HFIR PSA

In 1988, an internal events PRA was published (Johnson, 1988) this was followed by an external events analysis. The results were reported by Johnson (1991), and Flanagan (1990). The basic approach to risk is that of Kaplan (1981) that asks the questions What can happen, and How likciy is it and what are the consequences These are organized as triplets to characterize the risk 

Several initiating events are unique 1) large LOCA (6), 2) flow blockage events (4a. 4b, and 4d). and 3) fuel defects (4e). The analysis of these required special tools not found in coinmcrcial power plant PRAs. 

The high power density and narrow flow channels could cause fuel hot spots and flow starvation. Fuel experts at ORNL and ANL identified five types of defects three fuel IIIhomogeneities and two assembly errors to arrive at 4D, for fuel defects is 2.1 x 10-. / i 

The external events PSA was based on standard methods used for commercial reactor PSAs, Fire risk was estimated from commercial nuclear power plant data combined with industrial fire information. The seismic hazard was evaluated using a combination of the EPRI and LLNL ( UREG/CR-.3250) databases. Wind hazards were analyzed by EQE, Inc., using NRC-based nicihodulogy. 

The results are summarized in Table 11.3-3 for both internal and external results, the CDF from all causes is 7.4E-4/y of which internal events contribute 3.1E-4 and external events 2.9E-4. This number has been reduced by design, administrative, and operational procedure changes. 

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