Modeling of SPERT IV Reactivity Initiated Transient Tests in EUREKA-2/RR Code

EUREKA-2/RR code has been used for SPERT IV reactor benchmark calculations against the experimental results provided by IAEA (International Atomic Energy Agency) obtained for a series of transient tests initiated by step insertion of different magnitudes of positive reactivity with varying degrees of different controlled parameters such as reactor initial power, coolant temperature and coolant flow condition. 20 out of 39 tests that fall under forced convection mode have been considered for the present simulation provided the reactor scram system is disabled. Peak power and peak clad temperature due to transient have been calculated and it was found that although peak clad temperature values agreed, the peak power values seem to underestimate the experimental values. Further study appears to be needed to identify the limitations in modeling or examining the effect of input parameters during modeling to obtain the better simulation results.

Development of a Secondary SCRAM System for Fast Reactors and ADS Systems

One important safety aspect of any reactor is the ability to shutdown the reactor. A shutdown in an ADS can be done by stopping the accelerator or by lowering the multiplication factor of the reactor and thus by inserting negative reactivity. In current designs of liquid-metal-cooled GEN IV and ADS reactors reactivity insertion is based on absorber rods. Although these rod-based systems are duplicated to provide redundancy, they all have a common failure mode as a consequence of their identical operating mechanism, possible causes being a largely deformed core or blockage of the rod guidance channel. In this paper an overview of existing solutions for a complementary shut down system is given and a new concept is proposed. A tube is divided into two sections by means of aluminum seal. In the upper region, above the active core, spherical neutron-absorbing boron carbide particles are placed. In case of overpower and loss of coolant transients, the seal will melt. The absorber balls are then no longer supported and fall down into the active core region inserting a large negative reactivity. This system, which is not rod based, is under investigation, and its feasibility is verified both by experiments and simulations.