Basalt cores fissured

Table VI shows the concentrations of plutonium, neptunium, and uranium measured at the inlet and outlet of the unaltered and hydrothermally-altered basalt core fissures in the first five analog experiments (see Table I) Under conditions simulating a repository that was unaltered by groundwater interaction (Table I, Exp 1-3), both Np and Pu, in the concentrations developed in these analog experiments from the leaching of the waste form, were substantially retarded within the 14.6-cm basalt fissure In fact, as can be seen from Figure 4, almost all of Np activity was sorbed on the first one-third of the rock fissure The data in Figure 4 have an estimated error, based on counting statistics above, of approximately 2 counts per 1000 seconds Uranium retardation was determined to be not as complete ...

The fissured basalt cores and bentonite were altered by placing them in an autoclave under simulated groundwater at 320°C for 30 and 60 days to simulate 1000 y and 2000 y aging, respectively The waste-form wafers for both experiments were aged in the same manner by treating them for 17 days in saturated steam at 340°C The details of these procedures and the rationale for their use have been published previously (7). The effects of saturated steam on borosilicate glass were discussed in a recent publication (8) ... 

Changes in Analog Groundwater Composition The data in Figure 2 for the first three analog experiments (which used unaltered waste form, bentonite, and basalt cores) show that the groundwater exiting the basalt fissure reaches a steady-state composition for [Na+] and [Ca +] soon after the start of the experiment ... 

To test this model of the relationship of the surface absorption coefficient to the migration rate through the fissure, we constructed a model fissure. This was done by sealing a smooth slab cut from a basalt core to the face of a Teflon block that had a 0.0127-cm depression milled dovm its face. This then formed a Assure that was 0.0127 X 1 X 4 cm in size, tracer was dissolved in 10 ml of water and allowed to... 

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