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Abstract
W.F.G. van Rooijen, J.L. Kloosterman, T.H.J.J. van der Hagen, and H. van Dam,
Li-6 Based Passive Reactivity Control Devices for a Gas Cooled Fast Reactor,
Nuclear Technology, accepted, 2006.
In this paper reactivity control devices for a Generation IV Gas Cooled Fast Reactor are discussed. The proposed
devices use liquid Li-6 as absorber. The device is triggered by a freeze seal, and upon activation, the Li-6 is
irreversibly introduced into the core region by pressure differences. The device is dubbed Lithium Injection Module (LIM).
Transient thermohydraulic calculations were done using the CATHARE2 code on a simplified thermohydraulic model
of GFR600, a 600 MWth GCFR investigated in scope of the European GCFR-STREP. The thermohydraulic model uses
an accurate model of the ceramic fuel plates, and includes natural convection Decay Heat Removal (DHR) circuits.
To properly account
for power production during the transient, a synthetic decay power curve was made based on the ANS-5.1 law.
Loss of Flow and Control Rod Withdrawal/Ejection transients are presented. Neutronic calculations show that the
LIMs have a low reactivity worth between -2.1$ and -1.5$. Inspite of their low worth, the LIMs are capable of
keeping the reactor power bounded during all calculated transients. Shutdown is not always achieved, depending
on the kind of transient under consideration. For pressurized Loss of Flow, re-criticality due to Doppler feedback
may become problematic in the natural circulation phase. For rapid control rod ejections, the resulting very fast
power transients cause concern for material degradation. One LIM would be enough to control reactor power, but
redundancy may call for more than one LIM in the core.
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