• Nuclear Engineering and Technology
• /
• 제45권3호
• /
• pp.385-392
• /
• 2013

Zirconium and zirconium alloys are widely used as nuclear reactor core materials such as fuel cladding and guide tubes because they have excellent corrosion- and radiation-resistant properties. In the reactor core, zirconium alloys are subjected to high-energy neutron fluence, causing radiation-induced dislocation and growth. To discern a possible correlation between radiation-induced dislocation and growth, characteristics of dislocation and growth in zirconium and its alloys are examined. The radiation-induced dislocation including and dislocation loops is reviewed in various temperature and fluence ranges, and their growth behavior is examined in the same way. To further a fundamental understanding, radiation-induced growth prediction models are briefly reviewed. This research will assist in the design of zirconium based components as well as the safety analysis of various reactor conditions, in both research and commercial reactors.

• Nuclear Engineering and Technology
• /
• 제38권7호
• /
• pp.619-638
• /
• 2006

Low temperature irradiation can significantly harden metallic materials and often lead to strain localization and ductility loss in deformation. This paper provides a review on the radiation effects on the deformation of metallic materials, focusing on microscopic and macroscopic strain localization phenomena. The types of microscopic strain localization often observed in irradiated materials are dislocation channeling and deformation twinning, in which dislocation glides are evenly distributed and well confined in the narrow bands, usually a fraction of a micron wide. Dislocation channeling is a common strain localization mechanism observed virtually in all irradiated metallic materials with ductility, while deformation twinning is an alternative localization mechanism occurring only in low stacking fault energy(SFE) materials. In some high stacking fault energy materials where cross slip is easy, curved and widening channels can be formed depending on dose and stress state. Irradiation also prompts macroscopic strain localization (or plastic instability). It is shown that the plastic instability stress and true fracture stress are nearly independent of irradiation dose if there is no radiation-induced phase change or embrittlement. A newly proposed plastic Instability criterion is that the metals after irradiation show necking at yield when the yield stress exceeds the dose-independent plastic instability stress. There is no evident relationship between the microscopic and macroscopic strain localizations; which is explained by the long-range back-stress hardening. It is proposed that the microscopic strain localization is a generalized phenomenon occurring at high stress.

• Nuclear Engineering and Technology
• /
• 제52권8호
• /
• pp.1749-1755
• /
• 2020

In present study, TEM foils of Ni-Mo-Cr alloy were directly irradiated with 30 keV Ar ions to allow direct characterization. The defects evolution and element segregation after irradiation were investigated by TEM and HAADF-EDS linear scanning. At low irradiation doses (1.38 and 2.76 dpa), black dots were formed and grew with increasing dose. Complicated defects including peas-shaped dislocation loops, polygon dislocation networks and large loops were visible in samples irradiated to high doses (13.8 and 27.6 dpa). Meanwhile, dislocation channels appeared, in which defects were swept out. Significant Mo depletions at dislocation lines and grain boundaries were induced by irradiation due to large misfits between Mo-Ni atoms and high content of Mo.

• Nuclear Engineering and Technology
• /
• 제56권4호
• /
• pp.1277-1283
• /
• 2024

This study presents a radiation-induced thermal conductivity degradation (TCD) model of zirconium as compared to the conventional UO2 TCD model. We derived the governing factors of the radiation-induced TCD model, such as maximum TCD value and temperature range of TCD. The maximum TCD value was derived by two methods, in which 1) experimental result of 32 % TCD was directly utilized as the maximum TCD value and 2) a theoretical approach based on dislocation was applied to derive the maximum TCD value. Further, the temperature range of TCD was determined to be 437-837 K by 1) experimental results of post-annealing of irradiation hardening as compared to 2) the rate theory and thermal equilibrium. Consequently, the radiation-induced TCD model of zirconium was derived to be $f_r=1-{\frac{0.32}{1+{\exp}\,\{(T-637)/45\}}}$. Because the thermal conductivity of zirconium is one of the factors determining the storage and transport system, this newly proposed model could improve the safety analysis of spent fuel storage systems.

• Nuclear Engineering and Technology
• /
• 제52권1호
• /
• pp.148-154
• /
• 2020

The radiation induced segregation of Cr at grain boundaries (GBs) in Ferritic/Martensitic steels was modeled assuming vacancy and interstitialcy diffusion mechanisms. In particular, the dependence of segregation on temperature and grain boundary misorientation angle was analyzed. It is found that Cr enriches at grain boundaries at low temperatures primarily through the interstitialcy mechanism while depletes at high temperatures predominantly through the vacancy mechanism. There is a crossover from Cr enrichment to depletion at an intermediate temperature where the Cr:Fe vacancy and interstitialcy diffusion coefficient ratios intersect. The bell-shape Cr enrichment response is attributed to the decreasing void sinks inside the grains as temperature rises. It is also shown that low angle grain boundaries (LAGBs) and special Σ coincidence-site lattice (CSL) grain boundaries exhibit suppressed radiation induced segregation (RIS) response while high angle grain boundaries (HAGBs) have high RIS segregation. This different behavior is attributed to the variations in dislocation density at different grain boundaries.

• 공업화학
• /
• 제31권4호
• /
• pp.347-351
• /
• 2020

재료는 방사선과 상호작용을 통해 그 물리적, 화학적 특성이 변화하며 여러 방사선 중에서 전하를 띄고 있지 않아 침투깊이가 깊은 중성자 조사에 의한 금속소재의 조사손상은 원자력발전소의 안전과 관련해서 오랜 기간 동안 집중적인 연구대상이었다. 중성자 조사에 의한 조사손상은 초반 피코 초 스케일에서 벌어지는 원자단위의 점결함의 생성으로 시작되며 그 이후의 전개 양상은 전위 고리나 공극과 같은 미세구조상 결함으로 확인될 수 있다. 이러한 미세구조 상 결함의 형상과 분포에 따라 소재의 특성에 미치는 효과는 상이하게 된다. 그러므로 중성자 조건에 따른 미세구조를 예측하는 것은 매우 중요한 일로, 본 논문에서는 중성자 조사에 의한 재료 내의 미세구조 발달에 대해 리뷰한 뒤 조사된 소재의 미세구조 변화 예측에 널리 사용될 수 있는 상장 모델에 대해 간략히 소개하였다.

• 환경생물
• /
• 제23권4호
• /
• pp.398-404
• /
• 2005

Radioprotection is of practical importance for the normal tissues of tumor patients subject to radiotherapy, people with planned or accidental exposure to radiation, and the public and radiation workers. Since oxygen enhances radiation - induced biological damage, antioxidants should be related with the function as a radioprotectors. Ascorbic acid or caffeine is an essential component and antioxidant in the diet of humans and a small range of other mammals. The present study investigates functional radioprotection of caffeine and ascorbic acid against gamma radiation in irradiated C57BL/6N mice. Eight-week-old male C57BL/6N mice were irradiated with 6.5 Gy. A caffeine treated group was administered with $80mg\;kg^{-1}$ body weight by intraperitoneal injection, a single treatment 1 hr before irradiation. Ascorbic acid was administered $330\;mg\;L^{-1}$ in drinking water through all the experimental period. According to time schedules, animals were sacrificed by cervical dislocation. And the samples were collected 2 weeks after whole- body gamma irradiation. The caffeine treated group showed lower decrement of body and organ weights than the other experimental groups. The qualitative analysis of circulating testosterone in serum was performed by means of radioimmunoassay (RIA). The normal level of circulating testosterone was maintained by the treatment of caffeine and ascorbic acid. The change of weight of body and organ and the appearance of seminiferous tubules were improved by an effect of caffeine or ascorbic acid against irradiation. Taken together, caffeine and ascorbic acid protects impairment of spermatogenesis against gamma radiation and may act as a radio-protector.

• Nuclear Engineering and Technology
• /
• 제56권4호
• /
• pp.1490-1500
• /
• 2024

Helium-induced defect nucleation and accumulation in polycrystalline W and W0.5 wt%ZrC (W0.5ZrC) were studied in-situ using the transmission electron microscopy (TEM) combined with 40 keV He⁺ irradiation at 800 and 1000℃ at the maximum damage level of 1 dpa. Radiation-induced dislocation loops were not observed in the current study. W0.5ZrC was found to be less susceptible to irradiation damage in terms of helium bubble formation and growth, especially at lower temperature (800 ℃) when vacancies were less mobile. The ZrC particles present in the W matrix pin the forming helium bubbles via interaction between C atom and neighbouring W atom at vacancies. This reduces the capability of helium to trap a vacancy which is required to form the bubble core and, as a consequence, delays, the bubble nucleation. At 1000 ℃, significant bubble growth occurred in both materials and all the present bubbles transitioned from spherical to faceted shape, whereas at 800 ℃, the faceted helium bubble population was dominated in W.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
• /
• pp.311-311
• /
• 2013

The resistance switching memory devices have several advantages to take breakthrough for the limitation of operation speed, retention, and device scale. Especially, the metal-oxide materials such as ZnO are able to fabricate on the flexible and visible transparent plastic substrate. Also, the quantum dots (QDs) embedded in dielectric layer could be improve the ratio between the low and the high resistance becauseof their Coulomb blockade, carrier trap and induced filament path formation. In this study, we irradiated 0.2-MeV-electron beam on the ZnO/QDs/ZnO structure to control the defect and oxygen vacancy of ZnO layer. The metal-oxide QDs embedded in ZnO layer on Pt/glass substrate were fabricated for a memory device and evaluated electrical properties after 0.2-MeV-electron beam irradiations. To formation bottom electrode, the Pt layer (200 nm) was deposited on the glass substrate by direct current sputter. The ZnO layer (100 nm) was deposited by ultra-high vacuum radio frequency sputter at base pressure $1{\times}10^{-10}$ Torr. And then, the metal-oxide QDs on the ZnO layer were created by thermal annealing. Finally, the ZnO layer (100 nm) also was deposited by ultra-high vacuum sputter. Before the formation top electrode, 0.2 MeV liner accelerated electron beams with flux of $1{\times}10^{13}$ and $10^{14}$ electrons/$cm^2$ were irradiated. We will discuss the electrical properties and the physical relationships among the irradiation condition, the dislocation density and mechanism of resistive switching in the hybrid memory device.

• Radiation Oncology Journal
• /
• 제15권1호
• /
• pp.37-47
• /
• 1997

목적 : 방사선량에 EK른 급성폐손상을 병리조직학적으로 분석하고 예방목적으로 투요한 스테로이드의 효과를 확인하여 방사선에 의한 폐손상의 감소방안을 모색하고자 한다. 대상 및 방법 : 생후 30일 정도인 체중 25+2g의 ICR 마우스 120마리를 암수 구별없이 사용하였고, 대조군은 전폐선량이 각각 8Gy와 12Gy인 방사선조사만 시행한 군과 방사선조사와 생리식염수를 투여한 또다른 군으로 하엿으며, 실험군은 방사선조사와 스테로이드를 복강내로 투여한 군으로 하여 방사선량과 스테로이드투여에 따른 급성폐손상의 양상을 광학 현미경 및 투과 전자현미경을 이용하여 병리조직학적으로 분석하였다. 결과 : 8Gy 대조군에서는 경미한 염증세포의 침윤, I형 폐포상피세포는 세포질이 파괴되거나 폐포강내로 돌출하였으며, 폐포 모세혈관은 경미하게 확장되었고 내피세포의 세포질과 간질은 경한 부종을 보였다. 8Gy 실험군에서 대조군에 보였던 폐포상피세포 및 내피 세포의 변화가 정도가 매우 약하였으나 섬유모세포의 증식과 기저판의 파괴정도는 대조군과 비슷하였다. 12Gy 대조군에서는 8Gy 대조군과 비교하여 염증세포의 침윤이 증가되었고 폐포강내에는 파기된 조직 파편이 산재해 있었으며 폐실질의 출혈과 무기폐가 관찰되었다. 12Gy 실험군에서는 대조군에서 보이던 현저한 염증변화가 많이 감소하였으며 폐포벽의 부종과 무기폐는 대조군과 비교하여 많이 감소되었으나 섬유모세포의 증식과 기저판의 왜곡 및 파괴는 차이가 없었다. 결론 : 방사선조사에 의한 급성폐손상은 전폐조사량이 8Gy에서 12Gy로 증가함에 따라 염증 세포의 침윤, 페포상피세포의 손상, 모세혈관 내피세포의 손상, 간질의 부종정도가 증가하였으며, 방사선조사후 스테로이드를 2주일에서 4주일간 투여한 결과 이들 소견이 많이 감소하였으나 섬유모세포의 증식정도와 기저판의 변화는 조사된 방사선량이나 스테로이드 투여여부와 무관하였다.