modular condenser replacement at ano-1 solves

Reprinted From
PWR-Vol. 34, Proceedings of the International
Joint Power Generation Conference
Editors: S. R. Penfield, Jr., R. H. Hayes, and
R. McMullen
Book No. G01110 -1999
ASME International
The American Society of Mechanical Engineers
Three Park Avenue
New York, NY 10016-5990
MODULAR CONDENSER REPLACEMENT AT ANO-1 SOLVES
OPERATING PROBLEMS AND IMPROVES PERFORMANCE
Douglas Edgell
Project Lead Engineer
Entergy Operations, Inc.
Arkansas Nuclear One
1448 S.R. 333
Russelville, Arkansas 72801
Tel: 501-858-4489
Fax: 501-858-4955
Armond Davidian
Director of Engineering
Thermal Engineering International
5701 South Eastern Avenue
Los Angeles, California 90040
Tei: 323-838-1136
Fax: 323-726-2388
anticipated 8% power uprate. This paper will discuss the'
condenser optimization program from the design stage to final
installation.
Further, it was decided to completely shop fabricate these four
titanium tube bundles to minimize the site erection schedule. Each
bundle measuring over 44 ft (13.5 m) long, over 13 ft (4 m) wide, and
nearly 18 ft (5.5 m) tall, weighed 195,000 lbs (88,450 kg). The weight
and size of the bundles created a variety of fabrication,
transportation and installation challenges that required extensive
advanced planning, scheduling and coordination.
The complete installation of the redesigned condenser tube
bundles and waterboxes was accomplished during the Fourteenth
Refueling Outage of ANO-1 in 1997.
ABSTRACT
After 22 years of operation, the condenser tube bundles and
waterboxes at Arkansas Nuclear One, Unit 1 (ANO-1) had
deteriorated significantly, impairing operating performance,
reducing condenser reliability and increasing maintenance cost. An
extensive condition assessment performed in 1995 revealed a 34%
wall loss on the original Admiralty tubing and an erosion rate of 1.
7% annually. Additionally, Arkansas Nuclear One was considering
an 8% power uprate, which would place additional duty on the main
condenser. As a result, it was decided to completely reconstruct the
four condenser tube bundles serving the two low-pressure turbines
at Arkansas Nuclear One.
An evaluation of the available condenser tube materials was
performed to determine which material was best suited for service in
the single pass, single pressure condenser at ANO-1. All copper
based materials were excluded from consideration due to the
detrimental effect copper has on secondary chemistry and more
specifically steam generator integrity. Titanium and a variety of
stainless steel materials were evaluated, and ultimately titanium was
selected as the replacement condenser tube material for the rebuilt
condenser tube bundles due primarily to its corrosion resistance and
extensive operating experience in condenser service. An impressed
current cathodic protection system and epoxy waterbox coating was
also installed to prevent galvanic corrosion of the carbon steel
waterboxes. The cathodic protection system included local alarm
indication, to alert plant operating staff of any system malfunction
that could result in titanium hydriding. A . comparison of the heat
transfer characteristics of the existing condenser design with
Admiralty tubes and a new tube bundle design with titanium tubes
concluded that a new tube bundle design was required to optimize
the condenser performance and accommodate the
INTRODUCTION
Arkansas Nuclear One, Unit 1 (ANO-1), an 883 Mwe PWR, was
licensed for commercial operation in 1974. The original
Westinghouse turbine/condenser system consisted of a singlepressure, dual exhaust LP turbine exhausting to two, single
pressure, single pass surface condensers.
A condition assessment of the original condenser was performed
in 1995 which revealed the condenser had experienced several types
of tube degradation during the 22 years of previous service. The
failure mechanisms present in the ,condenser included: uniform ID
erosion, steam impingement, ammonia grooving, intergranular
corrosion, vibration damage, circumferential cracking, localized corr
osion, ID pitting, and mechanical damage. The most significant of
these was the circumferential cracking at or near mid-span between
support plates. The primary cause for this condition was increased
tube vibration due to uniform ID erosion. During this condition
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assessment, the average wall loss of the condenser tubes was
measured to be 34% less than the originally supplied tube wall
thickness. Even more significant, the erosion rate was estimated to be
1.7% annually.
In addition, copper deposition throughout the secondary system
from the Admiralty condenser tubing was detrimental to the integrity
of the steam generator tubing. Also, the secondary chemistry pH
suitable for the Admiralty tubing resulted in higher secondary
corrosion rates and more iron transport to the steam generators.
Finally, the adverse effects of circulating water contamination was a
threat to secondary chemistry limitation and damaging to the steam
generators.
After an exhaustive evaluation of all viable alternatives, it was
decided that the existing Admiralty condenser tubes and Muntz
tubesheets should be replaced with a new tube bundle design
utilizing titanium tubes and tubesheets. This evaluation considered
numerous other non-copper alloys ranging from 316L stainless steel
to AL6XN. The primary factors used to evaluate each material were
material compatibility with the site's brackish cooling water, initial
and future maintenance costs, plant performance, industry operating
experience and probable failure modes (corrosion, under deposit
pitting, biological fouling, etc.). It was further determined that this
replacement would be accomplished using shop fabricated tube
bundles and waterboxes to minimize required installation time. Each
tube bundle was to be completely shop assembled and thoroughly
tested before being shipped to ANO-1 for installation. In addition to
compensating for the difference in the thermal conductivity between
Admiralty and Titanium, the replacement condenser design was
required to optimize condenser performance at the contemplated 8%
power uprate condenser duty. Refer to Table 1 for comparative
performance requirements.
Also, the physical size and weight of the tube bundles presented
the project with many transportation and installation challenges.
These challenges necessitated an extraordinary level of coordination
between the various entities involved in this condenser tube bundle
and waterbox replacement project. The limited installation window
available with the scheduled refueling outage further enhanced this
level of coordination.
gauge titanium tubing in order to alleviate tube vibration during full
load operation with one bundle out of service.
New condenser waterboxes were designed to facilitate
installation, improve flow distribution to the tubes, and minimize
pressure drop. This was the critical interface piece between the new
condenser bundles and the existing circulating water piping in the
plant A sophisticated Finite Element Analysis program verified the
structural integrity of the new waterboxes, and subsequent shop
hydrostatic testing confirmed the results. Waterboxes were equipped
with an impressed current cathodic protection system and internal
epoxy coating to prevent galvanic corrosion of the carbon steel
surfaces.
The new titanium tube bundles were more erosion resistant, with
better deaeration capabilities. However, their lighter weight in spite of
a more compact tube field necessitated a thorough uplift analysis to
evaluate the integrity of the existing anchor bolts and the necessity for
additional anchoring.
The condenser bundles were fabricated to high quality standards
in a controlled shop environment Several shop mock up tests were
performed to determine the optimum tube pull out load, and the
required wall reduction for the rolled tubes. Prior to rolling and
welding, 100% base line eddy current testing of the tube bundles was
completed. Results of this test were stored on several tapes and were
submitted to ANO. Future in service eddy current examination can
be made and compared to base line results to determine wear.
All tube ends were rolled and welded using automatic welding
machines. Tube welds were checked for integrity using dye
penetrant testing, and also vacuum leak testing to verify the integrity
of the tube joints and the entire tube length. Once pronounced
sound, condenser modules were wrapped in specially designed tarps
and shipped to the site.
Figure 1 details the overall size and weight of one of the four
replacement condenser tube modules, and Figures 2, 3, and 4, show
the bundle manufacturing process at several stages.
BUNDLE TRANSPORTATION
With the massive size and heavy weight of each titanium tube
bundle, transportation logistics became a significant issue.
The Departments of Transportation in several states had to be
contacted to assure that roads, highways, and bridges would be
available for this transport Special permits and full time escorts were
required from the manufacturing plant to the job site to assure safety
and security of all involved. Limited height was a critical element
throughout the transportation route. Rail transportation was out of
the question due to oversize weight and dimensions, and truck
transportation was the most viable alternative at the time of shipment
Figure 5 shows how the trunnions welded into the bundles were
supported by the longitudinal "r beams, and Figure 6 shows the
special trailer arrangement developed for this transport purpose.
Essentially it could be celled a "double-pole" trailer where two
specially designed "r beams almost 15-f (4.6m) apart supported the
tube bundle suspended between them. The special trunnions
supported the tube bundle, reducing its overall height above the road
as much as possible. Since only one such special trailer was built, it
had to make four round trips from the manufacturing facility to ANO
to complete the delivery project. Waterboxes were shipped separately
to maintain the overall schedule and to keep bundle transportation
within allowable size and weight limitations.
MODULAR TITANIUM BUNDLE DESIGN
The design optimization program had to consider the required 8pereant power uprate utilizing the existing dreulating water system
while producing an efficient turbine output The difference between
the hestYtransibr coefficients of the original Admiralty tubing and the
new rolled/welded I inch (25. mm) diameter, 24 BWG and 22 BWG
titanium tubing (ASTM B338, Or. 2) provided a significant challenge
in the design of the new condenser bundles.
With the external envelope of the condenser intact, the condenser
design optimization had to consider several key elements.
Assessment of the existing circulating water pump capacity against
condenser backpressure with the new bundle design was of utmost
importance. Multiple cases of thermal/hydraulic design
combinations were analyzed balancing the circulating water system,
optimizing pumping efficiency, cooling water usage, MW output,
and hardware cost. Evaluation of the space constraints within the
existing condenser provided the final interface requirements with the
new modules. Spacing of the new support plates was reduced
considerably with the lighter
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PROJECT INSTALLATION
The installation phase of the condenser tube bundle and
waterbox replacement project presented numerous challenges for
the project team.
The first challenge was completing the condenser replacement
within the scheduled refueling outage duration of 42 days and 1
hour. This limitation affected every decision made on the project
from the beginning of the project.
The second challenge was the physical location of the
condenser, which was 19 feet below ground level. The only existing
access to the area was through a condenser tube pull pit, which was
approximately 10 feet shorter than the condenser tube bundles. To
provide access to the existing condenser shells, a large opening was
made in the side of the turbine building, which included the
removal of structural steel, interference piping and electrical
interferences. Figure 7 shows the bundle transportation at the site,
and the available access route to the condenser portal. Figures 8 and
9 shows the opening in the turbine building wall and the elevation
of the existing condenser shells relative to ground level. Figure 10
shows insertion of one of the tube bundles into the turbine building.
The third challenge was the proximity location of several
interferences outside the turbine building which greatly restricted
access to the condenser area. These interferences include the main
transformers and startup transformer #2 and associated electrical
buss ducts and 500 KV and 261 KV overhead power lines (Fig. 7).
These interferences precluded the use of a large crane to rig the
tube bundles into the tube pull pit. A specially designed gantry
crane capable of lifting, translating and rotating each tube bundle
was designed and assembled over the tube pull pit (Fig. 9). The
gantry included a specially designed lift frame that allowed the load
to be shifted while still suspended to locate center of gravity and
ensure that the tube bundles were kept level during the rigging
operation. The gantry also included a hydraulic turntable for better
control of the tube bundles while the bundles were rotated.
The fourth major challenge was the limited access to the
condenser inside the turbine building. To get the new tube bundles
and waterboxes into . the condenser, a large track was assembled in
the turbine building basement and extending into the condenser
shell (Fig. 8). Specially designed hydraulically powered rollers were
used in a load equalizing arrangement to ensure that each roller
shared 25% of the total.bundle load and to prevent damage to the
tube bundles. Also, specially designed carts were fabricated to allow
the replacement waterboxes to be moved into position through the
condenser shell using the rigging assembly available in the
condenser hotwell.
The fifth challenge was the removal of the existing condenser
tube bundles and waterboxes. After an extensive evaluation of all
available alternatives, it was decided that the existing condenser
tube bundles would be cut in half inside the condenser shell and
removed with waterbox attached. However, to move the tube
bundle halves with waterbox attached, each bundle would have to
be stiffened to allow the bundle to be both rolled out of the
condenser shell using the hydraulic rollers and lifted out of the tube
pull pit with the gantry crane.
The final challenge was estimating, planning, scheduling and
managing the resources and manpower required to complete a
construction project of this size with the available refueling outage
window.
CONCLUSION
The ANO-1 Condenser Project was successful in all phases of
the project including: initial condition assessment, project
feasibility study, competitive bid process, condenser re-design,
shop fabrication, bundle transportation and field installation. The
complete installation of the redesigned condenser tube bundles
and waterboxes was accomplished during the Fourteenth
Refueling Outage of ANO-1. The duration of the refueling outage
was 43 Days and 15 Hours. The Circulating Water Outage
required for the condenser replacement was 33 Days and 21 Hours.
Although a full ASME PTC 12.2 performance test was not
completed following the condenser tube bundle replacement, the
condenser backpressure for the redesigned condenser was
measured using plant instrumentation and the results indicated an
improvement of 0.19 inHg to 0.23 inHg when compared to the
backpressure of the original condenser at the same circulating
water temperature and condenser duty. To date, the replacement
condenser tube bundles have not experienced any in-service tube
leaks and unit has been operating reliably and efficiently.
REFERENCES
• Kurtz, S.A., Ward, R.L., Scluunerth, D.J., A Titanium Tubed
Modular Condenser Changeout at the Ravenswood
Generating Station, PWR — Vol. 12, Performance Monitoring
and Replacement of Heat Exchanger Components and
Materials, American Society of Mechanical Engineers, 1990.
• Heat Exchange Institute (HEI) Standards for Steam Surface
Condensers, Eight Edition - Addendum 1.
EPRI CS-3914 — Biofouling Detection Monitoring Devices —
March 1985
• EPRI CS-3844 — Condenser Procurement Guidelines — May
1985.
• EPRI CS-3200 — High Reliability Condenser Study — July
1983.
EPRI NP-2371 — Condenser Retubing Criteria Manual —
May 1982.
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