A modelling methodology for the description of helium behaviour accounting for the grain-size distribution

Physics-based meso-scale models of fission gas behaviour for fuel performance codes currently consider only the average grain size as physical parameter to describe the fuel microstructure. Nevertheless, information on the grain-size distribution is available for several metallographically characterized fuel samples. To extend the current modelling approach, we present new experimental data and develop a methodology to treat the fuel grain-size distribution based on multi-grain analysis. This is applied to describe helium behaviour from infused and annealed polycrystalline UO2 samples. The methodology consists of three steps: (1) Acquisition of the empirical grain distribution from sections of the polycrystals, (2) Calculation of the gas distribution factor pertaining to each grain size class after helium infusion, and (3) Simulation of the experimental annealing histories with input parameters weighted by the gas distribution factors. To perform the multi-grain analysis, we used the SCIANTIX code, which allows calculating the helium kinetics in a single fuel grain. The application of this methodology is promising because it can represent the dynamics of helium release more consistently with the physics of the fuel microstructure compared to the state-of-art approaches, and it can be suitable for application in fuel performance codes for different enhanced accident tolerant fuel concepts as outlined in our conclusions

On the Dalitz Plot Approach in Non-leptonic Charm Meson Decays

We claim that the non-resonant contribution to non-leptonic charm meson decays may not be constant in the phase space of the reaction. We argue that this can be relevant for any weak reaction. We discuss in detail the decay $D^+ \to K^- \pi^+ \pi^+$.Comment: Version accepted for publication in Physical Review Letters. 9 pages, Latex, including 2 figure

A rare case of pigmented villonodular synovitis after unicompartmental knee replacement: a case report

Pigmented villonodular synovitis is a benign proliferative disease involving the synovium. Pigmented villonodular synovitis is rare after replacement arthroplasty and has not been recognised and reported as a cause of failure of unicompartmental knee replacement in the literature

Studies of the decays D^0 \rightarrow K_S^0K^-\pi^+ and D^0 \rightarrow K_S^0K^+\pi^-

The first measurements of the coherence factor R_{K_S^0K\pi} and the average strong--phase difference \delta^{K_S^0K\pi} in D^0 \to K_S^0 K^\mp\pi^\pm decays are reported. These parameters can be used to improve the determination of the unitary triangle angle \gamma\ in B^- \rightarrow $\widetilde{D}K^-$ decays, where $\widetilde{D}$ is either a D^0 or a D^0-bar meson decaying to the same final state, and also in studies of charm mixing. The measurements of the coherence factor and strong-phase difference are made using quantum-correlated, fully-reconstructed D^0D^0-bar pairs produced in e^+e^- collisions at the \psi(3770) resonance. The measured values are R_{K_S^0K\pi} = 0.70 \pm 0.08 and \delta^{K_S^0K\pi} = (0.1 \pm 15.7)$^\circ$ for an unrestricted kinematic region and R_{K*K} = 0.94 \pm 0.12 and \delta^{K*K} = (-16.6 \pm 18.4)$^\circ$ for a region where the combined K_S^0 \pi^\pm invariant mass is within 100 MeV/c^2 of the K^{*}(892)^\pm mass. These results indicate a significant level of coherence in the decay. In addition, isobar models are presented for the two decays, which show the dominance of the K^*(892)^\pm resonance. The branching ratio {B}(D^0 \rightarrow K_S^0K^+\pi^-)/{B}(D^0 \rightarrow K_S^0K^-\pi^+) is determined to be 0.592 \pm 0.044 (stat.) \pm 0.018 (syst.), which is more precise than previous measurements.Comment: 38 pages. Version 3 updated to include the erratum information. Errors corrected in Eqs (25), (26), 28). Fit results updated accordingly, and external inputs updated to latest best known values. Typo corrected in Eq(3)- no other consequence

Helium solubility in oxide nuclear fuel: Derivation of new correlations for Henry’s constant

Helium plays an important role in determining nuclear fuel performance both in-pile (especially for MOX fuels and those at high burnup) and in storage conditions. Predictive models of helium behaviour are therefore a fundamental element in fuel performance codes. These models are based on the accurate knowledge of helium diffusivity (addressed in a previous paper, Luzzi et al. (2018)) and of helium solubility in oxide nuclear fuel. Based on all the experimental data available in the literature and after verification of the validity of Henry’s law we propose two correlations for Henry’s constant, kH (at m-3 MPa-1 ): kH = 1. 8·10^25·exp(-0.41/kT) for powders and kH = 4.1·10^24·exp(-0.65/kT) for single crystals, with the Boltzmann factor 1/kT in (eV-1). The correlation for Henry’s constant in powder samples is of interest for the analysis of helium behaviour in the fuel after the pulverization occurring during LOCA-like temperature transients, while the correlation for Henry’s constant in single-crystals is usable in meso-scale models describing helium behaviour at the level of fuel grains. The current lack of data for this fundamental property, especially for poly-crystalline samples, calls for new experiments

Observation of the Dalitz Decay Ds∗+→Ds+e+e−D_{s}^{*+} \to D_{s}^{+} e^{+} e^{-}

Using 586 $\textrm{pb}^{-1}$ of $e^{+}e^{-}$ collision data acquired at $\sqrt{s}=4.170$ GeV with the CLEO-c detector at the Cornell Electron Storage Ring, we report the first observation of $D_{s}^{*+} \to D_{s}^{+} e^{+} e^{-}$ with a significance of $5.3 \sigma$. The ratio of branching fractions \calB(D_{s}^{*+} \to D_{s}^{+} e^{+} e^{-}) / \calB(D_{s}^{*+} \to D_{s}^{+} \gamma) is measured to be $[ 0.72^{+0.15}_{-0.13} (\textrm{stat}) \pm 0.10 (\textrm{syst})]$, which is consistent with theoretical expectations

Updated Measurement of the Strong Phase in D0 --> K+pi- Decay Using Quantum Correlations in e+e- --> D0 D0bar at CLEO

We analyze a sample of 3 million quantum-correlated D0 D0bar pairs from 818 pb^-1 of e+e- collision data collected with the CLEO-c detector at E_cm = 3.77 GeV, to give an updated measurement of \cos\delta and a first determination of \sin\delta, where \delta is the relative strong phase between doubly Cabibbo-suppressed D0 --> K+pi- and Cabibbo-favored D0bar --> K+pi- decay amplitudes. With no inputs from other experiments, we find \cos\delta = 0.81 +0.22+0.07 -0.18-0.05, \sin\delta = -0.01 +- 0.41 +- 0.04, and |\delta| = 10 +28+13 -53-0 degrees. By including external measurements of mixing parameters, we find alternative values of \cos\delta = 1.15 +0.19+0.00 -0.17-0.08, \sin\delta = 0.56 +0.32+0.21 -0.31-0.20, and \delta = (18 +11-17) degrees. Our results can be used to improve the world average uncertainty on the mixing parameter y by approximately 10%.Comment: Minor revisions, version accepted by PR

Search for rare and forbidden decays of charm and charmed-strange mesons to final states h^+- e^-+ e^+

We have searched for flavor-changing neutral current decays and lepton-number-violating decays of D^+ and D^+_s mesons to final states of the form h^+- e^-+ e^+, where h is either \pi or K. We use the complete samples of CLEO-c open-charm data, corresponding to integrated luminosities of 818 pb^-1 at the center-of-mass energy E_CM = 3.774 GeV containing 2.4 x 10^6 D^+D^- pairs and 602 pb^-1 at E_CM = 4.170 GeV containing 0.6 x 10^6 D^*+-_s D^-+_s pairs. No signal is observed in any channel, and we obtain 90% confidence level upper limits on branching fractions B(D^+ --> \pi^+ e^+ e^-) < 5.9 x 10^-6, B(D^+ --> \pi^- e^+ e^+) K^+ e^+ e^-) < 3.0 x 10^-6, B(D^+ --> K^- e^+ e^+) \pi^+ e^+ e^-) < 2.2 x 10^-5, B(D^+_s --> \pi^- e^+ e^+) K^+ e^+ e^-) < 5.2 x 10^-5, and B(D^+_s --> K^- e^+ e^+) < 1.7 x 10^-5.Comment: 9 pages, available through http://www.lns.cornell.edu/public/CLNS