Early construction and operation of the highly contaminated water treatment system in Fukushima Daiichi Nuclear Power Station (III) – a unique simulation code to evaluate time-dependent Cs adsorption/desorption behavior in column system

Abstract

A simulation code was developed to evaluate the performance of the cesium adsorption instrument operating in Fukushima Daiichi Nuclear Power Station. Since contaminated water contains seawater whose salinity is not constant, a new model was introduced to the conventional zeolite column simulation code to deal with the variable salinity of the seawater. Another feature of the cesium adsorption instrument is that it consists of several columns arranged in both series and parallel. The spent columns are replaced in a unique manner using a merry-go-round system. The code is designed by taking those factors into account. Consequently, it enables the evaluation of the performance characteristics of the cesium adsorption instrument, such as the time history of the decontamination factor, the cesium adsorption amount in each column, and the axial distribution of the adsorbed cesium in the spent columns. The simulation is conducted for different operation patterns and its results are given to Tokyo Electric Power Company (TEPCO) to support the optimization of the operation schedule. The code is also used to investigate the cause of some events that actually occurred in the operation of the cesium adsorption instrument.

Early construction and operation of highly contaminated water treatment system in Fukushima Daiichi Nuclear Power Station (I) – Ion exchange properties of KURION herschelite in simulating contaminated water

“…Adsorption isotherm equations are essential in developing a simulation code for the zeolite column, which has been developed aiming at evaluating the performance and predicting the operating conditions [13]. Several standard isotherm equations are already proposed for the zeolite column applied to the radioactive solution treatment [14].…”

Early construction and operation of the highly contaminated water treatment system in Fukushima Daiichi Nuclear Power Station (II) – dynamic characteristics of KURION media for Cs removal in simulated contaminated water

“…A 20% relative concentration of Cs was observed at about 200 bed volumes in the case of a solution velocity of 14 cm/min (A-3) and the same concentration was observed after about 100 and 50 bed volumes at 34 cm/min (A-2) and 81 (A-4) cm/min solution velocities, respectively. The adsorbed kinetic parameters consisted of the film mass transfer parameter and the effective intra-particle diffusivity [19]. These results suggest that the adsorbed kinetic parameters were influenced with an increase of the solution velocity up to 600 bed volumes.…”

“…These results suggested that the adsorbed amount of Cs at the perfect breakthrough point was in agreement with that at the equilibrium. In addition, if the kinetic parameter (the film mass transfer parameter and the effective intraparticle diffusivity) [19] was different with the Cs concentration from 0.57 to 4.0 ppm, the shape of the breakthrough curve must be changed. As the breakthrough curve was lapped over between 0.57 and 4.0 ppm, as shown in Figure 7, it was considered that the adsorbed kinetic parameters, that consisted of the film mass transfer parameter and the effective intra-particle diffusivity, were not changed between 0.57 and 4.0 ppm.…”

“…The adsorbed amounts of Cs had an almost constant value of about 3 × 10 −2 mmol/g at approximately 6000 bed volumes in the solution velocity range from 14 to 81 cm/min as shown in Table 6. Furthermore, the adsorbed kinetic parameters will be quantifiable when the breakthrough curves will be analyzed in detail by the simulation code [19].…”

Early construction and operation of the highly contaminated water treatment system in Fukushima Daiichi Nuclear Power Station (IV) - Assessment of hydrogen behavior in stored Cs adsorption vessel

“…The core of the system is the vessels filled with zeolite media which adsorbs the Cs in the contaminated water. Just after the accident, Central Research Institute of Electric Power Industry has started various technical supports [1][2][3][4] for Tokyo Electric Power Company to establish the system smoothly and to operate the system safely and stably. The study reported in this article, conducted from June to August in 2011, is about an assessment on the behavior of hydrogen in the used zeolite vessels stored in the same site.…”