• Nuclear Engineering and Technology
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• v.50 no.8
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• pp.1234-1245
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• 2018

The risk of multi-unit nuclear power plants (NPPs) at a site has received considerable critical attention recently. However, current probabilistic safety assessment (PSA) procedures and computer code do not support multi-unit PSA because the traditional PSA structure is mostly used for the quantification of single-unit NPP risk. In this study, the main purpose is to develop a multi-unit Level 2 PSA method and apply it to full-power operating six-unit OPR1000. Multi-unit Level 2 PSA method consists of three steps: (1) development of single-unit Level 2 PSA; (2) extracting the mapping data from plant damage state to source term category; and (3) combining multi-unit Level 1 PSA results and mapping fractions. By applying developed multi-unit Level 2 PSA method into six-unit OPR1000, site containment failure probabilities in case of loss of ultimate heat sink, loss of off-site power, tsunami, and seismic event were quantified.

• Nuclear Engineering and Technology
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• v.52 no.5
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• pp.975-983
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• 2020

Since the Fukushima Daiichi accident in 2011, concerns for the safety of multi-unit Nuclear Power Plant (NPP) sites have risen. This is because more than 70% of NPP sites are multi-unit sites that have two or more NPP units and a multi-unit accident occurred for the first time. After this accident, Probability Safety Assessment (PSA) has been considered in many countries as one of the tools to quantitatively assess the safety for multi-unit NPP sites. One of the biggest concerns for a multi-unit accident such as Fukushima is that the consequences (health and economic) will be significantly higher than in the case of a single-unit accident. However, many studies on multi-unit PSA have focused on Level 1 & 2 PSA, and there are many challenges in terms of public acceptance due to various speculations without an engineering background. In this study, two kinds of multi-unit Level 3 PSA for multi-unit site have been carried out. The first case was the estimation of multi-unit risk with conservative assumptions to investigate the margin between multi-unit risk and QHO, and the other was to identify the effect of time delays in releases between NPP units on the same site. Through these two kinds of assessments, we aimed at investigating the level of multi-unit risk and understanding the characteristics of risk in a multiunit context.

• Nuclear Engineering and Technology
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• v.50 no.8
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• pp.1246-1254
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• 2018

The importance of performing Level 3 probabilistic safety assessments (PSA) along with a general interest in assessing multi-unit risk has been sharply increasing after the Fukushima Daiichi nuclear power plant (NPP) accident. However, relatively few studies on multi-unit Level 3 PSA have been performed to date, reflecting limited scenarios of multi-unit accidents with higher priority. The major difficulty to carry out a multi-unit Level 3 PSA lies in the exponentially increasing number of multi-unit accident combinations, as different source terms can be released from each NPP unit; indeed, building consequence models for the astronomical number of accident scenarios is simply impractical. In this study, a new approach has been developed that employs the look-up table method to cover every multi-unit accident scenario. Consequence results for each scenario can be found on the table, established with a practical amount of effort, and can be matched to the frequency of the scenario. Preliminary application to a six-unit NPP site was carried out, where it was found that the difference between full-coverage and cut-off cases could be considerably high and therefore influence the total risk. Additional studies should be performed to fine tune the details and overcome the limitations of the approach.

• Nuclear Engineering and Technology
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• v.50 no.8
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• pp.1217-1233
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• 2018

Following a surge of interest in multi-unit risk in the last few years, many recent studies have suggested methods for multi-unit probabilistic safety assessment (MUPSA) and addressed several related aspects. Most of the existing studies though focused on two-unit nuclear power plant (NPP) sites or used rather simplified probabilistic safety assessment (PSA) models to demonstrate the proposed approaches. When considering an NPP site with three or more units, some approaches are inapplicable or yield very conservative results. Since the number of such sites is increasing, there is a strong need to develop and validate practical approaches to the related MUPSA. This article provides several detailed approaches that are applicable to multi-unit Level 1 PSA for sites with up to six or more reactor units. To validate the approaches, a multi-unit Level 1 PSA model is developed and the site core damage frequency is estimated for each of four representative multi-unit initiators, as well as for the case of a simultaneous occurrence of independent single-unit initiators in multiple units. For this purpose, an NPP site with six identical OPR-1000 units is considered, with full-scale Level 1 PSA models for a specific OPR-1000 plant used as the base single-unit models.

• Nuclear Engineering and Technology
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• v.52 no.10
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• pp.2221-2229
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• 2020

After the Fukushima Daiichi nuclear power plant (NPP) accident, level 3 probabilistic safety assessment (PSA) has emerged as an important task in order to assess the risk level of the multi-unit NPPs in a single nuclear site. Accurate calculation of the radionuclide concentrations and exposure doses to the public is required if a nuclear site has multi-unit NPPs and large number of people live near NPPs. So, there has been a great need to develop a new method or procedure for the fast and accurate offsite consequence calculation for the multi-unit NPP accident analysis. Since the multi-unit level 3 PSA is being currently performed assuming that all the NPPs are located at the same position such as a center of mass (COM) or base NPP position, radionuclide concentrations or exposure doses near NPPs can be drastically distorted depending on the locations, multi-unit NPP alignment, and the wind direction. In order to overcome this disadvantage of the COM method, the idea of a new multiple location (ML) method was proposed and implemented into a new tool MURCC (multi-unit radiological consequence calculator). Furthermore, the MURCC code was further improved for the multi-unit level 3 PSA that has the arbitrary number of multi-unit NPPs. The objectives of this study are to (1) qualitatively and quantitatively compare COM and ML methods, and (2) demonstrate the strength and efficiency of the ML method. The strength of the ML method was demonstrated by the applications to the multi-unit long-term station blackout (LTSBO) accidents at the four-unit Vogtle NPPs. Thus, it is strongly recommended that this ML method be employed for the offsite consequence analysis of the multi-unit NPP accidents.

• Journal of Korean Academy of Nursing Administration
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• v.18 no.4
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• pp.414-423
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• 2012

Purpose: The purpose of this study was to investigate the impact of the unit-level nurse practice environment on nurse turnover intention in the small and medium sized hospitals. Methods: A cross-sectional study was conducted using a questionnaire survey with 308 nurses in 38 nursing units of 6 small and medium sized hospitals, having over 200 beds and under 300 beds and located in B metropolitan city. Data were collected from July 20 to August 10, 2011. Data were analyzed using hierarchical multiple regression. Results: The mean turnover intention in nurses of small and medium sized hospitals was $3.52{\pm}0.53$. Factors affecting turnover intention in the nurses included age, work unit, monthly income, number of night-duties, work hours per day and unit-level nurse practice environment. The unit-level nurse practice environment accounted for 15% of turnover intention when other variables were controlled. Conclusion: The results of the study indicate that nurse turnover intention is associated with the nurse practice environment at the unit level. Small and medium sized hospitals can improve nurse retention and lower turnover intention by changing the nurse practice environment of unit, such as creating better support services and nurse participation in hospital affairs.

• Quality Improvement in Health Care
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• v.9 no.2
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• pp.134-147
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• 2002

Background : As an empirical study, current research about the quality of social services carried out in general and teaching hospitals across the country. In the flux of health care reforms and market transformation, the quality of social services in the hospital becomes increasingly significant. Methods : A sample of total 80 hospitals, including general hospitals with one social worker at least and single-department hospital with two social workers or more, were identified nationwide through the registry of Korean Association of Medical Social Workers and Korean Association of Hospitals. The subjects of this survey were 80 leaders of social service units. The survey data from each subjects were measured to evaluate level of quality that service provider perceived of sample hospitals. Under the method of one-way ANOVA and multiple regression, the level of quality in social work service was analyzed. Results : The major findings were as following ; First, the level of quality perceived showed less score, especially the lowest was the score of quality of outcome. Second, the key variables of each hospital which turned out significantly different in quality of social work service were the departmental form of social work unit, unit leader's age, educational level, field experience, and job rank. Third, the level of quality of social work service correlated positively with the field experience of unit leader, the size of social work unit, the job rank of the unit leader. Conclusion : The most influential variables to the quality of social work service proved departmental form of social work unit, leader of social work unit. Therefore, to assure the proper level of quality, social work unit in hospital must be structured single, independent department in which entitled social worker is supposed to supervise and manage. And a leadership-development program for leaders in social work unit are strongly recommended.

• Journal of the Korean housing association
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• v.25 no.6
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• pp.39-47
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• 2014

The background of this study is to examine the structure of housing price of which characteristics are not equal but hierarchical in the apartment complexes. So, the purpose of this study is to analyze the influences of apartment complex characteristics on the housing price within the same regional boundary by HLM. The data used as dependent variables were the market prices of 938 units from 29 apartment complexes by stratified sampling. The 2nd level independent variables is the Housing complex characteristics which are composed of the housing complex & locational variables and the 1st level independent variables are the unit characteristics. The results are as follows. First, the first model shows that the 2nd level variables explains 68% of the housing prices. Second, the influential variables of the 1st level unit variable are 'dwelling exclusive area', 'floor of dwelling' and 'direction of dwelling'. Third, the influential variables of the housing complex variables in the 2nd level are 'lot area', 'the building-to-land ratio', 'the number of unit', 'the number of parking lots per unit', 'Green space area' and 'open space area per unit'. The last, the influential variables of the housing locational variables in the 2nd level are 'distance to subway and park' and the number of school and park within a radius of 1km.

• Journal of Korean Academy of Nursing
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• v.37 no.4
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• pp.586-593
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• 2007

Purpose: The purpose of this study was to describe patients' anxiety in the ICU and to investigate related factors on the anxiety level. Methods: An exploratory cross-sectional survey design was used. Forty-eight patients participated in the study. Questionnaires were asked to patients who had been cared in the ICUs. Results: Related to the anxiety level, the mean of the total anxiety score was 5.47, and 60% of the patients had moderate or severe level of anxiety. Patients from the coronary care unit had a significantly higher level of anxiety than those from surgical intensive care unit or pulmonary surgery care unit. Moreover, significantly different levels of anxiety were found among patients who had been stayed for 2, 3, or 4 days. Conclusion: Patients who were from the coronary care unit or had been stayed longer (up to 4 days) in the ICU were significantly associated with higher anxiety level.

• The Korean Journal of Applied Statistics
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• v.25 no.2
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• pp.293-300
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• 2012

When Binomial data are obtained, logit and logit mixed models are commonly used for small area estimation. Those models are known to have good statistical properties through the use of unit level information; however, data should be obtained as area level in order to use area level information such as spatial correlation or auto-correlation. In this research, we suggested a new small area estimator obtained through the combination of unit level information with area level information.