposal of TRU waste, a co-location disposal with high level waste, HLW, is being
considered. A part of TRU waste includes a large amount of nitrate salt, the effects of which have to be evaluated in a
safety assessment of co-location disposal.
Solubility is one of the important parameters for the safety assessment of HLW disposal. Large concentrations of
nitrate ions from TRU waste might affect the oxidation state and consequently the solubility of different radionuclides in
the HLW waste. In addition, it is necessary to consider complex formation of nitrate ions with radionuclides, as well as
the formation of ammonia by microbes and/or by reactions with reducing materials in the disposal facility. Consequently,
complex formation of ammonia with radionuclides must also be evaluated.
In the current study, the effects of nitrate salt on radionuclide solubility were investigated experimentally with
consideration given to the above perturbations. Solubility experiments of important and redox sensitive radionuclides,
Tc(IV), Np(IV) and Se(0), were performed using various concentrations of sodium nitrate (NaNO3) and of Np(V) in
NaNO3 solutions to investigate complex formation with NO3- ions. Solubility experiments of Pd(II), Sn(IV) and Nb(V)
using ammonium chloride (NH4Cl) solution were also undertaken to investigate complex formation with NH3/NH4+
ions. A chemical equilibrium model was applied to assist the interpretation of the experimental results. No significant
solubility enhancement was observed for Np and Se due to oxidation by nitrate ions. Tc solubility was, however,
increased by one order of magnitude under high nitrate concentrations. Solubility enhancement by complex formation of
nitrate ions with Np(V) was not observed. Solubility enhancement by complex formation of Sn and Nb were not also
observed, only Pd solubility was increased by complex formation with NH3/NH4+ ions. Tendencies of the enhancement
103