Beric E. Wells

Pretreatment Engineering Platform Phase 1 Final Test Report

Pacific Northwest National Laboratory (PNNL) was tasked by Bechtel National Inc. (BNI) on the River Protection Project, Hanford Tank Waste Treatment and Immobilization Plant (RPP-WTP) project to conduct testing to demonstrate the performance of the WTP Pretreatment Facility (PTF) leaching and ultrafiltration processes at an engineering-scale. In addition to the demonstration, the testing was to address specific technical issues identified in Issue Response Plan for Implementation of External Flowsheet Review Team (EFRT) Recommendations - M12, Undemonstrated Leaching Processes.( ) Testing was conducted in a 1/4.5-scale mock-up of the PTF ultrafiltration system, the Pretreatment Engineering Platform (PEP). Parallel laboratory testing was conducted in various PNNL laboratories to allow direct comparison of process performance at an engineering-scale and a laboratory-scale. This report presents and discusses the results of those tests.

Estimate of Hanford Waste Rheology and Settling Behavior

The U.S. Department of Energy (DOE) Office of River Protection’s Waste Treatment and Immobilization Plant (WTP) will process and treat radioactive waste that is stored in tanks at the Hanford Site. Piping, pumps, and mixing vessels have been selected to transport, store, and mix the high-level waste slurries in the WTP. This report addresses the analyses performed by the Rheology Working Group (RWG) and Risk Assessment Working Group composed of Pacific Northwest National Laboratory (PNNL), Bechtel National Inc. (BNI), CH2M HILL, DOE Office of River Protection (ORP) and Yasuo Onishi Consulting, LLC staff on data obtained from documented Hanford waste analyses to determine a best-estimate of the rheology of the Hanford tank wastes and their settling behavior. The actual testing activities were performed and reported separately in referenced documentation. Because of this, many of the required topics below do not apply and are so noted.

An Approach to Understanding Cohesive Slurry Settling, Mobilization, and Hydrogen Gas Retention in Pulsed Jet Mixed Vessels

The Hanford Waste Treatment and Immobilization Plant (WTP) is being designed and built to pretreat and vitrify a large portion of the waste in Hanford’s 177 underground waste storage tanks. Numerous process vessels will hold waste at various stages in the WTP. Some of these vessels have mixing-system requirements to maintain conditions where the accumulation of hydrogen gas stays below acceptable limits, and the mixing within the vessels is sufficient to release hydrogen gas under normal conditions and during off-normal events. Some of the WTP process streams are slurries of solid particles suspended in Newtonian fluids that behave as non-Newtonian slurries, such as Bingham yield-stress fluids. When these slurries are contained in the process vessels, the particles can settle and become progressively more concentrated toward the bottom of the vessels, depending on the effectiveness of the mixing system. One limiting behavior is a settled layer beneath a particle-free liquid layer. The settled layer, or any region with sufficiently high solids concentration, will exhibit non-Newtonian rheology where it is possible for the settled slurry to behave as a soft solid with a yield stress. In this report, these slurries are described as settling cohesive slurries.

Predicting Peak Hydrogen Concentrations from Spontaneous Gas Releases in Hanford Waste Tanks

Buoyant displacement gas release events (BDGRE) are spontaneous gas releases that occur in a few of the Hanford radioactive waste storage tanks when gas accumulation makes the sediment layer buoyant with respect to the liquid. BDGREs are assumed to be likely if the ratio of the predicted sediment gas fraction and neutral buoyancy gas fraction, or buoyancy ratio, exceeds unity. Based on the observation that the buoyancy ratio is also an empirical indicator of BDGRE size, a new methodology is derived that formally correlates the buoyancy ratio and the peak headspace hydrogen concentration resulting from BDGREs. The available data on the six historic BDGRE tanks, AN-103, AN-104, AN-105, AW-101, SY-103, and SY-101, are studied in detail to describe both the waste state and the corresponding distribution of BDGREs. The range of applicability of the buoyancy ratio-based models is assessed based on the modeling assumptions and availability of tank data. Recommendations are given for extending the range of the models applicability.

Feasibility Study on Using a Single Mixer Pump for Tank 241-AN-101 Waste Retrieval

The objective of this evaluation was to determine whether a single rotating pump located 20 ft off-center would adequately mix expected AN-101 waste. Three-dimensional, AN-101 pump jet mixing simulation results indicate that a single, 20-ft off-centered mixer pump would mobilize almost all solids even at the furthest tank wall for sludge yield strength up to 150 Pa or less. Because the yield strength of the AN-101 waste was estimated to be less than 150 Pa, the AN-101 pump mixing model results indicate that a single mixer pump would be suffice to mobilize bulk of the disturbed and diluted AN-101 solids.

Pump Jet Mixing and Pipeline Transfer Assessment for High-Activity Radioactive Wastes in Hanford Tank 241-AZ-102

The authors evaluated how well two 300-hp mixer pumps would mix solid and liquid radioactive wastes stored in Hanford double-shell Tank 241-AZ-102 (AZ-102) and confirmed the adequacy of a three-inch (7.6-cm) pipeline system to transfer the resulting mixed waste slurry to the AP Tank Farm and a planned waste treatment (vitrification) plant on the Hanford Site. Tank AZ-102 contains 854,000 gallons (3,230 m{sup 3}) of supernatant liquid and 95,000 gallons (360 m{sup 3}) of sludge made up of aging waste (or neutralized current acid waste). The study comprises three assessments: waste chemistry, pump jet mixing, and pipeline transfer. The waste chemical modeling assessment indicates that the sludge, consisting of the solids and interstitial solution, and the supernatant liquid are basically in an equilibrium condition. Thus, pump jet mixing would not cause much solids precipitation and dissolution, only 1.5% or less of the total AZ-102 sludge. The pump jet mixing modeling indicates that two 300-hp mixer pumps would mobilize up to about 23 ft (7.0 m) of the sludge nearest the pump but would not erode the waste within seven inches (0.18 m) of the tank bottom. This results in about half of the sludge being uniformly mixed in the tank and the other half being unmixed (not eroded) at the tank bottom.

Dynamics of Crust Dissolution and Gas Release in Tank 241-SY-101

Due primarily to an increase in floating crust thickness, the waste level in Tank 241-SY-101 has grown appreciably and the flammable gas volume stored in the crust has become a potential hazard. To remediate gas retention in the crust and the potential for buoyant displacement gas releases from the nonconvective layer at the bottom of the tank, SY-101 will be diluted to dissolve a large fraction of the solids that allow the waste to retain gas. The plan is to transfer some waste out and back-dilute with water in several steps. In this work, mechanisms and rates of waste solids dissolution and gas releases are evaluated theoretically and experimentally. Particular emphasis is given to crust dissolution processes and associated gas releases, although dissolution and gas release from the mixed-slurry and nonconvective layers are also considered. The release of hydrogen gas to the tank domespace is modeled for a number of scenarios. Under the tank conditions expected at the time of back-dilution, no plausible continuous or sudden gas release scenarios resulting in flammable hydrogen concentrations were identified.

Lateral Earth Pressure at Rest and Shear Modulus Measurements on Hanford Sludge Simulants

This report describes the equipment, techniques, and results of lateral earth pressure at rest and shear modulus measurements on kaolin clay as well as two chemical sludge simulants. The testing was performed in support of the problem of hydrogen gas retention and release encountered in the double- shell tanks (DSTs) at the Hanford Site near Richland, Washington. Wastes from single-shell tanks (SSTs) are being transferred to double-shell tanks (DSTs) for safety reasons (some SSTs are leaking or are in danger of leaking), but the available DST space is limited.

Retrieval and Pipeline Transfer Assessment of Hanford Tank 241-AN-105 Waste

This study assesses five steps for Tank 241-AN-105 waste retrieval and subsequent pipeline transfer: 1. Remove supernatant liquid waste from AN-105 and transfer it through a pipeline with inline dilution with water (1st liquid waste transfer). 2. Add water (as a diluent) to Tank AN-105. 3. Mix the saltcake waste and water with mixer pumps to dissolve soluble solids. 4. Let undissolved solids settle to the tank bottom. 5. Remove the resulting supernatant liquid waste from Tank AN-105 (2nd liquid waste transfer). To assess these five steps for waste retrieval and pipeline transfer, AN-105 waste rheology was measured and solids identified with bright field image, select area diffraction, and energy dispersive x-ray spectroscopy. By combining available in situ and laboratory data, an AN-105 specific viscosity model was developed that can change from several centiPoise of viscosity to tens of millions of centiPoise as a function of strain rate and solid concentration. This viscosity mo del was implemented into the AN-105 computer model to simulate pump jet mixing. The report also evaluates AN-105 slurry waste transfer to AP-102 and AP-104 through a 3-inch (0.07-m) pipeline.

Rayleigh-Taylor Instability within Sediment Layers Due to Gas Retention: Preliminary Theory and Experiments

In Hanford underground waste storage tanks, a typical waste configuration is settled beds of waste particles beneath liquid layers. The settled beds are typically composed of layers, and these layers can have different physical and chemical properties. One postulated configuration within the settled bed is a less-dense layer beneath a more-dense layer. The different densities can be a result of different gas retention in the layers or different degrees of settling and compaction in the layers. This configuration can experience a Rayleigh-Taylor (RT) instability where the less dense lower layer rises into the upper layer. Previous studies of gas retention and release have not considered potential buoyant motion within a settle bed of solids. The purpose of this report is to provide a review of RT instabilities, discuss predictions of RT behavior for sediment layers, and summarize preliminary experimental observations of RT instabilities in simulant experiments.