Power Plant Engineering

10.27 SAFETY PROBLEMS IN CHERNOBYL REACTOR DESIGN
10.27.1 SYSTEM DYNAMICS
A problem with RMBK-1000 reactor design is that the time constants for changes in thermal
output are short. Control depends on computer regulated feedback control systems. The human operator
could not react fast enough to manually control it without the automatic controls.

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NUCLEAR POWER PLANT
341
Neutron absorption and heat transfer coefficients are very different for water and steam, so neu-
tron flux and thermal output changes rapidly as water in the tubes through the core makes a transition
from hot water to steam.
10.27.2 ANOTHER SAFETY PROBLEM WITH THE DESIGN
The normal operating temperature of core tubes is greater than the ignition temperature of the
graphite blocks of the core (carbon) in an O
2
atmosphere. Its normal environment is an atmosphere with
no oxygen.
Heat exchange system :
One closed loop through reactor core and steam turbines
Secondary loop to condense steam to water after turbine
Construction problems :
Turbine building roof; specification said it should be fireproof. Materials for 1 km × 50 m fire-
proof roof was not available. Control cable conduits supposed to be fireproof. Material not available.
Exception granted. Cement and tiles, etc. Quality control problems. Director had to prioritize uses,
discard defective materials. Fittings often required remanufacture to meet specifications.
Hazard Potential of Water on Hot Graphite
Water Gas Reaction:
C + H
2
O
⇒
⇒
⇒
⇒
⇒
CO + H
2
Often used as a H
2
generator in freshman chemistry labs, it has a similar hazard if not carefully
controlled: