Advanced Nuclear Power - AREVA

Features
During the annual refueling
outage in June 2003 at the French
nuclear power plant Chinon Unit B1,
the steam generators were cleaned using
Framatome ANP’s High-Temperature
Chemical Cleaning (HTCC) process,
marking the first time that this process
had been deployed in France. The
quantity of deposits removed considerably
exceeded the initial estimates and,
when the plant was restarted, main
steam pressure was found to be
significantly higher.
The objective of the cleaning was
to improve steam generator integrity,
threatened by corrosion (intergranular
attack/stress corrosion cracking) mainly
at the first tube-to-tube support plate
intersection, and to enhance steam
generator thermal performance.
Framatome ANP’s HTCC process
was chosen because of its extensive
and widely acknowledged industrial
references, its effectiveness for
controlling corrosion of steam generator
Visual inspection – tubesheet
Visual inspection – flow
distribution plate
Chemical Cleaning Improves
Steam Generator Performance
Deposits
removed [kg]
Max. amount
predicted [kg]
Magnetite Copper
Deposit removal exceeds projections
structural materials, its low impact on
the critical path of plant outages and
the small amount of waste produced.
Two-Step Process
Produces Good Results
The HTCC process consists of two
steps: one applied at high temperature
to remove iron oxides, followed by
a second step at low temperature to
remove copper deposits. After the
copper step, a final rinse is performed.
On-site cleaning was preceded by a process
qualification and engineering phase
lasting nearly a year to tailor the process
to plant-specific needs and conditions
at the Chinon B1 steam generators.
The steam generator cleaning at Chinon
B1 took a total of 18 days, with only
4 being on critical path. These were
for the high-temperature iron-removal
step performed in the three steam
generators one after the other, each of
these operations taking 15 to 20 hours.
After the steam generators had been
cleaned, approximately 30 percent more
deposits had actually been removed
than initially predicted. No corrosion
of the steam generator tubes or any
high-alloy materials was found. The
associated base metal removal on
carbon steel surfaces remained within
the accepted and qualified limits.
Metal
Total
Salts
oxides removed
6818 563 707 55.1 8 145
5146 372 - 434 595 – 6 200
Difference + 1672 > + 129 + 112 – + 1945
Post cleaning results showed marked
improvement in steam generator thermal
performance. In fact, after plant restart,
main steam pressure was significantly
higher, although it was not possible to
completely restore it to its initial level
since a large number of steam generator
tubes in all three steam generators had
to be plugged during the outage due to
steam generator tube inspection findings.
After HTCC, non-destructive examinations
revealed the presence of residual
copper on the bottom part of many tubes
in the three steam generators. Copper, in
metallic form (conductive deposit),
disturbs eddy current signals, affecting
in-service inspection performance.
The elimination of deposits from the
lower sections of the steam generator
tube bundles and from flow-restricted
areas is expected to have a beneficial
effect on future secondary-side corrosion
behavior. This forecast is to be confirmed
by the next steam generator tube
inspection results.
Further Projects Upcoming
Based on the results of this first French
HTCC project using Framatome ANP
German and French crews, Electricité
de France (EDF) is considering
applying this process at other plants to
improve steam generator thermal
performance.
22 Advanced Nuclear Power N O 11 November 2004