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Abstracts
experimentally as the shotcrete material in construction of part of the 140m deep gallery in Horonobe URL. The
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. The 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
of Pd solubility were explained by the chemical equilibrium model.
This work was funded by ANRE: Agency for Natural Resources and Energy, of METI: Ministry of Economy, Trade
and Industry, of Japan.
7) 40047 – A study on groundwater infiltration in the Horonobe area, northern Hokkaido, Japan
Hideharu Yokota, Yamamoto Yoichi, Keisuke Maekawa, Minoru Hara, JAEA (Japan)
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. In the Horonobe area of northern Hokkaido, the Japan
Atomic Energy Agency (JAEA) has been carrying out the Horonobe Underground Research Laboratory (URL) Project to
understand characteristics of the geological environment. To obtain various hydrological data to estimate the recharge
rate by water balance, meteorological observation and observation of river flux, etc. in the Horonobe area (snowy cold
region) have been carried out. However, infiltration of water from the surface is difficult to clarify in detail because water
near ground surface is sensitive to external influence such as climatic variations. It is important for precise evaluation of
groundwater flow to understand shallow groundwater-flow systems (ground surface to tens of meters at depth) as a part
of hydraulic boundary conditions. In the Horonobe area, subsurface temperature and soil moisture content have been
observed at the URL (GL-0.7m to GL-2.3m) site since 2005 and at Hokushin Meteorological Station (HMS, GL-0.1m to
GL-1.1m) since 2008. As results of these observations, it is clear that similar processes operate at both sites. Subsurface
temperatures become lower with depth in the summer and higher with depth in the winter. The lowest subsurface
temperatures at the shallowest and deepest at depth are observed in the middle of April and early May respectively.
Concurrently, soil moisture content increases rapidly. In addition, the observed data also show that the subsurface
temperature is higher than 0°C throughout the year, and keeps decreasing until early May (snow-melting season). From
these results, it is suggested that, regardless of the air temperature, water at 0°C is supplied from the bottom of
snow-cover to ground surface by bottom snow melting due to the insulating effect of snow. Therefore, the subsurface
temperature firstly becomes the lowest at the shallowest depth. Subsequently, subsurface temperatures at greater depths
decrease as the cold water infiltrates to depth with time. For the estimation of boundary conditions in groundwater-flow
simulation, in this study, the shallow groundwater-flow system has been examined qualitatively on the basis of the
seasonal variation of the groundwater infiltration. Results have revealed the groundwater recharge occurring in a
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