BASED ON INFORMATION AVAILABLE TO DATE, WE CAN CONSTRUCT
THE FOLLOWING:

AT 1:23 AM, APRIL 26, 1986 AN EXPLOSION OCCURRED AT THE
CHERNOBYL NUCLEAR PLANT, UNIT 4

EXPLOSION IS SAID TO HAVE OCCURRED IN THE BUILDING WHICH
HOUSES THE REACTOR (SOVIETS CALL THIS THE MACHINE HALL)

AS A RESULT OF EXPLOSION, THE ROOF OF THE REACTOR BUILDING
CAUGHT FIRE

FIRE DAMAGE CAUSED A BREACH OF REACTOR CONTAINMENT

INITIAL RADIOACTIVE RELEASE

SUBSEQUENT INITIATION OF GRAPHITE FIRE

O THERE ARE MANY POSSIBLE SCENARIOS FOR CHERNOBYL THAT CAN LEAD

TO THE DAMAGED CORE.

=

0 WE STILL DO NOT KNOW ABOUT THE ACTUAL SEQUENCE OF EVENTS WERE.

SOME POSSIBILITIES ARE:

- EXPLOSION/FIRE IN TURBINE OR REACTOR BUILDING ULTIMATELY CAUSES LOSS OF CONTROL (COOLING) TO CORE. LEADS TO CORE UNCOVERY AND MELTDOWN

- EXPLOSION/FIRE IN TURBINE OR REACTOR BUILDING CAUSES FAILURE OF REACTOR BUILDING AND DAMAGES REACTOR

ROUGH DESCRIPTION OF A HEATUP SCENARIO

- PRIMARY COOLANT WATER BOILS OFF

- WITH REACTOR SHUT DOWN, NO HEAT GENERATION IN GRAPHITE

- FUEL AND GRAPHITE COOL AND APPROACH QUASI-THERMAL EQUILIBRIUM

- FUEL UNCOVERS OVER SEVERAL HOURS AND HEATS UP

- FUEL CLADDING OXIDATION AND FAILURE

- FUEL ASSEMBLY CASING FAILURE NEAR TOP OF CORE

- HIGH PRESSURE-HIGH TEMPERATURE STEAM AND OTHER GASES PRESSURIZE THE GRAPHITE CAVITY

- FAILURE OF GRAPHITE CAVITY ALLOWS AIR INGRESS TO CORE REGION

- GRAPHITE FIRE STARTED AND A CHEMICAL (GAS) EXPLOSION IS POSSIBLE

- GRAPHITE CONTINUES TO BURN OVER A LONG TIME

IT IS MOST LIKELY THAT THE SOVIETS DO NOT YET KNOW WITH CERTAINTY THE ACTUAL SEQUENCE OF EVENTS.

THIS IS SIMILAR TO OUR KNOWLEDGE OF THE SEQUENCE OF EVENTS

AT TMI-2 WITHIN THE FIRST WEEK OR SO AFTER THE ACCIDENT.