Nuclear Energy

Narora Accident
Take the Narora accident of 1993. It has been DAE’s closest approach to a catastrophic
accident. What is most worrisome about it is that the accident could have been foreseen and
prevented!
That's because the failure of the turbine blades was avoidable. In 1989, General Electric
informed the turbine manufacturer, Bharat Heavy Electricals Limited (BHEL), about a design flaw
which led to cracks in similar turbines around the world and recommended design modifications.
BHEL took prompt action and prepared detailed drawings for NPC, which operates the Narora
reactor. However, NPC took no action till after the accident!
Secondly, even after the turbine blade had failed, the accident could have been averted had
best manufacturing practices been followed. By the time the Narora reactor was being
manufactured, it was common understanding in the world reactor design industry that the power
supply should be encased in separate fire resistant ducts. This was one of the lessons drawn from
the fire at Browns Ferry in the US in 1975, and was made compulsory in the USA. Other countries
also adopted this measure. However, even though Narora plant was manufactured after all these
lessons had been drawn around the world, this practice was not followed for the Narora plant! As a
result, following the fire in the turbine building, the electric cables too caught fire and led to a
complete blackout in the plant.
Repeated Mistakes
The other problem with the DAE is that it does not draw lessons even after an accident has
occurred, leading to repeated accidents of the same type in different reactors. This is one of the
reasons for the Narora accident too. Excessive vibrations in the turbine bearings have been
common in Indian reactors. At RAPS-1, in 1981-82, after repeated shutdowns, it was finally
discovered that the problem was due to high vibrations of turbine bearings, and failure of turbine
blades was discovered. This led to a prolonged shutdown of more than 5 months; even after this
problem had apparently been fixed the reactor had to be shut down once again because of high
turbine bearing temperatures. Again in 1983, high vibrations were noticed in turbine generator
bearings and it was revealed that two blades in the second stage of the high pressure rotor had
sheared off at the root. In 1985, the first unit of the MAPS-1was shutdown repeatedly because of
high bearing vibrations in the turbine generator.
Even after the Narora accident of 1993, turbine problems have continued to plague other
reactors: Narora-2, RAPS-1 and Kaiga-2 have all had to suffer repeated shut downs due to high
turbine bearing vibrations / high bearing temperatures. In 1995, even after repeated shutdowns to
mitigate turbine problems, blades failed in the turbine of Narora-2. Not only that, despite the
accident in 1993, Narora-1 too had to be shutdown repeatedly in 1995 because of high vibrations of
the turbine generator bearing.
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