Chalk River Laboratories is a Canadian nuclear research facility located in Deep River, Renfrew County, Ontario, near the village of Chalk River, about 180 km north-west of Ottawa.CRL is a site of major research and development to support and advance nuclear technology, in particular CANDU reactor technology. CRL has expertise in physics, metallurgy, chemistry, biology, and engineering and unique research facilities. For example, Bertram Brockhouse, a professor at McMaster University, received the 1994 Nobel Prize in Physics for his pioneering work in neutron spectroscopy while at CRL from 1950-1962. Sir John Cockcroft was an early director of CRL and also a Nobel laureate. CRL produces about one-third of the world's supply of medical radioisotopes. It is owned and operated by Atomic Energy of Canada Limited. Wikipedia.
Liang Z.,Chalk River Laboratories
International Journal of Hydrogen Energy | Year: 2017
This paper presents vented combustion data gathered in a 120 m3 large scale vented combustion test facility at the Canadian Nuclear Laboratories. Experiments were performed with single volumes (57 or 120 m3), or two (60 and 57 m3 each) and three (25, 28 and 57 m3 each) interconnected volumes using lean H2-air mixtures (6-10 vol.% H2) under the initially quiescent or turbulent conditions. The effects of scaled vent area (Av/V2/3), number of connected volumes, initial turbulence and hydrogen concentration on dynamics of vented combustion are examined. The test results show that combustion in an interconnected multi-compartment geometry could produce significant flame acceleration and local pressure build-up for mixtures containing 8 vol.% or higher H2 in air due to flame jet ignition and flame interaction between compartments, resulting in much higher overpressures than in a single volume. © 2017 Hydrogen Energy Publications LLC.
News Article | December 20, 2016
The material, a formulation of iron, sodium, copper and arsenic created by Rice graduate student Yu Song in the laboratory of physicist Pengcheng Dai, is described this week in the journal Nature Communications. Dai said Song's recipe—which involves mixing ingredients in a pure argon atmosphere, sealing them in niobium canisters and baking them at nearly 1,000 degrees Celsius—produces a layered alloy in which iron and copper separate into alternating stripes. This striping is critical for the material's usefulness in explaining the origins of high-temperature superconductivity, said RCQM Director Qimiao Si. "By forming this regular pattern, Yu Song has physically removed disorder from the system, and that is crucially important for being able to say something meaningful about what's going on electronically," said Si, a theoretical physicist who has worked to explain the origins of high-temperature superconductivity and similar phenomena for nearly two decades. High-temperature superconductivity was discovered in 1986. It occurs when electrons pair up and flow freely in layered alloys like Song's new creation. Dozens of high-temperature superconducting alloys have been created. Most are complex crystals that contain a transition metal—typically iron or copper—and other elements. High-temperature superconductors are typically terrible conductors at room temperature and only become superconductors when they are cooled to a critical temperature. "The central problem of high-temperature superconductivity is to understand the precise relationship between these two fundamental states of matter and the phase transition between them," said Dai, professor of physics and astronomy at Rice. "The macroscopic change is evident, but the microscopic origins of the behavior are open to interpretation, largely because there are many variables in play, and the relationship between them is both synergistic and nonlinear." Dai said two schools of thought "developed from the very beginning of this field. One was the itinerant camp, which argues that both states ultimately arise from itinerant electrons. After all, these materials are metals, even if they may be poor metals." The other camp is the localized camp, which argues that fundamentally new physics arise—due to electron-electron interactions—at the critical point at which the materials transition from one phase to the other. Dai said measurements on Song's new material support the localized theory. In particular, the new material is the first member of a class of iron-based superconductors called pnictides (pronounced NIK-tides) that can be tuned between two competing phases: the superconducting phase in which electrons flow with no resistance, and a "Mott insulating" phase in which electrons become locked in place and do not flow at all. "The discovery that Yu Song made is that this material is more correlated, which is evident because of the Mott insulating phase," Dai said. "This is the first time anyone has reported an iron-based superconductor that can be continuously tuned from the superconducting phase to the Mott insulating phase." Samples were made and some tests were performed at RCQM. Additional tests were performed at Chalk River Laboratories' Canadian Neutron Beam Center in Ontario, the National Institute for Standards and Technology's Center for Neutron Research in Maryland, Brookhaven National Laboratory in New York, Oak Ridge National Laboratory's High Flux Isotope Reactor in Tennessee and the Paul Scherrer Institute's Advanced Resonant Spectroscopies beamline in Switzerland. "In the paper, we showed that if the interaction was weak, then even replacing 50 percent of the iron with copper would still not be sufficient to produce the insulating state," Si said. "The fact that our experimentalists have managed to turn the system to be Mott insulating therefore provides direct evidence for strong electron-electron interactions in iron pnictides. That is an important step forward because it suggests that superconductivity should be tied up with these strong electron correlations." Explore further: Material turns 'schizophrenic' on way to superconductivity More information: Yu Song et al. A Mott insulator continuously connected to iron pnictide superconductors, Nature Communications (2016). DOI: 10.1038/ncomms13879
Guzonas D.A.,Chalk River Laboratories |
Cook W.G.,University of New Brunswick
Corrosion Science | Year: 2012
Interest in materials degradation in supercritical water (SCW) increased significantly after the Generation IV International Forum selected the supercritical water-cooled reactor as one of six concepts for investigation. While a significant body of literature now exists on alloy corrosion in SCW, most studies have focused on the metal side of the metal-water interface. Using new data and a selective review of corrosion in SCW, this paper highlights how changes in SCW density change the corrosion mechanism, and highlights the close link between corrosion in SCW and high-temperature steam above 500°C. Key issues in test methodologies are also discussed. © 2012.
Duffey R.B.,Chalk River Laboratories |
Ha T.,Candesco Corporation
IEEE Transactions on Power Systems | Year: 2013
Power restoration following a large outage or widespread blackout is time critical and complex. A new method is presented for determining the timing and chance of electric power recovery and restoration. The present advance over previous work is explicitly integrating human, component and system reliability, which unifies the topic of power system restoration with the general theory for errors, accidents and outcomes for other technological systems. © 2012 IEEE.
Richardson R.B.,Chalk River Laboratories
Mechanisms of Ageing and Development | Year: 2014
Knudson's carcinogenic model, which simulates incidence rates for retinoblastoma, provides compelling evidence for a two-stage mutational process. However, for more complex cancers, existing multistage models are less convincing. To fill this gap, I hypothesize that neoplasms preferentially arise when stem cell exhaustion creates a short supply of progenitor cells at ages of high proliferative demand. To test this hypothesis, published datasets were employed to model the age distribution of osteochondroma, a benign lesion, and osteosarcoma, a malignant one. The supply of chondrogenic stem-like cells in femur growth plates of children and adolescents was evaluated and compared with the progenitor cell demand of longitudinal bone growth. Similarly, the supply of osteoprogenitor cells from birth to old age was compared with the demands of bone formation. Results show that progenitor cell demand-to-supply ratios are a good risk indicator, exhibiting similar trends to the unimodal and bimodal age distributions of osteochondroma and osteosarcoma, respectively. The hypothesis also helps explain Peto's paradox and the finding that taller individuals are more prone to cancers and have shorter lifespans. The hypothesis was tested, in the manner of Knudson, by its ability to convincingly explain and demonstrate, for the first time, a bone tumour's bimodal age-incidence curve. © 2014.
Rowan D.J.,Chalk River Laboratories
Journal of Environmental Radioactivity | Year: 2013
Steady state approaches, such as transfer coefficients or bioaccumulation factors, are commonly used to model the bioaccumulation of 137Cs in aquatic foodwebs from routine operations and releases from nuclear generating stations and other nuclear facilities. Routine releases from nuclear generating stations and facilities, however, often consist of pulses as liquid waste is stored, analyzed to ensure regulatory compliance and then released. The effect of repeated pulse releases on the steady state assumption inherent in the bioaccumulation factor approach has not been evaluated. In this study, I examine the steady state assumption for aquatic biota by analyzing data for two cesium isotopes in the same biota, one isotope in steady state (stable 133Cs) from geologic sources and the other released in pulses (137Cs) from reactor operations. I also compare 137Cs bioaccumulation factors for similar upstream populations from the same system exposed solely to weapon test 137Cs, and assumed to be in steady state. The steady state assumption appears to be valid for small organisms at lower trophic levels (zooplankton, rainbow smelt and 0+ yellow perch) but not for older and larger fish at higher trophic levels (walleye). Attempts to account for previous exposure and retention through a biokinetics approach had a similar effect on steady state, upstream and non-steady state, downstream populations of walleye, but were ineffective in explaining the more or less constant deviation between fish with steady state exposures and non-steady state exposures of about 2-fold for all age classes of walleye. These results suggest that for large, piscivorous fish, repeated exposure to short duration, pulse releases leads to much higher 137Cs BAFs than expected from 133Cs BAFs for the same fish or 137Cs BAFs for similar populations in the same system not impacted by reactor releases. These results suggest that the steady state approach should be used with caution in any situation where reactor releases are episodic or pulse in nature, even if the magnitude of these releases is small. © 2012 .
Kim S.B.,Chalk River Laboratories |
Korolevych V.,Chalk River Laboratories
Journal of Environmental Radioactivity | Year: 2013
The objective of this study is to quantify the relative amounts of exchangeable organically bound tritium (OBT) and non-exchangeable OBT in various vegetables. A garden plot at Perch Lake, where tritium levels are slightly elevated due to releases of tritium from a nearby nuclear waste management area and Chalk River Laboratories (CRL) operations, was used to cultivate a variety of vegetables. Five different kinds of vegetables (lettuce, cabbage, tomato, radish and beet) were studied. Exchangeable OBT behaves like tritium in tissue free water in living organisms and, based on past measurements, accounts for about 20% of the total tritium in dehydrated organic materials. In this study, the percentage of the exchangeable OBT was determined to range from 20% to 57% and was found to depend on the type of vegetables as well as the sequence of the plants exposure to HTO. © 2012.
Richardson R.B.,Chalk River Laboratories
International Journal of Radiation Biology | Year: 2011
Purpose: This paper reviews and reassesses the internationally accepted niches or 'targets' in bone marrow that are sensitive to the induction of leukaemia and primary bone cancer by radiation. Conclusions: The hypoxic conditions of the 10μm thick endosteal/osteoblastic niche where preleukemic stem cells and hematopoietic stem cells (HSC) reside provides a radioprotective microenvironment that is 2- to 3-fold less radiosensitive than vascular niches. This supports partitioning the whole marrow target between the low haematological cancer risk of irradiating HSC in the endosteum and the vascular niches within central marrow. There is a greater risk of induced bone cancer when irradiating a 50μm thick peripheral marrow adjacent to the remodelling/reforming portion of the trabecular bone surface, rather than marrow next to the quiescent bone surface. This choice of partitioned bone cancer target is substantiated by the greater radiosensitivity of: (i) Bone with high remodelling rates, (ii) the young, (iii) individuals with hypermetabolic benign diseases of bone, and (iv) the epidemiology of alpha-emitting exposures. Evidence is given to show that the absence of excess bone-cancer in atomic-bomb survivors may be partially related to the extremely low prevalence among Japanese of Paget's disease of bone. Radiation-induced fibrosis and the wound healing response may be implicated in not only radiogenic bone cancers but also leukaemia. A novel biological mechanism for adaptive response, and possibility of dynamic targets, is advocated whereby stem cells migrate from vascular niches to stress-mitigated, hypoxic niches. © 2011 Informa UK, Ltd.
Richardson R.B.,Chalk River Laboratories
Leukemia Research | Year: 2011
This paper speculates on the role of infection in modifying a young child's risk of promoting precursor B-cell acute lymphoblastic leukemia (ALL). It is suggested that the heat shock instigated by infections, particularly in infancy, stimulates Th1 pro-inflammatory cytokines and an apoptosis-inhibitory environment. This infective stress also increases the number of cooperating oncogenic mutations in pre-leukemic cells, especially if the primary adaptive immune response is delayed. The glucocorticoid release that follows leads to acute thymic involution, a decline in antitumor immunity, and maturation arrest of B-lymphocytes. The infective lymphoid recovery hypothesis addresses an apparent contradiction-that a non-hygienic environment primes the adaptive immune response and is protective against childhood ALL, while multiple infections occurring later increase the risk of childhood ALL. In affluent (compared to less-affluent) societies, the characteristic ALL incidence peak in early childhood, and the shortened time to diagnosis, arise from surviving recurrent infections and the accumulated loss and recovery of lymphoid tissue. Evidence supporting the hypothesis, such as the role of lymphoid tissue reconstitution cytokines that stimulate proliferation stress on B-cell progenitors, comes from the study of children with congenital syndromes that are susceptible to leukemia. © 2011.
Richardson R.B.,Chalk River Laboratories
Cell Cycle | Year: 2013
TP53's role as guardian of the genome diminishes with age, as the probability of mutation increases. Previous studies have shown an association between p53 gene mutations and cancer. However, the role of somatic TP53 mutations in the steep rise in cancer rates with aging has not been investigated at a population level. This relationship was quantified using the International Agency for Research on Cancer (IARC) TP53 and GLOBOCAN cancer databases. The power function exponent of the cancer rate was calculated for 5-y age-standardized incidence or mortality rates for up to 25 cancer sites occurring in adults of median age 42 to 72 y. Linear regression analysis of the mean percentage of a cancer's TP53 mutations and the corresponding cancer exponent was conducted for four populations: worldwide, Japan, Western Europe, and the United States. Significant associations (P ≤ 0.05) were found for incidence rates but not mortality rates. Regardless of the population studied, positive associations were found for all cancer sites, with more significant associations for solid tumors, excluding the outlier prostate cancer or sex-related tumors. Worldwide and Japanese populations yielded P values as low as 0.002 and 0.005, respectively. For the United States, a significant association was apparent only when analysis utilized the Surveillance, Epidemiology, and End Results (SEER ) database. This study found that TP53 mutations accounts for approximately one-quarter and one-third of the aging-related rise in the worldwide and Japanese incidence of all cancers, respectively. These significant associations between TP53 mutations and the rapid rise in cancer incidence with aging, considered with previously published literature, support a causal role for TP53 according to the Bradford-Hill criteria. However, questions remain concerning the contribution of TP53 mutations to neoplastic development and the role of factors such as genetic instability, obesity, and gene deficiencies other than TP53 that reduce p53 activity. © 2013 Landes Bioscience.