Large Scale Modelling of Damage and Failure of Nuclear Graphite Moderated Reactor

The UK Advanced Gas-Cooled reactors (AGRs) have cores made of graphite bricks with dual functions: as structural elements of the core, providing space for and separating fuel and control rods; and as moderator of the nuclear reaction. Nuclear graphite is a quasi-brittle material, where the dominant mechanism for failure is cracking. While cracking of isolated bricks is expected due to operation-induced changes in graphite microstructure and stress fields, these could be tolerated as far as the overall structural function of the core is maintained. Assessment of the whole core behaviour has been previously done with whole scale models where bricks have been considered as rigid body elements connected by elastic-brittle springs. This approach does not allow for the realistic assessment of the stresses in the bricks and associated brick cracking. Reported here are results from an ongoing project, which addresses this shortcoming. The proposed model uses deformable bricks with appropriate interactions, allowing for physically realistic whole core analysis. The results are focused on the damage that a graphite moderated reactor develops during a life cycle, how this affects the behaviour of the whole core, and how changes in bricks' behaviour impacts the core integrity. The proposed methodology is a major step towards high-fidelity assessment of AGRs' fitness for service, required for supporting continuous safe operation and life-extension decisions.

Mechanical Properties and Deterioration Instability of Filling Body with Gangue-Cement Material Based on AE Experiment

Gangue materials have been used to solve mine disasters with a support tunnel along the goaf and filling mining. Mastering the properties and damage characteristics of filling materials is an important basis for effective implementation. Based on the conventional uniaxial compression acoustic emission (AE) test, the effects of cementitious materials, ratio between water and cementitious material, gangue particle size, and grading parameters on the mechanical properties of gangue-cement samples were analyzed. The stage characteristics of compression deformation were studied. The fracture propagation characteristics and rock mass failure types induced by different graded gangues were revealed. The fracture forming mechanism from clustered damage and failure was interpreted. The results show that the compressive strength of the backfill increases with the increase of cementitious material; however, it decreases with the increase of water binder ratio. Controlling the proportion and dosage of materials was the key factor to realizing pumpability and stability. Combined with the deformation and AE characteristics, the failure stage of the backfill body is divided into three stages: linear deformation-low energy changing, block compression-high energy changing, and gentle stability-stable energy changing. Affected by the gangue distribution, the load in each stage will induce fracture to produce five distribution modes of single, turning, breakthrough, bifurcated, and collapsed surrounding gangue. In the process of loading failure, different gradation and particle sizes will also change its stress concentration characteristics, resulting in the transformation of rock failure types. The surface structure and roughness of gangue play an important role in the compressive performance of cement paste. The research results try to provide some guidance for efficient filling mining.

Eff ect of ursodeoxycholic acid in postcholecystectomy cholestatic hepatopathy verified by ultrasonography

Summary: Cholestasis syndrome is accompanied by a large number of diverse liver and biliary tract diseases. Many cholestatic changes are fully reversible in the fi rst phase. However, with long-term cholestasis, extensive hepatocyte dysfunction occurs, the disease progresses, and many cholestatic syndromes result in irreversible liver damage and failure. Cholestatic liver diseases represent an important group of liver diseases that are an indication for liver transplantation. Postcholecystectomy syndrome is an imprecisely defi ned term, which includes a set of ongoing or recurrent or new diffi culties of patients after gallbladder surgery. We distinguish between early postcholecystectomy syndrome immediately in the postoperative period, or late postcholecystectomy syndrome, which occurs months or even years later. Ultrasonography is the fi rst imaging examination method for diseases of the liver and hepatobiliary system. It is a non-invasive method, available, relatively cheap, easily repeatable, and it does not represent a burden for the patient. Common bile duct dilatation after cholecystectomy is a common accidental fi nding that is inconclusive in the absence of clinical symptomatology and with normal laboratory fi ndings. Ursodeoxycholic acid forms the basis of cholestasis therapy, the only treatment whose effi cacy in cholestatic liver disease has been demonstrated in randomized and long-term studies. A further positive is that many years of ursodeoxycholic acid administration are not accompanied by more serious side eff ects. This case report supports the concept of a prompt and at the same time deepening benefi cial eff ect of ursodeoxycholic acid treatment in patients with cholestatic hepatopathy verified by ultrasonography indicated for conservative treatment or refusing invasive treatment. Key words: cholestasis – postcholecystectomy syndrome – ultrasonography – ursodeoxycholic acid

Designing Public Health Policy to Curb Health and Economic Impact of Khat Chewing

Introduction and Background: Khat (Catha edulis Forsk) known for long period as an indigenous plant to Ethiopia, has many mixed effects and impact. Some consider it as a good means to socialize. Others consider it as a good source of income. Nowadays, as a result of its effect on health, public health concern is growing. However, there are no policies controlling these khat effects. Objective: To present policy option to curtail health and economic impact of khat chewing practice in Ethiopia. Methods: Narrative literature review was made to look into different effects of khat chewing with a particular reference to Ethiopia. Key findings khat chewing has stimulating, euphoric and addictive effects. It has a constricting effect on blood vessels leading to hypertension. It has also neuropsychiatric and physical consequences including aggression, suicidal ideation, anxiety, paranoia, manic behaviors, insomnia, depression, increased heart rate, anorexia and weight loss, dental and pulmonary problems. Additionally, khat abuse found linked to liver damage and failure. Conclusion: Given that medical risks of khat use are modest, or studies are not conclusive, there should be a regulatory framework with the objective of protecting consumers and community. This is best achieved by establishing processes for the quality control of khat and by regulating access and availability. Conclusive studies are very rare and even some are inadequate and contradictory. Most of the evidences on adverse effects of khat come from case reports and observational studies. Therefore, high quality research is justified.