STRESS EVALUATION METHOD OF BAFFLE FORMER BOLT AND ITS MAINTENANCE PROGRAM

ABSTRACT Baffle Former Bolt (BFB) is a fastening part of Reactor Vessel Internals (RVI) of PWR. BFB is made of type 347 or 316CW (cold work) stainless steel and it is known to have the risk of cracking caused by Irradiation Assisted Stress Corrosion Cracking (IASCC) under high neutron flux and tensile stress. To evaluate the time to crack of BFB, BFB's time-dependent stress change caused by irradiation creep (relaxation) and by the swelling deformation of a baffle structure should be obtained. The authors have developed the finite element (FE) analysis method to calculate time-dependent stress of BFB considering the irradiation effects. The method combines two kinds of models; "global model" to calculate the deformation of whole baffle structure and "local model" to calculate the peak stress at the stress concentrated area under the bolt head. Incorporating the above calculation method, a new BFB inspection and evaluation guideline has been established in Japan. The concept of the guideline is also outlined in the paper

Specific degradation of CRABP-II via cIAP1-mediated ubiquitylation induced by hybrid molecules that crosslink cIAP1 and the target protein

AbstractManipulation of protein stability with small molecules is a challenge in the field of drug discovery. Here we show that cellular retinoic acid binding protein-II (CRABP-II) can be specifically degraded by a novel compound, SNIPER-4, consisting of (−)-N-[(2S,3R)-3-amino-2-hydroxy-4-phenyl-butyryl]-l-leucine methyl ester and all-trans retinoic acid that are ligands for cellular inhibitor of apoptosis protein 1 (cIAP1) and CRABP-II, respectively. Mechanistic analysis revealed that SNIPER-4 induces cIAP1-mediated ubiquitylation of CRABP-II, resulting in the proteasomal degradation. The protein knockdown strategy employing the structure of SNIPER-4 could be applicable to other target proteins

Heavy Reflector type EPR benchmarking

International audienceAs part of the EPR studies on the heavy reflector conducted by EDF, a neutronic and thermalhydraulic calculation benchmark was initiated between EDF (France), MHI (Japan) in the MAI (Material Ageing Institute) and CVR (Czech Rep.) and Framatome (formerly AREVA NP). A previous similar benchmark between EDF and EPRI working with Westinghouse and Framatome had compared calculation results for a simplified PWR type internal structure 1. The analysis of the neutronic results in terms of calculated flux, dose and deposited energy showed that the methodologies were consistent despite some discrepancies in the neutronics results. Among the differences, the radial profiles of gamma heating were different with regard to the thickness of the component. This could have a significant effect for thicker components such as heavy reflectors. For the thermal hydraulics part, results showed a very good agreement in the case of an identical gamma heated field.Given the large thickness of the EPR or WWER 1000 lower core internal component, the MAI project on Internals has examined more specifically the deposited energy profile and has set up a new bench-mark based on a simplified heavy reflector geometry. Indeed, both Russian WWER 1000 and French EPR type of reactors have a heavy reflector and thus a substantial thickness of stainless steel. First of all, the objective for EDF, MHI, CVR and Framatome is to assess the neutronics loadings inside the vessel internals up to the vessel core. Then, using the same boundary conditions, EDF and MHI ran conjugate heat transfer calculations with their own numerical tools to determine the temperature of the internal structure. Two calculations have been performed, first with a common gamma heating rate and then with an in-house neutronic calculation. The objective of the first one was to evaluate the accuracy of the Computational Fluid Dynamics - Computational Heat Transfer (CFD-CHT). The second one has allowed an evaluation of the variation of the structure temperature induced by the gamma heating rate uncertainty. Thus, this work strengthens the complete participants’ calculation chain from particle transport model to temperature evaluation inside the vessel.The simplified geometry proposed for this benchmark seeks to combine both EPR and VVER1000 at-tributes. It has a double symmetry enabling the modelling of 1/4th of the heavy reflector and core barrel with three L-shaped assemblies. To cool down the structure, a flow goes up from the bottom to the top through 85 cooling holes. Flow rates, gamma heating rates and boundary conditions on the inner face of the baffle and outer face of the barrel are imposed.The model, common to all participants, has enabled the comparison of a set of calculated values includ-ing neutron and gamma flux mainly in the thermal area of the spectrum, dose (in dpa) due to neutrons, gamma heating rates and finally, temperature of the structure and of the cooling fluid.This paper presents comparison and first analysis of the participant’s results

Hidden chemical order in disordered Ba7Nb4MoO20 revealed by resonant X-ray diffraction and solid-state NMR

Abstract The chemical order and disorder of solids have a decisive influence on the material properties. There are numerous materials exhibiting chemical order/disorder of atoms with similar X-ray atomic scattering factors and similar neutron scattering lengths. It is difficult to investigate such order/disorder hidden in the data obtained from conventional diffraction methods. Herein, we quantitatively determined the Mo/Nb order in the high ion conductor Ba7Nb4MoO20 by a technique combining resonant X-ray diffraction, solid-state nuclear magnetic resonance (NMR) and first-principle calculations. NMR provided direct evidence that Mo atoms occupy only the M2 site near the intrinsically oxygen-deficient ion-conducting layer. Resonant X-ray diffraction determined the occupancy factors of Mo atoms at the M2 and other sites to be 0.50 and 0.00, respectively. These findings provide a basis for the development of ion conductors. This combined technique would open a new avenue for in-depth investigation of the hidden chemical order/disorder in materials