Power Plant Engineering

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:

2 CO + O 2 ⇒⇒⇒⇒⇒ 2 CO 2

2 H 2 + O 2 ⇒⇒⇒⇒⇒ 2 H 2 O

10.28 Other, Earlier, Soviet Nuclear Accidents

September 1982 — Chernobyl Unit 1, after 5 years service, was shut down for maintenance.

Restarted with some valves closed. Result: no water flow in a few channels. Explosion in core, a few

fuel rods melted. Some radioactivity escaped plant. No radiation survey was done outside plant. Streets

of Pripyat were hosed down. No announcement to population. Emergency core cooling system saved

plant. Chief Engineer, his deputy, and chief operator of the shift were all demoted and transferred.

1980 Kursh power station. RBMK-1000 plant had a power outage.

Reactor damaged because control rods and circulation driven by electric motors/pumps failed.

Time delay to start diesel generators was 40 seconds During which, power surge damaged some fuel

rods. Solution : design a special generator to tap turbine power as it spun down during shutdown, to

power emergency equipment.

Oct. 1982. Armyansk nuclear power station. Explosion. Subsequent fire destroyed turbine

building.

Fall 1983 Chernobyl Unit 4 startup. Certification team saw anomalous power surge when

control rod insertion starts. Considered minor, had been seen in another reactor. No explanation,

not documented.