Ammonia concentration modeling based on retained gas sampler data

Terrones, Guillermo; Palmer, B.J.F.; Cuta, Judith M.

doi:10.2172/548906

Cited by 3 publications

(3 citation statements)

References 10 publications

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“…• Palmer et al (1996) and Terrones et al (1997), who modeled ammonia transfer through the crust, supernatant, and settled solid layers of waste in an undisturbed tank based on RGS data. These models typically predict higher ammonia concentrations and closer approaches to equilibrium than are borne out by the few observations.…”

Section: Theoretical Modeling Of Ammonia Releasesmentioning

confidence: 99%

Review of the Technical Basis of the Hydrogen Control Limit for Operations in Hanford Tank Farms

Mahoney¹,

Stewart²

2002

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The radioactive waste in Hanford tanks generates a flammable gas mixture and releases it into the tank headspace. The potential hazard resulting from flammable gas generation requires that controls be established to prevent ignition and halt operations if gas concentrations reach levels of concern. A control limit of 6,250 ppm hydrogen has been in use at Hanford for several years when only hydrogen is monitored. The hydrogen-based control limit is intended to conservatively represent 25% of the lower flammability limit of a gas mixture, accounting for the presence of flammable gases other than hydrogen, with ammonia being the primary concern. This report reviews the technical basis of the current control limit based on observed and projected concentrations of hydrogen and ammonia representing a range of gas release scenarios. The conclusion supports the continued use of the current 6,250-ppm hydrogen control limit.iv v

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Section: Theoretical Modeling Of Ammonia Releasesmentioning

confidence: 99%

Review of the Technical Basis of the Hydrogen Control Limit for Operations in Hanford Tank Farms

Mahoney¹,

Stewart²

2002

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“…Terrones et al (1997) modeled ammonia transport on several of the tanks for which RGS data were available. They calculated ammonia concentration profiles that were calibrated with the RGS ammonia measurements.…”

Section: 10mentioning

confidence: 99%

Flammable gas issues in double-contained receiver tanks. Revision 2

Peurrung¹,

Mahoney²,

Stewart³

et al. 1998

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SummaryFour double-contained receiver tanks (DCRTs) at Hanford will be used to store salt-well pumped liquids from tanks on the Flammable Gas Watch List. This document was created to serve as a technical basis or reference document for flammable gas issues in DCRTs. The document identifies, describes, evaluates, and attempts to quantify potential gas carryover and release mechanisms. It estimates several key parameters needed for these calculations, such as initial aqueous concentrations and ventilation rate, and evaluates the uncertainty in those estimates. It justifies the use of the Schumpe model for estimating vapor-liquid equilibrium constants. It identifies several potential waste compatibility issues (such as mixing and pH or temperature changes) that could lead to gas release and provides a basis for calculating their effects. It evaluates the potential for gas retention in precipitated solids within a DCRT and whether retention could lead to a buoyant displacement instability (rollover) event. It discusses rates of radiolytic, thermal, and corrosive hydrogen generation within the DCRT. It also describes in detail the accepted method of calculating the lower flammability limit (LFL) for mixtures of flammable gases.The report incorporates these analyses into two models for calculating headspace flammability, one based on instantaneous equilibrium between dissolved gases and the headspace and one incorporating limited release rates based on mass-transfer considerations. Finally, it demonstrates the use of both models to estimate headspace flammable gas concentrations and minimum ventilation rates required to maintain concentrations below 25% of the LFL. The report describes the methodology, the results at the only known (but probably highly underestimated) ventilation rate of 3 cfh, and the parametric sensitivity of the results.However, no actual predictions of DCRT headspace flammability are implied. This document is intended to provide background information for future DCRT modeling and recommendations for improving the technical basis of modeling. Although modeling results are presented here, the waste properties and potential pumping scenarios are so variable as to require case-by-case modeling for a safety basis. This document, therefore, does not and cannot provide a safety basis but rather guidance (based on current knowledge) as to conditions that a safety basis should meet.We have identified no major flaws in the approach previously published in a calc-note by Hedengren et aL (1997). Although we developed a somewhat different mathematical model for predicting flammable gas concentrations within the DCRT, we found little difference between our predictions and those from Hedengren et aL when the same initial dissolved gas concentrations were assumed. We also found that for most purposes the assumption of equilibrium does not produce large overestimates of DCRT headspace flammability until ventilation rates are much higher than the 3 cfh assumed in the other analyses. The analyses in this document in...

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“…(a) Using several measured parameters such as the concentration of ammonia in the dome space and within the sludge layer, the model can predict the rate of diffusion of ammonia within the nonconvective solids (sludge) layer. Recent results (Terrones et al 1997) reveal that the predicted effective diffusion coefficient of ammonia within the sludge layer is comparable to the rate of diffusion of ammonia in pure water. However, this value is nearly 20 times higher than the expected value of the diffusion coefficient of ammonia in a brine solution to be based on the Stokes-Einstein equation.…”

Section: O Introductionmentioning

confidence: 99%

Nuclear magnetic resonance measurement of ammonia diffusion in dense solid-liquid slurries

Bobroff¹,

Phillips²,

Shekarriz³

1997

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Executive SummaryThe diffusion of ammonium ions in aqueous solutions was measured by nuclear magnetic resonance (NMR) using the pulsed field gradient (PFG) method. The ammonium ions were obtained from aqueous solutions of ammonium chloride, ammonium sulfate, ammonium bicarbonate, and ammonium hydroxide. The translational diffusion of the ammonium ions was determined by measuring the diffusion of nitrogen nuclei (14N and 15N) in solution. Our results showed that the ammonium diffusion coefficient can be measured in aqueous solutions with concentrations as low as 20 x 10-3 M. Typical values measured for the diffusion coefficient of the ammonium ion are 2 x 10-5 cm2h (&lo%), similar to the values found for pure water. Due to the effect of the solution pH upon the NMR relaxation parameters for 14N, measurements are constrained to pH values below 8.5. However, 15N labeled ammonia is less sensitive to the solution pH, extending the measurement range to pH of 9.5. Diffusion measurements were conducted with solutions of varying viscosity and porosity. The results show that the solution viscosity has a measurable impact on the diffusion coefficient. The diffusion coefficient is almost inversely proportional to the relative viscosity of the solution, irrespective of how the viscosity is increased. Further, a randomly-packed porous bed of 200 mm PMMA resulted in a reduction of -30% in the diffusion coefficient as a result of hindered diffusion.

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Ammonia concentration modeling based on retained gas sampler data

Cited by 3 publications

References 10 publications

Review of the Technical Basis of the Hydrogen Control Limit for Operations in Hanford Tank Farms

Review of the Technical Basis of the Hydrogen Control Limit for Operations in Hanford Tank Farms

Flammable gas issues in double-contained receiver tanks. Revision 2

Nuclear magnetic resonance measurement of ammonia diffusion in dense solid-liquid slurries

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