Post-irradiation Heat Treatment Research Articles

An assessment of the influence of microstructure and test conditions on the irradiation growth phenomenon in zirconium alloys

Experiments have been carried out to study the irradiation growth phenomenon in zirconium and its alloys. Polycrystalline zirconium, annealed and cold-worked Zircaloy-2, and annealed Zr-2.5%Nb have been irradiated at 353 and 553 K up to neutron doses of 5 × 10 25 n/m 2. Dimensional changes occurring in-reactor and during post-irradiation heat treatment were measured. The results are interpreted in terms of the present understanding of the physical processes involved in the irradiation growth phenomenon.

Alkali-labile Sites and Post-irradiation Effects in Gamma-irradiated Biologically Active Double-stranded DNA in Aqueous Solution

Gamma-irradiation of double-stranded RF-DNA of bacteriophage phi X174 in aqueous solution in the presence of oxygen produces at least one type of alkali-labile site. It is lethal and gives rise to breaks by alkali and is identical with the damage which becomes manifest by post-irradiation heat treatment. The effect of alkali is dependent on temperature. Furthermore, the excision repair system is not involved in eliminating lethal nucleotide damage in RFI-DNA.

Further Observations on A533-B Steel Plate Tailored for Improved Radiation Embrittlement Resistance

A series of advanced investigations on the radiation performance of four 6-in-thick plates from a large (30-ton) commercial melt of A533-B steel is described. The melt represented the first commercial scale demonstration test of improved radiation embrittlement resistance through the control (minimization) of selected residual impurity elements. Melt specifications emphasized the attainment of a low copper and phosphorus content; one half of the melt was modified, however, by a copper addition (0.03 percent Cu increased to 0.13 percent Cu). Initial plate tests described superior 550 F (288 C) radiation resistance, in terms of notch ductility retention, for the primary melt composition and verified the detrimental influence of impurity copper on irradiation behavior. Promising capability of the primary melt composition for very high fluence (∼2.5 × 1020 n/cm2 > 1 MeV) service is shown by the current investigations. In addition, a significant influence of copper content on radiation resistance is revealed for a broad range of exposure temperatures. A dependence of 650 F (343 C) postirradiation heat treatment response (notch ductility recovery) on copper content was also found. Charpy-V versus dynamic tear test performance and tensile strength trends with temperature are examined for low (<450 F, 121 C) and elevated (550 to 585 F, 288 to 307 C) temperature irradiation conditions.

Ferrite formation in neutron irradiated type 316 stainless steel

Magnetic measurements were made on Type 316 stainless steel specimens that had been neutron irradiated to fluences of 1.8 × 1022 neutrons/cm2 at 425°C and 3.5 × 1022 neutrons/ cm2 (E > 0.1 MeV) at 500 and 600°C. A significant increase of magnetization was observed for the irradiated specimens compared to the unirradiated specimens. The shape of the magnetization vs field curves showed that the irradiated specimens contained many small superparamagnetic particles. The magnetic particles are assumed to be the ferrite phase although other possibilities cannot be excluded. The amount and distribution of the magnetic phase varied with pre-irradiation and post-irradiation heat treatment. The maximum value of magnetization was equivalent to 3.6 pct ferrite in a specimen annealed 100 h at 760°C before irradiation and 1 h at 500°C after irradiation at 425°C.

Microstructure and tensile behavior of solid-state polymerized polyoxymethylene

Abstract Tensile testing of polyoxymethylene fibers formed by solid-state polymerization of trioxane needles has been performed. Specimens were polymerized by an isochronal, isothermal postirradiation heat treatment following irradiation at constant dose rate but at varying total dose (1.55–7.44 Mrad). It is found that the elastic modulus, “yield strength,” and ultimate tensile strength increase smoothly with irradiation dose up to a dose of 3.88 Mrad at room temperature. There were, however, significant decreases in all mechanical properties measured in going from 3.88 to 7.44 Mrad (second highest to highest dose). X-ray rotation photographs indicate no observable difference in structure or orientation for the several specimens. Density gradient column results show a density peaking at 3.88 Mrad dose. A small peak in melting point vs irradiation time is also noted at this dose level. Finally and most markedly, the diameter of the fibrillar crystallites which make up the polymer fiber decreases with incre...

Precipitation kinetics of inert-gas bubbles in solids; a computer model

Computer simulation techniques are used in this work to describe the precipitation kinetics of inert-gas bubbles in solids. By means of a predictor-corrector method, the temporal evolution of a size distribution of bubbles, growing under the coupled diffusive influx of gas atoms and lattice vacancies, is evaluated numerically. Applications are then made to analyses of the in-reactor growth of fission-gas bubbles in UO 2 as well as the growth, during post-irradiation heat treatment, of bubbles in UO 2 and gamma-uranium. It is found that the rate of vacancy flow to bubbles can play an important role in determining rates of precipitation.

Behavior of Helium Gas Bubbles in Neutron-Irradiated Beryllium

Transmission electron microscopic observations were made on hot-rolled Be sheet prepared from cast ingots irradiated to about 5 × 1019 nvt(fast) in JRR-2. The aim of the study was to elucidate the effect of irradiation on changes in microstructure and the effect of pre-irradiation heat treatment on the formation of He gas bubbles during post-irradiation annealing. The formation and growth of He bubbles during post-irradiation annealing was distinctly less inhibited in the Be irradiated as hot-rolled than in the metal irradiated after recrystallization treatment. In the former case, He bubbles could be observed upon post-irradiation treatment of only 3hr at 750°C, while in the latter case, a similar formation of bubbles could, only be seen after a final treatment at 900°C for 50 hr. The difference thus observed in the tendency of bubble formation depends upon the grain boundary mobility during post-irradiation heat treatment. The nucleation and growth of bubbles occurred preferentially at the grain boundar...

NMR Measurements on 60Co γ-Ray Irradiated Polytetrafluoroethylene with High Radiation Doses

The effects of 60Co γ-irradiation and post-irradiation heat treatment on NMR line of PTFE are studied over the temperature range -50°C to 50°C for a total dose of 8.9×108R. Lowering of transition temperature associated with crystalline regions of PTFE, narrowing of the line width of broad component, broadening of the line width of narrow component, and appearance of very sharp line component are observed in the NMR line shape of the irradiated PTFE. When the irradiated PTFE is annealed near the melting temperature, the very sharp line component disappears and the transition temperature shifts to higher temperature, differing from that of the unirradiated PTFE. This difference is considered to be associated with the decrease in the average molecular weight of the irradiated PTFE. Changes resulting from post-irradiation heat treatment can be attributed to the removal of defects and low molecular weight products trapped within PTFE. No charge is observed in the line width or narrow component by post-irradiation heat treatment.

Radiation effects in homopolymers and dilute copolymers of vinyl acetate

The effects of small doses of gamma radiation on linear and branched poly(vinyl acetate) were investigated. When irradiated in vacuum at ambient temperature and then heated to 60°C after irradiation, the linear polymer increases in molecular weight with dose as expected for a random cross-linking process. The branched polymer undergoes an additional reaction which appears to involve rapid, preferential scission at approximately one sixth of the branch locations and which goes to completion well before the gel point. Copolymers with trace amounts of a-methyl groups (0.1–10 groups per 1000 main chain carbon atoms) were prepared to simulate branching. These materials were highly sensitive to post-irradiation heat treatment compared with the homopolymers, although the numbers of trapped radicals were the same in all samples according to e.s.r. measurements. Crosslinking rate increases with a-methyl content as judged by gel point values on annealed samples, reaching a maximum near three a-methyl groups per 1000 vinyl acetate units and decreasing again at high a-methyl contents.

The annealing of radiation damage in tungsten investigated by field-ion microscopy

Annealed tungsten wire has been reactor-irradiated to a dose of 10 17 n. v. t. ( > 1 MeV), and specimens for field-ion microscopy prepared from the wire. Vacancies could be identified in certain regions of the field-ion microscope image, and the size and shape of small clusters of vacancies could be found by careful field-evaporation. Using the field evaporation technique the clustering of vacancies has been followed in specimens that were unirradiated, irradiated, and given certain post-irradiation heat treatments. The only interstitial defects seen arose from impurities. Specimens examined after being annealed in stage III ( ~ 400°C), showed fewer single vacancies, and there was a simultaneous increase in the number of small vacancy clusters. It is concluded that stage III annealing in tungsten may be associated with the migration of single vacancies to small clusters, rather than the migration of an interstitial defect.

The Effect of Post-Irradiation Heat Treatment on Polytetra-fluoroethylene

The Effect of Post-Irradiation Heat Treatment on Polytetra-fluoroethylene

Lattice contractions associated with the neutron irradiation of self-bonded silicon carbide

Abstract Self-bonded SiC has been irradiated at 250° and 700°c to fast neutron doses of 4·77 × 1020 and 1·98 × 1020 n.v.t. respectively. The unit cells of the phases present (Si, α- and β-SiC) have been measured after irradiation and after various post-irradiation heat treatments. Under certain conditions the Si and α-SiC lattice parameters decreased below their unirradiated values.

Density–dose behavior of irradiated polytetrafluoroethylene

AbstractThe nature of the room temperature density–dose relationships in polytetrafluoro‐ethylene (PTFE) have been studied over the dose range of 104 to 109 rads. Under various conditions, samples of PTFE were irradiated in combinations of neutron and gamma (reactor and 60Co) radiation fields resulting in density increases up to approximately 5%. For the dose range 105 to 108 rads, the increase in density measured at 0°C. is approximately proportional to the logarithm of the radiation dose. For doses less than about 105 rads, the increase in density appears to be directly proportional to the dose, while above 108 rads the density reaches a maximum and then begins to decrease. By examining the changes in slope and displacement of the curves which occur under various conditions, several effects are discernible. Compared to the effects of γ‐rays alone, the density increase per dose in the 105 to 108 rad region is lower for cases where both neutrons and γ‐rays are present in the radiation field. This may suggest that competing processes are involved in producing density changes. The discernible difference between effects of γ‐radiation and reactor radiation appears to be unique in polymers. The ambient temperature during irradiation and the post‐irradiation heat treatment of the specimens affect the changes in density. For dose rates over the range 0.1 × 106 to 13 × 106 rads/hr., no dose rate effects have thus far been observed. The feasibility of using PTFE for some types of radiation dosimetry has been demonstrated, and its possible usefulness is being investigated.

On the mechanism of inactivation of antibody activity by cobalt-60 gamma radiation-I

Experimentally determined relationships between 60Co radiation dose and inactivation of combining activity of anti-PAB indicated that a relatively large number of reactions were associated with inactivation. A progressive increase in gross molecular disorganization with increasing radiation dose was indicated by a change in viscosity. Some degree of molecular rearrangement was also suggested by an increased availability of an average of two to three disulphide bonds for reduction after irradiation in presence of urea. The molecular rearrangement suggested by viscosity and disulphide analysis is probably related to the inactivation process, rather than to mere secondary radiation-induced damage of material already inactivated, since, they were first measurable at doses of 7 × 10 4 and 15 × 10 4 rads, respectively, as compared to D 37 of 35 × 10 4 rads. The irradiated material was found to contain, in addition to a grossly denaturated fraction insoluble at low ionic strength, some subtly denaturated fractions. These fractions were demonstrated by such sensitive techniques as elimination patterns in rabbits and rates of tryptic hydrolysis. Augmented inactivation above, that resulting from irradiation alone, was demonstrated to follow mild post-irradiation heat treatment (40–41° for 3 hr). This increased heat-induced inactivation was not accompanied by detectable changes in viscosity or in the number of disulphide bonds available for reduction. It appeared to relate to the presence of molecular species, in irradiated antibody solution, that had undergone almost complete disorganization of combining sites, since stabilization of combining site by p-iodobenzoic added before heat treatment could not protect against the additional loss of activity. The degree of inactivation relating to the alternative possibility of free radical reactions with a critical group(s) in the combining site was evaluated by blocking experiments with specific haptens and was found to be insignificant.

Free Radical Concentration in Irradiated Bacterial Spores and Vegetative Cells as Measured by the ESR Method

In a previous investigation, the effect of postirradiation heat treatment on the colony-forming ability of dry spores of Bacillus subtilis was demonstrated (1). When an anoxic heat treatment was applied to irradiated spores, the 37 % survival dose (D37) became almost two times as high as that of untreated spores. This effect was first found in Bacillus megaterium spores by Powers and co-workers (2, 3). They proposed that the ionizing radiation causes three different classes of damage in living cells, one of which is at least partially restorable by the heat treatment. They also observed the corresponding effect on the pattern of the electron spin resonance (ESR) spectrum (4). The heat effect, however, was not found in the transforming ability of DNA extracted from irradiated B. subtilis spores (1). If the damage produced in DNA is a primary cause of death of irradiated cells, why did the DNA activity not show the heat effect? It was suggested in the previous paper that the high total dose used for the irradiation of the DNA might hinder the heat effect. The present experiment was designed to investigate the intracellular mechanism of the heat effect from the physical aspect. The criterion for biological damage is the behavior of radiation-produced free radicals as measured by the electron spin resonance method. Preliminary results were reported previously (5). On the other hand, the previous investigation (1) showed no heat effect on vegetative B. subtilis and other biological materials as well. The second question is whether the heat effect is a unique phenomenon found only in spores. For investigating this problem, dry vegetative cells were subjected to the ESR measurement. The results obtained were compared with the results on spores.

Sensitivity of Artemia eggs to gamma-irradiation. 8. Modification of amount of radiation-induced free radicals by post-irradiation treatments.

SummaryThe effects of heat or hydration treatment after irradiation on hatchability of, and the decay of free radicals in dry eggs of Artemia were examined. Immediately after irradiation with 480 kr of 60Co γ-rays, the eggs were heated at 100°c for 5 min, or hydrated at 4°c for 30 min, and re-desiccated with the aid of a vacuum pump for 2 hours. After these treatments, the hatchability of eggs did not change if they were examined just after treatment, but the amount of free radicals produced by irradiation instantly decreased as measured by E.S.R.In the irradiated eggs, the hatchability decreased during storage for one week under dried conditions. After post-irradiation heat treatment, the decrease in hatchability was reduced. If the irradiated eggs were hydrated, re-desiccated and stored for a few weeks, the hatchability did not decrease during the storage period. Free radicals in the irradiated eggs decayed rapidly after heat or hydration treatment. The possible role of the decay of free radicals in bio...

Effect of Post-irradiation Heat Treatment on the Elevated Temperature Embrittlement of Irradiated Stainless Steel

THE effect of reactor irradiation on the mechanical properties of structural materials at elevated temperatures is of importance to nuclear reactor technology.

The Effects of Preirradiation and Postirradiation Temperature Treatments on the X-Ray Sensitivity of Seeds of Hordeum

Dry (approximately 4% water content) seeds of Himalaya barley, when heated prior to irradiation, underwent little or no storage injury; also, the increase in injury due to aerobic hydration was as great 48 hours after irradiation as it was immediately thereafter. The effectiveness of preirradiation heat-treatments in reducing seedling injury depended on both the length of the heat-treatment and the temperature; it had no effect if hydration intervened between heating and irradiation. Postirradiation storage of seeds at elevated temperatures (75 deg C) caused an increase in injury over short storage periods but brought about a thermorecovery over longer storage periods. Preliminary experiments with acute postirradiation heat-treatments indicated that they, like preirradiation heat-treatments, decreased the amount of injury throughout the storage period. lrradiated seeds stored at dry ice temperature (- 78 deg C) showed virtually no increase in injury over long storage periods, and, as with preirradiation heat-treated seeds, they retained their sensitivity to aerobic hydration. The effects of preirradiation heat-treatment and postirradiation storage over a wide range of temperatures on the response of irradiated seeds to storage and to aerobic hydration, when combined with earlier work on these two parameters, suggest that they are alternative ways of magnifying a primarymore » radiation event. (auth)« less

A metallographic study of swelling in alpha-particle irradiated aluminum and aluminum alloys

The behavior of helium in aluminum and aluminum alloys was studied by metallographic examination of samples irradiated with alpha particles and subsequently annealed. The post-irradiation anneal produces a 2 mil wide band of helium bubbles approximately 15 mils below the surface of the sample. The appearance, size, and density of the helium bubbles were studied as a function of post-irradiation heat treatment. The results indicate that the swelling resistance of aluminum at 400° and 550° C is not improved by alloying. Also, quantitative measurements of swelling showed that surface tension is the dominant restraint to swelling when the gas bubble radii are smaller than one micron.

The role of fission gas re-solution during post-irradiation heat treatment

On heating irradiated fissile material, the fission gas content in the lattice is such that it is supersaturated only with respect to the larger bubbles which are present and re-solution of smaller bubbles may occur at a rate depending primarily on the solubility and diffusion rate of the gas. This process is analysed in detail. The analysis is applied to experimental results on post-irradiation heating of uranium in the γ-phase and a preliminary assessment is made of the heat of solution of the fission gases and the associated entropy factor.