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Title: Observation and Measurement of Se-79 in SRS High-Level Tank Fission Product Waste

Abstract

The authors report the first observation of confirmed Se-79 activity in Savannah River Site high level fission product waste. Se-79 was measured after a seven step chemical treatment to remove interfering activity from Cs-137, Sr-90, and plutonium at levels 105 times higher than the observed Se-79 content and to remove Tc-99 at levels 300 times higher than observed Se-79. Se-79 was measured by liquid scintillation beta-decay counting after specific tests to eliminate uncertainties from possible contributions from Tc-99, Pm-147, Sm-151, Zr-93, or Pu-241, whose beta-decay spectra could appear similar to that of Se-79, and whose content would be expected at levels near or greater than Se-79.

Authors:
Publication Date:
Research Org.:
Savannah River Site (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
761147
Report Number(s):
WSRC-MS-99-00341
TRN: US0004385
DOE Contract Number:
AC09-96SR18500
Resource Type:
Conference
Resource Relation:
Conference: Conference title not supplied, No location, No date; Other Information: PBD: 21 Aug 2000
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; SELENIUM 79; FISSION PRODUCTS; SAVANNAH RIVER PLANT; LIQUID SCINTILLATION DETECTORS; TANKS; HIGH-LEVEL RADIOACTIVE WASTES; CONCENTRATION RATIO

Citation Formats

Dewberry, R.A. Observation and Measurement of Se-79 in SRS High-Level Tank Fission Product Waste. United States: N. p., 2000. Web.
Dewberry, R.A. Observation and Measurement of Se-79 in SRS High-Level Tank Fission Product Waste. United States.
Dewberry, R.A. Mon . "Observation and Measurement of Se-79 in SRS High-Level Tank Fission Product Waste". United States. doi:. https://www.osti.gov/servlets/purl/761147.
@article{osti_761147,
title = {Observation and Measurement of Se-79 in SRS High-Level Tank Fission Product Waste},
author = {Dewberry, R.A.},
abstractNote = {The authors report the first observation of confirmed Se-79 activity in Savannah River Site high level fission product waste. Se-79 was measured after a seven step chemical treatment to remove interfering activity from Cs-137, Sr-90, and plutonium at levels 105 times higher than the observed Se-79 content and to remove Tc-99 at levels 300 times higher than observed Se-79. Se-79 was measured by liquid scintillation beta-decay counting after specific tests to eliminate uncertainties from possible contributions from Tc-99, Pm-147, Sm-151, Zr-93, or Pu-241, whose beta-decay spectra could appear similar to that of Se-79, and whose content would be expected at levels near or greater than Se-79.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Aug 21 00:00:00 EDT 2000},
month = {Mon Aug 21 00:00:00 EDT 2000}
}

Conference:
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  • Closure of the remaining tanks and final disposition of the radioactive waste is a high priority task at both Savannah River Site (SRS) and Hanford. The radioactive waste in the tanks are generally found in layers: supernate (on top) containing soluble fission products, and salt-cake and sludge (on the bottom of the tank) containing insoluble actinides. One strategy for minimizing the waste volume is to segregate the low curie salt waste from the high curie salt supernate by draining the supernate and interstitial salt solution from the salt-cake. The retrieval of the interstitial fluid will require knowledge of relevant propertiesmore » of salt-cake waste including drainage parameters, more specifically, its hydraulic properties. The hydraulic parameters of the salt-cake have significance with respect to: 1) Kinetics of the retrieval process; and 2) Equilibrium conditions of the drainage. While the saturated hydraulic properties of the salt waste (hydraulic conductivity in the vertical and horizontal direction) can be used to determine the kinetics of the flow through the salt waste, the unsaturated properties are needed in order to assess not only the time frame of tank drainage but also the equilibrium conditions. How much and how fast fluid can be drained at given initial and boundary conditions (atmospheric pressure and temperature) can be analyzed. A series of dissolution and drainage experiments was conducted using S-112, S-109 and Tank 41 simulants in a pilot-scale column (1' diameter, 10' high). The major goal of these experiments was to determine the hydraulic parameters of flow through the column and the dissolution patterns upon addition of fresh water. The hydraulic experiments were conducted using interstitial fluid as well as fresh water. A series of one-step outflow experiments were used to evaluate the drainage patterns for salt-bed heights ranging from 1' to 8'. Measured data include bulk densities and saturated hydraulic conductivities as a function of temperature, and water retention characteristics for ambient temperature. Experiments in the range of 22-43 deg. C confirmed that the hydraulic conductivity in the vertical direction is strongly dependent on the temperature with variations most likely caused by physical-chemical changes in the salt-cake structure and the viscosity of the interstitial fluid. Evidence for the changes in salt-cake structure include: increased effluent specific gravity to 1.47, appearance of voids in the column, and a 10% reduction of the column height. A two-orders-of-magnitude difference in viscosity was observed when the temperature increased from 22 deg. C to 43 deg. C. The liquid retention parameters were determined using static retention points (derived from the multi-step outflow time series). Inverse analyses of the outflow data yielded additional unsaturated hydraulic conductivity parameters. The inverse analysis was performed by fixing saturated and residual water contents and the pore connectivity factor. Numerical simulations showed that the amount of drained fluid is directly related to van Genuchten's shape parameters n and {alpha} . On the other hand, the rate of drainage was directly related to saturated hydraulic conductivity. The recommended values for {alpha} and n with uncertainties in the parenthesis are respectively: 3.2(0.32) 1/m and 2.6(0.4). The recommended value for saturated hydraulic conductivity of salt-cake is 6.0E-06(3E-06). This work provides critical data about unsaturated hydraulic properties which can be used in numerical models to better predict removal of interstitial liquid from tanks that directly impact tank and site cleanup schedule and costs. (authors)« less
  • The solidification of high-level wastes is being evaluated as a method for final control of high-level nuclear wastes. The high temperatures required in the solidification process cause the volatilization of small amounts of fission products, primarily ruthenium and cesium. In order to determine cleanup requirements, a good understanding must be gained as to the quantities of fission products volatilized and how these quantities relate to operating conditions. The Pacific Northwest Laboratory, operated by Battelle-Northwest for the U.S. Department of Energy, has been investigating ruthenium and cesium volatilization in various calciners. Studies have been made using both simulated (nonradioactive) and radioactivemore » feedstock. The ongoing investigations have indicated that the semivolatile fission product losses are small enough to be controlled by off-gas cleanup treatment. During recent spray calcination of simulated high-level liquid waste, not more than 0.2 percent of the ruthenium and 0.1 percent of the cesium were lost to the off-gas system. Decontamination factors of about 600 for ruthenium and 1150 for cesium have been obtained across the spray calciner.« less
  • During normal operations at the Savannah River Site (SRS), tanks containing high-level radioactive waste are continuously ventilated to prevent accumulation of hydrogen gas within the vapor space. However, during some maintenance operations, the ventilation is temporarily halted. During a 1990 ventilation outage, hydrogen accumulated in a tank vapor space much more rapidly than expected. The accelerated rate of hydrogen evolution was traced to an air sparge within the tank solution which significantly increased the rate of hydrogen mass transfer from the liquid waste to the vapor space.
  • High level radioactive waste tanks at the Savannah River Site are high in salt content. The average Total Dissolved Solids (TDS) content is approximately 25%. For ICP-MS optimum signal stability and to reduce blockage of nebulizers and sampling orifices, it is usual to limit analyte solutions to a TDS content of nominally < 0.2%. Dilution to this level to reduce the matrix effect may push some analytes of interest below detectable levels. Five commercially available nebulizers were evaluated in a field study as part of the ICP-MS measurement system for their performance in a high salt matrix. The nebulizers surveyedmore » were a meinhard concentric, cross-flow, micro-concentric (MCN), V-groove, and a direct injection nebulizer (DIN). Analytes spiked into non-radioactive diluted salt solutions ranging from nominal 0.25--1.0% TDS were repetitively analyzed with the goal of determining stability of response signal and magnitude of any signal loss/suppression resulting from the diluted salt matrix. The cross-flow nebulizer provided the most stable signal for all salt matrices with the smallest signal loss/suppression due to this matrix. The DIN exhibited a serious lack of tolerance for TDS; possibly due to physical de-tuning of the nebulizer efficiency.« less
  • Solubility testing with actual High Level Waste tank sludge has been conducted in order to evaluate several alternative chemical cleaning technologies for the dissolution of sludge residuals remaining in the tanks after the exhaustion of mechanical cleaning and sludge sluicing efforts. Tests were conducted with archived Savannah River Site (SRS) radioactive sludge solids that had been retrieved from Tank 5F in order to determine the effectiveness of an optimized, dilute oxalic/nitric acid cleaning reagent toward dissolving the bulk non-radioactive waste components. Solubility tests were performed by direct sludge contact with the oxalic/nitric acid reagent and with sludge that had beenmore » pretreated and acidified with dilute nitric acid. For comparison purposes, separate samples were also contacted with pure, concentrated oxalic acid following current baseline tank chemical cleaning methods. One goal of testing with the optimized reagent was to compare the total amounts of oxalic acid and water required for sludge dissolution using the baseline and optimized cleaning methods. A second objective was to compare the two methods with regard to the dissolution of actinide species known to be drivers for SRS tank closure Performance Assessments (PA). Additionally, solubility tests were conducted with Tank 5 sludge using acidic and caustic permanganate-based methods focused on the “targeted” dissolution of actinide species.« less