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The Micro-Pocket Fission Detector (MPFD) is a small-form-factor real-time fission chamber. MPFD performance has been simulated in the Advanced Test Reactor Critical Facility located at Idaho National Laboratory. The neutron and gamma-ray flux profiles and magnitudes were simulated using MCNP in the near-core B-8 irradiation position. These simulations were performed at 69 discrete axial locations inside the B-8 position 55 for three separate orientations of the nearby hafnium outer shim control cylinders and at a power level of 700 W(thermal). The resulting neutron and gamma-ray flux values were used to determine the MPFD response for various fissile masses and detector gas pressures. The optimal gas-operating pressure was determined to be between 30 and 60 psig. The required fissile layer mass was determined to be between 0.5 to 1.0 µg of 235U. Additionally, the gamma ray to fission fragment interaction rate was determined to be 1.43 × 103 with average energy deposition for gamma rays and fission fragments in 30 psig argon gas to be 1 keV and 3.5 MeV, respectively. [ABSTRACT FROM AUTHOR]

Micro-Pocket Fission Detectors (MPFDs) can be used to monitor a neutron flux within the core of a nuclear reactor. When assembled into an array, MPFDs can be used to simultaneously monitor the neutron flux at multiple locations within the reactor. One permutation of the MPFD is designed to be deployed into an iron wire flux port, typical for most research and commercial reactors. A single 5-node MPFD array was fabricated at deployed into a dry flux port within the central thimble of the Kansas State University TRIGA Mk. II research nuclear reactor. The sensitivity of each MPFD node at operating voltages of +50 V, +100 V, and +200 V was observed and an optimal operating voltage of +100 V was identified. No cross-talk was observed between instrument channels during real-time neutron flux measurement. Linear power tracking and real-time response to reactor power were both observed between 10 kWth and 100 kWth reactor power. [ABSTRACT FROM AUTHOR]

Advancements in nuclear reactor core modeling and computational capability have encouraged further development of in-core neutron sensors. Micro-Pocket Fission Detectors (MPFDs) have been fabricated and tested previously, but successful testing of these prior detectors was limited to single-node operation with specialized designs. Described in this work is a modular, four-node MPFD array fabricated and tested at Kansas State University (KSU). The four sensor nodes were equally spaced to span the length of the fuel-region of the KSU TRIGA Mk. II research nuclear reactor core. The encapsulated array was filled with argon gas, serving as an ionization medium in the small cavities of the MPFDs. The unified design improved device ruggedness and simplified construction over previous designs. A 0.315-in. (8-mm) penetration in the upper grid plate of the KSU TRIGA Mk. II research nuclear reactor was used to deploy the array between fuel elements in the core. The MPFD array was coupled to an electronic support system which has been developed to support pulse-mode operation. Neutron-induced pulses were observed on all four sensor channels. Stable device operation was confirmed by testing under steady-state reactor conditions. Each of the four sensors in the array responded to changes in reactor power between 10 kWth and full power (750 kWth). Reactor power transients were observed in real-time including positive transients with periods of 5, 15, and 30 s. Finally, manual reactor power oscillations were observed in real-time. [ABSTRACT FROM AUTHOR]

Preparation of thin U- and Th-coated 0.3 mm diameter Pt working electrodes by the cyclic potential sweep method is described. Uranyl- and thorium hydroxide layers were electrodeposited from ethanol solutions containing 0.02 M natural uranyl and 0.02 M natural thorium nitrate, each with 3.6 M ammonium nitrate. The cell for electrodeposition was specially developed in order to accommodate the small working electrodes for this research by including a working electrode probe, 3-D translation stage, and microscope. The source material deposition was analyzed using digital microscopy and scanning electron microscopy, and confirmed using x-ray fluorescence measurements. The appropriate potential range for electrodeposition was determined to be −0.62 V to −0.64 V for a 0.3 mm diameter Pt working electrode placed 1 cm from the counter electrode. Smooth, uniform deposition was observed near the central region of the working electrode, while surface cracking and crystalline formations were found near the edge of the working electrode. The final procedure for sample substrate preparation, electrolytic solution preparation and electrodeposition are described. [ABSTRACT FROM AUTHOR]

Objective Massive perivillous fibrin deposition ( MPFD) and maternal floor infarction ( MFI) are related placental lesions often associated with fetal death and fetal growth restriction. A tendency to recur in subsequent pregnancies has been reported. This study was conducted to determine whether this complication of pregnancy could reflect maternal antifetal rejection. Methods Pregnancies with MPFD were identified ( n = 10). Controls consisted of women with uncomplicated pregnancies who delivered at term without MPFD ( n = 175). Second-trimester maternal plasma was analyzed for panel-reactive anti- HLA class I and class II antibodies. The prevalence of chronic chorioamnionitis, villitis of unknown etiology, and plasma cell deciduitis was compared between cases and controls. Immunohistochemistry was performed on available umbilical vein segments from cases with MPFD ( n = 4) to determine whether there was evidence of complement activation (C4d deposition). Specific maternal HLA-antibody and fetal HLA-antigen status were also determined in paired specimens ( n = 6). Plasma CXCL-10 concentrations were measured in longitudinal samples of cases ( n = 28 specimens) and controls ( n = 749 specimens) by ELISA. Linear mixed-effects models were used to test for differences in plasma CXCL-10 concentration. Results (i) The prevalence of plasma cell deciduitis in the placenta was significantly higher in cases with MPFD than in those with uncomplicated term deliveries (40% versus 8.6%, P = 0.01), (ii) patients with MPFD had a significantly higher frequency of maternal anti- HLA class I positivity during the second trimester than those with uncomplicated term deliveries (80% versus 36%, P = 0.01); (iii) strongly positive C4d deposition was observed on umbilical vein endothelium in cases of MPFD, (iv) a specific maternal antibody against fetal HLA antigen class I or II was identified in all cases of MPFD; and 5) the mean maternal plasma concentration of CXCL-10 was higher in patients with evidence of MPFD than in those without evidence of MFPD ( P < 0.001). Conclusion A subset of patients with MPFD has evidence of maternal antifetal rejection. [ABSTRACT FROM AUTHOR]

An updated method of preparing thin, uranium-coated, 0.25-mm diameter platinum electrodes using the cyclic potential sweep method is described. Sixty-four samples were prepared using a 0.2 M UO 2 (NO 3) 2 solution with 19.695% enriched uranium. Improvements were made to the sample preparation, electrodeposition, and analysis methods, producing smoother samples with more uniform surface features than prior work. Alpha-particle spectrometry was used to determine the mass of uranium deposited on each sample. The average mass of uranium deposited on the metallic electrode from 100 potential sweep cycles was 0.987 × 10−7 g with a standard deviation of 0.860 × 10−7 g. Removing the outliers reduces the average deposited mass to 0.741 × 10−7 g with a standard deviation of 0.410 × 10−7 g. A smooth, uniform deposition was observed over the entire electrode after deposition and no cracking or crystalline formations were observed. This improved method of electrodeposition remains an attractive method of depositing fissile material onto small metallic substrates for the fabrication of Micro-Pocket Fission Detectors. [ABSTRACT FROM AUTHOR]