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Early results on the environmental integrity of W-88 o-ring seals

Description: The author reports experimental measurements for the argon and oxygen permeability coefficients for the new EPDM material (SR793B-80) used for the environmental o-ring seals of the W88. The results allow the author to refine the argon gas analysis modeling predictions for W88 surveillance units. By comparing early surveillance results (up to four years in the field) with the modeling, the author shows that (1) up to this point in time, leakage past the seals is insignificant and (2) the argon approach should be able to inexpensively and easily monitor both integrated lifetime water leakage and the onset of any aging problems. Finally, the author provides a number of pieces of evidence indicating that aging of the SR793B-80 material will not be significant during the expected lifetime of the W88.
Date: April 1, 1993
Creator: Gillen, K. T.
Partner: UNT Libraries Government Documents Department

Prediction of elastomer lifetimes from accelerated thermal-aging experiments

Description: For elastomers that will be used in applications involving long lifetimes, it is often necessary to first carry out and model accelerated aging experiments at higher than ambient temperatures, and then extrapolate the results in order to make lifetime predictions at the use temperature. Continuing goals in such endeavors are to better understand potential problems with such modeling approaches and to find ways of improving confidence in the predictions when the data are extrapolated. In this paper we will address several important issues involved in these procedures for elastomers exposed to air (oxygen), and discuss some potentially useful techniques and approaches which can increase confidence in lifetime predictions.
Date: September 1, 1997
Creator: Gillen, K.T. & Clough, R.L.
Partner: UNT Libraries Government Documents Department

A critical assessment of the Arrhenius oven-aging methodology

Description: The Arrhenius approach assumes a linear relation between log time to material property change and inverse absolute temperature. For elastomers, ultimate tensile elongation results are often used to confirm Arrhenius behavior, even though the ultimate tensile strength is non-Arrhenius. This paper critically examines the Arrhenius approach. Elongation vs air-oven aging temperature for a nitrile rubber, gives an E{sub a} of 22 kcal/mol; however this does not hold for the tensile strength, indicating degradation. Modulus profiling shows heterogeneity at the earliest times at 125 C, caused by diffusion-limited oxidation (DLO). Tensile strength depends on the force at break integrated over the cross section, and nitrile rubbers aged at different temperatures experience different degrees of degradation in the interior. Modulus at the surface, however, is not affected by DLO anomalies. Severe mechanical degradation will occur when the edge modulus increases by an order of magnitude. 7 figs, 3 refs.
Date: April 1, 1993
Creator: Gillen, K. T. & Clough, R. L.
Partner: UNT Libraries Government Documents Department

General solutions for the oxidation kinetics of polymers

Description: The simplest general kinetic schemes applicable to the oxidation of polymers are presented, discussed and analyzed in terms of the underlying kinetic assumptions. For the classic basic autoxidation scheme (BAS), which involves three bimolecular termination steps and is applicable mainly to unstabilized polymers, typical assumptions used singly or in groups include (1) long kinetic chain length, (2) a specific ratio of the termination rate constants and (3) insensitivity to the oxygen concentration (e.g., domination by a single termination step). Steady-state solutions for the rate of oxidation are given in terms of one, two, three, or four parameters, corresponding respectively to three, two, one, or zero kinetic assumptions. The recently derived four-parameter solution predicts conditions yielding unusual dependencies of the oxidation rate on oxygen concentration and on initiation rate, as well as conditions leading to some unusual diffusion-limited oxidation profile shapes. For stabilized polymers, unimolecular termination schemes are typically more appropriate than bimolecular. Kinetics incorporating unimolecular termination reactions are shown to result in very simple oxidation expressions which have been experimentally verified for both radiation-initiated oxidation of an EPDM and thermoxidative degradation of nitrile and chloroprene elastomers.
Date: August 1, 1996
Creator: Gillen, K.T.; Clough, R.L. & Wise, J.
Partner: UNT Libraries Government Documents Department

Methods for Predicting More Confident Lifetimes of Seals in Air Environments

Description: We have been working for many years to develop improved methods for predicting the lifetimes of polymers exposed to air environments and have recently turned our attention to seal materials. This paper describes an extensive study on a butyl material using elevated temperature compression stress-relaxation (CSR) techniques in combination with conventional oven aging exposures. The results initially indicated important synergistic effects when mechanical strain is combined with oven aging, as well as complex, non-Arrhenius behavior of the CSR results. By combining modeling and experiments, we show that diffusion-limited oxidation (DLO) anomalies dominate traditional CSR experiments. A new CSR approach allows us to eliminate DLO effects and recover Arrhenius behavior. Furthermore, the resulting CSR activation energy (E{sub a}) from 125 C to 70 C is identical to the activation energies for the tensile elongation and for the oxygen consumption rate of unstrained material over similar temperature ranges. This strongly suggests that the same underlying oxidation reactions determine both the unstrained and strained degradation rates. We therefore utilize our ultrasensitive oxygen consumption rate approach down to 23 C to show that the CSR E{sub a} likely remains unchanged when extrapolated below 70 C, allowing very confident room temperature lifetime predictions for the butyl seal.
Date: March 5, 1999
Creator: Celina, M.; Gillen, K.T. & Keenan, M.R.
Partner: UNT Libraries Government Documents Department

Nuclear power plant accident simulations of gasket materials under simultaneous radiation plus thermal plus mechanical stress conditions

Description: In order to probe the response of silicone door gasket materials to a postulated severe accident in an Italian nuclear power plant, compression stress relaxation (CSR) and compression set (CS) measurements were conducted under combined radiation (approximately 6 kGy/h) and temperature (up to 230{degrees}C) conditions. By making some reasonable initial assumptions, simplified constant temperature and dose rates were derived that should do a reasonable job of simulating the complex environments for worst-case severe events that combine overall aging plus accidents. Further simplification coupled with thermal-only experiments allowed us to derive thermal-only conditions that can be used to achieve CSR and CS responses similar to those expected from the combined environments that are more difficult to simulate. Although the thermal-only simulations should lead to sealing forces similar to those expected during a severe accident, modulus and density results indicate that significant differences in underlying chemistry are expected for the thermal-only and the combined environment simulations. 15 refs., 31 figs., 15 tabs.
Date: July 1, 1997
Creator: Gillen, K.T. & Malone, G.M.
Partner: UNT Libraries Government Documents Department

Characterization of aging in organic materials on atomic-, meso- and macro-length scales by {sup 13}C NMR spectroscopy

Description: A fundamental understanding of aging in an organic material requires that one understand how aging affects the chemical structure of a material, and how these chemical changes are related to the material`s macroscopic properties. This level of understanding is usually achieved by examining the material on a variety of length scales ranging from atomic to meso-scale to macroscopic. The authors are developing and applying several {sup 13}C nuclear magnetic resonance (NMR) spectroscopy experiments to characterize the aging process of organic materials over a broad range of length scales. Examples of studies which range from atomic to macroscopic will be presented.
Date: October 1, 1997
Creator: Assink, R.A.; Jamison, G.M.; Alam, T.M. & Gillen, K.T.
Partner: UNT Libraries Government Documents Department

Evidence that Arrhenius high-temperature aging behavior for an EPDM o-ring does not extrapolate to lower temperatures

Description: Because of the need to significantly extend the lifetimes of weapons, and because of potential implications of environmental O-ring failure on degradation of critical internal weapon components, the authors have been working on improved methods of predicting and verifying O-ring lifetimes. In this report, they highlight the successful testing of a new predictive method for deriving more confident lifetime extrapolations. This method involves ultrasensitive oxygen consumption measurements. The material studied is an EPDM formulation use for the environmental O-ring the W88. Conventional oven aging (155 C to 111 C) was done on compression molded sheet material; periodically, samples were removed from the ovens and subjected to various measurements, including ultimate tensile elongation, density and modulus profiles. Compression stress relaxation (CSR) measurements were made at 125 C and 111 C on disc shaped samples (12.7 mm diameter by 6 mm thick) using a Shawbury Wallace Compression Stress Relaxometer MK 2. Oxygen consumption measurements were made versus time, at temperatures ranging from 160 C to 52 C, using chromatographic quantification of the change in oxygen content caused by reaction with the EPDM material in sealed containers.
Date: September 1, 1997
Creator: Gillen, K.T.; Wise, J.; Celina, M. & Clough, R.L.
Partner: UNT Libraries Government Documents Department

Better Methods for Predicting Lifetimes of Seal Materials

Description: We have been working for many years to develop better methods for predicting the lifetimes of polymer materials. Because of the recent interest in extending the lifetimes of nuclear weapons and the importance of environmental seals (o-rings, gaskets) for protecting weapon interiors against oxygen and water vapor, we have recently turned our attention to seal materials. Perhaps the most important environmental o-ring material is butyl rubber, used in various military applications. Although it is the optimum choice from a water permeability perspective, butyl can be marginal from an aging point-of-view. The purpose of the present work was to derive better methods for predicting seal lifetimes and applying these methods to an important butyl material, Parker compound B6 12-70.
Date: March 16, 1999
Creator: Celina, M.; Gillen, K.T. & Keenan, M.R.
Partner: UNT Libraries Government Documents Department

Limitations of the Arrhenius Methododolgy

Description: The Arrhenius methodology has been utilized for many years to NOV 171998 predict polymer lifetimes in various applications. Unfortunately, there are numerous potential limitations associated with this methodology, o ST I many of which can lead to non-Arrhenius behavior. This paper will review several of these limitations, including a brief mention of diffusion-limited oxidation (DLO) effects and a more extensive discussion of the implication of changes in the effective Arrhenius activation energy E. or in the dominant reactions as the temperature changes. Changes in Ea or in the dominant reactions with temperature can happen for any material, making extrapolations beyond the experimental temperature range problematic. Unfortunately, when mechanistic changes occur, they invariably result in a reduction in effective Arrhenius activation energy, leading to lower than expected material lifetimes. Thus it is critically important to derive methods for testing the Arrhenius extrapolation assumption. One approach that we have developed involves ultrasensitive oxygen consumption measurements. Results from the application of this approach will be reviewed.
Date: October 27, 1998
Creator: Celina, M.; Clough, R.L. & Gillen, K.T.
Partner: UNT Libraries Government Documents Department

New method for predicting lifetime of seals from compression-stress relaxation experiments

Description: Interpretation of compression stress-relaxation (CSR) experiments for elastomers in air is complicated by (1) the presence of both physical and chemical relaxation and (2) anomalous diffusion-limited oxidation (DLO) effects. For a butyl material, the authors first use shear relaxation data to indicate that physical relaxation effects are negligible during typical high temperature CSR experiments. They then show that experiments on standard CSR samples ({approximately}15 mm diameter when compressed) lead to complex non-Arrhenius behavior. By combining reaction kinetics based on the historic basic autoxidation scheme with a diffusion equation appropriate to disk-shaped samples, they derive a theoretical DLO model appropriate to CSR experiments. Using oxygen consumption and permeation rate measurements, the theory shows that important DLO effects are responsible for the observed non-Arrhenius behavior. To minimize DLO effects, they introduce a new CSR methodology based on the use of numerous small disk samples strained in parallel. Results from these parallel, minidisk experiments lead to Arrhenius behavior with an activation energy consistent with values commonly observed for elastomers, allowing more confident extrapolated predictions. In addition, excellent correlation is noted between the CSR force decay and the oxygen consumption rate, consistent with the expectation that oxidative scission processes dominate the CSR results.
Date: June 1, 1998
Creator: Gillen, K.T.; Keenan, M.R. & Wise, J.
Partner: UNT Libraries Government Documents Department

Equipment qualification issues research and resolution: Status report

Description: Since its inception in 1975, the Qualification Testing Evaluation (QTE) Program has produced numerous results pertinent to equipment qualification issues. Many have been incorporated into Regulatory Guides, Rules, and industry practices and standards. This report summarizes the numerous reports and findings to date. Thirty separate issues are discussed encompassing three generic areas: accident simulation methods, aging simulation methods, and special topics related to equipment qualification. Each issue-specific section contains (1) a brief description of the issue, (2) a summary of the applicable research effort, and (3) a summary of the findings to date.
Date: November 1, 1986
Creator: Bonzon, L.L.; Wyant, F.J.; Bustard, L.D. & Gillen, K.T.
Partner: UNT Libraries Government Documents Department

Explanation of enhanced mechanical degradation rate for radiation- aged polyolefins as the aging temperature is decreased

Description: Degradation rates are normally increased by increasing the responsible environmental stresses. We describe results for a semi-crystalline, crosslinked polyolefin material that contradicts this assumption. In particular, under combined radiation plus thermal environments, this material mechanically degrades much faster at room temperature than it does at elevated temperatures. The probable explanation for this phenomenon relates to the importance on mechanical properties of the tie molecules connecting crystalline and amorphous regions. Partial melting and reforming/ reorganization of crystallites occurs throughout the crystalline melting region (at least room temperature up to 126 C), with the rate of such processes increasing with an increase in temperature. At low temperatures, this process is sufficiently slow such that a large percentage of the radiation-damaged tie molecules will still connect the amorphous and crystalline regions at the end of aging, leading to rapid reductions in tensile properties. At higher temperatures, the enhanced annealing rate will lead, during the aging, to the establishment of new, undamaged tie molecules connecting crystalline and amorphous regions. This healing process will reduce the degradation rate. Evidence in support of this model is presented.
Date: May 1, 1994
Creator: Gillen, K. T.; Clough, R. L.; Wise, J. & Malone, M. G.
Partner: UNT Libraries Government Documents Department

Novel Techniques Applied to Polymer Lifetime Predictions

Description: A study aimed at testing the Arrhenius life prediction approach is described. After aging elastomeric materials at several elevated (accelerated) temperatures, a modulus profiling apparatus was used to demonstrate the complicated diffusion-limited oxidation anomalies are typically present under accelerated oven-aging conditions. By using surface modulus results (oxidation less to a monotonic increase in modulus), estimates are made of the true activation energy (E{sub a}) appropriate to the oxidation reactions dominating degradation. Even though macroscopic properties should be influenced by the diffusion-limited oxidation complications, ultimate tensile elongation results were found to be correlated to the true E{sub a}. This implies that cracks initiate at the hardened surface of the material and then quickly propagate through the less oxidized interior. If values of E{sub a} obtained from accelerated exposures can be determined and rationalized, another important question involves the Arrhenius assumption that E{sub a} remains constant in the extrapolation region. Preliminary data from two ultra-sensitive techniques (oxygen consumption and microcalorimetry) aimed at testing this fundamental assumption are described.
Date: December 31, 1993
Creator: Gillen, K. T.; Wise, J. & Clough, R. L.
Partner: UNT Libraries Government Documents Department

A test of the Arrhenius extrapolation assumption for a nitrile rubber

Description: The Arrhenius relation predicts a linear relation between log of time to property change and inverse absolute temperature, with the Arrhenius activation energy E{sub a} given from the slope. For a nitrile rubber, Arrhenius behavior is observed for elongation vs air-oven aging temperature, with a E{sub a} of 22 kcal/mol. Confidence in extrapolation to low temperatures can be increased by measuring oxygen consumption. From 95 to 52 C, the E{sub a} for oxygen consumption is identical to that for elongation; however, below 52 C, the E{sub a} for oxygen consumption drops slightly to 18 kcal/mol, indicating that the extrapolation assumption probably overestimates the tensile property lifetime by a factor of about 2 at 23 C.
Date: August 1, 1994
Creator: Gillen, K. T.; Wise, J. & Clough, R. L.
Partner: UNT Libraries Government Documents Department

Argon gas analysis to predict water leakage into the W88

Description: Analyses of the internal argon gas concentrations monitored on surveillance units of the W84 indicates that field aging of this weapon for times up to {approximately}4 years does not lead to important increases in the rate at which water leaks into the interior of the weapon. This implies that the EPDM environmental seals used on the W84 do not age significantly over this time period. By comparing the percentages of oxygen and argon in the internal atmosphere, an estimate of the oxygen consumption rate is made for a typical W84 unit. The argon gas analysis approach is then applied to the W88, which is sealed with a new EPDM material. Predictive expressions are derived which relate the anticipated argon gas concentrations of future, field-returned units to their water leakage rates. The predictions are summarized in convenient plots, which can be immediately and easily applied to surveillance data as reported. Since the argon approach is sensitive enough to be useful over the entire lifetime of the W88, it can be used to point out leaking units and to determine whether long-term aging has any significant effect on the new EPDM material. 11 refs., 10 figs., 3 tabs.
Date: August 1, 1990
Creator: Gillen, K.T.
Partner: UNT Libraries Government Documents Department

Predictive aging results for cable materials in nuclear power plants

Description: In this report, we provide a detailed discussion of methodology of predicting cable degradation versus dose rate, temperature, and exposure time and its application to data obtained on a number of additional nuclear power plant cable insulation (a hypalon, a silicon rubber and two ethylenetetrafluoroethylenes) and jacket (a hypalon) materials. We then show that the predicted, low-dose-rate results for our materials are in excellent agreement with long-term (7 to 9 years), low dose-rate results recently obtained for the same material types actually aged under nuclear power plant conditions. Based on a combination of the modelling and long-term results, we find indications of reasonably similar degradation responses among several different commercial formulations for each of the following generic'' materials: hypalon, ethylenetetrafluoroethylene, silicone rubber and PVC. If such generic'' behavior can be further substantiated through modelling and long-term results on additional formulations, predictions of cable life for other commercial materials of the same generic types would be greatly facilitated. Finally, to aid utilities in their cable life extension decisions, we utilize our modelling results to generate lifetime prediction curves for the materials modelled to data. These curves plot expected material lifetime versus dose rate and temperature down to the levels of interest to nuclear power plant aging. 18 refs., 30 figs., 3 tabs.
Date: November 1, 1990
Creator: Gillen, K.T. & Clough, R.L.
Partner: UNT Libraries Government Documents Department

Complex oxidation effects in polymer degradation

Description: The authors are working to understand why predictions of degradation behaviors and rates, based on accelerated thermal aging experiments, often fail to match with aging of polymers under service conditions. A main goal of these studies is to develop more reliable lifetime prediction methodologies.
Date: September 1, 1994
Creator: Clough, R. L.; Gillen, K. T. & Wise, J.
Partner: UNT Libraries Government Documents Department

{sup 17}O NMR investigations of oxidative degradation in polymers

Description: We have initiated studies using both solution and solid state magic angle spinning {sup 17}O NMR for a series of oxidatively aged polymers. This short note reports the solution {sup 17}O NMR for oxidatively degraded polypropylene, ethylene-propylene-diene, polyisoprene, and nitrile rubber. Enriched O{sub 2} is used during the accelerated aging. 3 figs, 7 refs.
Date: December 31, 1996
Creator: Alam, T.M.; Celina, M.; Assink, R.A.; Gillen, K.T. & Clough, R.L.
Partner: UNT Libraries Government Documents Department

DOE-sponsored cable aging research at Sandia National Laboratories

Description: Cables have been identified as critical components requiring detailed technical evaluation for extending the lifetime of Light Water Reactors beyond 40 years. This paper highlights some of the DOE-sponsored cable aging studies currently underway at Sandia. These studies are focused on two important issues: the validity of the often-used Arrhenius thermal aging prediction method and methods for predicting lifetimes in combined thermal-radiation environments. Accelerated thermal aging results are presented for three cable jacket and insulation materials, which indicate that hardening of the outside surface has an Arrhenius temperature dependence and correlates well with reductions in ultimate tensile elongation. This suggests that the indentor approach is a promising NDE technique for cable jacket and unjacketed insulation materials installed in thermally-dominated regions of nuclear power plants.
Date: December 1, 1995
Creator: Gillen, K.T.; Clough, R.L.; Celina, M.; Wise, J. & Malone, G.M.
Partner: UNT Libraries Government Documents Department

Correlation of Chemical and Mechanical Property Changes During Oxidative Degradation of Neoprene

Description: The thermal degradation of a commercial, stabilized, unfilled neoprene (chloroprene) rubber was investigated at temperatures up to 140 C. The degradation of this material is dominated by oxidation rather than dehydrochlorination. Important heterogeneous oxidation effects were observed at the various temperatures investigated using infrared micro-spectroscopy and modulus profiling. Intensive degradation-related spectral changes in the IR occurred in the conjugated carbonyl and hydroxyl regions. Quantitative analysis revealed some differences in the development of the IR oxidation profiles, particularly towards the sample surface. These chemical degradation profiles were compared with modulus profiles (mechanical properties). It is concluded that the profile development is fundamentally described by a diffusion-limited autoxidation mechanism. Oxygen consumption measurements showed that the oxidation rates display non-Arrhenius behavior (curvature) at low temperatures. The current results, when compared to those of a previously studied, clay-filled commercial neoprene formulation, indicate that the clay filler acts as an antioxidant, but only at low temperatures.
Date: July 1, 1999
Creator: Celina, M.; Wise, J.; Ottesen, D.K.; Gillen, K.T. & Clough, R.L.
Partner: UNT Libraries Government Documents Department

Thermal Degradation Studies of A Polyurethane Propellant Binder

Description: The thermal oxidative aging of a crosslinked hydroxy-terminated polybutadiene (HTPB)/isophorone diisocyanate (IPDI) based polyurethane rubber, used as a polymeric binder in solid propellant grain, was investigated at temperatures from 25 C to 125 C. The changes in tensile elongation, polymer network properties and chain dynamics, mechanical hardening and density were determined with a range of techniques including modulus profiling, solvent swelling, NMR relaxation and O{sub 2} permeability measurements. We critically evaluated the Arrhenius methodology that is commonly used with a linear extrapolation of high temperature aging data using extensive data superposition and highly sensitive oxygen consumption experiments. The effects of other constituents in the propellant formulation on aging were also investigated. We conclude that crosslinking is the dominant process at higher temperatures and that the degradation involves only limited hardening in the bulk of the material. Significant curvature in the Arrhenius diagram of the oxidation rates was observed. This is similar to results for other rubber materials.
Date: June 12, 1999
Creator: Assink, R.A.; Celina, M.; Gillen, K.T.; Graham, A.C. & Minier, L.M.
Partner: UNT Libraries Government Documents Department

Theoretical and experimental investigations of fullerene derivatives: C{sub 60}H{sub 2}, C{sub 60}H{sub 4}, C{sub 70}H{sub 2} and C{sub 60}(CH{sub 2}){sub 2}

Description: Hydroboration of C{sub 7}0 in toluene yields a 2:1 mixture of 1,9-C{sub 70}H{sub 2} and 7,8-C{sub 70}H{sub 2}. Equilibration of these two isomers in the presence of a Pt catalyst reveals a free energy difference of 1.4 {plus_minus} 0.2 kcal/mol. Whereas semiempirical calculations have been found to predict the energy ordering of many fullerene derivatives incorrectly, ab initio Hartree-Fock (HF) calculations have been found to yield quantitative predictions of experiment. The HF/6-31G* level energy separation of 1,9-C{sub 70}H{sub 2} and 7,8-C{sub 70}H{sub 2} of 1.3 kcal/mol is in excellent agreement with experiment. Relative stabilities of isomers of bis(methano)fullerenes were found to parallel those of analogous C{sub 60}H{sub 4} isomers. Density functional theory (DFT) methods have been tested and are equivalent in accuracy to HF methods if similar basis sets are used. C{sub 60}H{sub 2} and C{sub 60}H{sub 4} can be efficiently produced on larger ({ge} 50 mg) scales with diimide generated from potassium azodicarboxylate and acetic acid in o-dichlorobenzene.
Date: December 31, 1993
Creator: Jacobs, S. J.; Gillen, K. T.; Cahill, P. A.; Henderson, C. C. & Rohlfing, C. M.
Partner: UNT Libraries Government Documents Department