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ADS Safety Analyses

Currently different designs for an ADS are under investigation. The maximum incineration rate for an ADS would exist in a system with pure MA fuel (dedicated fuel) and without any fertile material as U238 or Th232. The use of pure dedicated fuel leads to a deterioration of safety parameters in the core.

In the following some typical results are displayed for comparing the core behavoir of a dedicated ADS with a thorium fueled ADS under transient and accident conditions.

 

Comparison of core behavoir for transient conditions:

  Comparison of a beam transient (source strength nominal, doubled, switched off and on) in an ADS reactor core either with dedicated fuel or U233/Th232 oxide fuel

 

  Comparison of a reactivity transient within the subcriticality margin in an ADS reactor with dedicated fuel and U233/Th232 oxide fuel

 

Comparison of core behavoir for accident conditions:

 

  Mechanistic simulation and nuclear power trace of an unprotected (beam-on) LOF in a thorium core

  Mechanistic simulation and nuclear power trace of an unprotected (beam-on) LOF in a dedicated core

 

Current analyses show that there might exist a safety problem for a transmuter ADS with pure MA fuel (Am, Cm) and that power transients could occur under unfavorable conditions. The thorium core in contrary behaves benign even in the case of core melting and disruption.

Proposals are currently made and investigations are performed to assure the safety of an ADS with dedicated fuel. Inherent and passive safety measures should be implemented and strengthend to prevent severe transients and/or mitigate consequences. To cope with the possibility of accidents in an ADS e.g. fertile material could be introduced. Also the ideas concerning passive beam stoppers and proposals investigated in the critical cores related to controlled material relocation (CMR) are investigated if they can be implemented into the ADS safety strategy.

 

FURTHER INVESTIGATIONS OF PDS-XADS

Within the 5th Framework Program of the European Union the so-called Preliminary Design Studies of an Experimental Accelerator-Driven System (PDS-XADS) are performed by Ansaldo. The configuration of this ADS and its core arrangement are shown in the following figure. For the safety investigations, the SIMMER-III code has been adapted to the needs of describing a sub-critical core with a strong external neutron source, a treatment of Pb/Bi flow and requirements of other ADS specifics.


Recently two studies of unprotected transients are carried out. One deals with unprotected loss of flow transient (ULOF) and the other is concerning reactivity perturbations, namely, the beam trip (BT), unprotected transient over current (UTOC), and unprotected transient over power (UTOP).