Numerical Modeling of 90Sr and 137Cs Transport from a Spill in the B-Cell of the 324 Building, Hanford Site 300 Area

Abstract

SummaryIn October 1986, a spill of a highly radioactive waste stream containing cesium ( 137 Cs) and strontium ( 90 Sr) occurred in the B-Cell of the 324 Building in the 300 Area of the Hanford Site. The spill is estimated to have contained approximately 1.3 million curies of radioactivity. An unknown fraction of this spill was lost to the subsurface through a leak in the sump in the floor of B-Cell.To characterize the extent of contamination under the 324 Building, a pit was excavated on the north side of the building in 2010 by Washington Closure Hanford LLC (WCH). Horizontal closed-end steel access pipes were installed under the foundation of the building from this pit and were used for measuring temperatures and exposure rates under the B-Cell. The deployed sensors measured elevated temperatures of up to 61 °C (142 °F) and exposure rates of up to 8,900 R/hr. WCH suspended deactivation of the facility because it recognized that building safety systems and additional characterization data might be needed for remediation of the contaminated material. The characterization work included additional field sampling, laboratory measurements, and numerical flow and transport modeling.Laboratory measurements of sediment physical, hydraulic, and geochemical properties were performed by Pacific Northwest National Laboratory (PNNL) and others. Geochemical modeling and subsurface flow and transport modeling also were performed by PNNL to evaluate the possible extent of contamination in the unsaturated sand and gravel sediments underlying the building. Historical records suggest that the concentrated 137 Cs-and 90 Sr-bearing liquid wastes that were spilled in B-Cell were likely from a glass-waste repository testing program associated with the Federal Republic of Germany (FRG). Incomplete estimates of the aqueous chemical composition (no anion data provided) of the FRG waste solutions were entered into a geochemical speciation model and were charge balanced with nitrate to estimate waste composition. Additional geochemical modeling was performed to evaluate reactions of the waste stream with the concrete foundation of the building prior to the stream entering the subsurface.One-dimensional (1-D) and three-dimensional (3-D) flow and transport simulations were performed using the STOMP simulator. Vertically oriented 1-D reactive transport simulations were conducted for three different water release scenarios using a reaction network that considered aqueous speciation, ion exchange, and mineral precipitation and dissolution reactions. The 1-D simulations were performed to evaluate the potential influence of waste chemistry and ion-exchange processes on vertical radionuclide transport for a range of possible water release rates. Three-dimensional simulations were also performed using a linear adsorption isotherm (K d ) model to provide estimates of the possible extent of contamination in both the vertical and lateral directions underlying the B-Cell. K d values in the 3-D model were adjusted, although not optimized, to obtain im...

Colloquium : Neutrino detectors as tools for nuclear security

“…Industrial-scale reprocessing results in significant quantities of liquid, highly radioactive wastes. Historically, for the nuclear weapons programs of the US and USSR, these wastes have been stored in underground tank farms and their corrosion presents a major problem due to the risk of ground water contamination (Jaraysi et al, 2006;Rockhold et al, 2012). Given that 90 Sr is extracted into the aqueous phase in the PUREX process, these RW tanks also contain large quantities of 90 Sr and thus are the source of detectable neutrino emissions.…”

Antineutrino Monitoring of Spent Nuclear Fuel

“…At the time, a large amount of strontium-90 and caesium-137, with a total activity of 1.3 MCi was released from a hot cell. Half of it leaked into the ground and is now presumed to be located within a 10 meter × 10 meter area about 2 meters below ground level [31]. In 2010, a pit was excavated ∼ 20 meters from the spill to drive long steel pipes into the affected area, thus allowing the deployment of temperature and activity sensors.…”

System-Scale Model of Aquifer, Vadose Zone, and River Interactions for the Hanford 300 Area - Application to Uranium Reactive Transport

“…All excavated waste sites were then backfilled to grade with "clean" sediments and re-vegetated with native plants. Most of the planned 300 Area building decommissioning and demolition activities are now complete, with the exception of the 324 Building (Rockhold et al 2012).…”

“…The 300 Area, located in the southeast corner of the Hanford Site (Figure 1.1), has been the subject of a great deal of field characterization and scientific inquiry for more than two decades owing primarily to a persistent groundwater uranium plume (Peterson et al 2008;. In addition to uranium, there are several other contaminants of concern in the 300 Area (Rockhold et al 2012;Peterson 2005), some of which are described briefly at the end of this section. The system-scale model described herein represents a tool for integrating all available characterization and monitoring data with experimentally validated process models for contaminant transport and fate in the subsurface.…”

“…Finally, other contaminants of concern are briefly discussed. Some of the information in Section 1 is from previous reports (Peterson et al 2008;Rockhold et al 2012) but is reviewed here for completeness. Section 2 provides details on model development and inverse parameter estimation.…”