Retained Hydrogen Literature Study for DWPF

Abstract

SRNL-STI-2019-00394 Revision 0 vi volume, purge rate, and power input, this data cannot be directly applied to the DWPF, but it is important to note that hydrogen is released over a finite time, rather than instantaneously. Previous work by SRNL and PNNL has measured the rheology of Hanford sludge, and shown the rheology (i.e., yield stress or shear strength) to increase as the sludge is allowed to settle. Changes in sludge rheology need to be considered when assessing changes to the DWPF retained hydrogen program. A comparison of buoyancy and inertial forces under SRAT operating conditions (1-10 Pa yield stress, 1.38 g/mL density, 65 or 130 rpm, 9,000 gallons of feed) on the bubbles (approximated as 300 micron diameter) found the inertial forces to be more than 350,000 times larger than the buoyancy forces. With this ratio of forces, the gas bubbles generated will follow the fluid motion in the SRAT, and only release when they reach the slurry-vapor interface. An informal Lattice Boltzmann Computation Fluid Dynamics calculation was performed on a SRAT type vessel. The liquid was assumed to have a density of 1 g/mL and a viscosity of 20 cP. In the simulation, approximately 50% of the bubbles were released to the vapor space over ~80 seconds. The simulation showed the bubbles to follow the liquid flow, and only release when they reached the liquid surface.

Modeling DWPF Hydrogen Gas Retention and Release

“…The search also identified a Lattice-Boltzmann computational fluid dynamics (CFD) software that could model and predict hydrogen release from DWPF vessels. 2 SRR requested Savannah River National Laboratory (SRNL) personnel to pursue this software and focus the model for hydrogen gas retention and release to provide evidence that might justify more realistic assumptions. 3 The work included the following 5 tasks:…”

“…The amount of the tracer (i.e. hydrogen) leaving the slurry as a function of time, R(t), is described by equation [2].…”

“…At this range of bubble sizes, the momentum forces from the impeller and fluid motion greatly exceed the buoyancy forces acting on the bubbles. 2 The graph on the right shows the concentration of hydrogen in the head space as a function of bubble size and time. Again, there is no significant effect of bubble size.…”

“…Figure 23 and Table 4 show the results. The range of yield stress was selected to include the yield stress of the slurry in Sludge Batch 8 (7.2 Pa) 23 , the design basis for the SRAT (1.5 -5 Pa) 2,23,24 , the design basis for the SME and MFT (2.5 -15 Pa) 2,23,24 , and the maximum yield stress measured during sludge batch qualification testing (21 Pa) 2 . The results show that between a yield stress of 1.5 Pa and 21 Pa, yield stress has a small effect on the release of hydrogen from the slurry in the SRAT (a 27% increase in the time to release 50% of the hydrogen between 1.5 Pa and 21 Pa).…”

Tank 49H Solids Disturbance Analysis

“…However, its simulation results have been compared with data for other SRS applications such as impeller mixing of tanks and jet mixing of miscible liquids. 13 It is a tool to complement the analysis performed in the previous section and to evaluate alternative approaches to preventing added liquid in Tank 49H from disturbing the solid particles on the bottom of the tank. In addition, the M-Star® software provides a method to quantify the mass of solid particles that are disturbed by the "plunging jet".…”