MACRO - THE SAGA CONTINUES

Sandia National Laboratories/New Mexico (SNL/NM) has mixed low-level waste (MLLW) with upcoming deadlines under a Compliance Order with the State of New Mexico and the waste doesn't meet the waste acceptance criteria at commercial treatment facilities. Because of the radiological content, the waste was more suited for alternate debris treatment such as macroencapsulation (MACRO) instead of traditional shredding and stabilization. In 2001 SNL/NM personnel visited the Ashtabula Environmental Management Project (AEMP) and observed their macroencapsulation process. In August 2002 the MACRO system was transferred from AEMP to SNL, and SNL/NM contracted with AEMP for technical assistance in deploying the technology. The mixed waste debris treated by AEMP was bulk debris that had passed through a drying process. At SNL/NM, on-site treatment was needed for bagged waste, including waste that has been excavated from a landfill. Although soil has been brushed away from the debris items in the waste, there is residual moisture in the waste. In addition, work at SNL/NM is performed in a building without temperature controls and waste forms are exposed to the daily temperature swings typical in a desert environment. SNL/NM experienced problems with some waste forms cracking soon after being removed from the mold and with other "perfect" waste forms developing cracks weeks or months after creation. This paper describes SNL/NM's efforts to develop an on-site MACRO process to provide crack- free waste forms and to optimize the process to meet SNL/NM waste management needs. SNL/NM modified the process by adding heat blankets to the exterior of the molds to control cooling and used additional reinforcement (hardware cloth from the local home improvement store) to relieve internal stresses in the waste form. This paper also describes SNL/NM's investigation into methods to repair cracked waste forms.