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...