18 research outputs found
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Development of a standard for calculation and measurement of the moderator temperature coefficient of reactivity in water-moderated power reactors
The contents of ANS 19.11, the standard for ``Calculation and Measurement of the Moderator Temperature Coefficient of Reactivity in Water-Moderated Power Reactors,`` are described. The standard addresses the calculation of the moderator temperature coefficient (MTC) both at standby conditions and at power. In addition, it describes several methods for the measurement of the at-power MTC and assesses their relative advantages and disadvantages. Finally, it specifies a minimum set of documentation requirements for compliance with the standard
Use of Mutagenesis, Genetic Mapping and Next Generation Transcriptomics to Investigate Insecticide Resistance Mechanisms
Insecticide resistance is a worldwide problem with major impact on agriculture and human health. Understanding the underlying molecular mechanisms is crucial for the management of the phenomenon; however, this information often comes late with respect to the implementation of efficient counter-measures, particularly in the case of metabolism-based resistance mechanisms. We employed a genome-wide insertional mutagenesis screen to Drosophila melanogaster, using a Minos-based construct, and retrieved a line (MiT[w−]3R2) resistant to the neonicotinoid insecticide Imidacloprid. Biochemical and bioassay data indicated that resistance was due to increased P450 detoxification. Deep sequencing transcriptomic analysis revealed substantial over- and under-representation of 357 transcripts in the resistant line, including statistically significant changes in mixed function oxidases, peptidases and cuticular proteins. Three P450 genes (Cyp4p2, Cyp6a2 and Cyp6g1) located on the 2R chromosome, are highly up-regulated in mutant flies compared to susceptible Drosophila. One of them (Cyp6g1) has been already described as a major factor for Imidacloprid resistance, which validated the approach. Elevated expression of the Cyp4p2 was not previously documented in Drosophila lines resistant to neonicotinoids. In silico analysis using the Drosophila reference genome failed to detect transcription binding factors or microRNAs associated with the over-expressed Cyp genes. The resistant line did not contain a Minos insertion in its chromosomes, suggesting a hit-and-run event, i.e. an insertion of the transposable element, followed by an excision which caused the mutation. Genetic mapping placed the resistance locus to the right arm of the second chromosome, within a ∼1 Mb region, where the highly up-regulated Cyp6g1 gene is located. The nature of the unknown mutation that causes resistance is discussed on the basis of these results
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Validation of ANS-5. 1 as the decay heat standard at the Savannah River Plant
The Savannah River Laboratory (SRL) is upgrading the methods used to predict the post shutdown decay heat of the Savannah River reactors by implementing procedures based on the ANS Decay Heat Power in Light Water Reactors standard. This approach takes advantage of the large volume of research used in developing the standard and establishes compatibility with the nuclear industry. To qualify the decay heat standard for use, a series of comparisons were made between detailed decay heat calculations performed using the SHIELD code system and results obtained from the standard
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Development of a standard for calculation and measurement of the moderator temperature coefficient of reactivity in water-moderated power reactors
The moderator temperature coefficient of reactivity (MTC) is an important parameter in safety analyses for thermal reactors. A positive MTC can exacerbate the severity of heatup transients, while a negative MTC can worsen the severity of cooldown transients. In particular, a strongly negative MTC is the major determinate of the severity of the steamline-break accident for pressurized water reactors (PWRs). Conversely, positive and negative MTCs can mitigate the severity of cooldown and heatup transients, respectively. Consequently, the accurate measurement and prediction of MTCs is an important factor in demonstrating that power reactors can be operated safely. ANS 19.11, the standard for ``Calculation and Measurement of the Moderator Temperature Coefficient of Reactivity in Water-Moderated Power Reactors,`` recently has been approved as a national standard by the American National Standards institute (ANSI) and the American Nuclear Society (ANS). At present, the scope of the standard is limited to PWRs, because that is the only type of power reactor currently sited in the US for which measurement of the MTC is required. The standard addresses the calculation and measurement of the MTC, and it also addresses the calculation of the ITC