FLUIDIZED BED STEAM REFORMER (FBSR) PRODUCT: MONOLITH FORMATION AND CHARACTERIZATION

Abstract

The most important requirement for Hanford's low activity waste (LAW) form for shallow land disposal is the chemical durability of the product. A secondary, but still essential specification, is the compressive strength of the material with regards to the strength of the material under shallow land disposal conditions, e.g. the weight of soil overburden and potential intrusion by future generations, because the term ''near-surface disposal'' indicates disposal in the uppermost portion, or approximately the top 30 meters, of the earth's surface. The THOR{reg_sign} Treatment Technologies (TTT) mineral waste form for LAW is granular in nature because it is formed by Fluidized Bed Steam Reforming (FBSR). As a granular product it has been shown to be as durable as Hanford's LAW glass during testing with ASTM C-1285-02 known as the Product Consistency Test (PCT) and with the Single Pass Flow Through Test (SPFT). Hanford Envelope A and Envelope C simulants both performed well during PCT and SPFT testing and during subsequent performance assessment modeling. This is partially due to the high aluminosilicate content of the mineral product which provides a natural aluminosilicate buffering mechanism that inhibits leaching and is known to occur in naturally occurring aluminosilicate mineral analogs. In order for the TTT Na-Al-Si (NAS) granular mineral product to meet the compressive strength requirements (ASTM C39) for a Hanford waste form, the granular product needs to be made into a monolith or disposed of in High Integrity Containers (HIC's). Additionally, the Hanford intruder scenario for disposal in the Immobilized Low Activity Waste (ILAW) trench is mitigated as there is reduced intruder exposure when a waste form is in a monolithic form. During the preliminary testing of a monolith binder for TTT's FBSR mineral product, four parameters were monitored: (1) waste loading (not optimized for each waste form tested); (2) density; (3) compressive strength; and (4) durability must not be compromised--binding agent should not react with the NAS product and binding agent should not create an unfavorable pH environment that may cause accelerated leaching. It is the goal of the present study to survey cementitious waste forms based on Ordinary Portland Cement (OPC), Ceramicrete, and hydroceramic binders by correlating waste loading, density and compressive strength and then determine if these binders affect the product performance in terms of the PCT response. This will be done by making a one-to-one comparison of the PCT response measured on granular NAS mineral product (mixed bed and fines products) with the PCT response of the monolithed NAS product in the different binders. Future studies may include, refining the above binders, and examining other binders. It is likely that binders formed from kaolin would be most compatible with the chemistry of the THOR{reg_sign} mineral waste form which is made by steam reforming of kaolin and sodium rich wastes. The economics of production on a large scale have yet to be investigated for any of the binders tested.