Oxidation post-irradiation

Studies of the influence of irradiation on the kinetics of oxidation have been confined to post-irradiation work. In general, prior irradiation increases reactivity, although there are considerable inconsistencies in the enhancements obtained The effects can be derived from an increased surface area associated with the swelling voids produced in the metal by the irradiation, and can also probably arise to a lesser extent from chemical effects of the fission products. 

Ultrasonic irradiation of 25-mL solutions of bivalent sulfur at pH 10 (borate, I = 0.06 M) resulted in a linear decrease of [S(—II)] with sonication time. A post-irradiation oxidation of sulfide to sulfate was observed and was attributed to the subsequent thermal reaction of HS- with H202, which was... 

On the other hand, inhibiting effect of nitroxylic radical at irradiation is not observed owing to its strong action as photosensitizer. Photosensitization is absent after irradiation in dark reaction and nitroxylic radical displays its inhibiting action. That is why oxidation after irradiation (post-effect) is not observed (Figure 2.7, curve 2). 

F.C. Klaassen, et al., Post irradiation examination of irradiated americium oxide and uranium dioxide in magnesium aluminate spinel. J. Nucl. Mater. 319, 108-117 (2003). 

Chemical evidence for trapped free radicals has been obtained by the observation of various reactions initiated by these radicals after irradiation. These are those of grafting, oxidation, isotope exchange and post-irradiation crosslinking. 

Due to the free-radical character of both the y-radiation induced transformation and oxidation in the post-irradiation phase, free-radical scavenging stabilizers - phenols and amines - effectively protect PO [11,226,227]. This was confirmed by excellent antioxidant/antiradiant effects of DP A, PNA and PD in particular in the post-y-irradiation phase of PO and elastomers [11]. Oligomeric DHQ 21 or its combination with 9b efficiently stabilized EPDM or X-LPE used as insulation materials for electric cables exposed to irradiation doses up to 2MGy at a dose rate 300 Gy h 1 [242]. 

Peroxy radicals are known to be formed on exposure of irradiated PMMA to O. Thus in the presence of some oxidative degradation would take place but its nature is most likely different from that of the degradation in the absence of Oj. The addition of benzene and many free radical scavengers e.g., allyl thiourea) also protects PMMA against radiation-induced degradation. PMMA undergoes grafting by direct irradiation, post-irradiation by trapped free radicals or on irradiation in a blend [Chapiro, 1962]. 

When a polymer is irradiated below the melting temperature of crystallites, the polyfunctional monomer remains in the amorphous regions. Gels of polypropylene crosslinked in the presence of butadiene are crystalline which is a manifestation of the formation of crosslinks at the lamellar surfaces [79]. The presence of hexadecane and hexadecene-1 in isotactic polyiroiylene increases the rate of termination of radicals formed in the irradiated polymer and the oxidative post-effect is reduced as well as the deterioration of mechanical properties is less than in a polymer without additives [80]. 

Post-irradiation oxidative effects lead to a considerable deterioration of the mechanical properties of polypropylene and of its blends with a low content of polyethylene. The elongation at the breaking point of the polymer falls sharply even at doses of lower than 100 kGy which are used for example during the sterilization of medical instruments. In blends consisting of more than 30% w. of low density polyethylene, the influence of post-irradiation oxidative effects is markedly diminished [151]. 

SUPERFACT). Four types of mixed actinide oxide fuels were prepared at the Institute in accordance with the homogeneous fuel concepts (SF14,SF15). The fuels have been irradiated in the PHENIX power station and are curraitly undergoing post-irradiation examinations at the Institute. 

Kleykamp, H. (b) Post-irradiation examination and composition of the residues from nitric acid dissolution experiments of high-bumup fuel. J. Nucl. Materials 171, 181 — 188 (1990) Kleykamp, H., Paschoal, J. O., Pejsa, R., Thiimmler, F. Composition and structure of fission product precipitates in irradiated oxide fuels Correlation with phase studies in the Mo-Ru-Rh-Pd and BaO-U02-Zr02-Mo02 systems. J. Nucl. Materials 130, 426-433 (1985) Kopp, D., Munzel, H. Release of volatile carbon-14 containing products from Zircaloy. J. Nucl. Materials 173, 1-6 (1990)... 

The best estimate of the extent of hydrogen generation from the Zircaloy—H2O reaction corresponded to an oxidation of about 50% of the cladding and shroud inner liner. Additional hydrogen was estimated to have been produced from the oxidation of stainless steel and Inconel components. The data obtained from the hydrogen measurements agreed well with the results obtained in the post-irradiation examinations of the test bimdle. 

The release of tritium from irradiated oxide powders was studied by the method of post-irradiation annealing. At 400 to 660C, the release was a diffusion-controlled process. The diffusion coefficient of T in the two powders used was given by ... 

---