Integrated TRAC/MELPROG analyses of a PWR station blackout
The first complete, coupled, and largely mechanistic analysis of the entire reactor-coolant system during a station blackout (TMLB') core-meltdown accident has been made with MELPROG/TRAC. The calculation was initiated at the start of the transient and ended with a late recovery of cooling. Additional cooling provided by water from the primary system delayed events relative to a standalone MELPROG calculation. Natural circulation within the vessel was established and primary-relief-valve action did little to disturb this flow. In addition, it was calculated directly that the hot leg reached a failure temperature long before vessel failure. Beyond relocation of the core, we have calculated the boiloff of the water in the lower head and have estimated the time of vessel failure to be at about 14,700 s into the transient. For ''nominal'' corium-water heat transfer, the boiloff process (steam-production rate) is slow enough that the relief valves prevent pressurization beyond 17.5 MPa. Parametric cases with increased corium-water heat transfer resulted in steaming rates beyond the capability of the relief valves, leading to pressures in excess of 19.2 MPa. Natural convection flow around the loop, if started by removing the water in the loop seal, was blocked by a relatively less-dense hydrogen/steam mixture that flowed to the top of the steam generator. Emergency core-cooling system activation late in the transient (after core slump) resulted in rapid cooling of the periphery of the debris region but slower cooling in the interior regions because of poor water penetration.
- Research Organization:
- Los Alamos National Lab., NM (USA)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 6174335
- Report Number(s):
- LA-UR-87-167; CONF-870816-3; ON: DE87005102
- Country of Publication:
- United States
- Language:
- English
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22 GENERAL STUDIES OF NUCLEAR REACTORS
220900* -- Nuclear Reactor Technology-- Reactor Safety
ACCIDENTS
BLACKOUTS
COMPARATIVE EVALUATIONS
COMPUTERIZED SIMULATION
COOLING SYSTEMS
ENERGY SYSTEMS
ENERGY TRANSFER
FLUID MECHANICS
HEAT TRANSFER
HYDRAULICS
MECHANICS
MELTDOWN
PARAMETRIC ANALYSIS
PWR TYPE REACTORS
REACTOR ACCIDENTS
REACTOR COMPONENTS
REACTOR COOLING SYSTEMS
REACTORS
SIMULATION
STEADY-STATE CONDITIONS
TRANSIENT OVERPOWER ACCIDENTS
WATER COOLED REACTORS
WATER MODERATED REACTORS