Risk upper bound

Acceptable defined as 10 risk (upper bound). Based on mouse and rat bioassay (10 risk). 

The level of safety of a repository for high level radioactive wastes shall be such that the predicted risk of a health effect in a year from a repository to an individual of the critical group from disruptive events not covered by Principle No. 5 is less than a risk upper bound apportioned by national authorities from an individual limit of risk of health effects of one in a hundred thousand per year. 

The judgement that is made as to the level of risk that should not be exceeded is that the risk upper bound from events not covered by the use of a dose upper bound should be no greater than the risk from doses at the dose upper bound. 

The implication of this principle is that risks of health effects from events that are highly improbable will be very small compared to any risk upper bound, and analysis of such events need not be included in a risk assessment for a repository. ... 

All radiation exposures that may result from the disposal of high level radioactive wastes shall be as low as reasonably achievable, economic and social factors being taken into account. The dose and risk upper bounds as defined in Principles Nos 5 and 6 shall be overriding constraints. 

As expressed by Principle No. 3, the individual dose and risk upper bounds applicable today should in principle be sustained indefinitely without a cut-off time to respect our responsibility for protection of human descendants. However,... 

Reliability for Phase 1 of the Probabilistic Risk An ysis DPST-37-642 Nuclear Fuel Cycle upper bounds exchangers, relays, tans for systems. ... 

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. 

Because the slope factor is often an upper 95 percentile confidence limit of the probability of response based on experimental animal data used in tlie multistage model, tlie carcinogenic risk estimate will generally be an upper-bound estimate. Tliis means tliat tlie EPA is reasonably confident tliat tlie true risk will not exceed the risk estimate derived tlirough use of tliis model and is likely to be less than tliat predicted. 

Tables (3-1, 3-2, and 3-3) and figures (3-1 and 3-2) are used to summarize health effects and illustrate graphically levels of exposure associated with those effects. These levels cover health effects observed at increasing dose concentrations and durations, differences in response by species, minimal risk levels (MRLs) to humans for noncancer end points, and EPA s estimated range associated with an upper- bound individual lifetime cancer risk of 1 in 10,000 to 1 in 10,000,000. Use the LSE tables and figures for a quick review of the health effects and to locate data for a specific exposure scenario. The LSE tables and figures should always be used in conjunction with the text. All entries in these tables and figures represent studies that provide reliable, quantitative estimates of No-Observed-Adverse-Effect Levels (NOAELs), Lowest-Observed-Adverse-Effect Levels (LOAELs), or Cancer Effect Levels (CELs).

Estimated Upper-Bound Human Cancer Risk Levels This is the range associated with the upper-bound for lifetime cancer risk of 1 in 10,000 to 1 in 10,000,000. These risk levels are derived from the EPA s Human Health Assessment Group s upper-bound estimates of the slope of the cancer dose response curve at low dose levels (qi ). 

Because of its carcinogenic potential, the EPA-recommended concentration for trichloroethylene in ambient water is zero. However, because attainment of this level may not be possible, levels that correspond to upper-bound incremental lifetime cancer risks of 10, lO , and 10 are estimated. 

Qi — The upper-bound estimate of the low-dose slope of the dose-response curve as determined by the multistage procedure. The q, can be used to calculate an estimate of carcinogenic potency, the incremental excess cancer risk per unit of exposure (usually pg/L for water, mg/kg/day for food, and pg/m for air). 

Estimated Upper Bound Human Cancer Risk Levels... 

When considering individual risk, there is commonly considered to be an upper bound, above which the risk is judged to be intolerable and for which action must be taken to reduce the risk. Figure 4.1, taken from the HSE (Ref. 46), illustrates this concept. If the risks are in the region above the horizontal line, the activities, as constituted, exceed tolerable levels. Re-... 

If an upper bound of 10-4 is adopted for maximum individual risk, from single events, then occupants of Building 2 are at, or slightly above, the upper-bound limit, while occupants of Building 3 appear to be in a region of tolerable risk. Also, from inspection of the data, it appears the individual risk to occupants of both buildings is almost 30 times greater from Process Unit 2 than from Process Unit 1. 

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