Statistical arguments towards the development of an advanced embrittlement correlation method for reactor pressure vessel materials

An embrittlement correlation method is one of the most important techniques used to ensure the integrity of pressure vessel steels in nuclear power plants. In Japan, the embrittlement correlation method is being addressed in accordance with the Japan Electric Association Code (JEAC 4201), which was developed using actual measured data on the irradiation embrittlement of pressure vessel steels. In the present study, to develop more reliable methodologies, statistical arguments were made concerning the embrittlement data. With regard to a set of residual data defined in JEAC 4201 as a collection of differences between the measured and calculated ΔDBTT (ductile-to-brittle transition temperature shift) values, a statistical relationship between the population and samples was found, and then, the sampling errors in the mean values of the residuals were identified as key for establishing a more reliable correlation method. Using this relationship, it was noted that when predicting the amount of irradiation embrittlement for a particular plant using the JEAC 4201 correlation method, the deviation associated with sampling errors needed to be corrected. Based on this finding, a more appropriate interpretation was found for the so-called MC correction in JEAC 4201, and moreover, a new correction method was developed within the Bayesian estimation framework

Effects of Irrigation Methods on the Growth of Petunia Grown in Heat Fusion Polyester Fiber Hardened Medium without Polythylene Pot

Recenty, polyethylene pots(PP) present a significant environmental issue for waste disposal. To develop bedding plant production system without PP, properties of compacted medium hardened by heat fusion polyester fiber were investigated. Effects of irrigation methods on the growth of vegetative propagated petunia grown in medium without PP were investigated. The effect of medium type was not as significant as the difference in water loss per pot. Water loss per pot of medium without PP was about two times greater than medium held in PP. No compacted medium disintegrated easily without root-ball formation, and in 20 days after cutting about half of non-compacted medium had disintegrated. Compacted medium did not disintegrate before rooting. Medium type did not significantly affect rooting rates, plant heights, leaf numbers and fresh weights when transplanted to medium. Also, cell or pot medium type did not significantly affect plant heights, flower numbers, leaf numbers and fresh weights. Non-compacted medium without PP easily disintegrated with overhead irrigation. Subirrigation and much overhead irrigation had similar effect on growth when planted in containers.However, less overhead irrigation had significantly lower growth. Moreover, in less overhead irrigation, non-compacted medium without PP had remarkably lower growth than compacted medium without PP. In, conclusions, compacted medium without PP did not affect the growth of bedding plants whenever water and nutrient regime was well regulated. Compacted pot medium was easy to transplant since it did not disintegrate. Therefore, it was considered practical and feasible to use compacted medium without PP for bedding plant production

Super-saturated hydrogen effects on radiation damages in tungsten under the high-flux divertor plasma irradiation

Tungsten is a prime candidate as the divertor material of the ITER and DEMO reactors, which would be exposed to unprecedentedly high-flux plasmas as well as neutrons. For a better characterization of radiation damages in the tungsten under the divertor condition, we examine influences of super-saturated hydrogen on vacancies in the tungsten. The present calculations based on density functional theory (DFT) reveal unusual phenomena predicted at a super-saturated hydrogen concentration: (1) strongly enhanced vacancy concentration with the super-saturated hydrogen concentration is predicted by a thermodynamics model assuming multiple-hydrogen trapping, i.e. hydrogen clusters formation, in the vacancies; and (2) DFT molecular dynamics revealed that hydrogen clusters can prevent a vacancy from recombining with the neighboring crowdion-type self-interstitial-atom. This suggests that neutron damage effects will be increased in the presence of the hydrogen clusters

Light-induced propulsion of a giant liposome driven by peptide nanofibre growth

Light-driven nano/micromotors are attracting much attention, not only as molecular devices but also as components of bioinspired robots. In nature, several pathogens such as Listeria use actin polymerisation machinery for their propulsion. Despite the development of various motors, it remains challenging to mimic natural systems to create artificial motors propelled by fibre formation. Herein, we report the propulsion of giant liposomes driven by light-induced peptide nanofibre growth on their surface. Peptide-DNA conjugates connected by a photocleavage unit were asymmetrically introduced onto phase-separated giant liposomes. Ultraviolet (UV) light irradiation cleaved the conjugates and released peptide units, which self-assembled into nanofibres, driving the translational movement of the liposomes. The velocity of the liposomes reflected the rates of the photocleavage reaction and subsequent fibre formation of the peptide-DNA conjugates. These results showed that chemical design of the light-induced peptide nanofibre formation is a useful approach to fabricating bioinspired motors with controllable motility

Effect of Combination of Overhead Irrigation and Subirrigation on the Growth of Bedding Plants Grown in Polyester Fiber Medium Hardened by Heat Fusion, without use of Polyethylene Pots

The effects of irrigation methods on several bedding plants without polyethylene pots using compacted polyester fiber medium hardened by heat fusion were investigated. The characteristics of overhead irrigation with a tray collecting runoff water (combination of overhead irrigation and subirrigation) were investigated at the same time. Irrigation usage (the amount of water supplied per pot / amount of irrigation water) with a combination of overhead irrigation and subirrigation was improved compared to overhead irrigation alone. The growth of garden type Cyclamen grown under a combination of both overhead irrigation and subirrigation was significantly greater than that grown in either wick irrigation, ebb & flow irrigation or overhead irrigation. Notably, smaller growth was achiered in garden type cyclamen grown with overhead irrigation. The growth of Vinca grown in a combination of overhead irrigation and subirrigation was significantly greater than that grown with overhead irrigation alone. The irrigation amount had no effect on the growth of Vinca regardless of irrigation method. The growth of Petunia was greater with increased amounts of irrigation water. However, the growth of Pansy grown under overhead irrigation was significantly greater than that grown in a combination of overhead irrigation and subirrigation. These results suggest that a combination of overhead irrigation and subirrigation method in bedding plant production without polyethylene pots is generally suitable since the plants grow without drought stress. However, it may be suggested that the amount of irrigation water should be as low as possible in the winter season or with sensitive species in order to prevent waterlogging injury.熱融着性ポリエステル繊維固化培地を利用したポットレス花壇苗生産における灌水方法として，水受けトレイを用いた頭上灌水（頭上底面灌水）の実用性を検討した．頭上灌水と比較して頭上底面灌水では灌水効率（培地に吸収された灌水量／灌水量）が大幅に改善できた．ガーデンシクラメンの生育は頭上底面灌水区で最もよく，次いでひも灌水，底面灌水の順であり，頭上灌水区で最も生育が抑制された．ニチニチソウでは頭上灌水より頭上底面灌水区で生育が改善されたが，灌水量には差はほとんどみられなかった．ペチュニアでは灌水量が多いほど，専用トレイに溜める水量が多いほど生育が旺盛になった．しかし，パンジーでは頭上底面灌水によって生育が抑制された．ポットレス花壇苗生産では頭上底面灌水が最も適切であったが，蒸発散の少ない冬期や過湿に弱い種においては灌水量をできるだけ少なくすべきと考えられた

Development of methodology to optimize management of failed fuels in light water reactors

Fuel cladding is one of the key components in a fission reactor that confines radioactive materials inside a fuel tube. During reactor operation, however, cladding is sometimes breached, and radioactive materials leak from the fuel pellet into the coolant water through the breach. The primary coolant water is therefore monitored so that any leak is quickly detected; coolant water is periodically sampled, and the concentration of radioactive iodine 131 (I-131), for example, is measured. Depending on the measured leakage concentration, the faulty fuel assembly with leaking rod is removed from the reactor and replaced immediately or at the next refueling. In the present study, an effort has been made to develop a methodology to optimize the management for replacement of faulty fuel assemblies due to cladding failures using measured leakage concentration. A model numerical equation is proposed to describe the time evolution of an increase in I-131 concentration due to cladding failures and is then solved using the Monte Carlo method as a function of sampling rate. Our results indicate that, to achieve rationalized management of failed fuels, higher resolution to detect a small amount of I-131 is not necessarily required, but more frequent sampling is favorable

Irradiation Correlation of Microstructural Changes in Metals : A Computational Study of Collision Cascades

報告番号: 甲10538 ; 学位授与年月日: 1994-03-29 ; 学位の種別: 課程博士 ; 学位の種類: 博士(工学) ; 学位記番号: 博工第3195号 ; 研究科・専攻: 工学系研究科システム量子工学専

金属中の微細構造変化に関する照射相関 : 衝突カスケ-ドの計算機シミュレ-ション

University of Tokyo (東京大学

Helium Cavity Swelling in RAFM Steel under Different Irradiation Fields: Reaction Rate Theory-Based Analysis

A reduced-activation ferritic/martensitic (RAFM) steel is expected as a blanket structural material in a nuclear fusion DEMO reactor. The blanket structural material suffers from fusion neutron bombardments which induce a huge production of irradiation defects such as vacancies, interstitials, helium atoms, and their clusters. Especially helium is known to strongly enhance cavity swelling and high temperature intergranular embrittlement. For a design of the DEMO reactor, it is necessary to develop a methodology that can mechanistically interpret the existing experimental irradiation data and predict the helium effects in the fusion DEMO environment. The objective of this study is to mechanistically understand the helium effects on the cavity swelling in RAFM steel, focused on the nucleation and growth processes of helium bubbles under a wide range of irradiation conditions: temperature, dpa rate, and helium production rate.20th International Conference of Fusion Reactor Material

Interstitial Diffusion of C Interacting with Ambient H in Tungsten Crystals

Negative binding energies between interstitial C (octahedral) and H (tetrahedral) in a bulk crystal of W (bcc) were obtained with the first-principle calculations, which indicate repulsive interaction in the interstitial C-H pair. The electron cloud associated to the each interstitial atom was analyzed with Bader\u27s method. This analysis gives negative fractional charges of ?0.35 and ?0.37 for the interstitial C and H, respectively, supporting the repulsive interaction between them. Interstitial diffusion of C was studied including influences of ambient H atoms in the mean field approximation and the ergodic assumption. The calculated diffusion coefficients are significantly increased by the repulsive interaction with the H atoms