Chalk River Laboratories

About: Chalk River Laboratories is a based out in . It is known for research contribution in the topics: Neutron diffraction & Neutron scattering. The organization has 2297 authors who have published 2700 publications receiving 73287 citations.

Inhaled uranium ore dust and lung cancer risk in rats.

Abstract: Using a nose-only inhalation system, male Sprague-Dawley rats were exposed 4.2 h d(-1), 5 days per week for 65 weeks to one of two concentrations of natural uranium ore dust aerosol (44% U, 50 mg m(-3) and 19 mg m(-3)) without significant radon content. After inhalation exposure ceased, the rats were allowed to live for their natural lifetime. Lung uranium burdens, measured at the time of death of each animal, declined exponentially after dust inhalation ceased, and the rate of decline was independent of the initial lung burden. Lymph node specific burdens ranged from 1 to 60 fold greater than the specific lung burden in the same animal. No lymph node tumors were observed. The frequency of primary malignant lung tumors was 0.016, 0.175 and 0.328 and primary non-malignant lung tumors 0.016, 0.135 and 0.131 in the control, low and high aerosol exposed groups, respectively. There was no difference in tumor latency between the groups. Absorbed dose to the lung was calculated for each animal in the study. The average doses for all the animals exposed to the low and high dust aerosol concentrations were 0.87 Gy and 1.64 Gy respectively, resulting in an average risk of malignant lung tumors of about 0.20 tumors per animal per Gy in both groups. The frequency of primary lung tumors was also calculated as a function of dose increment for both exposed groups individually and combined. The data indicate that, in spite of the above result, lung tumor frequency was not directly proportional to dose. However, when malignant lung tumor frequency was calculated as a function of dose rate (as measured by the lung burden at the end of dust inhalation) a direct linear relationship was seen (p < 0.01) suggesting dose rate may be a more important determinant of lung cancer risk than dose. Conversely, non-malignant lung tumors were significantly correlated with low lung burdens (p = 0.01). We conclude that chronic inhalation of natural uranium ore dust alone in rats creates a risk of primary malignant and non-malignant lung tumor formation and that malignant tumor risk was not directly proportional to dose, but was directly proportional to dose rate.

A Review of Pellet–Clad Interaction Behavior in Zirconium Alloy Fuel Cladding

Abstract: Pellet–clad interaction (PCI) in zirconium alloy cladding has been a long-standing concern in the context of nuclear fuel reliability. Mitigation measures have constrained operational limits in combination with modifying the manufacturing process of the cladding, such as adding a composite layer or a protective coating to the inner surface of the cladding. The foregoing remedies have satisfactorily resolved the problem at the expense of restricted operational performance (i.e., maximum power, power ramp limits, and burnup) that limit potential revenue in operation. With the continuing interest in extending performance limits of conventional nuclear fuels and consideration of new fuel designs, current mitigation measures may become less effective, necessitating research efforts to develop new solutions. The objective of this article is to present the current state of understanding of the PCI phenomenon, outline current mitigation strategies, and discuss advancements in experimental and computational techniques to further elucidate the problem. The ultimate goal is to develop a sound scientific understanding of the PCI phenomenon to improve engineering solutions and optimize operational parameters to enhance performance, while maintaining a high level of reliability and safety.

Asymbiotic nitrogen fixation and soil metabolism in three Ontario forests

Abstract: Field and laboratory incubations were used to assess nitrogenase (acetylene reduction) activity, nitrogen mineralization and respiration in three mature forests in the northern hardwoods—boreal transition zone of eastern North America. A 66-yr-old jack pine (Pinus banksiana Lamb.) forest had 45.41 ha−1 of forest floor, ca 33% more than older mixedwood and hardwood forests in the same vicinity. Jack pine forest floor was more acid, mineralized only one-third as much N and half as much C during laboratory incubations, had little or no nitrogenase activity on eight sampling dates during the growing season, and contained 40- to 70-fold lower numbers of N2-fixing bacteria. Low nutrient turnover in older jack pine stands may result in buildup of surface organic horizons and declining tree growth. At the moister hardwood site, temperature variations largely accounted for seasonal trends in C2H2 reduction: activity at the drier mixedwood site increased following rainfall events. Although asymbiotic N2 fixation in surface soils is a small N input (< 1 kg ha−1 yr−1) compared to precipitation in these more productive northern forests, it may stimulate litter decay and N dynamics.