Bulletin 2/2010 - Siempelkamp NIS

SIEMPELKAMP | NUCLEAR TECHNOLOGY
Main screen with overview
and operating map
In 1994 NIS supplied the Gundremmingen nuclear power plant
with a core simulator which was completely replaced two years
ago. After the refueling cycle was completed, NIS had to ensure
that the simulator was correctly coupled to the fuel assemblies
inside the reactor core.
In this way, NIS does its share in making sure that the power
plant can supply a large city like Munich and the surrounding
communities with electricity for one year.
One power plant unit has a capacity of 1,340,000 kW which
would be enough to supply e.g. 1.34 million hot plates of an
electric kitchen stove with electricity.
Together with other monitoring and control systems, the NIS
core simulator makes its contribution to a safe, reliable, and economical
electricity generation. This is reason enough to take a
closer look at the core simulator concept.
Core simulator: a sophisticated system
The core simulator is a computer system that simulates the reactor
core. By doing so it monitors the physical properties of the reactor.
Inside the nuclear reactor a neutron collides with a uranium isotope.
During this collision, the uranium absorbs the neutron,
fi ssions into two smaller isotopes releasing two to three additional
neutrons. The fi ssion process, which takes place inside the fuel
rods fi lled with uranium pellets, produces energy. The fuel rods
become hot. Consequently, the water (cooling element) sur-
rounding the fuel rods becomes hot and begins to boil. The
generated steam spins the turbine and drives the generator.
If a fuel element becomes too hot in one area, it becomes
unusable. This means there is a maximum temperature for the
fuel element that cannot be exceeded. This temperature, however,
cannot be measured, only computed.
This is when the core simulator comes into play: Its primary part
is a program that computes the neutron distribution and the resulting
heat generation inside the nuclear reactor. This program
simulates the resulting heat generated for each of the approx.
72,000 fuel elements inside the 784 fuel assemblies, which make
up the core, in 24 axial planes. The program compares the results
with the allowable limit value and provides a warning if the calculated
results come too close to the limit value. All this happens
automatically. Every fi ve seconds the measured data is recorded
and no later than 30 seconds the results can be seen on the
screen.
The perspective of the reactor operator:
everything at a glance
In reality the core simulator supports the reactor operator with
the challenging day to day tasks. The reactor operator has the
core simulator directly on screen in front of him. A green bar on
the overview image means everything is under control.
Let‘s look over the shoulder of the reactor operator onto
the main screen: At the top right-hand side you can see the
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