Technically Chornobil (Ukrainian spelling) was not a containment breach because there was no containment, in the sense of the containment structure used in Western-style LWR plants. Worst-case accidents for LWR systems do not involve the rapid power transient experienced by the RBMK systems in certain operating regimes because the feedback mechanisms are just too strong. BORAX and SPERT showed that light-water moderated reactor transients have neither the energy release or dynamics of the RMBK accident potential.
The report makes an important contribution by analyzing some reactor accidents that are worse than the DBAs. Specifically, the report treats:
(1) the LOCA-without-ECCS type of core meltdown;
(2) a class of accidents called "transients," which basically come under this author's category of power-cooling mismatch accidents (PCMAs) and heat exchange accidents; and
(3) the spontaneous reactor vessel rupture. The power excursion accidents (PEAs)and the worst forms of PCMAs are essentially excluded. More- over, on the basis of certain assumptions, the report treats the "transients" and the reactor vessel rupture as no worse than a LOCA without ECCS (slow core meltdown), which is not the worst course these accidents could take.
(The report's treatment of the LOCA-without-SCRAM-type accident was examined earlier; see pp. 34 -39.) In short, the report is grossly inadequate in scope.
Looking at the Three Mile Island incident - The NRC report points to a LOCA caused by a faulty valve - compounded by
Bad training
faulty human-machine interface
bad sensors
bad/untested emergency procedures
Subsequent visual examination of the rector core showed far more damage than was initially thought, but reactor breach did not ocurr.
A lot of lessons were learned, and changes were made. All good stuff.
That nobody was injured seems to smack of the "no danger from fallout" pronouncements back in the day of open air testing.