SUNDAY, MAY 11, 1986
DAYA BAY PLANT DIFFERENCES STRESSED
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THE NUCLEAR POWER PLANT BEING BUILT AT DAYA BAY IS OF A TYPE TOTALLY DIFFERENT TO THAT AT CHERNOBYL IN THE SOVIET UNION, THE FRENCH FIRM MAKING THE NUCLEAR EQUIPMENT, FRAMATOME, HAS EMPHASISED.
PRESSURISED WATER REACTORS (PWR'S) WILL BE INSTALLED AT DAYA BAY WHEREAS CHERNOBYL HAS GRAPHITE REACTORS BASED ON A DESIGN THAT WESTERN NUCLEAR ENGINEERS NOW CONSIDER LARGELY OUTMODED.
+GRAPHITE REACTORS OF THE SOVIET MODEL DATE BACK ALMOST TO ORIGINAL CONCEPTS IN USING NUCLEAR POWER FOR PRODUCING ELECTRICITY, + THE DIRECTOR OF ELECTRICAL AND MECHANICAL SERVICES, MR GRAHAM OSBORNE, SAID IN DISCUSSING DIFFERENCES PINPOINTED BY FRAMATOME.
GRAPHITE IS A PARTICULARLY PURE FORM OF CARBON BUT IS UNSTABLE AT HIGH TEMPERATURES, AND IN THE EVENT OF OVER-HEATING IT POSES A FIRE RISK.
THE GRAPHITE--BETWEEN 1 700 AND 2 000 TONS WERE USED IN THE STRICKEN CHERNOBYL REACTOR--MODERATES THE NUCLEAR PROCESS SO THAT THE EVENTUAL GENERATION OF ELECTRIC POWER IS REGULATED. WATER IS USED AS A COOLANT.
HOWEVER, IN A PWR PRESSURISED WATER ACTS AS BOTH MODERATOR
AND COOLANT, AND NO OTHER MATERIAL IS REQUIRED.
BECAUSE OF THE HUGE AMOUNT OF GRAPHITE NEEDED, THE 'RBMK' TYPE REACTOR AT CHERNOBYL HAS A CORE VOLUME MUCH LARGER THAN THAT FOR A PWR THOUGH THE OUTPUT OF POWER WILL BE THE SAME.
THE RBMK'S CORE HAS A DIAMETER OF 12.2 METRES AND A HEIGHT OF SEVEN METRES, WHEREAS THE DAYA BAY PWR WILL BE THREE METRES IN DIAMETER AND 3.6 METRES IN HEIGHT.
IN THE RBMK, THE URANIUM FUEL ASSEMBLIES AND THE COOLING WATER ARE CONTAINED IN ABOUT 1 660 THIN PRESSURE TUBES MADE OF A ZIRCONIUM ALLOY. SHOULD THERE BE SERIOUS OVER-HEATING, THE ZIRCONIUM MAY BURN BY SELF-IGNITION IN CONTACT WITH WATER, PRODUCING A LARGE QUANTITY OF HYDROGEN.
OVER-HEATING IN A FUEL ASSEMBLY MAY ALSO CAUSE THE GRAPHITE TO IGNITE, LEADING TO AN INTENSE FIRE, AS OCCURRED AT CHERNOBYL.
+
THESE DANGERS DO NOT ARISE IN A PWR, WHICH CONTAINS THE URANIUM RODS IN ONE SINGLE THICK PRESSURE VESSEL MADE OF STEEL, AND USES WATER AS BOTH MODERATOR OF THE NUCLEAR PROCESS AND COOLANT.
/ANOTHER MAJOR ...................