Framtome Magazin 4/02 - AREVA

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COMBO: A New System for
Continuous Measurement of
Boron Concentration
In PWRs, a boric acid solution
is added to the reactor coolant to
control reactivity. As core burnup
increases, the boric acid content
in the coolant is gradually reduced.
Monitoring of the boron concentration
in systems conveying reactor coolant
for purposes of reactivity control is
important for plant safety, particularly
when the plant is in the shutdown
condition and during core loading.
Framatome ANP has developed
a system called COMBO (continuous
measurement of boron concentration)
that is installed on a pipe or vessel,
with no system modifications necessary.
This makes COMBO ideal for backfitting
as well – in all types of PWRs.
On-Line Monitoring
Offers Advantages
Today, it is standard practice to
measure boric acid concentration in
PWR coolant on a non-continuous
basis via chemical analysis (titration),
necessitating extensive laboratory
support. However, continuous monitoring
has a number of advantages:
• On-line monitoring of boron
concentration in the reactor coolant
system and reactor auxiliary systems
enables operating crews to respond
much more rapidly to disturbances,
thereby delivering an important
safety enhancement.
• Plant economy is improved due to
shorter shutdown and startup
times, and to reduced personnel
and material resources.
Positive Operating
Experience Already Gained
in the Field
The system performed for the first
time at Grafenrheinfeld (Germany)
from 1996 to 1999. The measuring
equipment, characterized
by its small dimensions and ease
and speed of installation, was installed
directly on the main piping of the
volume control system.
A total of 18 COMBO systems
have been monitoring boron concentration
in the coolant treatment
and cleanup system at the VVER-type
PWR units, Mochovce 1 and 2
(Slovak Republic) since 1998 and
1999, respectively. Plants equipped
with VVER-type reactors, in particular,
have a greater need for boron
monitoring in the reactor auxiliary
systems due to the system design and
configuration specific to these plants.
A further COMBO system was
installed in 2002 at Isar 2 (Germany)
for monitoring the fuel pool.