Data Package for Secondary Waste Form Down-Selection—Cast Stone

Abstract

Executive SummaryThe objective of the data packages being generated for four potential waste forms for solidification/ stabilization of Hanford liquid secondary waste streams is to identify, evaluate, and summarize the existing information. This Cast Stone data package includes information available in the open literature and from data obtained from testing currently underway at Pacific Northwest National Laboratory (PNNL). As used at Hanford, the term Cast Stone describes a "grout"-based waste form made predominantly with fly ash and blast furnace slag (BFS) with lesser amounts of Portland cement as the starting dry blend. At Savannah River, this waste form is called Saltstone. The blend of grout reagents in Saltstone has been constant (45 weight percent [wt%] Grade 100 slag cement, 45 wt% Class F fly ash, and 10-wt% Type I/II Portland cement) since the Saltstone Disposal Facility began production in the early 1990s. At Hanford, some cementitious variants to Cast Stone have also been investigated, in which either the fly ash or the BFS is absent or replaced with another material. In this data package, these Cast Stone variants are included for completeness in the review. However, almost all the current Cast Stone waste form testing performed at PNNL uses a dry blend consisting of 47-wt% blast furnace slag (Grade 100), 45-wt% fly ash (Class F), and 8-wt% Portland cement (Type I/II). The sources of the three dry blend ingredients used at Hanford and Savannah River differ and may have subtle impacts on the physical and chemical attributes of the subsequent waste forms. The compositions of the secondary waste simulants used for the PNNL Cast Stone studies also differ from the simulants and actual wastes solidified at Savannah River; although both are caustic-, saline-and sodium-dominated solutions. The Hanford secondary waste simulants anion composition contains much less nitrate/nitrite than the waste streams solidified at Savannah River.Available literature on Cast Stone and Saltstone was reviewed with an emphasis on determining how Cast Stone and related grout waste forms performed in relationship to various criteria that will be used to decide whether a specific type of waste form meets acceptance criteria for disposal in the Integrated Disposal Facility (IDF) at Hanford. The draft waste acceptance criteria include the following requirements or targets:• acceptable leachate concentrations (less than the Universal Treatment Standards in 40 CFR 268) for Resource Conservation and Recovery Act (RCRA) metals using the Toxicity Characteristic Leach Procedure (TCLP) leach test• low bleed water criteria (i.e., no bleed water is tolerated after 28 days of curing)• low leachability index (LI) values for sodium (LI>6), technetium-99 (target LI>9) and iodine-129 (target LI>11)• minimum compressive strength of 500 psi (3.45 MPa).Other attributes of the Cast Stone process were compared with additional criteria, such as:• worker and public safety concerns• cost effectiveness versus other candidate waste forms in regard to ...

Technetium and Iodine Getters to Improve Cast Stone Performance

“…The Cast Stone baseline dry blend mix currently used is 8 wt% Portland cement Type I/II, 45% Class F fly ash, and 47% Grade 100 or 120 blast furnace slag. Based on preliminary studies of secondary waste simulants (Sundaram et al 2011;Mattigod et al 2011a), other data reviewed by Serne and Westsik (2011), and the general similarity of liquid secondary wastes to LAW (both are high-sodium, nitrate-dominated caustic brines), Cast Stone may also be a worthy candidate for immobilization of liquid LAWs. Therefore, Cast Stone is also being evaluated as a supplemental immobilization technology to provide the necessary LAW treatment capacity to complete the tank waste cleanup mission in a timely and cost-effective manner.…”

The function of Sn(II)-apatite as a Tc immobilizing agent

“…A possible application of the Tc removal ability of Sn-A is in the fabrication of low [26,42] although the short term measurements do not account for any potential long term release of Tc due to exposure to the dissolved oxygen in vadose zone pore water and susceptibility of Tc(IV) species to reoxidation. [43] Therefore an opportunity exists for improved retention of Tc within cementitious waste forms.…”

Supplemental Immobilization Cast Stone Technology Development and Waste Form Qualification Testing Plan

“…The following sections describe the Cast Stone waste form, its container and the production process for preparing the waste form. The Cast Stone data package prepared by Serne and Westsik (2011) provides a detailed compilation of work on the Cast Stone waste form.…”