Risk assessment Level

To estimate the benefit from this potential design alternative, the core damage sequences resulting from a failure of IRWST injection are assumed to be averted. Core damage sequences resulting from a failure of IRWST injection correspond to probabilistic risk assessment Level I accident classification 3BE thus, release category 3BE would be eliminated. 

The ECPI approach has been adopted by the European Commission in their "Technical Guidance Document on the Risk Assessment of Notified New Substances" as the model for assessment of environmental exposure from additives in plastics. It is important to note, however, that due to the effect of ultraviolet degradation and microbial attack, a significant proportion of the emissions from flexible PVC consists of plasticizer degradation products. In these instances, therefore, the level of plasticizers appearing in the environment will be significantly less than indicated by the plasticizer loss data. 

The analysis of a risk—that is, its estimation—leads to the assessment of that risk and the decision-making processes of selecting the appropriate level of risk reduction. In most studies this is an iterative process of risk analysis and risk assessment until the risk is reduced to some specified level. The subjec t of acceptable or tolerable levels of risk that coiild be applied to decision making on risks is a complex subject which will not oe addressed in this section. 

The aim of a risk assessment is to develop a product which is safe for the proposed market. A safe product is any product which, under normal or reasonably foreseeable conditions of use, including duration, presents no risk or only the minimum risk compatible with the product s use and which is consistent with a high level of protection for consumers (DTI, 1994). In attempting to protect products against failure in service and, therefore, the user or environment, difficulty exists in ascertaining the... 

Arguably, risk assessment from exposure to carcinogens merits special consideration because of the low levels of exposure capable of producing an adverse response in certain individuals coupled with the often long time-lag (latency period) between exposure and onset of disease. 

It has been traditional to subject workers to higher risks than the public, (a) Write a short discussion of the equities of this practice with consideration for the fact the worker may leave employment that imposed a long term risk, (b) The Nevada Test Site has been selected as a possible location for a high level waste repository. For purposes of the risk assessment, the workers in the repository will be treated as workers with subsequent higher allowable risk. There are many other workers at NTS. Discuss whether these should be treated as workers or public, (c) If they are treated... 

A risk assessment analyses systems at two levels. The first level defines the functions the system must perform to respond successfully to an accident. The second level identifies the hardware for the systems use. The hardware identification (in the top event statement) describes minimum system operability and system boundaries (interfaces). Experience shows that the interfaces between a frontline system and its support systems are important to the system cs aluaiion and require a formal search to document the interactions. Such is facilitated by a failure modes and effect analysis (FMEA). Table S.4.4-2 is an example of an interaction FMEA for the interlace and support requirements for system operation. 

EPRI NP-5664 is a study based on interviews of personnel at 10 utilities and 15 NRC personnel regarding the usefulness of PSA (they use the term PRA - probabilistic risk assessment). The general utility motivation for using PSA is to demonstrate an acceptably low level of risk to the NRC. Some utilities applied PSA to individual systems, functions, or issues. These smaller [ir(>grams served to train a PSA cadre and introduce PSA to other utility personnel and management. 

The Pickering A Risk Assessment (PARA) (Ontario Hydro, 1995) is also a level 3 PSA for 1 of the 4 units at Pickering. A difference between PARA and DPSE is that sequences beyond the design basis were modeled using the MAAP-CANDU codes with best estimate assumptions. Other parts of the analysis used licensing-type conservative assumptions. 

In May 1988, a Level-1 PSA was undertaken as part of the general risk assessment at DOE facilities. Revision 0 was completed, and reviewed by BNL, DOE and contractors. The revised report was available July 1990 (Azarm, 1990). The broad objective of the HFBR PRA program is to enhance the safety and operational activities throughout the. remaining lifetime of the reactor... 

Eide, S. A. et al., 1990a, Advanced Test Reactor Level 1 Probabilistic Risk Assessment, ANS Topical Meeting, The Safety, Status, and Future of Non-Commercial tors and Irradiation Facilities, Boise ID, Sept. 31 - October 4,1990. 

Neill, D.T. et al., 1990b, Omega West Reactor, Level 1, Probabilistic Risk Assessment, Idaho State University, College of Engineering, LANL, LA-UR-90-962. 

Risk assessment, a synthesis of the preceding three steps, which aims to assess both qualitatively and quantitatively the risks induced by a chemical at a given or at different exposure levels. 

In the North Sea this is often done with detailed quantified risk assessments and the calculation of an overall IRR or risk of total loss of structure. Mitigation measures are incorporated until it can be shown that risk levels meet a minimum criteria and the cost of further mitigation has such high cost to benefit ratios that further mitigation is no longer practicable. ... 

Risk measurement. Few companies have undertaken the quantitative risk assessments necessary to indicate the level of risk they face for... 

Generally, the slope factor is a plausible upper bound estimate of the probability of a response per unit intake of a ehemieal over a lifetime. The slope factor is used in risk assessments to estimate an upper-bound lifetime probability of an individual developing cancer as a result of e.xposure to a particular level of a potential carcinogen. Slope factors should always be accompanied by the weight-of-evidence classification to indicate the strength of the evidence that the agent is a human carcinogen. Calculational details are presented below. 

Numerous qualitative approaches to risk assessment have been employed. Some sample categorizations follow. Health risks may be divided into risk levels as provided below ... 

Uncertainty on tlie other hand, represents lack of knowledge about factors such as adverse effects or contaminant levels which may be reduced with additional study. Generally, risk assessments carry several categories of uncertainly, and each merits consideration. Measurement micertainty refers to tlie usual eiTor tliat accompanies scientific measurements—standard statistical teclmiques can often be used to express measurement micertainty. A substantial aniomit of uncertainty is often inlierent in enviromiiental sampling, and assessments should address tliese micertainties. There are likewise uncertainties associated with tlie use of scientific models, e.g., dose-response models, and models of environmental fate and transport. Evaluation of model uncertainty would consider tlie scientific basis for the model and available empirical validation. 

The risk assessment steps and the risk characterization are influenced by uncertainty and variability. Variability arise from heterogeneity such as dose-response differences within a population, or differences in contaminant levels in tlie environment. Uncertainty on tlie other lumd, represents lack of knowledge about factors such as adverse effects or contaminant levels. 

PBPK models improve the pharmacokinetic extrapolations used in risk assessments that identify the maximal (i.e., the safe) levels for human exposure to chemical substances (Andersen and Krishnan 1994). PBPK models provide a scientifically sound means to predict the target tissue dose of chemicals in humans who are exposed to environmental levels (for example, levels that might occur at hazardous waste sites) based on the results of studies where doses were higher or were administered in different species. Figure 3-4 shows a conceptualized representation of a PBPK model. 

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