CATALYTIC INTERACTIONS OF RHODIUM, RUTHENIUM, AND MERCURY DURING SIMULATED DWPF CPC PROCESSING WITH HYDROGEN GENERATION
Simulations of the Defense Waste Processing Facility (DWPF) Chemical Processing Cell (CPC) vessels were performed as part of the ongoing investigation into catalytic hydrogen generation. Rhodium, ruthenium, and mercury have been identified as the principal elemental factors affecting the peak hydrogen generation rate in the DWPF Sludge Receipt and Adjustment Tank (SRAT) for a given acid addition. The primary goal of this study is to identify any significant interactions between the three factors. Noble metal concentrations were similar to recent sludge batches. Rh ranged from 0.0026-0.013% and Ru ranged from 0.010-0.050% in the dried sludge solids, while initial Hg ranged from 0.5-2.5 wt%. An experimental matrix was developed to ensure that the existence of statistically significant two-way interactions could be determined without confounding of the main effects with the two-way interaction effects. The nominal matrix design consisted of twelve SRAT cycles. Testing included: a three factor (Rh, Ru, and Hg) study at two levels per factor (eight runs), two duplicate midpoint runs, and two additional replicate runs to assess reproducibility away from the midpoint. Midpoint testing can identify potential quadratic effects from the three factors. A single sludge simulant was used for all tests. Acid addition was kept effectively constant except to compensate for variations in the starting mercury concentration. Six Slurry Mix Evaporator (SME) cycles were performed to supplement the SME hydrogen generation database. Some of the preliminary findings from this study include: (1) Rh was linked to the maximum SRAT hydrogen generation rate in the first two hours after acid addition in preliminary statistical modeling. (2) Ru was linked conclusively to the maximum SRAT hydrogen generation rate in the last four hours of reflux in preliminary statistical modeling. (3) Increasing the ratio of Hg/Rh shifted the noble metal controlling the maximum SRAT hydrogen generation rate from Rh to Ru when Ru was at its fission yield ratio to Rh. (4) The inhibiting effect of Hg on hydrogen generation apparently does not require much mercury in terms of moles Hg/mole Rh (or Ru). Once the initial impact is realized, the benefit of additional Hg in reducing the hydrogen generation rate was minimal. Sludge Batch 3 and 4 simulant test data confirm this. (5) Low Hg runs do not necessarily bound high Hg runs for the maximum hydrogen generation rate over the full SRAT-SME cycle. Two of the four Rh-Ru combinations had a cross-over point where the hydrogen generation rate in high Hg run went from always lower to always higher than in the low Hg run. One cross-over was in the SRAT and one was in the SME. Maximum hydrogen generation rates in the high Hg runs could exceed the maximum hydrogen generation rates from the low Hg runs. (6) SME cycle hydrogen generation rates during the first decon canister dewatering period were similar to the rates at the end of the SRAT reflux period. (7) Corrosion of 400 series stainless steel shafts significantly impacted the hydrogen generation rate in two runs. (8) Preliminary data analysis indicates that several additional SRAT runs are needed to replace suspect data in the original set of twelve runs. A more detailed statistical evaluation is expected to occur once replacement run data from several additional SRAT runs has been obtained.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-08SR22470
- OSTI ID:
- 940023
- Report Number(s):
- WSRC-STI-2008-00235; TRN: US200823%%757
- Country of Publication:
- United States
- Language:
- English
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