Page 281 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

HAZARDOUS MATERIALS STORAGE 259

to terminate in 20 years. The two basins are still being used for storage of nuclear
waste. It is reported that the fuel rods in open canisters corroded with the subsequent
release of isotopes into the water. Basin cleanup waste removal and groundwater con-
tamination were reported.

4.14.1.1 Cask Design for Permanent Storage of Nuclear Waste Aging because
of exposure to radiation from radioactive elements and aging because of exposure to
corrosion are of concern in long-term storage of nuclear waste. The heat generated
by radiation can also increase the corrosion rate. Several cask designs with different
materials of construction such as carbon steel, stainless steel, and concrete construc-
tion have been advanced.
At present, all the nuclear waste generated is solid waste. This waste is noncorro-
sive, and the risk for internal corrosion damage is minimal. The considerable amounts
of liquid nuclear waste can cause internal corrosion problems. It is also possible that
any moisture in solid waste can also lead to corrosion. The tanks, although buried,
are exposed to groundwater and are prone to external corrosion. The consequences
of leaks in nuclear waste storage tanks or container are numerous: damage to envi-
ronment, loss of public trust, and exposure to radiation. Thus it is fair to state that
long-term extrapolations must be made to ensure the structural integrity of the nuclear
waste storage containers for centuries to come.
The scientific activity with respect to corrosion of permanent storage containers
continues as evidenced by: a literature review and a summary of plutonium oxide
and metal storage packing failures (37). Metal oxidation in nonairtight packages with
gas pressurization was identified as the most common mechanism of packaging fail-
ure. Another corrosion problem was observed in hydrogen/oxygen recombination and
generation of plutonium storage environment. The service life of steel in concrete for
the storage of low-level waste has been predicted (38).
The US Nuclear Regulatory Commission and the Department of Environment
(DOE) collaborated on the needed research into the effects of corrosion processes
on the lifetime of the containers. The designers are facing a wide range of problems
with respect to material issues. In nuclear waste containers, corrosion can occur in
both inside and outside the containers. The issues that require attention are general
and localized corrosion of the waste package outer barrier; methods for corrosion rate
measurements; documentation on materials such as alloy 22 and titanium; the influ-
ence of silica deposition on the corrosion of metal surfaces; stability of passive film on
welded and aged material; electrochemical potentials; microbiologically influenced
corrosion (MIC); stress distribution because of laser peening and induction anneal-
ing; SCC and its influence on rock fall impact strength; dead load stressing and the
effects of fabrication sequence and of welding.
4.14.1.2 Effect of Location Site on Corrosion of Nuclear Waste Storage
Containers The plan consists of a permanent nuclear depository to build at a
relatively dry site with a depth of several hundred meters below the earth’s surface. It
is envisaged that the presence of water will eventually corrode the storage containers.
In the United States, the Yucca Mountain site is reported to be a good location