fast reactors and fuel dispersal accidentsdisper

[gj_vargo@ccmail.pnl.gov]

     This is in response to Alex's questions on fast reactors and another 
     thread on fuel dispersal accidents.
     
     There are two operating FBRs in the former Soviet Union.  The BN-350 
     at Shevchenko in Kazakhstan is a dual purpose reactor.  It generates 
     electricity (~50 MWe) with the balance of the thermal energy being 
     used for desalination.  The plant's equivalent output is ~350MWe.  A 
     larger version, the BN-600 at Beloyarsk is used entirely for energy 
     production.  Both reactors use enriched U fuel (for some reason, they 
     have not developed a MOX cycle for these).
     
     Regarding fuel dispersal accidents - my knowledge is limited to 
     commercial power reactors.  UO2 will rapidly disperse (i.e., change 
     from pellets to powder) and breach cladding if the enthalpy exceeds 
     ~280 cal/gm.  The only way to achieve such a condition is with a 
     reactivity accident (e.g., BWR control rod drop during cold startup 
     <<1% power when the core is not coupled by steam voids.)  This is one 
     of the BWR design basis accidents and it is addressed by establishing 
     control rod patterns that minimize the "worth" of individual control 
     rods during startup.  I can't speak to the possibility of such a fuel 
     dispersal accident occurring out of core with highly enriched U fuel.
     
     George J Vargo     
     Pacific Northwest National Laboratory
     gj_vargo@pnl.gov