The dissolution rate of spent nuclear fuel under environmental conditions has been studied heavily to understand the impacts of a failed waste package on potential radionuclide release from a geologic repository. Multiple countries have evaluated these scenarios in oxidizing and reducing environments respective to their relevant repository conditions. The repository environment (e.g., water chemistry, temperature, oxygen content) and the fuel itself (i.e., chemical composition of the fuel) both heavily impact the dissolution rate of the spent fuel. This work examined the impact that rare earth element dopants (Ce, Nd, Yb) have on the fuel dissolution under repository relevant conditions with decreasing oxidizing conditions using a single pass flowthrough system. UO2 samples were doped with Ce, Nd, or Yb with concentrations between 1 and 5 at%. The addition of dopants to the samples reduced the dissolution rates on most samples relative to pure UO2 samples. Preliminary experiments that occurred in a less oxidizing environment showed a reduction in dissolution rate compared to fully oxidizing conditions. The results within highlight the importance of dopant behavior in used fuel dissolution modeling.

This report presents the results of testing two rods after heat treatment at 400C for 8 hours and compares to the results from FY 2021 of similar rods that were tested as baseline. The heat treatment resulted in a decrease in yield stress.

o} stab flank. The round thread had a 0{sup o} load flank and 20{sup o} stab flank. Most of the testing was performed on the round thread form. Both a coupled connection design and an integral connection design were tested. The coupling was a pin by pin (male) thread, with the pipe having a box (female) thread. Both designs have outside and inside diameters that are flush with the pipe body. Both designs also contain a small external shoulder. The test procedure selected for this evaluation was the newly written ISO 13679 procedure for full scale testing of casing and tubing connections. The ISO procedure requires a variety of tests that includes makeup/breakout testing, internal gas sealability/external water sealability testing with axial tension, axial compression, bending, internal gas thermal cycle tests and limit load (failure) tests. This test was performed with four coupled samples and included most of these loads. Two integral samples were also included for limit load testing ISO makeup/breakout tests are divided into three types--initial makeup, IML1, repeated makeup within the same sample, MBL, and repeated makeup using several samples called round robin, RR. IMU and MBL were performed in this project. The ISO sealing and structural procedure is divided into four primary tests and identified as Series A, B, C and Limit Load (failure). Series A and B test to 95% actual yield of the pipe and Series C uses 90% of actual yield. Samples 1 and 3 were tested to Series A and the loads are shown in Figure 1. For these samples, the axial compression was limited to 75% pipe body yield, which was set by Mr. Watts at the beginning of the test. Samples 2 and 4 were tested to Series B with loads shown in Figure 2. This series included 20 degrees per 100 feet bending but no external pressure. Due to premature leaks, no samples were subjected to Series C which included mechanical and thermal cycles. Samples 5 and 6 were tested to failure. The project started with the selection and purchase of a popular size of oilfield pipe, which was 7-inch OD, 32 pound per foot, P-110 casing. While the connections were being threaded, material tensile tests were performed to get the actual strength of the 7-inch pipe. The first samples contained a square thread form. Excessive galling was experienced during the first series of makeup/breakout tests and Mr. Watts decided to change the thread form and remachine the samples. The second samples had a round thread form and performed very well in the makeup/breakout tests. Basically no galling occurred of any consequence. Samples 1 and 3 were to be tested with external water (ISO Series A) while samples 2 and 4 were to be tested with bending (ISO Series B, no external pressure). Testing of all four samples started with tension and internal gas pressure. During this initial pressure testing, samples 1, 3 and 4 developed leaks and the test was stopped before any external pressure or bending was applied. Sample 2 successfully tested to ISO Load Point 5 which included bending before developing a leak. Figure 3 shows the loads at which the samples leaked and the relative pipe body performance capability. Sample 1 and end A of sample 2 held a high pressure while samples 3, 4 and end B of sample 2 leaked at relatively low pressures. All of these leaks were with nitrogen gas pressure. After reviewing the results, it was believed that several conditions may have contributed to the premature leaks: The BOL 2000 thread lubricant contains solid particles that are larger than the solid particles in API 5A2 compound. Possibly the large particles prevented tight thread contact necessary for gas leak tightness. The BOL 2000 lubricant may have caused or at least contributed to the yielding of the pin end during makeup. Pin inward deformation was found in some pins subsequent to testing and breakout. Excessive yielding of the pin or box will contribute to poor thread contact and leakage. The connections were made up to full or near full shoulder contact. This causes the end of the pin to be stressed near the yield strength. This along with the interference caused by the thread compound may cause excessive pin hoop stresses and yielding which in turn gives relatively loose thread contact. This behavior is present when repeated makeup and breakout occurs.

The extraction of hexavalent actinides An(VI) by tri-butyl phosphate (TBP) was investigated by electronic absorption and vibrational spectroscopies. Through a series of spectral subtractions, vibrational spectra associated with TBP, TBP-HNO(3)adducts, and An(VI)-TBP complexes could be isolated. Investigation of U(VI) extracts indicated spectral features consistent with the formation of the expected [UO2(NO3)(2)(TBP)(2)] complex, but spectral features of other species were clearly evident. Likewise, multiple species were evident in the electronic absorption and vibrational spectra of TBP phases generated by extraction of Pu(VI). Although definitive characterization of the additional species formed could not be achieved in this work, it is hypothesized that they contain 3:1 TBP-to-An(VI) stoichiometry.

On-line monitoring based on optical spectroscopy provides unprecedented insight into the chemical composition of process streams or batches. Amplifying this approach through utilizing multiple forms of optical spectroscopy in sensor fusion can greatly expand the number and type of chemical species that can be identified and quantified. This is demonstrated herein, on the analysis of used nuclear fuel recycling streams: highly complex processes with multiple target and interfering analytes. The optical techniques of visible absorbance, near-infrared absorbance, and Raman spectroscopy were combined to quantify plutonium(III, IV, VI), uranium(IV, VI), neptunium(IV, V, VI), and nitric acid. Chemometric modeling was used to quantify analytes in process streams in real time, and results were successfully used to enable immediate process control and generation of a product stream at a set composition ratio. This represents a significant step forward in the ability to monitor and control complex chemical processes occurring in harsh chemical environments.

The co-decontamination (CoDCon) project was established in FY 2016 with the objectives of (a) evaluating the uncertainty in the uranium (U)/plutonium (Pu) ratio in a mixed U/Pu product from a tributyl phosphate (TBP)–based solvent extraction flowsheet, and (b) developing and demonstrating on-line optical spectroscopy for real-time monitoring of key components (e.g., Pu, U, and HNO3 concentrations) in the process solutions. We were interested in assessing the accuracy and precision to which a specific uranium-to-plutonium (U/Pu) ratio can be achieved, which for the purposes of this project was set at a U/Pu mass ratio of 7/3. The uncertainty associated with achieving this specific target U/Pu ratio was investigated during five flowsheet tests using laboratory-scale solvent extraction equipment. In addition, optical spectroscopic techniques were incorporated into the CoDCon solvent extraction testing system, allowing real time monitoring of all input and output process streams. Two CoDCon flowsheet tests were performed in FY 2018 using a simple dissolved fuel simulant containing only U (~1 M) and Pu (~15 mM) in nitric acid (HNO3; ~3 M). In FY 2019, two additional flowsheet tests were performed. For the first of these (CoDCon Run 3), the dissolved fuel simulant was similar to that used in the first two tests, with the inclusion of 1 mM neptunium (Np). The second test conducted in FY 2019 (CoDCon Run 4) used a more representative dissolved fuel simulant, including addition of non-radioactive fission product elements. A fifth CoDCon flowsheet test (CoDCon Run 5) was conducted in FY 2020, with the following additional objectives: (1) routing of the technetium (Tc) in the simulated dissolved fuel solution to the solvent extraction raffinate, and (2) routing of the Np in the simulated dissolved fuel solution to the U/Pu product. All tests used a bank of sixteen 2 cm centrifugal contactors. The tests involved first loading the solvent (30 vol% TBP dissolved in n-dodecane) with U and Pu (and Np, for Run 5), then the Pu (and Np) was stripped from the loaded solvent with a U(IV) solution (~50 mM) and the flowsheet conditions were adjusted such that some U partitioned into the Pu-containing product stream. The amount of U accompanying the Pu was monitored in real time using optical spectroscopic techniques coupled with chemometric modeling. Based on the real-time spectroscopic measurement of the U/Pu ratio, adjustments were made to the flowrate of the fresh TBP solvent phase used to scrub U from the aqueous Pu-containing product. This proved to be a very effective way to control the U/Pu mass ratio in the product. This report presents the results of the CoDCon Run 5 test. The flowsheet tested in Run 5 was substantially different than that run in the prior tests, especially the solvent loading section of the flowsheet. Two key changes were made. First, based on the objective to extract all the Np and route it with the U/Pu product, pentavalent vanadium [V(V)] was added to the feed and scrub solutions. The purpose of the V(V) was to convert all the Np to the +6 oxidation state, which is extractable by TBP. Second, a high acid (8 M HNO3) scrub was added to the flowsheet to scrub the Tc from the solvent. This was followed by a low acid scrub (0.05 M HNO3) to reduce the residual HNO3 concentration in the solvent prior to the Pu stripping step. The output from the low acid scrub was collected separately, rather than routing towards the raffinate. The modifications to the solvent loading part of the flowsheet were only partially successful. The treatment with V(V) was effective at converting the Np to Np(VI). Only 1.3% of the Np remained in the raffinate solution. However, ~40% of the Np stripped out of the solvent in the low acid scrub step; nearly 20% of the Pu also was stripped from the solvent during the low acid scrub. For further development, either modifications to the flowsheet, or concentration and recycle of the low acid stream into the

ABSTRACT Understanding the fundamental rates of transfer and complex formation is crucial in maintaining optimal efficiency and effectivity in solvent extraction. Methodologies to analyze solvent extraction systems are lacking in that they are commonly performed off-line in subsequent experiments. Thus, a method to proficiently investigate solvent extraction systems in a Lewis cell using in situ Raman spectroscopy paired with chemometric modeling has been developed to allow for on-line analysis and monitoring. Forward and reverse interfacial transfer coefficients for the extraction of nitric acid by tributyl phosphate, a process crucial to used nuclear fuel reprocessing, were measured by spectroscopic monitoring of both phases simultaneously in a two-phase solvent extraction system. Concentration data was derived from the chemometric modeling using Raman spectra. The concentration data was fit to a nonlinear least squares regression model to allow for the calculation of the transfer coefficients in the system. The reverse interfacial transfer coefficient, kr, was determined along with the parameter 95% confidence intervals and 95% prediction intervals. The forward interfacial transfer coefficient, kf, was then back calculated from kr and the aqueous phase and organic phase equilibrium concentrations. The average calculated values of kr and kf were 2.56 (± 0.50) × 10−5 m s−1 and 4.75 (± 1.13) × 10−6 m s−1, respectively. The information obtained regarding solvent extraction parameters and transfer can be applied in the study of systems of higher complexity, involving complex formation and their transfer across a liquid:liquid interface.

Microfluidic devices provide ideal environments to study solvent extraction. When droplets form and generate plug flow down the microfluidic channel, the device acts as a microreactor in which the kinetics of chemical reactions and interfacial transfer can be examined. Here, we present a methodology that combines chemometric analysis with online micro-Raman spectroscopy to monitor biphasic extractions within a microfluidic device. Among the many benefits of microreactors is the ability to maintain small sample volumes, which is especially important when studying solvent extraction in harsh environments, such as in separations related to the nuclear fuel cycle. In solvent extraction, the efficiency of the process depends on complex formation and rates of transfer in biphasic systems. Thus, it is important to understand the kinetic parameters in an extraction system to maintain a high efficiency and effectivity of the process. This monitoring provided concentration measurements in both organic and aqueous plugs as they were pumped through the microfluidic channel. The biphasic system studied was comprised of HNO3 as the aqueous phase and 30% (v/v) tributyl phosphate in n-dodecane comprised the organic phase, which simulated the plutonium uranium reduction extraction (PUREX) process. Using pre-equilibrated solutions (post extraction), the validity of the technique and methodology is illustrated. Following this validation, solutions that were not equilibrated were examined and the kinetics of interfacial mass transfer within the biphasic system were established. Kinetic results of extraction were compared to kinetics already determined on a macro scale to prove the efficacy of the technique.