Deposit
Minimization
Treatment
By Richard Seel, Dominion Nuclear.
Richard Seel
Rick Seel serves as Supervisor Nuclear
Engineering Project Management for
Dominion Nuclear at Millstone Power
Station where he
is responsible for
the execution of all
phases of major
project design,
development and
implementation at
the station. His
resume includes
over 40 years of
engineering and
project management
experience
managing technical
projects in the
aerospace and
nuclear industry
including DOD, DOE and commercial
nuclear. He holds Bachelor’s and
Master’s Degrees in Mechanical
Engineering from Rensselaer
Polytechnic Institute.
Nuclear Energy Institute’s Top Industry
Practice (TIP) Awards highlight the
nuclear industry’s most innovative
techniques and ideas.
This innovation won a 2015 Vendor
Award.
The team members who participated
included: Richard Seel, Generation
Project Manager; Michael Stark,
Steam Generator Program Owner; Lew
Crone, Supervisor Nuclear Chemistry;
Joe Rigatti, Manager Nuclear Site
Engineering, Dominion Nuclear.
Summary
Through the years, the level of
deposition within the secondary side
of the four Millstone Unit 3 (MP3)
steam generators (SGs) had continued
to increase, and by 2013 the deposit
inventory was estimated to be greater than
7,000 pounds per SG. With considerable
broach hole blockage diverting flow, tube
support wear became a significant issue.
Additionally, a steady reduction of
thermal efficiency was noted.
Therefore, Millstone Engineering
and Chemistry personnel, working in
conjunction with AREVA, developed
a plan to significantly reduce the steam
generator deposit inventory. Conventional
thinking would have led the plant to
assume that hard
chemical cleaning
(e.g., EPRI/ Steam
Generator Owners
Group
(SGOG))
was the only viable
solution. By thinking
outside the box,
Millstone’s plan will
address the problem
at a significantly
lower cost.
A key component
of
the
Millstone
plan
involved
the
application
of
AREVA’s soft chemical cleaning process,
Deposit Minimization Treatment (DMT),
during two consecutive refueling outages. By
implementing the process during two outages,
maximum deposit removal is accomplished
with no outage schedule impact, while
capitalizing on the reduced complexity and
significantly lower implementation cost.
The first application, fall 2014
refueling outage, resulted in the removal
of 11,552 pounds of magnetite and copper
from the four MP3 steam generators,
a record for soft chemical cleaning
processes. The MP3 DMT application
also yielded significant financial (greater
than $20,000,000) and dose savings
(approximately 10 person-rem) when
compared to hard chemical cleaning, as
well as minimal corrosion to the steam
generator materials. The process had no
impact on outage schedule and involved
no personnel radiation exposure, and
upon plant startup following the refueling
outage, MP3 experienced a greater than
12 psi steam pressure increase attributed
to the DMT cleaning.
This fourth DMT application in the
US, and first at Millstone, incorporated
innovative process improvements which
further reduced waste processing time
and removed a record quantity of deposit
material. With the simplified system
design, the DMT process mitigated the
safety hazards often associated with
hard chemical cleaning applications. The
DMT chemical process eliminated the
hazardous chemical agent, hydrazine, and
the chelant, Ethylenediaminetetraacetic
acid (EDTA), with the use of the organic
chemical compound, oxalic acid. The use
of ozone for waste decomposition has
reduced the need for hydrogen peroxide,
thus further reducing the risk of hazardous
chemical exposure and the cost associated
with procurement. This technology
is transferrable as a process with a
simplified application methodology,
which enables it to be applied to nearly
any industrial component that requires
cleaning (e.g, piping systems, Balance of
Plant Heat Exchangers, etc.).
In summary, DMT itself has
changed over time to better match
customer needs. DMT was developed
as a preventative maintenance process
that would be performed to lower the
deposit inventory in small increments.
However the industry needed a process
to remediate greater portions of their
existing inventory without the large
expense and outage impact of an EPRI
style process or hard chemical cleaning.
As part of the MP3 deposit management
plan, DMT has demonstrated its cost
effectiveness and versatility.
Safety Response
With over 30,000 man hours worked
injury free, this project also provided a
dose savings for the outage of 10 person-
rem. One of the features of the DMT
process is the simplicity of the equipment
required for the application. The process
system has a single connection to the
steam generator via the blowdown
system piping which is external to
containment. This stands in stark contrast
with hard chemical cleaning processes
which typically require multiple direct
connections to the steam generator via
handholes and manways, and requires
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NuclearPlantJournal.com Nuclear Plant Journal, March-April 2016
