• Nuclear Engineering and Technology
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• 제50권5호
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• pp.639-647
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• 2018

In this study, the effects of selecting water/silver nanofluid as both a coolant and a reactivity controller during the first operating cycle of a light water nuclear reactor are investigated. To achieve this, coupled neutronic-thermo-hydraulic analysis is employed to simulate the reactor core. A detailed VVER1000/446 reactor core is modeled in monte carlo code (MCNP), and the model is verified using the porous media approach. Results show that the maximum required level of silver nanoparticles is 1.3 Vol.% at the beginning of the cycle; this value drops to zero at the end of cycle. Due to substitution of water/boric acid with water/Ag nanofluid, reactor operation time at maximum power extends to 357.3 days, and the energy generation increases by about 27.3%. The higher negative coolant temperature coefficient of reactivity in the presence of nanofluid in comparison with the water/boric acid indicates that the reactor is inherently safer. Considering the safety margins in the presence of the nanofluid, minimum departure from nucleate boiling ratio is calculated to be 2.16 (recommendation is 1.75).

• 한국식품과학회지
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• 제27권4호
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• pp.618-624
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• 1995

우리나라에서 식품중 농약잔류 허용기준의 적합성을 평가하고 Codex 기준의 수용 가능성을 검토하기 위하여 허용기준치와 한국인의 식품계수 만을 적용한 농약성분의 이론적 최대섭취량을 계산한 다음 ADI 값과 비교하였다. 국내에서 허용기준이 설정된 105개 농약성분의 ADI 대비율은 대부분이 80% 이하 수준을 유지하고 있으나 ADI를 초과하는 농약은 13개 성분이었다. 한편 Codex 기준이 있는 82개 농약성분에서 ADI를 초과하는 농약은 20개 성분에 이르고 있다. 한국기준 또는 Codex 기준에서 ADI를 초과하는 22개 성분에 대해서는 그 원인을 지적하였으며 안전마진 확보를 위한 대책이 마련되어야 할 것이다.

• Nuclear Engineering and Technology
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• 제56권2호
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• pp.359-374
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• 2024

A high-fidelity numerical analysis methodology was proposed for evaluating the fuel rod cladding integrity of a Prototype Gen IV Sodium Fast Reactor (PGSFR) during normal operation and Design basis events (DBEs). The MARS-LMR code, system transient safety analysis code, was applied to analyze the DBEs. The results of the MARS-LMR code were used as boundary condition for a 3D computational fluid dynamics (CFD) analysis. The peak temperatures considering HCFs satisfied the cladding temperature limit. The temperature and pressure distributions were calculated by ANSYS CFX code, and applied to structural analysis. Structural analysis was performed using ANSYS Mechanical code. The seismic reactivity insertion SSE accident among DBEs had the highest peak cladding temperature and the maximum stress, as the value of 87 MPa. The fuel cladding had over 40 % safety margin, and the strain was below the strain limit. Deformation behavior was elucidated for providing relative coordinate data on each active fuel rod center. Bending deformation resulted in a flower shape, and bowing bundle did not interact with the duct of fuel assemblies. Fuel rod maximum expansion was generated with highest stress. Therefore, it was concluded that the fuel rod cladding of the PGSFR has sufficient structural safety margin during DBEs.

• Nuclear Engineering and Technology
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• 제56권3호
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• pp.980-992
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• 2024

Steam line break accident (SLB) in the nuclear reactor is one of the representative Non-LOCA accidents in which thermal-hydraulics and neutron kinetics are strongly coupled each other. Thus, the multi-scale and multi-physics approach is applied in this study in order to examine a realistic safety margin. An entire reactor coolant system is modelled by system scale node, whereas sub-channel scale resolution is applied for the region of interest such as the reactor core. Fuel performance code is extended to consider full core pin-wise fuel behaviour. The MARU platform is developed for easy integration of the codes to be coupled. An initial stage of the steam line break accident is simulated on the MARU platform. As cold coolant is injected from the cold leg into the reactor pressure vessel, the power increases due to the moderator feedback. Three-dimensional coolant and fuel behaviour are qualitatively visualized for easy comprehension. Moreover, quantitative investigation is added by focusing on the enhancement of safety margin by means of comparing the minimum departure from nucleate boiling ratio (MDNBR). Three factors contributing to the increase of the MDNBR are proposed: Various geometric parameters, realistic power distribution by neutron kinetics code, Radial coolant mixing including sub-channel physics model.

• Composites Research
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• 제14권4호
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• pp.8-14
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• 2001

위성체 시스템은 발사 과정중에 매우 극심한 하중상태에 놓이게 된다. 따라서 위성체 시스템의 구조적 안정성을 보장하기 위하여 발사 과정중에 시스템에 발생할 수 있는 모든 하중상태에 대해서 위성체 시스템 모든 부분의 안전율 (M.S. : Margin of Safety)는 양의 값이 되어야 한다. 본 논문은 위성체 안테나 시스템의 동적 특성을 분석하기 위하여 모드해석을 수행하였고, 준정적 하중이 시스템에 부과될 때 응력해석 결과를 나타내었다. 위성체 시스템 제작에 사용된 샌드 위치 구조물에 대한 파손경향을 조사하였고, 샌드위치 구조물의 외피를 일방향 프리프레그를 다양한 각도로 적층하여 구성하였을 때 시스템의 거동변화를 관찰하였다.

• 한국도로학회논문집
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• 제12권2호
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• pp.25-31
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• 2010

현 도로설계기준은 설계속도에 기반하여 선형설계에 관한 지침을 제시하고 있으며, 이는 설계속도가 도로 공용 후에 운전자의 주행 속도와 거의 동일할 것임을 전제하고 있다. 도로 평면 곡선부의 설계도 주어진 설계속도에 따라 운전자가 쾌적성을 유지한 채 통과할 수 있는 최소곡선반경을 기준으로 제시하고 있다. 그러나 쾌적성에 기초한 횡방향 미끄럼마찰계수는 실제 습윤노면에서 관측되는 물리적인 횡방향 미끄럼마찰계수보다 낮기 때문에 기준에 제시된 곡선반경은 최소의 의미보다는 권장 값으로 보는 것이 합리적이다. 아울러, 최소곡선반경보다 여유로운 설계 값을 선호하는 실무관행으로 도로 공용 후 운전자의 주행속도는 설계속도를 상회하여 설계속도가 주행속도를 대표하지 못하는 결과를 초래하고, 결과적으로 현 설계기준의 주요전제를 위반하게 될 것으로 본다. 이러한 연구 가정을 검토하기 위해 지방부 도로에서 노면 미끄럼 마찰계수와 운전자의 주행속도를 조사하였다. 연구결과로, 쾌적성에 기반한 미끄럼 마찰계수와 물리적인 미끄럼마찰계수와의 차이에 따른 안전여유를 정량적으로 제시했고, 안전여유 및 설계관행에 따른 여유로운 설계로 인해 설계속도와 주행속도 간에 괴리가 발생함을 제시했다. 이를 토대로, 현 설계속도 기반의 선형설계는 최소기준과 더불어 설계속도와 주행속도 사이의 괴리를 최소화할 수 있는 선형 설계 관리 방안이 마련될 필요가 있다.

• 한국압력기기공학회 논문집
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• 제13권1호
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• pp.1-15
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• 2017

After Kyeongju earthquake occurred in September 12, 2016, the seismic safety of nuclear power plants became important issue in our country. The seismic safety of nuclear power plant against beyond design basis earthquake became very important to secure the public safety. In this paper, the current status of the seismic safety assessment methodology is reviewed and some aspects for the reliability improvement of the seismic safety assessment results are proposed. Seismic margin analysis and probabilistic seismic safety assessment have been used for the seismic safety evaluation of a nuclear power pant. The basic procedure and the related issues and proposals for the probabilistic seismic safety assessment are investigated.

• Nuclear Engineering and Technology
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• 제53권6호
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• pp.1747-1755
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• 2021

This paper presents floating absorber for safety at transient (FAST) which is a passive safety device for sodium-cooled fast reactors with a positive coolant temperature coefficient. Working principle of the FAST makes it possible to insert negative reactivity passively in case of temperature rise or voiding of coolant. Behaviors of the FAST in conventional oxide fuel-loaded and metallic fuel-loaded SFRs are investigated assuming anticipated transients without scram (ATWS) scenarios. Unprotected loss of flow (ULOF), unprotected loss of heat sink (ULOHS), unprotected transient overpower (UTOP) and unprotected chilled inlet temperature (UCIT) scenarios are simulated at end of life (EOL) conditions of the oxide and the metallic SFR cores, and performance of the FAST to improve the reactor safety is analyzed in terms of reactivity feedback components, reactor power and maximum temperatures of fuel and coolant. It is shown that FAST is able to improve the safety margin of conventional burner-type SFRs during ULOF, ULOHS, UTOP and UCIT.

• Journal of Gastric Cancer
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• 제1권1호
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• pp.24-31
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• 2001

Purpose: Despite knowledge of the adverse effects of resection-line disease, surgeons continue to perform inadequate resections. This demonstrates the need for a more aggressive approach to assessment of resection margins at operation. Materials and Methods: Seven hundred fifteen gastric cancer patients who were operated on at our hospital from 1992 to 1998 were included in this analysis. Various clinicopathological factors, including resection-line involvement, were ascertained from the surgical and histopathological records. Results: Of the 715 evaluable patients, 27 patients ($3.8\%$) had involvement of one or both resection lines; in 10 patients the proximal resection line only, in 16 the distal resection line only, and 1 both resection lines were involved. Presence of resection-line involvement was significantly associated with T3 and T4 stage, N (+) stage, M (+) stage, type of operation (total gastrectomy), tumor location (entire stomach), size$\geq$11 cm), and gross type of tumor (Borrmann 4 type). When performing a distal subtotal gastrectomy, no involvement was found when the cranial and caudal distances between the lesion and the line of transection was equal to or greater than 2 cm and 3 cm, respectively, for early cancer and 7 cm and 3 cm, respectively, for advanced cancer. When performing a total gastrectomy for upper 1/3 or middle 1/3 gastric cancer, no involvement was found when the cranial distances between the lesion and the line of transection were equal to or greater than 3 cm and 4 cm, respectively, without distinction of the presence of serosal invasion. Conclusions: The difference in survival between positive and negative margin patients is limited to the group of patients with curative surgery. An important principle of treatment is that the entire tumor must be removed with a 3 cm distal margin and a 2- to 7 cm margin depending on the location and the depth of wall invasion of the tumor, to provide histologically negative margins.

• 한국산업보건학회지
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• 제17권2호
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• pp.120-130
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• 2007

A oxygen generating closed-circuit SCBA for escape from fire will be newly developed and then a program for estimating service time for it should be required. A SCBA made on an experimental basis consisted of five components such as half facepiece (mask), $KO_2$ box, oxygen reservoir, $CO_2$ remover and hood. The half mask had a good fitting performance since fit factors for 10 subjects were all above 100. It was found that height of subjects should be the best variable to estimate service time. Measured service time was inversely correlated with height of subjects. Service life time could be estimated by interpolation and extrapolation using inverse relationship between height and measured service time, for example, 28 minutes for male and female of 170 cm during resting, 10 minutes at the walk of 4 km/h and 5 minutes at the walk of 6 km/h considering safety margin of 20%. The study implies that program for estimating service time for the SCBA should require subject's height, speed of walk (4 km/h and 6 km/h) and fit testing. Considering safety margin, selecting younger subjects would be better. The study on the number of subjects and selecting facial dimensions should be more needed for the final program.