POWER February 2011 - 12

perimental tidal projects. According to
officials from Nova Scotia Power Inc.
and Irish company OpenHydro, which
partnered to demonstrate a 400-metric
ton turbine, recovery of the device just
a year after deployment showed that
all 12 blades from the unit's core were
missing. The rest of the structure, an
innovative open-center design, was in
" excellent condition overall, " as OpenHydro
CEO James Ives noted. " It's too
early to be certain, but it appears this
is the result of the tidal regime being
much stronger than we initially believed, "
he said, adding that a detailed
analysis would provide more information
and guide the next design and deployment
decisions.
Ukraine Opens Chernobyl
to Visitors
The Ukraine will on April 26 mark 25 years
after explosions at the Chernobyl Nuclear
Power Plant (then in the Ukrainian Soviet
Socialist Republic) resulted in a fire that
sent a plume of radioactive fallout into the
atmosphere and over an extensive area.
The catastrophe-much cited as the worst
nuclear accident in the world-was said to
have directly caused 50 deaths and indirectly
caused a total of 4,000 deaths as a
consequence of increased cancer risk.
But time, in its quintessential way
of healing wounds, has allowed the socalled
" zone of alienation " to recover
modestly. Last December, Ukraine's
Minister of Emergency Situations Viktor
Baloga told reporters that starting
in January 2011, the 19-mile exclusion
zone around Chernobyl's sealed Reactor
No. 4 would be opened to the public
(Figure 5). Helen Clark, an administrator
for the United Nations Development
Program, standing alongside Baloga on
Dec. 12, explained one reason for the
opening to reporters: " This is the story
of the mighty men at the cost of their
lives have taken control of nuclear danger.
This is the story of families who
left their homes. It's sad pages of life
in Ukraine, but they should not only tell
the world, but also show [what] happened
here. " The minister's office also
reportedly said the site's opening would
enable it to recover while revealing a
" great economic potential in Ukraine. "
The government says that background
radiation in the accident zone remains
well above normal, but it is far from
being a wasteland: Flora and fauna
have returned to the abandoned city of
Pripyat. Among the minister's immedi12
Readers
Write
In the September and October 2010 issues,
POWER Contributing Editor David
Daniels explored the causes and damage
mechanisms of condenser tube leaks
( " Taming Condenser Tube Leaks, " Part
I and Part II). Dennis J. Schumerth,
Valtimet's director of business development,
took issue with several of Daniels'
statements regarding the proper use of
titanium condenser tubes. We have given
Schumerth the opportunity to express
his concerns and for Daniels to reply.
Schumerth: I believe the article
does not accurately represent the track
record of titanium condenser tube materials.
Titanium has performed without
one reported corrosion event in a
surface condenser application for over
40 years. In Part II, Daniels noted
that " Series 300 stainless steel alloys,
such as 304 and 316L, are now fairly
common in new construction in both
freshwater and seawater applications. "
Historically, neither of these alloys are
considered appropriate for seawater
applications.
Daniels: I stand corrected. I should
have said that stainless steel alloys are
common in freshwater condensers.
Schumerth: One paragraph in Part
II states that " Titanium alloys, though
typically considered immune to corrosion
from the cooling water side, have
failed due to impingement from saturated
steam dump lines in the condenser. "
Condenser tube failures can occur with
any tube material but have been particularly
troubling with steam dump lines
in combined cycle (CCGT) plants. These
cyclic fatigue failures have been classically
related to improper operation or
design of the plant digital control system,
manufacturing deficiencies, or a
suspect condenser specification.
Daniels: The theme of both articles
was that, regardless of the condenser
metallurgy, the plant must remain vigilant
and quickly identify and correct any
contamination from a condenser tube
leak before it damages the rest of the
steam cycle-not to recommend one
type of condenser tubing over another.
The intended message of this paragraph
was that, just because a plant has a tiwww.powermag.com
tanium
condenser, it doesn't mean that
it will never get a condenser tube leak.
Titanium tubes can fail due to erosion
from poorly designed steam headers or
from freezing, just like any other condenser
tube material.
Schumerth: Later in the same paragraph,
the article notes that " they
[titanium tubes] can also suffer from
failures if steel tools scratch and penetrate
the protective titanium oxide
layer. " The technical literature supports
this concern, suggesting precautions
be taken with all titanium
alloys to remove or avoid surface iron
contamination, but this type of pitting
does not occur below 170F, well
above the typical condenser operating
temperatures. Indeed, carbon steel
condenser tube cleaning apparatus are
commonly used.
Daniels: I appreciate the enlightenment
and will research that point further.
Schumerth: The author also states
that " A very few cases of corrosion
in titanium tubes have even been ascribed
to MIC. " We disagree. The technical
literature and our experience has
identified many materials susceptible
to MIC while titanium was identified as
immune to any attack.
Daniels: I agree that titanium alloys
are generally considered immune
to MIC. The cases where MIC was suspected
on Ti Grade 2 were under very
unusual conditions where SRB bacteria
destroyed the protective oxide coating
on the titanium. This is certainly not a
normal condition for power plant condensers,
as was clearly pointed out in
the article.
Schumerth: The author also states,
" However, titanium tubes are still subject
to biofilm accumulations that can
slow the flow, etc. " This statement
should include just about all tube materials
rather than just titanium.
Daniels: The sentence just prior
states that stainless steel tubes often
have MIC issues and that MIC is an allencompassing
problem in condenser
tube materials and that titanium tubes
are not immune to biofilm accumulations.
POWER
| February 2011
http://www.powermag.com
POWER February 2011

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