UCB-NE-108 user's manual Page: 2 of 11
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The purpose of this manual is to provide users of UCB-NE-108 with the information necessary to use UCB-
DESCRIPTION OF THE CODE
UCB-NE-1081 is a computer code for calculating the fractional release ratel of readily soluble radionuclides
that are released from nuclear waste emplaced in water-saturated porous media, and transported through
layers of porous media. Waste placed in such environments will gradually dissolve. For many species such as
actinides and rare earths, the process of dissolution is governed by the exterior flow field, and the chemical
reaction rate or leaching rate.3 In a spent-flel waste package the soluble cesium and iodine accumulated
in fuel-cladding gaps, voids, and grain boundaries of spent fuel rods are expected to dissolve rapidly when
groundwater penetrates the fuel cladding.4 UCB-NF,108 is a code for calculating the release rate at the
interface of two layers of porous material, such as the backfill around a high-level waste package and natural
rock, to check compliance with the U. S. Nuclear Regulatory Commission's (USNRC) subsystem performance
objective. It is an implementation of the analytic solution given below.
The situation studied is shown in Figure 1. Waste face an internal gap or void space and is exposed in turn
to two layers of porous media. The first layer of thickness 6 can be a backfill in a nuclear waste package, and
the second the natural rock.
We define the origin at the interface of the two layers.
The governing equations are
8c De 82c1 D
at=DA e - st, -b < s<0, t> 0, Dlm ()
8t2 8s KD
6 = D28 -32 , z>,t>0,D2 r (2)
where c is the species concentration in ground water [M/L3],
D is the species diffusion coefficient (L2/t],
K is the species retardation coefficient,
e is the porosity,
A is the decay constant [t-9,
and subscripts 1 and t refer to the layer closer to the waste and further away respectively.
The side conditions are
ci(z,0) = 0, -b < s < 0, (3)
c2(Z,0) = 0, z > 0 (4)
CI(At) = c2(O,t), t > 0 (5)
1 = - c2D z =0, t > 0 (6)
=ct -c2at at_
c2(oo,t) = 0, t > 0 (7)
The species concentration in the two regions is coupled by a mass balance equation over the void volume V
with surface area S
-V ___(-_ ) = D ( + AVc (-b, t), t > 0 (8)
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Kang, C.H. & Lee, W.W.L. UCB-NE-108 user's manual, report, April 1, 1989; [Berkeley,] California. (https://digital.library.unt.edu/ark:/67531/metadc1108864/m1/2/: accessed March 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.