Page 407 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

CORROSION DAMAGE, DEFECTS, AND FAILURES 385

the El Al 747 crash, Boeing has also been trying to upgrade the 747 fleet. Specific
targets on these models included fabricating new parts for the pylon-to-wing attach-
ment for the Pratt & Whitney engines and the cost and time efficiency of inspection
protocol.

5.3.7.4.22 Nuclear Reactor with a Hole in the Head On March 6, 2002, personnel
repairing one of the five cracked control rod drive mechanism (CRDM) nozzles at
Davis-Besse Nuclear Plant, Oak Harbor, Ohio, discovered extensive damage to the
reactor vessel head. The reactor vessel head is a dome-shaped structure made from
carbon steel housing the reactor core. The reactor vessel head is placed such that it can
be removed when the reactor is shut down to allow spent nuclear fuel to be replaced
with fresh fuel. The CRDM nozzles connect motors mounted on a platform above
the reactor vessel head to control rods inside the reactor vessel. Reactor operators
withdraw control rods from the reactor core to start the operation of the plant and
insert the control rods to shut down the operation of the reactor.
The reactor core at the Davis-Besse Nuclear Plant sits within a metal pot designed
to withstand pressures up to 17 MPa. The reactor vessel has 15-cm thick carbon steel
walls and has adequate strength. The water used for cooling the reactor contains boric
acid, which is corrosive to carbon steel. Hence, the inner surface of the reactor vessel
is covered with a 0.6-mm thick layer of stainless steel. But water routinely leaked on
to the reactor vessel’s outer surface.
Because the outer surface is made of carbon steel without stainless steel protec-
tion, boric acid attacked the carbon steel until it reached the back side of the inner
liner. High pressure inside the reactor vessel pushed the stainless steel outward into
the cavity formed by the boric acid. Bending of stainless steel without breaking was
observed. The cooling water remained inside the reactor vessel because of the thin
layer of stainless steel. The plant’s owner ignored many warning signs over the years,
which led to this situation.
This corrosion problem exposed the problems within the staff of the regulatory
commission, which wanted prompt inspections of all the 68 plants wherein this prob-
lem may occur. The regulatory commission relented and gave the owners permission
to delay, leaving enough time for the hole in the lid to grow. Plants are generally
designed with emergency equipment to cope with leaks, but the designs do not envis-
age failure of thick steel in that location.
A subsequent investigation by the Commission’s inspector general found poor
communications within the staff of the agency itself. The Commission had a pho-
tograph taken during a refueling shutdown break in 2000 that showed evidence of
corrosion damage, but the responsible personnel failed to correct the situation.

5.3.7.4.23 Piping Rupture Caused by Flow Accelerated Corrosion A piping rup-
ture caused by flow accelerated corrosion occurred at Mihama-3 at 3:28 pm on August
9, 2004, killing four and injuring seven people. One of the injured men died later mak-
ing a total of five fatalities. The rupture was in the condensate system, upstream of
the feed-water pumps. According to Japan’s Nuclear and Industrial Safety Agency,