Abdellatif M. Yacout

Degradation Analysis Estimates of the Time-to-Failure Distribution of Irradiated Fuel Elements

Failure times of components are traditionally used to evaluate their reliability. An alternate approach is to analyze the degradation data accumulated during the component`s testing or during its normal operation. Degradation analysis is particularly useful when it is not possible to observe a significant number of failures. This is the case for metallic integral Fast Reactor fuel pins irradiated in Experimental Breeder Reactor II, where failures have not taken place under normal operating conditions. A degradation analysis methodology is presented and applied to these pins. The time-to-failure distribution for the fuel pins is estimated based on a fixed threshold failure model. The confidence intervals of the distribution are calculated using a parametric bootstrap method.

Radiation-induced synergistic effects of athermal and thermal mechanisms on erosion and surface evolution of advanced electrode and condenser optics materials

In extreme ultraviolet lithography (EUVL) environments transient plasma dynamics dictate conditions for particle/surface interactions. A critical challenge facing EUVL development is optic component lifetime both in gas-discharge produced plasmas (GDPP) and laser-produced plasmas (LPP) devices. Optic components are exposed to impingent species, impurities (H,C,O,N) and debris leading to their degradation and consequently limiting 13.5 nm light reflection intensity. Experiments in the PRIME (Particles and Radiation Interaction with Matter Experiments) facility at the Argonne National Laboratory study the synergy between radiation-induced athermal and thermal mechanisms that influence the behavior of EUVL materials (electrodes and condenser optics) under irradiation conditions including: incident particle energy (50 eV - 5 keV), angle-of-incidence (near-normal to oblique), incident flux (1011-1017 ions/cm2/s), surface coatings (impurity: C,O or capping layers: Ru, W), and surface temperature (100 - 1000 C). Results of electrode and optical component interaction with singly-charged inert gases (Xe) are presented. Critical issues under study include: radiation enhanced diffusion, radiation induced segregation, preferential sputtering, collisional mixing, surface segregation, surface amorphization, thermal diffusion and thermal spike evolution. Experiments in PRIME will be complemented with atomistic modeling to study how these mechanisms modify surfaces and how these mechanisms can work synergistically to introduce solutions to enhance component lifetime of electrode and condenser optic materials.

Investigation of High-Energy Ion-Irradiated MA957 Using Synchrotron Radiation under In-Situ Tension

In this study, an MA957 oxide dispersion-strengthened (ODS) alloy was irradiated with high-energy ions in the Argonne Tandem Linac Accelerator System. Fe ions at an energy of 84 MeV bombarded MA957 tensile specimens, creating a damage region ~7.5 μm in depth; the peak damage (~40 dpa) was estimated to be at ~7 μm from the surface. Following the irradiation, in-situ high-energy X-ray diffraction measurements were performed at the Advanced Photon Source in order to study the dynamic deformation behavior of the specimens after ion irradiation damage. In-situ X-ray measurements taken during tensile testing of the ion-irradiated MA957 revealed a difference in loading behavior between the irradiated and un-irradiated regions of the specimen. At equivalent applied stresses, lower lattice strains were found in the radiation-damaged region than those in the un-irradiated region. This might be associated with a higher level of Type II stresses as a result of radiation hardening. The study has demonstrated the feasibility of combining high-energy ion radiation and high-energy synchrotron X-ray diffraction to study materials’ radiation damage in a dynamic manner.

3.23 – Metal Fuel Performance Modeling and Simulation

This chapter describes the current status of metal fuel modeling and simulation, in particular, the constituent migration model and the simulation codes: LIFE-METAL and ALFUS. The outlines of the model and the codes are explained, and the results of irradiation behavior simulation are also shown. The model and the codes are capable of simulating metal fuel irradiation behavior, but still have some points that need improvement.

Sodium Fast Reactor Fuels and Materials: Research Needs.

An expert panel was assembled to identify gaps in fuels and materials research prior to licensing sodium cooled fast reactor (SFR) design. The expert panel considered both metal and oxide fuels, various cladding and duct materials, structural materials, fuel performance codes, fabrication capability and records, and transient behavior of fuel types. A methodology was developed to rate the relative importance of phenomena and properties both as to importance to a regulatory body and the maturity of the technology base. The technology base for fuels and cladding was divided into three regimes: information of high maturity under conservative operating conditions, information of low maturity under more aggressive operating conditions, and future design expectations where meager data exist.

Average Irradiation Temperature for the Analysis of In-Pile Integral Measurements

Integral parameters of reactor fuel pins are usually measured after long periods of irradiation, where each period can extend over a number of irradiation cycles. Examples of these parameters include cladding diametral strain and parameters involved in the evaluation of fuel/cladding chemical interaction and fuel restructuring. Analysis of these parameters requires knowledge of calculated irradiation parameters, which can vary between irradiation cycles and within the cycles. Irradiation temperature is one such parameter. A calculated weighted average temperature that takes into account the fluctuations in temperature between irradiation cycles is introduced. The work discusses the justification for using this temperature and a methodology for its validation. The methodology is based on comparing calculated average temperatures with temperatures inferred from the postirradiation examination of restructured binary metallic fuel pins in the Experimental Breeder Reactor II. The analysis shows reasonable agreement between the two temperatures. The peak irradiation temperatures, which are usually used in the analysis, were out of the range of the temperatures inferred from the experimental observations, showing the importance of using the average temperature.

Radiation-induced precipitation at the alloy surface during ion bombardment☆

Abstract A kinetic approach to model radiation-induced formation of a precipitate layer on the surface of a binary alloy during ion bombardment is described. Sample calculations were performed for the case of Ni3Si coating on a NiSi alloy surface. The strong coupling between Si atoms and radiation-generated defect fluxes causes a significant Si enrichment at the surface, which gives rise to the formation of a precipitate layer when it exceeds the Si solubility limit. The stability of this layer depends on the competition between the rates of precipitation and sputtering. Both the receding surface and the moving precipitate/matrix interface were accounted for by means of a mathematical scheme of boundary immobilization. The dependences of the precipitation kinetics and the development of solute concentration profiles in the alloy matrix on bombardment temperature, ion flux and alloy composition were examined.

Dynamical behavior of the implant profile during ion implantation at elevated temperatures

The evolution of the implant distribution in time and space during elevated temperature ion implantation has been theoretically investigated using a comprehensive kinetic model. The implanted atoms were allowed to interact with the surface and with radiation-induced point defects. The synergistic effects of Gibbsian segregation, preferential sputtering, displacement mixing, radiation-enhanced diffusion, and radiation-induced segregation, as well as the influence of spatially nonuniform defect production were taken into account. The effects of the dynamical changes in the ion and damage distributions during implantation were also incorporated, by updating these distributions at high doses, using information obtained from TRIM calculations. Model calculations were performed for Al{sup +} and Si{sup +} implantation into Ni. 4 refs., 2 figs.

Simulated Fission Gas Behavior in Silicide Fuel at LWR Conditions

As a promising candidate for the accident tolerant fuel (ATF) used in light water reactors (LWRs), the fuel performance of uranium silicide (U3Si2) at LWR conditions need to be well-understood. However, existing experimental post-irradiation examination (PIE) data are limited to the research reactor conditions, which involve lower fuel temperature compared to LWR conditions. This lack of appropriate experimental data significantly affects the development of fuel performance codes that can precisely predict the microstructure evolution and property degradation at LWR conditions and therefore evaluate the qualification of U3Si2 as an AFT for LWRs. Considering the high cost, long timescale, and restrictive access of the in-pile irradiation experiments, this study aims to utilize ion irradiation to simulate the inpile behavior of the U3Si2 fuel. Both in situ TEM ion irradiation and ex situ high-energy ATLAS ion irradiation experiments were employed to simulate different types of microstructure modifications in U3Si2. Multiple PIE techniques were used or will be used to quantitatively analyze the microstructure evolution induced by ion irradiation so as to provide valuable reference for the development of fuel performance code prior to the availability of the in-pile irradiation data.

Sodium fast reactor safety and licensing research plan. Volume II.

Expert panels comprised of subject matter experts identified at the U.S. National Laboratories (SNL, ANL, INL, ORNL, LBL, and BNL), universities (University of Wisconsin and Ohio State University), international agencies (IRSN, CEA, JAEA, KAERI, and JRC-IE) and private consultation companies (Radiation Effects Consulting) were assembled to perform a gap analysis for sodium fast reactor licensing. Expert-opinion elicitation was performed to qualitatively assess the current state of sodium fast reactor technologies. Five independent gap analyses were performed resulting in the following topical reports: (1) Accident Initiators and Sequences (i.e., Initiators/Sequences Technology Gap Analysis), (2) Sodium Technology Phenomena (i.e., Advanced Burner Reactor Sodium Technology Gap Analysis), (3) Fuels and Materials (i.e., Sodium Fast Reactor Fuels and Materials: Research Needs), (4) Source Term Characterization (i.e., Advanced Sodium Fast Reactor Accident Source Terms: Research Needs), and (5) Computer Codes and Models (i.e., Sodium Fast Reactor Gaps Analysis of Computer Codes and Models for Accident Analysis and Reactor Safety). Volume II of the Sodium Research Plan consolidates the five gap analysis reports produced by each expert panel, wherein the importance of the identified phenomena and necessities of further experimental research and code development were addressed. The findings from these five reports comprised the basis for the analysis in Sodium Fast Reactor Research Plan Volume I.