Off-site Consequences Research Articles

Severe accident source terms for a sodium-cooled fast reactor

In order to support the demonstration of a risk-informed approach to the design optimization of a sodium-cooled fast reactor (SFR), it was necessary to make realistic estimates of the consequences of severe accident scenarios. This paper describes the database, models, and assumptions used to estimate the offsite consequences of characteristic severe accident scenarios. As required for comparison with the NRC’s technology neutral framework limit curve, the offsite dose at one mile from the plant boundary is calculated using conservative meteorology.The reference plant design is a 1000MWt pool-type design with metallic fuel. Because an integrated analysis tool comparable to MELCOR does not exist for SFR accident scenario analysis, it was necessary to write a computer code that would assess release of radionuclides from the fuel and transport within the reactor primary system and to link those analyses with results from existing computer codes that assess the dynamic response of the reactor, containment thermal–hydraulics, and radionuclide transport processes within the containment. The analyses indicate that the offsite source terms for SFR severe accident scenarios tend to be small because of the low melting temperature of the fuel, likelihood of significant retention of fission products within the sodium pool, augmentation of containment deposition processes by interaction with sodium oxide aerosols, and small driving force for release from the containment to the environment. A number of major sources of modeling uncertainty are identified as requiring further development effort. An integrated modeling capability, similar to the MELCOR code, is required to direct further research and ultimately to support the licensing of an SFR.

RAPID-N: Rapid natech risk assessment and mapping framework

Natech accidents at industrial plants are an emerging risk with possibly serious consequences. For the mitigation of natech risk, authorities need to identify natech prone areas in a systematic manner. In order to facilitate probabilistic natech risk mapping, a unified methodology was developed that is based on the estimation of on-site natural hazard parameters, determination of damage probabilities of plant units, and assessment of probability and severity of possibly triggered natech events. The methodology was implemented as an on-line, extensible risk assessment and mapping software framework called RAPID-N, which allows rapid local and regional natech risk assessment and mapping with minimal data input. RAPID-N features an innovative data estimation framework to complete missing input data, such as on-site natural hazard parameters and plant unit characteristics. The framework is also used for damage assessment and natech consequence analysis, and allows easy modification of input parameters, dynamic generation of consequence models according to data availability, and extension of models by adding new equations or substituting existing ones with alternatives. Results are presented as summary reports and interactive risk maps, which can be used for land-use and emergency planning purposes by using scenario hazards, or for rapid natech consequence assessment following actual disasters. As proof of concept, the framework provides a custom implementation of the U.S. EPA's RMP Guidance for Offsite Consequence Analysis methodology to perform natech consequence analysis and includes comprehensive data for earthquakes. It is readily extendible to other natural hazards and more comprehensive risk assessment methods.

Understanding Incident Response to Unplanned Releases at Chemical Facilities

The chemical industry is responsible for process management safety at all of its facilities, especially those that have off-site consequences in the event of an unplanned release. This research is analyzing the current practices for emergency response for chemical facilities and will provide a model that could be utilized by small or large chemical facilities. Business process modeling was used to capture information requirements of extant incident response for chemical facilities. It will determine what technologies, specifically software and information systems, could be utilized to improve the chemical facility emergency response mechanism. The results will provide an optimal process model for an improved solution for an emergency response mechanism. This research-in-progress will produce a model emergency response mechanism, represented in a business process model, for a typical chemical facility.

A STUDY ON METHODOLOGY FOR IDENTIFYING CORRELATIONS BETWEEN LERF AND EARLY FATALITY

The correlations between Large Early Release Frequency (LERF) and Early Fatality need to be investigated for riskinformed application and regulation. In Regulatory Guide (RG) -1.174, while there are decision-making criteria using the measures of Core Damage Frequency (CDF) and LERF, there are no specific criteria on LERF. Since there are both huge uncertainties and large costs needed in off-site consequence calculation, a LERF assessment methodology needs to be developed, and its correlation factor needs to be identified, for risk-informed decision-making. A new method for estimating off-site consequence has been presented and performed for assessing health effects caused by radioisotopes released from severe accidents of nuclear power plants in this study. The MACCS2 code is used for validating the source term quantitatively regarding health effects, depending on the release characteristics of radioisotopes during severe accidents. This study developed a method for identifying correlations between LERF and Early Fatality and validates the results of the model using the MACCS2 code. The results of this study may contribute to defining LERF and finding a measure for riskinformed regulations and risk-informed decision-making.

Development of web-based Off-Site Consequence Analysis Program (OSCAP) for extending ILRT intervals and its application

For an offsite consequence analysis, MELCOR Accident Consequence Code System (MACCS) II code is widely used as a tool. In this study, the algorithm of web-based Off-Site Consequence Analysis Program (OSCAP) using the MACCS II code was developed for an integrated leak rate test (ILRT) interval extension and Level 3 probabilistic safety assessment (PSA), and verification and validation (V&V) of the program was performed. The main input data of the MACCS II code are meteorological data, population distribution data and source term data. However, it requires lots of time and efforts to generate the main input data for an offsite consequence analysis using the MACCS II code. For example, the meteorological data are collected from each nuclear power site in real time, but the formats of the raw data collected are different from each other as a site. To reduce efforts and time for risk assessments, the web-based OSCAP has an automatic processing module which converts the format of the raw data collected from each site in Korea to the input data format of the MACCS II code. The program also provides an automatic function of converting the latest population data from Statistics Korea, the National Statistical Office, to the population distribution input data format of the MACCS II code. In case of the source term data, the program includes the release fraction of each source term category resulting from Modular Accident Analysis Program (MAAP) code analysis and the core inventory data from ORIGEN code analysis. These analysis results of each plant in Korea are stored in a database module of the web-based OSCAP, so a user could select the defaulted source term data of each plant without handling source term input data. For V&V of the web-based OSCAP, the following analyses were performed. First of all, an offsite consequence analysis for reference plants was carried out using only the MACCS II code, and using the web-based OSCAP based on both methodologies of NUREG-1493 and NEI interim report. Secondly, the results of the offsite consequence analysis were compared with each other. Lastly, a sensitivity analysis was accomplished for the main input data of the meteorological data and the population distribution data using the web-based OSCAP. It is considered that the program can remarkably reduce man-power on performing a periodic risk assessment according to extending ILRT intervals, and Level 3 PSA. Also, the program can be applied to making accident management plan (AMP) and quantitative health objective (QHO), and to the field of public acceptance (PA).

Importance of location dependencies such as cable and pipe runs when identifying the vital areas

Abstract Vital area analysis study and its application for nuclear facilities have been performed since the late 1970s. The Korea Atomic Energy Research Institute (KAERI) has performed a development of VAI methodology since the early 2000s, and the Vital area Identification Package Expert (VIPEX) was developed to identify vital areas using the conventional Probabilistic Safety Assessment (PSA) models, including internal and external PSA models. This study is to demonstrate the applicability of KAERI's VAI methodology to a hypothetical facility containing processes that could have unacceptable onsite and offsite consequences if interrupted due to a security threat, and to identify the importance of location dependencies, such as cable and pipe runs, when identifying the vital areas. The hypothetical facility is assumed to be a nuclear material processing and storage facility in order to identify the vital areas. The target sets and Top Event Prevention Sets (TEPS) are calculated by two conditions: the first condition is to analyze the target sets and TEPS with information of the cable and pipe runs, and the second is to analyze them without it. It is necessary to consider cable and pipe runs in order to determine accurate and realistic TEPS. If the information about cable and pipe runs of a nuclear power plant is not considered when determining TEPS, it is absolutely impossible to acquire complete TEPS, and the results are distorted. When determining TEPS, it is more efficient, and requires lower costs than other methods using location fault trees to use the plant-specific internal and external PSA models including the information of cable and pipe runs.

Using Sediment Deposited in Small Reservoirs to Quantify Sediment Yield in Two Small Catchments of Iran

Sediment deposition in reservoirs is a serious off-site consequence of soil erosion in Semnan Province, Iran. So far insufficient and less reliable sediment yield data have been collected for these regions. The large number of available sediment deposition rates in reservoirs makes the use of reservoir sediments very attractive for regional-scale studies of sediment delivery. This paper however discusses a methodology combination of both source fingerprinting technique and reservoir sediment survey to provide reliable data on sediment yields of geological formation for two small catchments, Iran. The study first assessed the volume and mass of deposited sediment in reservoirs. Secondary a fingerprinting technique have been used to identify the contribution and then specific sediment yield of each geological formation to reservoir sediment. Results indicate that there is some variation in specific sediment yield (SSY) among geological formations in two catchments: i.e. 10.31 t ha-1 year-1 to 0.41 t ha -1 year -1 and emphasize the importance of Quaternary units and Upper Red formations as the dominant surface source within two catchments. This is the important finding to support design and implementation of sediment control strategies in these catchments.

Adoption of soil conservation practices in Belgium: An examination of the theory of planned behaviour in the agri-environmental domain

Soil erosion is a problem with serious on-site and off-site consequences. There exists a broad series of measures to mitigate soil erosion, unfortunately policy makers observe little voluntary adoption. This paper reports on a study to elicit the factors explaining adoption of soil erosion control practices in Belgium. Following a socio-psychological approach, the theory of planned behaviour (TPB), adoption of cover crops, reduced tillage and buffer strips is evaluated using linear regression techniques. Results show that the most explaining factor is attitude towards the soil conservation practice. The TPB adapted to include perceived control and difficulty appears to provide a suitable framework for evaluating adoption of erosion control measures in Belgium. Future interventions directed at promoting erosion control measures should be directed at changing the attitude of farmers. Further study is, however, required in order to elucidate the cognitive foundations of the negative attitude of a majority of farmers towards the implementation of erosion control practices.

The Internet and the Environmental Protection Agency: Public Access to Toxic Chemical Off-Site Consequence Information

(2009). The Internet and the Environmental Protection Agency: Public Access to Toxic Chemical Off-Site Consequence Information. Free Speech Yearbook: Vol. 44, No. 1, pp. 95-106.

Development of radiation risk assessment simulator using system dynamics methodology

The potential magnitudes of radionuclide releases under severe accident loadings and offsite consequences as well as the overall risk (the product of accident frequencies and consequences) are analyzed and evaluated quantitatively in this study. The system dynamics methodology has been applied to predict the time-dependent behaviors such as feedback and dependency as well as to model uncertain behavior of complex physical system. It is used to construct the transfer mechanisms of time dependent radioactivity concentration and to evaluate them. Dynamic variations of radio activities are simulated by considering several effects such as deposition, weathering, washout, re-suspension, root uptake, translocation, leaching, senescence, intake, and excretion of soil. The time-dependent radio-ecological model applicable to Korean specific environment has been developed in order to assess the radiological consequences following the short-term deposition of radio-nuclides during severe accidents nuclear power plant. An ingestion food chain model can estimate time dependent radioactivity concentrations in foodstuffs. And it is also shown that the system dynamics approach is useful for analyzing the phenomenon of the complex system as well as the behavior of structure values with respect to time. The output of this model (Bq ingested per Bq m−2 deposited) may be multiplied by the deposition and a dose conversion factor (Gy Bq−1) to yield organ-specific doses. The model may be run deterministically to yield a single estimate or stochastic distributions by “Monte-Carlo” calculation that reflects uncertainty of parameter and model uncertainties. The results of this study may contribute to identifying the relative importance of various parameters occurred in consequence analysis, as well as to assessing risk reduction effects in accident management.

Development of Health Effect Assessment Software Using MACCS2 Code

The extended regulatory interests in severe accidents management and enhanced safety regulatory requirements raise a need of more accurate analysis of the effect to the public health by users with diverse disciplines. This facilitates this work to develop web-based radiation health effect assessment software, RASUM, by using the MACCS2 code and HTML language to provide diverse users (regulators, operators, and public) with easy understanding, modeling, calculating, analyzing, documenting and reporting of the radiation health effect under hypothetical severe accidents. The engine of the web-based RASUM uses the MACCS2 as a base code developed by NRC and is composed of five modules such as development module, PSA training module, output module, input data module (source term, population distribution, meteorological data, etc.), and MACCS2 run module. For verification and demonstration of the RASUM, the offsite consequence analysis using the RASUM frame is performed for such as early fatality risk organ does, and whole body does for two selected scenarios. Moreover, CCDF results from the RASUM for KSNP and CANDU type reactors are presented and compared.

Risk-informed emergency planning requirements for Koeberg Nuclear Power Station

This paper presents an overview of the use of risk insights to aid the derivation of the requirements for the Koeberg Emergency Plan. The methodology and the results are presented. This methodology is based on using the Koeberg risk assessment to the worst credible severe accident scenario, which then becomes the reference accident. The off-site consequences of this reference accident are then assessed. These off-site consequences are then compared with the criteria for each protective action such as sheltering and evacuation. This approach is a blend of deterministic and probabilistic approaches, which conforms to international standards and can be used to optimise emergency planning. It is also a holistic approach that allows plant modifications that improve plant safety to be balanced against a reduction in the magnitude of the off-site emergency planning requirements.

Spatial Patterns of Surface Soil Magnetism and Soil Redistribution Across a Fallow Field, Northern Alabama

Distributed assessments of total soil loss from agricultural fields are important for understanding both on-site and off-site consequences of historical and current erosion. In this study, the potential for using cheap and rapid measurements of soil magnetism to identify relative degrees of total soil loss is tested in a fallow field in northern Alabama. This is accomplished by defining and mapping erosion categories based on two different magnetic measurements, and an existing soil magnetism model describing soil loss in a nearby field. Surface soil magnetism patterns generally accord with Revised Universal Soil Loss Equation soil loss estimates, but may contain more useful information regarding historical soil redistribution (mass balance at a point) for the fallow field tested. Due to current limitations of the technique and the intrinsic complexity of soilscapes, the best use of magnetic surveying at this time is likely to be in rapid erosion reconnaissance.

MELCOR/MACCS simulation of the TMI-2 severe accident and initial recovery phases, off-site fission product release and consequences

MELCOR has become the preferred code of the Swiss nuclear industry and of PSI for severe accident analysis, on account of its integrated systems-level approach and validation against experiments and more detailed codes, while MACCS is commonly used by safety authorities for independent assessment of off-site consequences, in particular health effects. The present work arises out of a programme to assess MELCOR independently using empirical data consistent with the recommendations of the OECD/CSNI validation matrix for core degradation codes. The MELCOR 1.8.5RD calculations are based on a model for phases 1 and 2 provided by the code developers but with a simplified thermal hydraulic noding in certain regions and the inclusion of a simple representation of the fission product release and transport pathways. The model has also been extended to simulate phases 3, 4, and the continuing initial period of core recovery and stabilisation. These calculations are a first attempt to demonstrate a MELCOR–MACCS capability to simulate the whole plant accident sequence beyond phase 4, including the containment response and off-site consequences arising from fission product release from the containment. Emphasis is placed on the overall accident evolution and whole plant response, rather than the detailed behaviour. Results are compared with observed and deduced data for the major accident signatures and rough estimates for exposure based on off-site monitoring. The results provide a good basis for the NPP analysis foreseen.

Assessing the value of pulp mill biomass savings in a climate change conscious economy

Pulp mills use significant amounts of biofuels, both internal and purchased. Biofuels could contribute to reach greenhouse gas emission targets at competitive costs. Implementing process integration measures at a pulp mill in order to achieve pulp production with less use of energy (biofuels) has not only on-site consequences but also off-site consequences, such as substitution of fossil fuels elsewhere by the saved pulp mill biofuels, and less on-site electric power generation. In this paper a method, a linking model, is suggested to analyse pulp mill biofuel saving measures when carbon dioxide (CO 2) external costs are internalised. The linking model is based on equilibrium economics and links information from CO 2 constrained energy market future scenarios with process integration measures. Pulp mill economics and marginal energy market CO 2 response are identified. In an applied study, four process integration measures at a Swedish pulp mill were analysed using five energy market future scenarios emanating from a Nordic energy model. The investigated investment alternatives for biofuel savings all result in positive net annual savings, irrespectively of the scenario used. However, CO 2 emissions may increase or decrease depending on the future development of the Nordic energy market.

Specific sediment yield in Tigray-Northern Ethiopia: Assessment and semi-quantitative modelling

Sediment deposition in reservoirs is a serious off-site consequence of soil erosion in Tigray (Northern Ethiopia). So far insufficient and less reliable sediment yield data have been collected for Northern Ethiopia. Nor are there any adaptable methodologies for sediment yield assessment in the country as a whole, which could be used when designing new reservoirs. This study addresses those problems by (1) undertaking reservoir sediment deposition measurements and (2) by calibrating and adapting the Pacific Southwest Inter Agency Committee (PSIAC) and the Factorial Scoring Model (FSM) sediment yield assessment models to Ethiopian conditions. Field rating of catchment characteristics and the sediment yield data from the reservoir survey were used for calibration and validation of the models. Our reservoir survey indicates that specific sediment yield (SSY) varies significantly between catchments: i.e. 487 t km −2 year −1 to 1817 t km −2 year −1 with an average of 1054 (± 446) t km −2 year −1. Since the variability of SSY is high between the studied reservoirs, care should be taken in the study area to adopt representative SSY values during reservoir and soil water conservation planning. The PSIAC SSY prediction is found to fit well with observed SSY without adjustment. While the FSM was found to have, after modifying the description of factors and incorporating new controlling factors, a good fit between the predicted and observed SSY. Studies of the relationship between the known sediment yield rates and the catchment conditions using semi-quantitative approaches such as PSIAC and FSM can be of substantial benefit in extrapolating data for areas where no detailed information is available in a cheap and quick way. However, calibration and modification of such models may be necessary if they are to be used beyond the region where they were developed.

Chlorine transfer hose failure

On the morning of 14 August 2002, a 1 in. transfer hose used in a rail tank car unloading operation at DPC Enterprises, near Festus, Missouri, catastrophically ruptured and initiated a sequence of events that led to the release of 48,000 pounds of chlorine —a toxic gas—into neighboring areas. The facility repackages bulk dry liquid chlorine into 1 ton containers and 150 pound cylinders for commercial, industrial, and municipal use in the St. Louis metropolitan area. Fortunately, the wind direction on the day of the release limited the effects of the chlorine plume on the surrounding community. However, 63 people sought hospital treatment due to exposure, and hundreds of others were affected by the release (the community was advised to shelter-in-place for 4 h, and traffic was halted on Interstate 55 for 1.5 h). The US Chemical Safety and Hazard Investigation Board (CSB) investigated this incident for the following reasons: • Potential catastrophic off-site consequences to the public. • Large quantity of chlorine released. • Prolonged release duration. • Wide use of chlorine within the US and potential for similar incidents at other facilities. This paper presents the lesson-learned from this incident to help prevent similar occurrences. This paper is based on US Chemical Safety and Hazard Investigation Board Report Number 2002-04-I-MO, which was approved by the Board on 1 May 2003. This paper has not been independently approved by the Board and is published for general informational purposes only. Every effort has been made to accurately present the contents of the Board-approved report in this paper. Any material in the paper that did not originate in the Board-approved report is solely the responsibility of the author and does not represent an official finding, conclusion, or position of the Board. A complete copy of the Board investigation report upon which this paper is based is available on the CSB website at http://www.csb.gov “Completed Investigations.”

Offsite consequence analysis of liquefied chlorine gas spill at a water treatment plant in Malaysia

Malaysia, like any other country has experienced a number of chemical accidents in the past, hence the necessity to undertake thorough consequence analysis to mitigate similar occurrences in future. The water treatment plant in question keeps more than 18.6 MT (metric tonnes) of chlorine to disinfect water for the community in municipal area. However, chlorine is a hazardous chemical that can cause serious injuries, loss of life and damage to properties and environment if not handled properly. Hence using the Environmental Protection Agency (EPA) methodology an offsite consequence analysis was conducted to determine the potential impacts in the event of catastrophic release of chlorine at the water treatment plant. A “worst‐case release scenario” and “alternative scenario” were developed for the treatment plant. The results obtained from the use of TRACE software showed that a potential hazard exists, even under average annual weather conditions. Within a 6 km radius, an estimated number of 102 000 people within the zone for a 3 ppm chlorine exposure may be affected due to a worst‐case release. The consequence isopleth for the respective chlorine concentration indicates that the chlorine plume is directed towards the administration building and process unit facilities of the plant. Hence, it is critical to ensure that all personnel within the plant are provided with sufficient training on the emergency response plan and the application of the relevant personnel protective equipment (PPE) in the event of accidental releases. Although the hazard exists, the risk to the public may be low. An alternative release scenario would be limited due to the use of safety and mitigation systems incorporated into the chlorinating system, but the plant requires other supporting safety measures to supplement the existing facility's inherent safety. Such measures are essential to ensure that in the event of a potential incident at the plant onsite and offsite effects could be minimised to ensure the risk is as low as reasonably practicable (ALARP).

Legume-based farming in Southern Australia: developing sustainable systems to meet environmental challenges

Development of legume-based farming systems has resulted in Australian agriculture being globally competitive. There is now political pressure for agriculture to become accountable for ‘off-site’ environmental consequences. Farming systems relying on annual species are unsustainable because of a mismatch between the supply and demand of water and N, resulting in N leakage to streams or groundwater. Rainfall in excess of plant requirements coupled with N build-up, permeable soils, limited opportunities for reduction and proximity to surface or groundwater present risks for leakage of NO 3–N. We present examples of N leakage from legume systems in southern Australia, where rainfall exceeds 450 mm yr −1, and the evidence suggesting that leakage contributes to stream and groundwater pollution. N build-up in autumn through mineralisation of organic-N from legume-based systems often exceeds 100 kg N ha −1 and N leakage losses can be 15–35 kg N ha −1 yr −1. Stream and groundwater N pollution issues are emerging. Surface water quality problems are already apparent in Victoria although the contribution from legumes, N fertilisers and point sources remains unresolved. Examples of groundwater problems where legumes are a contributing factor have been recorded in New South Wales (NSW), South Australia (SA), Western Australia (WA) and Victoria. In Victoria, areas at risk of N groundwater contamination are found along the Great Dividing Range and in southern Victoria. Groundwater pollution causes concern because once problems are found they take decades to reverse. Stores of N in the unsaturated zone combined with limited N monitoring in groundwater suggests that early detection is unlikely. Solutions for reducing off-site consequences are outlined and include management to prevent water and N leakage happening, capture of N before it reaches waterways or groundwater and low input systems including land retirement. For scientists interested in N fixation and biological mediation, future research areas include increasing the proportion of perennials in farming systems, better control of N supply and demand through improved technology and us of N fertiliser, use of nitrification inhibitors and studies of the potential for N immobilisation and reduction through denitrification, both within and below the root zone. Integrated management strategies that address environmental implications from point/micro-scale to paddock and catchment scales are needed as are considerations of other environmental consequences. Research priorities will change from maximising N fixation for profitability towards balancing profitability and environmental goals for more sustainable systems.

A Study on Risk Assessments Using the MACCS Code for a Nuclear Power Plant

A consequence analysis includes assessment of effects on health and environment caused by radioisotopes released from severe accidents of nuclear power plants. In this study the consequence analysis to assess effects on health and environment caused by released radioisotopes has been performed for a nuclear power plant, Ulchin 3 & 4 using ORIGEN, MELCOR, MACCS code and IPE results. The core inventory and release fraction, respectively, are calculated by both the ORIGEN and the MELCOR code to produce the magnitudes of source terms amount for each radionuclide. And the MACCS code is utilized to calculate the offsite consequence by the amount of an atmospheric release of radioactive nuclides. Three parameters, such as the release height, the heat content, and the duration time, are used as important factors to perform the best estimate analysis and sensitivity analysis with respect to the measure of early fatalities and latent cancer fatalities. The results of this study may contribute to identifying the relative importance of various parameters occurred in consequence analysis as well as to assessing risk reduction accident management strategies.