119 The radionuclides migration model for the active bottom sediment phase is written as: ??? ?? = ??? ??(?)? ???? ? ?????(1 ? ?) + (??? ? ???) ? ??? (IX-14) The deposition and resuspension term are written as: ??? = ??(?)??(?)?(?) ???? ?1 ? ?? ??? ????? ?? < ??? (IX-15) ??? = ???? ??? ? ?? ??? ? 1? ???? ?? > ??? (IX-16) and: ??? = 0 ???? ?? > ??? (IX-17) ??? = 0 ???? ?? < ??? (IX-18) The di?usion terms of the radionuclide migration model for the dissolved phase and the LPM phase are solved by a particle tracking random-walk model. The location of a particle for sequential time steps with a time interval ?t is determined from: ?(? + ??) = ?(?) + ??? + ?? (IX-19) ?(? + ??) = ?(?) + ??? + ?? (IX-20) ?(? + ??) = ?(?) + ??? + ?? (IX-21) where (x, y, z)[t] and (x, y, z)[t + ?t] are the positions of a particle at the start and the end of a time step, respectively. The second and third terms on the right hand side of Eqs. IX-19–21 represent the movement of a particle due to advection and turbulent di?usion, respectively, in the ocean current. By using a uniform random number R(0) between 0 and 1, the di?usion terms can be expressed as [IX-6]: ?? = ?? = ?24????(0.5 ? ?(0)) (IX-22) ?? = ?24????(0.5 ? ?(0)) (IX-23) The concentration at each unit Eulerian cell, Cijk (Bq/m3), is calculated by summing up the contribution of each particle to the cell as follows: ???? = ? ???? ???,????? (IX-24) Su?xes i, j and k represent the cell number in the x?, y? and z? directions, respectively. The qn is the radioactivity (Bq) of the n?th particle and bn,ijk is the contribution ratio of the n?th particle to the corresponding Eulerian cell (ijk). This ratio is defined as the overlapping ratio of a Lagrangian cell whose center is the particle position to the Eulerian model cell. Vijk = H?x?y?z is the volume of the Eulerian model cell. Radioactive decay is considered for each Eulerian cell. The interactions between each phase are also calculated by using a stochastic method. The calculation techniques of this method are given in Ref. [IX-2].