Measuring and Predicting Fission Product Noble Metals in SRS HLW Sludges

Abstract

EXECUTIVE SUMMARYThe noble metals Ru, Rh, Pd, and Ag were produced in the Savannah River Site (SRS) reactors as products of the fission of U-235. Consequently they are in the High Level Waste (HLW) sludges that are currently being immobilized into a borosilicate glass in the Defense Waste Processing Facility (DWPF). The noble metals are a concern in the DWPF because they catalyze the decomposition of formic acid used in the process to produce the flammable gas hydrogen. As the concentration of these noble metals in the sludge increases, more hydrogen will be produced when this sludge is processed.a In the SRS Tank Farm it takes approximately two years to prepare a sludge batch for processing in the DWPF. This length of time is necessary to mix the appropriate sludges, blend them to form a sludge batch and then wash it to enable processing in the DWPF. This means that the exact composition of a sludge batch is not known for ~two years. During this time, studies with simulated nonradioactive sludges must be performed to determine the desired DWPF processing parameters for the new sludge batch. Consequently, prediction of the noble metal concentrations is desirable to prepare appropriate simulated sludges for studies of the DWPF process for that sludge batch. These studies give a measure of the amount of hydrogen that will be produced when that sludge batch is processed. This report describes in detail the measurement of these noble metal concentrations in sludges and a way to predict their concentrations from an estimate of the lanthanum concentration in the sludge. Results for two sludges are presented in this report. These are Sludge Batch 3 (SB3) currently being processed by the DWPF and a sample of unwashed sludge from Tank 11 that will be

DWPF Recycle Evaporator Shielded Cells Testing

“…A technical report has been recently issued concerning the form and fate of C-14 in the DWPF process. 15 The C-14 is present as a carbonate in the sludge and is neutralized by nitric and formic acids and evolved as CO 2 during SRAT processing. Table 5 presents the results of the calculations for the radioactive analytes not reported in Table 4.…”

“…For example, masses 107 and 109 were added together for the Ag. See reference WSRC-TR-2005-00098 for details15 . Calculation required to obtain concentration using available data for the blended feed, concentrate, and decontamination factors.…”

Actual waste demonstration of the nitric-glycolic flowsheet for sludge batch 9 qualification

“…Note that prior to the supernatant mercury measurements, AD performed permanganate-SRNL-STI-2016-00327 Revision 1 persulfate digestions on the acidified/diluted sample aliquots. For palladium, rhodium, ruthenium, and silver, the results were calculated utilizing measurements based on mass numbers 101-110, per the method documented by Bibler [6]. For uranium, the results were calculated by summing the measurements of mass numbers 233-236 and 238.…”

“…Canister decontamination water additions and removals (6) Frit and water additions and water removal 2Final dewater SRNL-STI-2016-00327 Revision 1 Figure 3-7 shows the helium, oxygen, and nitrogen concentrations during the SME cycle. The drops in helium correspond to breaches in the vessel: five decontamination water additions plus two frit/water additions.…”

“…Canister decontamination water additions and removals (6) Frit and water additions and water removal 2Final dewater SRNL-STI-2016-00327 Revision 1 Like the SRAT cycle, hydrogen was not detected during the SME cycle. Hydrogen was detected when mixing began (see .…”