MIT22_081JF10_lec22b

MIT22_081JF10_lec22b -...

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Unformatted text preview: 1.818J/2.65J/2.650J/10.291J/10.391J/11.371J/ 22.081J/22.811J/ESD166J SUSTAINABLE ENERGY Prof. Michael W. Golay Nuclear Engineering Dept. PROBABILISTIC RISK ANALYSIS 1 INTRODUCTION OF THE BASIC ELEMENTS OF PROBABILISTIC RISK (PRA) ANALYSES Fault Trees Risk Data Uncertainties Nuclear Power Plant PRA Structure Typical Results 2 THE PRE-PRA ERA (prior to 1975) Management of (unquantified at the time) uncertainty was always a concern. Defense-in-depth and safety margins became embedded in the regulations. Defense-in-Depth is an element of the NRCs safety philosophy that employs successive compensatory measures to prevent accidents or mitigate damage if a malfunction, accident, or naturally caused event occurs at a nuclear facility. [Commissions White Paper, February, 1999] Design Basis Accidents are postulated accidents that a nuclear facility must be designed and built to withstand without loss to the systems, structures, and components necessary to assure public health and safety. 3 TECHNOLOGICAL RISK ASSESSMENT Study the system as an integrated socio-technical system. Probabilistic Risk Assessment (PRA) supports Risk Management by answering the questions : What can go wrong? (accident sequences or scenarios) How likely are these scenarios? What are their consequences? Risk = Expected consequences = Prob i Consequence i Sequences,i 4 DEFINITION OF RISK Event Risk Vector (Set) of Expected Consequences From an Event r For an Event of Type i, the Associated Risk Vector, R i , r r R i = C i = (Probability of Event, i) * (Set of Consequences of Event, i) = [(Frequency of Event, i) * (Time Interval of Interest)] * (Set of Consequences of Event, i) CORE DAMAGE RISK DUE TO N DIFFERENT CORE DAMAGE EVENTS r R total = r R i i = 1 N = p i i = 1 N Consequence 1, i Consequence M, i Total Risk is the Sum Over All Possible Events of the Risks Associated with Each Event, Respectively RISK CALCULATION C a C b C n C Risk = C i p i = = i, All Event Sequences C = Vector of consequences associated with the i th event sequence = Probability of the i th event sequence p i = Mean, or expected, consequence vector = Mean, or expected, consequence of type a, summed over all event sequences C C a EXAMPLE C i = Offsite acute fatalities due to event i Offsite latent fatalities due to event i Onsite acture fatalities due to event i Onsite latent fatalities due to event i Offsite property loss due to event i Onsite property loss due to event i Costs to other NPPs due to event i THE HAZARD (some fission-product isotopes) Isotope Half-Life Volatility Health Hazard 131 I 8 d Gaseous External whole-body radiation; internal irradiation of thyroid; high toxicity 89 Sr 54 y Moderately Bones and lungs volatile 106 Ru 1 y Highly volatile Kidneys 137 Cs 33 y Highly volatile Internal hazard to whole body 7 DECAY HEAT...
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MIT22_081JF10_lec22b -...

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