Agenda - 11-17-1998 - 5a - Laserfiche WebLink

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26 Nuc~e.7r Waste Orsposal Crrs+s Defense-m-depth protects public health and safet~• +n the unlikely event the reactor cure is damaged fulluwin;; an unlikely lus~-uf-coolant accident. The defense-in-depth cun~ept diswssed fur the pustulated pipe break event is svs- tematLCally applied to all design basis transients, accidents, and events-water line break. steam line break, generator load rejection, inadvertent valve closure, spurious relief .•alve opening, pump seizure. control system failure, earthquake, and many other. 1Vuclear pu~~~er plants are nut inherently safe, but they are safe- ly operated through risk management based un defense-in-depth. Defense-in-.iepth also applies when handling spent fuel assemblies. The design basis fuel handling accident pustulates the drop of an irradiated Euel assembly from the maximum possible height. Tu satisfy the first defense-in-depth principle, the fuel grapple is equipped ~•'ith interluclcs that present a fuel assem- bly from being inadsertently released. Tu satisfy the second defense-in-depth prindple, the storage racks are designed to restrict the damage from a dropped fuel assembly to that assembly and the small number of fuel assemblies it impacts. Tu satisfy the third defense-in-depth principle, the ventilation system for the fuel handling area processes air through filters before discharging it to the atmosphere. thug limiting the radioactivity released into the en~'ironment. Again, defense-in-depth protects public health and safety in the unlikely went that irra- diated fuel assemblies are damaged fullu~sing an unlikely fuel handling accident. Public health and safety is prutt~cted ~.•hen at least one of the three defense- in-depth elements remains unbroken. [f an accident Weyer occurs, then mitigation and containment features remain unchallenged. if a major accident occurs,-then the public is protected if either mitigating features prevent fuel damage or con- tainment features prevent uncontrolled release ui radiuactt~•ity. Therefore, all three defense-in-depth principles must br breached fur the public to be jeopar- dized by nuclear power plant operation. Defense-in-depth's salue u clearly evi- dent in the t..•o wont nuclear pu~.•er plant accidents-Three ~•tile Island and Chernobyl. the T'nree Mni~er~is~ande TAcc edent it ~ plant [n tl~e predawn hours near Harrisburg, [ ennsslvania, expenenced the ~.•orst accident in Lnited Stites commercial nuclear pu~~'er history. The Tivl[-'_ accident bran as an innocuous transient that interrupted feedwater tlu~s to the steam generator at this P~~ plant. Then a backup system failed to supply auxiliary feed~sater to the steam ~;eneratur. Heat transfer from the reactor coolant system to the secundarv loop ;tapped after the steam generators bulled dry un the secundarv side. ~n equiF" ment hilure allowed the uncontrolled release ut coolant from the primary sys- tem. The operating staff. relv,n ~m tilsr level indicatwns and una"are of the rea~tur coolant rm'enturv fuss, turned utf the emer~enry pump. that had auto- mahcally ;carted providing mak~uF~ eater to the traitor coolant system. Dehn~ ed of cu~~lins~ eater, the T~II-'_ reactor ~orc ~,yerit~•atvd. r5S