• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 추계학술발표회논문집(1)
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• pp.713-718
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• 1997

In the TMI-2 accident, approximately twenty(20) tons of molten core material drained into the lower plenum. Early advanced light water reactor (LWR) designs assumed a lower head failure and incorporated various measures for ex-vessel accident mitigation. However, one of the major findings from the TMI-2 Vessel Investigation Project was that one part of the reactor lower head wall estimated to have attained a temperature of 1100$^{\circ}C$ for about 30 minutes has seemingly experienced a comparatively rapid cooldown with no major threat to the vessel integrity. In this regard, recent empirical and analytical studies have shifted interests to such in-vessel retention designs or strategies as reactor cavity flooding, in-vessel flooding and engineered gap cooling of the vessel Accurate thermohydrodynamic and creep deformation modeling and rupture prediction are the key to the success in developing practically useful in-vessel accident/risk management strategies. As an advanced in-vessel design concept, this work presents the COrium Attack Syndrome Immunization Structures (COASIS) that are being developed as prospective in-vessel retention devices for a next-generation LWR in concert with existing ex-vessel management measures. Both the engineered gap structures in-vessel (COASISI) and ex-vessel (COASISO) are demonstrated to maintain effective heat transfer geometry during molten core debris attack when applied to the Korean Standard Nuclear Power Plant(KSNPP) reactor. The likelihood of lower head creep rupture during a severe accident is found to be significantly suppressed by the COASIS options.

• Nuclear Engineering and Technology
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• 제28권3호
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• pp.229-246
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• 1996

A mechanistic model has been developed to predict the release behavior of fission gas during steady-state irradiation of LWR UO$_2$ fuel. Under the assumption that UO$_2$ grain surface is composed of fourteen identical circular faces and grain edge bubble can be represented by a triangulated tube around the circumference of three circular grain faces, it introduces the concept of continuous formation of open grain edges tunnels that is proportional to grain edge swelling. In addition, it takes into account the interaction between the gas release from matrix to grain boundary and the reintroduction of gas atoms into the matrix by the irradiation-induced re-solution of grain face bubbles. It also treats analytically the behavior of intragranular, intergranular, and grain edge bubbles under the assumption that both intragranular and intergranular bubbles are uniform in both radius and number density. Comparison of the present model with experimental data shows that the model's prediction produces reasonable agreement for fuel with centerline temperatures of 1000 to 140$0^{\circ}C$, wide scatter band for fuel with centerline temperatures lower than 100$0^{\circ}C$, and underprediction for fuel with centerline temperatures higher than 140$0^{\circ}C$.

• Nuclear Engineering and Technology
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• 제30권6호
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• pp.541-554
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• 1998

A computer code COSMOS has been developed based on the CARO-D5 for the thermal analysis of LWR UO$_2$ and MOX fuel rod under steady-state and transient operating conditions. The main purpose of the COSMOS, which considers high turnup characteristics such as thermal conductivity degradation with turnup and rim formation at the outer part of fuel pellet, is to calculate temperature profile across fuel pellet and fission gas release up to high burnup. A new mechanistic fission gas release model developed based on physical processes has been incorporated into the code. In addition, the features of MOX fuel such as change in themo-mechanical properties and the effect of microscopic heterogeneity on fission gas release have been also taken into account so that it can be applied to MOX fuel. Another important feature of the COSMOS is that it can analyze fuel segment refabricated from base irradiated fuel rods in commercial reactors. This feature makes it possible to analyze database obtained from international projects such as the MALDEN and RISO, many of which were collected from refabricated fuel segments. The capacity of the COSMOS has been tested with some number of experimental results obtained from the HALDEN, RISO and FIGARO programs. Comparison with the measured data indicates that, although the COSMOS gives reasonable agreement, the current models need to be improved. This work is being performed using database available from the OECD/NEA.

• Nuclear Engineering and Technology
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• 제41권6호
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• pp.753-764
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• 2009

JAEA started the LSTF experiments in 1985 for the fourth stage of the ROSA Program (ROSA-IV) for the LWR thermal-hydraulic safety research to identify and investigate the thermal-hydraulic phenomena and to confirm the effectiveness of ECCS during small-break LOCAs and operational transients. The LSTF experiments are underway for the ROSA-V Program and the OECD/NEA ROSA Project that intends to resolve issues in thermal-hydraulic analyses relevant to LWR safety. Six types of the LSTF experiments have been done for both the system integral and separate-effect experiments among international members from 14 countries. Results of four experiments for the ROSA Project are briefly presented with analysis by a best-estimate (BE) code and a computational fluid dynamics (CFD) code to illustrate the capability of the LSTF and codes to simulate the thermal-hydraulic phenomena that may appear during SBLOCAs and transients. The thermal-hydraulic phenomena dealt with are coolant mixing and temperature stratification, water hammer up to high system pressure, natural circulation under high core power condition, and non-condensable gas effect during asymmetric SG depressurization as an AM action.

• Nuclear Engineering and Technology
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• 제17권1호
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• pp.8-15
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• 1985

Debris bed내·외로부터 깨스유량을 갖는 debris/water 열적상호작용 해석모델이 중대사고 분석을 위해 제시되었다. 제시된 모델은 증기 소비, debris bed에서 수소 생성, 유입깨스 및 화학반응열에 대한 인자들을 포함하고 있으며, 금속-물반응 및 debris/concrete 작용으로 인한 깨스 생성을 평가하기 위해 MARCH code에 도입시켰다. 그 결과 수소원은 격납용기 과도압력에 큰 영향을 미치나 debris bed로 대류깨스 냉각과 콘크리트로 전도 열손실은 debris bed 냉각성에 조그마한 영향을 주는 것으로 나타났다. 하지만 debris 인자의 재가열과 재용융은 콘크리트와 상호작용에 의해 상당히 지연될 수 있다.

• Nuclear Engineering and Technology
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• 제51권5호
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• pp.1218-1230
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• 2019

A sub-channel solver, named ${\underline{S}}teady$ and ${\underline{T}}ransient$ ${\underline{A}}nalyzer$ for ${\underline{R}}eactor$ ${\underline{T}}hermal$ hydraulics (START), has been developed using the homogenous model for two-phase conditions of light water reactors. The code is developed as a fast and accurate TH-solver for coupled and multi-physics calculations. START has been validated against the NUPEC PWR Sub-channel and Bundle Test (PSBT) database. Tests like single-channel quality and void-fraction for steady state, outlet fluid temperature for steady state, rod-bundle quality and void-fraction for both steady state and transient conditions have been analyzed and compared with experimental values. Results reveal a good accuracy of solution for both steady state and transient scenarios. Axially different values for turbulent mixing coefficient are used based on different grid-spacer types. This provides better results as compared to using a single value of turbulent mixing coefficient. Code-to-code evaluation of PSBT results by the START code compares well with other industrial codes. The START code has been parallelized with the OpenMP algorithm and its numerical performance is evaluated with a large whole PWR core. Scaling study of START shows a good parallel performance.

• Nuclear Engineering and Technology
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• 제53권11호
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• pp.3665-3674
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• 2021

One of the important parts of the in-core fuel management is loading pattern optimization (LPO). The loading pattern optimization as a reasonable design of the in-core fuel management can improve both economic and safe aspects of the nuclear reactor. This work proposes the hybrid of fuzzy logic controller with harmony search algorithm (HS) for loading pattern optimization in a pressurized water reactor. The music improvisation process to find a pleasing harmony is inspiring the harmony search algorithm. In this work, the adjustment of the harmony search algorithm parameters such as the bandwidth and the pitch adjustment rate are increasing performance of the proposed algorithm which is done through a fuzzy logic controller. Hence, membership functions and fuzzy rules are designed to improve the performance of the HS algorithm and achieve optimal results. The objective of the method is finding an optimum core arrangement according to safety and economic aspects such as reduction of power peaking factor (PPF) and increase of effective multiplication factor (Keff). The proposed approach effectiveness has been tried in two cases, Michalewicz's bivariate function problem and NEACRP LWR core. The results show that by using fuzzy harmony search algorithm the value of the fitness function is improved by 15.35%. Finally, with regard to the new solutions proposed in this research it could be used as a trustworthy method for other optimization issues of engineering field.

• Nuclear Engineering and Technology
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• 제54권12호
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• pp.4731-4742
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• 2022

RBMK fuel assemblies differ from other LWR FA due to a specific arrangement of the fuel rods, the low enrichment, and the used burnable absorber - erbium. Therefore, there is a challenge to adapt modeling tools, developed for other LWR types, to solve RBMK problems. A set of 10 different depletion simulation schemes were tested to estimate the impact on reactivity and spent fuel composition of possible SCALE code options for the neutron transport modelling and the use of different nuclear data libraries. The simulations were performed using cross-section libraries based on both, VII.0 and VII.1, versions of ENDF/B nuclear data, and assuming continuous energy and multigroup simulation modes, standard and user-defined Dancoff factor values, and employing deterministic and Monte Carlo methods. The criticality analysis with burn-up credit was performed for the SFP loaded with RBMK-1500 FA. Spent fuel compositions were taken from each of 10 performed depletion simulations. The criticality of SFP is found to be overestimated by up to 0.08% in simulation cases using user-defined Dancoff factors comparing the results obtained using the continuous energy library (VII.1 version of ENDF/B nuclear data). It was shown that such discrepancy is determined by the higher U-235 and Pu-239 isotopes concentrations calculated.

• 임산에너지
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• 제21권1호
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• pp.65-75
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• 2002

본 연구는 주요 활엽수종을 대상으로 인위적으로 광선의 강도를 달리한 유묘의 생장과 물질생산량에 대한 수목의 생장패턴을 구명하기 위하여 실시되었다. 연구대상 수종은 자작나무, 박달나무, 느티나무, 고로쇠나무, 산벚나무, 쥐똥나무 등이며, 자연전광을 100%, 38-62%, 22-28%, 7-20%, 2-6%로 조절된 피음포지를 조성후 2년간 실시한 결과는 다음과 같았다. 일반적으로 양수로 분류되는 수종으로서 전광에서의 묘고와 근원경의 상대생장율이 자작나무와 박달나무는 피음 강도가 강한 투광을 2-6% 처리구보다 약 2배 이상 우수한 생장율을 나타냈다. 내음성이 상대적으로 강하다고 분류되는 수종의 묘고와 근원경 생장율은 투광을 38∼62% 피음 처리구에서 고로쇠나무와 쥐똥나무는 다른 처리구에 비해 양호한 생장을 보였다. 대부분의 수종에서 피음처리 수준에 따른 광량 감소와 함께 총물질생산량이 급격히 감소하였고, 잎과 줄기의 비율이 뿌리에 비해 증가하는 경향을 보였다. 유묘의 T/R율은 대부분의 수종이 피음의 강도가 강할수록 T/R율이 높아지는 경향으로 전광처리구 0.6∼3.2보다 투광을 2-6% 피음 처리구가 1.1∼5.0으로 높게 나타냈다. 전체적으로 비교할 때 조사 대상의 모든 활엽수 묘목에서 피음처리에 의한 광량이 감소할수록 SLA가 증가하는 경향으로, LAR과 LWR에서도 유사한 경향을 보여 광환경의 변화에 따른 피음의 강도가 강할수록 통계적으로 유의적인 차이를 보이며 증가하였다. 그러나 자작나무의 경우에는 LWR이 점진적으로 증가하다가 투광을 6% 미만의 최강피음 처리구에서 급격히 감소하는 경향을 보였다. 이러한 결과는 강한 피음에 의한 식물테의 물질생산 저하가 엽면적 및 엽량의 감소등 수체 내의 생리적 특성에 영향을 미친 것으로 생각된다.향상되었음을 알 수 있다. 이상의 결과에서 다양한 개입활동들이 환자의 치료순응도를 향상시키는 데 기여할 수 있음을 제시할 수 있다. 그러나 계량적 메타분석 기준에 부합되는 연구의 논문 수가 제한적이라는 한계점이 있으며, 연구에 사용되는 개입방법의 시도가 더욱 다양화될 필요성이 제시되고 있어 향후 이와 관련된 많은 연구들이 활성화되기를 기대한다.bscessation은 수술 후 4개월에서 7개월 사이에 발생하므로 follow-up 은 8개월까지 이루어져야 한다.장 싫어하는 것으로 나타났으며, 갈색란(Brown)과 난각색이 갈색에 가까운 시료(Trt-Brown)사이와 백색란(White)과 백색에 가까운 시료(Trt-White) 사이에는 통계적으로 유의차가 없었다. 난각색과 영양이 상관이 없다는 것을 교육한 후 실시한 두 번째 설문에서는 갈색에 가까운 계란(Tn-Brown)을 가장 좋아하여 1순위와 2순위가 바뀐 것 이외에는 첫 번째 질문의 결과와 같았다. 결론적으로 현재 우리나라에서는 갈색 정도의 차이 문제이지 갈색란을 좋아함을 알 수 있었고, 교육에 의해 조금씩은 고정 관념을 바꿀 수 있는 가능성을 확인할 수 있었다.ique impact at 0.70 km/s and 0.91 km/s were compared with experimental results and Eulerian hydrocode CTH simulation results. The Lagrangian code NET3D is superior to Eulerian code CTH in the computational accuracy. Agreement with the experimentally obtained final deformed cross-sections of the projectile is

• 한국작물학회지
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• 제38권4호
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• pp.343-349
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• 1993

본 연구는 벼의 시대적 장려품종들 사이의 수량형질이나 생리적 형질에서의 변화를 살펴 육종에 의한 수량증대의 원인을 밝히고, 생리적 형질의 개량을 통한 수도 수량증대 방안을 찾아 보고져 행하여졌다. 1911년부터 1988년도 사이의 8기의 장려품종을 선택하여 재배한 후 수량형질들을 조사하고 생장해석을 통해 생리적 형질들의 값을 측정하여 품종변천에 따른 이들 형질들의 변이를 비교하였다. 최근에 올수록 장려품종들의 간장은 짧아 졌으며 '70년대 이후의 품종들의 등숙률이나 수확지수는 그 이전의 품종보다 높아 졌으나, 주당수수, 수당입수, 그리고 년입중의 변이에서는 시대적 품종변천에 따른 일정한 경향이 없었다. 순동화율, 엽면적비율, 상대엽면적, 그리고 엽중비율에 있어서도 최신 품종에서 아무런 개량을 찾아 볼 수 없었으며 육종을 통한 수도의 수량증대가 있었다면 그것은 주로 도숙병 저항성 품종 육성이나 단간종의 개발에 따른 도복 감소를 통한 등숙율의 향상과 수확지수의 증대에 기인하였음을 알 수 있었다. 수량증대를 위해서는 순동화율의 증대와 수확지수의 증대가 병행하여 이루워 지는 것이 필요하며 광투과율을 높이기 위해서는 도복이 억제되는 한 장간종을 육성하는 것이 중묘할 것으로 나타났다. 순동화율은 엽면적비율과 부의 상관관계가 있어서 이들을 동시에 증대시키는 것은 어려울 것으로 생각되나 순동화율이 상대생장율에 미치는 기여도는 엽면적비율의 그것보다 커, 순동화율이 높은 품종선발이 보다 유리할 것으로 생각된다. 또한 엽중비율의 증대를 통한 엽면적비율의 증가가 상대생장율을 높이는데 보다 효과적일 것으로 생각된다.