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

Abstracts
impacts of natural events and processes. Consequently, we could outline the impacts of natural events and processes on
geological environment including hydrogeology, hydrochemistry and their evolutions. -We have been planning to
develop and apply a methodology of groundwater flow and solute transport analysis to the shallow part, the Horonobe
coastal area and around the URL. <strong>The</strong>se techniques would become a basis for future site specific safety assessment in
Japan.
SESSION D6: Waste Treatment and Non-Reactor
1) 40105 – Estimation of Radioactivity of Graphite Blocks in Tokai Power Station using Statistical Method
Masaaki Nakano, Fuji Electric Holdings Co., Ltd. (Japan);
Hisashi Mikami, Fuji Electric Systems Co., Ltd. (Japan);
Hideaki Ichige, Shinich Tsukada, JAPC (Japan)
Tokai Power Station (graphite moderated, gas-cooled reactor, GCR) stopped its commercial operation in March
1998 and is decommissioning now. Since graphite blocks in Tokai reactor core are major low level wastes (LLWs), the
realistic and reasonable method to estimate radioactivity of graphite blocks is required for final disposal and its licensing
procedure. In general, LLWs, which were installed in or around a reactor core, have large radioactivity, theoretical
calculations can be applied to the estimation of the radioactivity. This paper describes the concept of the method using
statistical approach to determine the radioactivity of the graphite blocks in the reactor core. This method directly
considers the variations of input calculation conditions, for example, compositions of impurity elements, irradiation
neutron flux and irradiation period. In this paper, the variations of the compositions of impurity elements were
statistically considered with the mean value and the standard deviation that were determined with elemental analyses.
Many activation calculations were performed with the compositions that were determined with pseudorandom numbers,
the mean value and the standard deviation. <strong>The</strong> calculated radioactivities distribute also statistically and a mean value and
a standard deviation of radioactivity can be determined. <strong>The</strong> distribution of calculated radioactivities shows consistency
to radiochemical analyses of graphite blocks from the reactor core and this shows that the method is applicable to the
estimation of the graphite block radioactivity. Furthermore, this method can be considered to reduce over-excess
estimation margin and can obtain reasonable radioactivity rather than using maximum or conservative values of all input
conditions. This method is now being developed and approved as one of basic procedure for determining the
radioactivity of wastes by Standards Committee of the Atomic Energy Society of Japan.
2) 40115 – <strong>The</strong> treatment of hexavalent chromium in waste liquid from Fugen Decommissioning
Yuki Yahiro, Seiji Yamamoto, Koji Negishi, Hitoshi Sakai, Tadashi Fukushima,
Norimasa Yoshida, Toshiba Corporation (Japan); Nobuo Ishizuka, Yuji Sato, Wataru Fujiwara, JAEA (Japan)
<strong>The</strong> prototype Advanced <strong>The</strong>rmal Reactor (ATR) Fugen Nuclear Power Station of JAEA terminated its operation in
2003 and is under decommissioning. In cooling water (90m3) for iron-water shield concrete surrounding the core region,
hexavalent chromium (K2CrO4) was dissolved as corrosion inhibitor. <strong>The</strong> hexavalent chromium has to be reduced to
trivalent chromium, for the safety. Authors had developed a new treatment technique for the waste liquid containing
hexavalent chromium with small amount of secondary waste. We manufactured and installed test equipment, and we
treated the waste liquid in Fugen. We added formic acid as pH adjuster in the water and hydrogen peroxide to reduce
hexavalent chromium to trivalent chromium. <strong>The</strong> residual hydrogen peroxide was decomposed to oxygen and water with
iron catalysis and UV lamp. <strong>The</strong>n cationic species, such as trivalent chromium and potassium, in waste liquid were
removed by cation exchange resin. <strong>The</strong> hydrogen peroxide and iron catalysis were added again to decompose the residual
formic acid to carbon dioxide gas and water. Next, the residual hydrogen peroxide was decomposed by catalase. Finally,
all the ionic species in the waste liquid were removed by mixed resin. It was confirmed that the concentration of
hexavalent chromium could be reduced to below 0.5ppm and total chromium concentration to below 2.0ppm. This value
is below the water pollution prevention law. It took 5 days for the whole treatment of 5m3 waste liquid containing the
hexavalent chromium 340ppm.
3) 40201 – Characterization of Radioactive Waste from Side Structural Components of a CANDU Reactor for
Decommissioning Applications in Korea
Rizwan Ahmed, Gyunyoung Heo, Kyung Hee University (Korea Rep.);
Dong-Keun Cho, Jongwon Choi, KAERI (Korea Rep.)
Reactor core components and structural materials of nuclear power plants to be decommissioned have been
irradiated by neutrons of various intensities and spectrum. This long term irradiation results in the production of large
number of radioactive isotopes that serve as a source of radioactivity for thousands of years for future. Decommissioning
of a nuclear reactor is a costly program comprising of dismantling, demolishing of structures and waste classification for
disposal applications. <strong>The</strong> estimate of radio-nuclides and radiation levels forms the essential part of the whole
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