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

Abstracts
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. <strong>The</strong> 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. <strong>The</strong>refore, 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
snow-covered region. In the future, it is planed that quantitative assessments will be made by the observed data of the
weighing lysimeter.
8) 40051 – Effective Use of Uranium Resources and Dissolution of Recovery Uranium Storage Accumulation by a
Uranium Multi-recycle System
Yuzo Yamashita, Yuzo Yamashita, Takeshi Nakamura, Kyushu University (Japan)
<strong>The</strong> uranium recovered from LWR spent fuels, containing an amount of U-235 comparable to that in the natural
uranium, can be recycled as uranium fuels for LWRs by re-enrichment using a conventional centrifuge cascade. However,
the remade fuel is inferior to the original fuel produced from the natural uranium on the burn-up performance, because
the former includes U-236 as neutron absorber which is yielded in the spent fuel and then enhanced in re-enrichment
process. <strong>The</strong>refore, a few times recycle of recovered uranium may be available but its successive multi-recycle is not
recommendable because of successive decline in burn-up resulting from U-236 accumulating in remade fuels. In this
study, an idea of uranium fuel recycling is proposed which is of the feed-back of recovered uranium to a natural uranium
enriching cascade. Since this cascade processes a mixture of natural and recovered uranium, the product contains U-236
enriched but diluted with the U-236-free bulk of natural uranium. In this process, the concentration of U-236 in the fuels
reaches a balance with increase in recycle times. <strong>The</strong> multi-recycling fuels perform the burn-up degrees in PWRs
declining but comparing favorably with convetional uranium ones. <strong>The</strong> multi-recycling system not only makes effective
use of nuclear fuel resources, but also dissolves the problem of accumulating inventory in the storage of recovered
uranium taking the major volume of spent fuels.
9) 40053 – Advanced ORIENT Cycle - Progress on Fission Product Separation and Utilization
Isao Yamagishi, Masaki Ozawa, JAEA (Japan); Hitoshi Mimura, Tohoku Univ.(Japan);
Shohei Kanamura, Koji Mizuguchi, Toshiba Corporation (Japan)
Fission reaction of U-235 generates more than 40 elements and 400 nuclides in the spent fuel. Among them, 31
elements are categorized as rare metals. Typical yields of Pd, Ru, Rh (PGM) and Tc as rare metals will reach around
11kg, 13kg, 4kg and 3kg, respectively per metric ton of the reference FBR spent fuel (150GWd/t, cooled 5 years). Based
on a ground swell on enhancements of minimization of radio-ecological impacts and economical expenditures, nuclear
fuel cycle concept itself is required to be changed. Adv.-ORIENT (Advanced Optimization by Recycling Instructive
Elements) Cycle strategy was hence drawn up for the minimization of radioactive waste and utilization of
elements/nuclides in the wastes simultaneously., and has been developed at Japan Atomic Energy Agency. <strong>The</strong> present
paper deals with the separation process of fission products in the Adv.-ORIENT Cycle, which consists of the
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