In order to develop the hydraulic model of the ECC water bypass and the refill period at a PWR-LOCA, flashing transient and the downcomer Counter Current Flow Limit (CCFL) experiments were conducted ...with the large scale Cylindrical Core Test Facility (CCTF). The ECC water was bypassed by the two phase mixture swelled from the lower plenum to the downcomer at the flashing transient experiments. This swelling behavior was predicted well by using the void fraction correlation proposed by Okabe & Murao. The CCFL correlation based on Battelle experiments predicted well the bypass of the ECC water and its penetration into the lower plenum at the CCFL experiment.
These swelling and CCFL models were combined to form the best estimate analytical model which was applied to a large break LOCA of a commercial PWR. Calculated results showed that (1) the proposed model predicted the existence of water at the initiation of the refill, (2) the present licensing calculation was conservative because it assumed no water at this time, and (3) this conservativeness mainly came from the neglect of the water in the downcomer at the ECC water bypass period.
The swelling of the two-phase mixture in the lower plenum governs the Emergency Core Cooling (ECC) water bypass and the refill of the lower plenum at the end of blowdown phase of a PWR-LOCA. In order ...to develop an analytical model of the swell behavior, a visual air-water experiment was performed by simulating the flashing in the lower plenum. In the experiment, two layers, i. e. the froth at the lower portion and the liquid deficient layer at the upper portion were observed in the lower plenum. And it was observed that the liquid drops were ejected from the froth surface and carried to the downcomer by the ascending air flow. Based on these results, a new correlation was developed for the overall averaged void fraction of the lower plenum. This correlation was applied to the CREARE flashing experiments and good comparisons were obtained between the calculated and the measured mass transients in the lower plenum.
Development of Hybrid Safety Systems for Next-Generation PWR Makihara, Yoshiaki; Sugizaki, Takayoshi; Okabe, Kazuharu ...
Transactions of the Japan Society of Mechanical Engineers Series B,
1993/09/25, Letnik:
59, Številka:
565
Journal Article
Odprti dostop
Design requirements for the next-generation LWR have been investigated by many organization. In summary, these investigations suggest that improvement in plant safety is required through the ...evaluation of system simplification, reliability enhancement and preclusion of human factors. Hybrid safety systems, which are combinations of passive safety systems and active safety systems, have the possibility to satisfy the design requirements for next-generation LWR. This article shows the configuration of hybrid safety systems by describing the system selection process and then shows the results of system simplification.
Design requirements for the next-generation LWR have been investigated by many organization. In summary, these investigations suggest that improvement in plant safety is required through the ...evaluation of system simplification, reliability enhancement and preclusion of human factors. Hybrid safety systems, which are combinations of passive safety systems and active safety systems, have the possibility to satisfy the design requirements for next-generation LWR. This article shows the configuration of hybrid safety systems by describing the system selection process and then shows the results of system simplification.
Delirium is a critical challenge in the intensive care unit (ICU) or high care unit (HCU) setting and is associated with poor outcomes. There is not much literature on how many patients in this ...setting are assessed for delirium and what tools are used. This study investigated the status of delirium assessment tools of patients in the ICU/HCU. We conducted a multicenter prospective observational study among 20 institutions. Data for patients who were admitted to and discharged from the ICU/HCU during a 1-month study period were collected from each institution using a survey sheet. The primary outcome was the usage rate of delirium assessment tools on an institution- and patient-basis. Secondary outcomes were the delirium prevalence assessed by each institution's assessment tool, comparison of delirium prevalence between delirium assessment tools, delirium prevalence at the end of ICH/HCU stay, and the relationship between potential factors related to delirium and the development of delirium. Result showed that 95% of institutions used the Intensive Care Delirium Screening Checklist (ICDSC) or the Confusion Assessment Method for the ICU (CAM-ICU) to assess delirium in their ICU/HCU, and the remaining one used another assessment scale. The usage rate (at least once during the ICU/HCU stay) of the ICDSC and the CAM-ICU among individual patients were 64.5% and 25.1%, and only 8.2% of enrolled patients were not assessed by any delirium assessment tool. The prevalence of delirium during ICU/HCU stay was 17.9%, and the prevalence of delirium at the end of the ICU/HCU stay was 5.9%. In conclusion, all institutions used delirium assessment tools in the ICU/HCU, and most patients received delirium assessment. The prevalence of delirium was 17.9%, and two-thirds of patients had recovered at discharge from ICU/HCU.Trial registration number: UMIN000037834.
Histidine decarboxylase (HDC) represents the sole enzyme that produces histamine in the body. The present work investigated the role of endogenous histamine in carbachol- and gastrin-induced gastric ...acid secretion with HDC-knockout (HDC-/-) mice. Acid secretion was measured in either mice subjected to acute fistula production under urethane anesthesia or conscious mice that had previously undergone pylorus ligation. In wild-type mice, carbachol and gastrin significantly stimulated acid secretion, increasing gastric mucosal histamine. In contrast, in HDC-/- mice, carbachol and gastrin had little impact when either delivered alone or together. Nonetheless, the two agents achieved a synergistic effect when delivered together with exogenous histamine, stimulating acid secretion in HDC-/- mice. Such synergism was abolished by the histamine H2-receptor antagonist famotidine. cAMP involvement in acid secretion was also examined with theophylline, a phosphodiesterase inhibitor, and forskolin, an adenylate cyclase activator. In wild-type mice, theophylline significantly increased acid secretion, enhancing carbachol- and gastrin-stimulated acid secretion. In contrast, in HDC-/- mice, theophylline failed to exert an effect on basal acid secretion, as well as carbachol- and gastrin-stimulated acid secretion. Although forskolin interacted with carbachol, allowing acid secretion in HDC-/- mice, similar results were not achieved with gastrin. Such results suggest that 1) histamine is essential for carbachol- and gastrin-stimulated gastric acid secretion in mice; and 2) histamine-induced cAMP production contributes to the in vivo response to carbachol or gastrin.
The physiologic significance of the M(3) muscarinic receptor is unclear due to an absence of specific ligand. In the present study, M(3) receptor knockout (KO) mice were used to elucidate the role of ...M(3) receptors in gastric acid secretion and gastric mucosal integrity.
M(3) KO versus wild-type mice aged 1 month to 2 years were included. Gastric acid secretion was assessed by both direct intragastric pH measurement and pylorus ligation. Serum gastrin and gastric mucosal histamine levels were determined by radioimmunoassay and enzyme-linked immunosorbent assay, respectively. Morphologic analysis was performed by both immunohistochemistry and transmission electron microscopy.
Fasted M(3) KO mice exhibited higher intragastric pH, lower acid output after pylorus ligation, a lower proportion of active parietal cells, and higher serum gastrin levels than fasted wild-type mice. Acid secretion in response to carbachol, histamine, gastrin 17, and 2-deoxy-D-glucose was impaired in the mutant mice. Although carbachol was still able to cause approximately 30% acid output in M(3) KO mice, the acid secretion was inhibited by pirenzepine or famotidine. Despite remarkable hypergastrinemia in M(3) KO mice, there were no trophic responses in the oxyntic mucosa with respect to the mucosal thickness, proliferation rate, and numbers of parietal and enterochromaffin-like cells. Cholecystokinin type 2 receptor antagonist YM022 was without the effect in M(3) KO mice.
The present study shows that M(3) receptors are essential for basal acid secretion, a fully acid secretory response to histamine and gastrin, and the trophic responses of oxyntic mucosa to gastrin.
Pharmacological agents, such as histamine H(2) receptor antagonists and acid pump inhibitors, are now the most frequently used treatment for such acid-related diseases as gastroduodenal ulcers and ...reflux esophagitis. Based on increased understanding of the precise mechanisms of gastric acid secretion at the level of receptors, enzymes, and cytoplasmic signal transduction systems, further possibilities exist for the development of effective antisecretory pharmacotherapy. Gastrin CCK(2) receptor antagonists and locally active agents appear to represent promising therapies for the future. Development of gene targeting techniques has allowed production of genetically engineered transgenic and knockout mice. Such genetic technology has increased the investigative power for pharmacotherapy for not only antisecretory agents, but also treatment of mucosal diseases, such as atrophy, hyperplasia, and cancer. Elucidation of the origin of gastric parietal cells also represents an interesting investigative target that should allow a better understanding of not only acid-related diseases, but also the evolution of the stomach as an acid-secreting organ.
Histamine plays an important role in the regulation of gastric acid secretion; however, its role in maintenance of gastric morphology remains unclear. To clarify the necessity of histamine for ...gastric mucosal development and maintenance, we evaluated two different kinds of mice that lacked either mast cells (one of the gastric histamine-producing cell types) or histidine decarboxylase (HDC; a histamine-synthesizing enzyme). Measurements of stomach weight, intragastric pH, mucosal histamine levels, as well as serum gastrin and albumin levels were performed in mice. Gastric mucosal appearance was examined by immunohistochemical techniques. Although gastric mucosal histamine levels in mast cell-deficient mice were half of those observed in the wild-type mice, intragastric pH, serum gastrin levels, and gastric morphology at 12 mo were unchanged compared with the wild-type mice. In contrast, HDC-deficient mice possessed no detectable gastric histamine, but did exhibit hypergastrinemia, as well as marked increases in intragastric pH and stomach weight compared with the wild-type mice. Histological analysis revealed that 9-mo-old HDC-deficient mice demonstrated hyperplasia in the oxyntic glandular base region, as well as increased numbers of parietal and enterochromaffin-like cells. These results indicate that enterochromaffin-like cell-derived histamine is potentially involved in gastric mucosal morphology regulation.
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