NE 568- Reactor Safety
Dr. Jose N. Reyes, Jr.
Department of Nuclear Engineering
Spring Term 2000
Risk
• Risk: The likelihood of experiencing a defined set of
undesired consequences.
– Involves both “likelihood” and “consequences” of an event.
• Likelihood: Slightly different then probability. Implies that
some subjective judgement is used as a basis for
determining the probability of an event. Typically
assumes:
– Magnitude of consequences will remain relatively constant (e.g.
fatalities /yr) with time.
– All members of the population are equally exposed or susceptible
to risk.
Risk
SOCIETAL RISK = FREQUENCY x MAGNITUDE
• Risk (Consequences/time)
• Frequency (Events/time)
• Magnitude (Consequence/Event)
e.g.:
(15 x 106 Accidents/yr) x ( 1 Death/300 accidents) = 50,000 Deaths/yr
Frequency Magnitude = Societal Risk
Risk
INDIVIDUAL RISK = SOCIETAL RISK/(POPULATION AT RISK)
e.g.: If 200 million people in US:
(50,000 Deaths/yr)/(200 x 106 people) = 2.5 x 10-4 Deaths/(person-yr)
Societal Risk / Pop. At Risk = Individual Risk
or 25 Deaths/100,000 people
Risk
INDIVIDUAL RISK = SOCIETAL RISK/(POPULATION AT RISK)
e.g.: If 200 million people in US:
(50,000 Deaths/yr)/(200 x 106 people) = 2.5 x 10-4 Deaths/(person-yr)
Societal Risk / (Pop. At Risk) = Individual Risk
or 25 Deaths/100,000 people
Risk
• Cost Risks for Injuries and Property Damage are expressed
in terms $Dollar values associated with injuries and/or
property damage.
Cost Risk = (Total $ Value)/ (Population at Risk)
Safety
• Safety is defined as the relative absence of risk.\
• No human activity is risk free!
Attitudes Towards Risk
• Types of activities with a fatality risk greater than 1 x 10-3
deaths/yr to the general public are generally unacceptable.
– cars ~ 3 x 10-4 deaths/(person-yr)
– falls ~1 x 10-4 deaths/(person-yr)
– fires ~4 x 10-5 deaths/(person-yr)
– drowning ~4 x 10-5 deaths/(person-yr)
– firearms ~1 x 10-5 deaths/(person-yr)
– poisoning ~1 x 10-5 deaths/(person-yr)
– lightning ~8 x 10-7 deaths/(person-yr)
• However risks of 10-3 occur in some sports, etc. Why?
Attitudes Towards Risk
• High Risk Activities are usually on the order of theDisease
Mortality Rate :
10-2 deaths/(person-yr)
• Low Risk Activities are usually on the order of the Natural
Hazards Mortality Rate:
10-6 deaths/(person-yr)
Attitudes Towards Risk
• Acceptability Towards Risk depends on
• Benefits of activity
• Voluntary Nature of Activity
• Consequence Distribution
• Perception
Risk Analysis
• Risk analysis is a technique of identifying, characterizing,
quantifying and evaluating hazards.
• Two Phases:
– A qualitative step of identifying, characterizing and ranking
hazards.
– A quantitative step of risk evaluation, which includes estimating
likelihood and consequences of hazard occurrence.
• After quantifying risks:
– risk management, risk-benefit, cost-benefit analysis to minimize
the likelihood of occurrence of hazard or to develop mitigation
plans.