Dissolution of Plutonium Metal in 8-10 M Nitric Acid

Abstract

The H-Canyon facility will be used to dissolve Pu metal for subsequent purification and conversion to plutonium dioxide (PuO 2) using Phase II of HB-Line. To support the new mission, the development of a Pu metal dissolution flowsheet which utilizes concentrated (8-10 M) nitric acid (HNO 3) solutions containing potassium fluoride (KF) is required. Dissolution of Pu metal in concentrated HNO 3 is desired to eliminate the need to adjust the solution acidity prior to purification by anion exchange. The preferred flowsheet would use 8-10 M HNO 3 , 0.015-0.07 M KF, and 0.5-1.0 g/L Gd to dissolve the Pu up to 6.75 g/L. An alternate flowsheet would use 8-10 M HNO 3 , 0.1-0.2 M KF, and 1-2 g/L B to dissolve the Pu. The targeted average Pu metal dissolution rate is 20 mg/min-cm 2 , which is sufficient to dissolve a "standard" 2250-g Pu metal button in 24 h. Plutonium metal dissolution rate measurements showed that if Gd is used as the nuclear poison, the optimum dissolution conditions occur in 10 M HNO 3 , 0.04-0.05 M KF, and 0.5-1.0 g/L Gd at 112 to 116 C (boiling). These conditions will result in an estimated Pu metal dissolution rate of ~11-15 mg/min-cm 2 and will result in dissolution times of 36-48 h for standard buttons. The recommended minimum and maximum KF concentrations are 0.03 M and 0.07 M, respectively. The maximum KF concentration is dictated by a potential room-temperature Pu-Gd-F precipitation issue at low Pu concentrations. Testing at 8-10 M HNO 3 , 0.1-0.2 M KF, and 1-2 g/L B demonstrated that ~20-35 mg/min-cm 2 Pu metal dissolution rates can be achieved at 112 to 116 C (boiling). The concentration of B in solution did not have a significant effect on dissolution rate. The data also indicate that lower KF concentrations would yield dissolution rates for B comparable to those observed with Gd at the same HNO 3 concentration and dissolution temperature. The low-temperature Pu precipitation issue associated with the use of Gd does not occur for dissolution with B; however, the B concentration must be maintained below the H 3 BO 3 solubility limit and the KF concentration must not exceed the value where B precipitates as KBF 4. To confirm that the optimal conditions identified by the dissolution rate measurements can be used to dissolve Pu metal up to 6.75 g/L in the presence of representative concentrations of Fe and Gd or B, a series of experiments was performed to demonstrate the flowsheets. In three of the five experiments, the offgas generation rate during the dissolution was measured and samples were analyzed for hydrogen gas (H 2). The use of 10 M HNO 3 containing 0.03-0.05 M KF, 0.5-1.0 g/L Gd, and 1.9 g/L Fe resulted in complete dissolution of the metal in 2.0-3.5 h. When B was used as the neutron poison, 10 M HNO 3 solutions containing 0.05-0.1 M KF, 1.9 g/L Fe, and 1 g/L B resulted in complete dissolution of the metal in 0.75-2.0 h. All experiments were performed using a dissolution temperature of 100 C. No residues were observed following the dissolutions in either the Gd or B system. Dissolut...

Small-Scale Testing of Plutonium (Iv) Oxalate Precipitation and Calcination to Plutonium Oxide to Support the Mox Feed Mission

“…The first feed source was δ-phase Pu metal dissolved using 8-10 M nitric acid (HNO 3 ), potassium fluoride (KF), and either gadolinium (Gd) or boron (B). 7 The second feed source was a mixed PuO 2 batch (termed HBL-11-OX8 or 3013 DE Feed) that was fused with sodium peroxide and dissolved in 8 M HNO 3 . The 3013 DE Feed contained impurities that are listed in Appendix A.…”

Technical Basis for Doe Standard 3013 Equivalency Supporting Reduced Temperature Stabilization of Oxalate-Derived Plutonium Oxide Produced by the Hb-Line Facility at Savannah River Site

“…The dissolution time and conditions are expected to be sufficient to completely dissolve all metal charged to the dissolver (Pierce, 2011;Rudisill and Pierce, 2012). In the unlikely event that any incompletely dissolved metal particles remain after dissolution and are transferred from the Canyon dissolver to HBL, some of the particles could persist in the process and be collected along with the oxalate precipitate during filtration.…”

Flowsheet Evaluation for the Dissolving and Neutralization of Sodium Reactor Experiment Used Nuclear Fuel

“…The accuracy of the density meter is 0.001 g/cm 3 for solutions with viscosity < 100 mPa*s and density < 2 g/cm 3 . The density meter was checked prior to operation by measuring the density of water at room temperature.…”

“…The experimental configuration for these studies was modeled after the apparatus in a recent report 3 , where dissolver solution is added into a glass reaction vessel, placed onto a hot plate-stirrer, and heated to 50-100 °C. A 75 mL dissolver solution volume was selected for dissolutions based on the available mass of Th metal, the calculated total gas production, and the minimum solution needed to completely cover the one inch square thorium coupon.…”

“…After the oxide film is breached at any point(s), several different metal HNO 3 reactions can take place to dissolve the thorium or oxidize it to ThO 2 . Fluoride in solution first attacks the oxide to form an oxyfluoride which can then be dissolved by HNO 3 . The following Equations were derived from Karraker's work in which HF was used.…”