Potential for the Rapid Transport of Plutonium In Groundwater as Demonstrated By Core Column Studies
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POTENTIAL FOR THE RAPID TRANSPORT OF PLUTONIUM IN GROUNDWATER AS DEMONSTRATED BY CORE COLUMN STUDIES D.R. CHAMP, W.F. MERRITT, and J.L. YOUNG Toe Cnalk River Nuclear Laboratories Atomic Energy of Canada Limited Chalk River, Ontario Canada, KOJ iJO
INTRODUCTION The mobility of radionuclides in
groundwater flow systems can be signifi-
cantly altered by processes such as complexation,
sorption on particulates,
hydrolysis, precipitation and the formation of colloids.
vide potentially significant pathways for transport of radionuclides in biosphere.
Previous soil column studies
or
Such processes prothe
demonstrated that radiocesium could
be transported by particulates and that the process was likely mediated by micro-organisms.
That observation provided a plausible mechanism to explain
the anomalously rapid transport of small amounts of cesium-137 released from glass blocks buried below the water table at the Chalk River Nuclear 2 Laboratories The behaviour of plutonium in
soils is
apparently covered largely by pro-
cesses which influence the chemistry of the Pu (IV)
ion.
Wildung et al3 main-
tained that higher oxidation states are reduced to Pu (IV) which can then undergo extensive hydrolysis to produce insoluble products. should effectively inhibit Pu transport in
the biosphere.
Such reactions However,
ation with organic and inorganic ligands can stabilize Pu (IV) lysis and increase its
solubility.
complex-
against hydro-
Analysis of surface soils that contain Pu
has shown that a small percentage of the Pu remains in as colloidal particles4 and therefore is
solution predominantly
available for transport.
has examined the potential for the transport of Pu in
This study
a groundwater flow system
through the use of laboratory columns prepared from "undisturbed" horizontal cores taken from saturated zone soils adjacent to the glass block site.
The
columns were spiked with 239Pu, continuously eluted with groundwater from the glass block site, and the activity and physical-chemical characteristics of the 239Pu in
the effluent determined following various manipulations of the
column elution conditions. MATERIALS AND METHODS Pu Solution - The Pu solution contained 76.8, 19.7, 2.9, 0.5 and 0.1 atom % 239Pu, 240Pu, 241Pu, 242Pu, and 238Pu respectively. In the text the predomi-
746
nant isotope,
239Pu, is
used when referring to this mix of isotopes.
Soil Columns - Soil columns were prepared from undisturbed horizontal cores of uncontaminated saturated zone sand taken upgradient of the glass block site. The columns (4.5 cm x 11 cm,
void volume -54 mL) were equilibrated for 1 to 3
months with groundwater,
taken from a well adjacent to the site, with an up-i ward flow of approximately 45 cm-d (approximately 3 times the groundwater flow rate at the site).
Columns were loaded with 80 pg (10 pCi or 3.1xlO5 Bg)
of 239Pu, obtained by a 100-fold dilution of a stock 239Pu solution (8 M HNO3), and eluted with groundwater.
The column effluent was collected for analysis.
Effluent Analysis - 239
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