VARIABILITY OF KD VALUES IN CEMENTITIOUS MATERIALS AND SEDIMENTS
Measured distribution coefficients (K{sub d} values) for environmental contaminants provide input data for performance assessments (PA) that evaluate physical and chemical phenomena for release of radionuclides from wasteforms, degradation of engineered components and subsequent transport of radionuclides through environmental media. Research efforts at SRNL to study the effects of formulation and curing variability on the physiochemical properties of the saltstone wasteform produced at the Saltstone Disposal Facility (SDF) are ongoing and provide information for the PA and Saltstone Operations. Furthermore, the range and distribution of plutonium K{sub d} values in soils is not known. Knowledge of these parameters is needed to provide guidance for stochastic modeling in the PA. Under the current SRS liquid waste processing system, supernate from F & H Tank Farm tanks is processed to remove actinides and fission products, resulting in a low-curie Decontaminated Salt Solution (DSS). At the Saltstone Production Facility (SPF), DSS is mixed with premix, comprised of blast furnace slag (BFS), Class F fly ash (FA), and portland cement (OPC) to form a grout mixture. The fresh grout is subsequently placed in SDF vaults where it cures through hydration reactions to produce saltstone, a hardened monolithic waste form. Variation in saltstone composition and cure conditions of grout can affect the saltstone's physiochemical properties. Variations in properties may originate from variables in DSS, premix, and water to premix ratio, grout mixing, placing, and curing conditions including time and temperature (Harbour et al. 2007; Harbour et al. 2009). There are no previous studies reported in the literature regarding the range and distribution of K{sub d} values in cementitious materials. Presently, the Savannah River Site (SRS) estimate ranges and distributions of K{sub d} values based on measurements of K{sub d} values made in sandy SRS sediments (Kaplan 2010). The actual cementitious material K{sub d} values and solubility values differ from the sandy sediments. The K{sub d} value range and distribution currently used in the PA are estimated to range between 0.25*K{sub d} and 1.75*K{sub d}, where the minimum and maximum values of the ranges reflect the 95% confidence level for the mean K{sub d} value (Kaplan 2010). The objective of the research with cementitious materials was to measure the range and distribution of a monovalent (Cs) and I{sup -} (anion), divalent (Sr), and trivalent (Eu) ions for a variety of laboratory-prepared saltstone surrogate samples to establish a K{sub d} range other than that which is presently used in the PA. It has been observed in laboratory samples that cure temperature profiles can affect properties such as heat of hydration, permeability, porosity, compressive strength, and set time (Harbour et al. 2009). The intent was to identify a range and distribution that could be used by stochastic modelers for the PA. Furthermore, the intent was to replace the arbitrarily selected distributions based on geological sandy sediments and to base it on actual cementitious materials. The scope of this study did not include understanding saltstone sorption mechanisms responsible for increasing or decreasing sorption. Similar to the work with cementitious materials, the purpose of the Pu sediment K{sub d} dataset was not to attempt to understand through statistics how to better understand Pu sorption to sediments or to lower Pu K{sub d} variance. The sediment Pu K{sub d} data is included in this study because it is a key risk driver for the PAs on the SRS, and there is presently no direct studies of Pu variability in SRS soils. Instead the distribution of Pu sediment K{sub d} values was assumed to be similar to other cations, as presented by Kaplan (2010).
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-08SR22470
- OSTI ID:
- 1034390
- Report Number(s):
- SRNL-STI-2011-00672; TRN: US1200858
- Country of Publication:
- United States
- Language:
- English
Similar Records
Carbon-14 geochemistry at the Savannah River Site
OPERATIONAL AND COMPOSITIONAL FACTORS THAT AFFECT THE PERFORMANCE PROPERTIES OF ARP/MCU SALTSTONE GROUT
Related Subjects
54 ENVIRONMENTAL SCIENCES
ACTINIDES
BLAST FURNACES
CURING
ENVIRONMENTAL EXPOSURE
FISSION PRODUCTS
FLY ASH
GROUTING
HYDRATION
LIQUID WASTES
PERMEABILITY
PLUTONIUM
POROSITY
PORTLAND CEMENT
RADIOACTIVE WASTE FACILITIES
RADIOISOTOPES
SEDIMENTS
SLAGS
SOILS
SOLUBILITY
SORPTION
STORAGE FACILITIES
TANKS
WASTE FORMS