During mid-seventies, a need was felt for a research reactor with higher neutron flux to meet the growing demands for radioisotopes and research in basic sciences and engineering. In view of this, a 100MW (thermal) research reactor was constructed. It is heavy water cooled, moderated and reflected thermal reactor, employing metallic natural uranium as fuel.
Reactor core components were designed by seismic coefficient method as per the national standard IS 1893 and as per the safety requirement provisions prevailing that time. Present requirement is to qualify the facility as per the Design Basis Earthquake currently being used for BARC facilities. As per this requirement, core components of the reactor have been re-evaluated for present loadings. Three dimensional finite element model of calandria vault along with calandria vessel, annular shield assembly, end shield assembly, coolant channels, deck plates, inlet plenum, upper sub-shell, top plenum and upper sub-shell extension has been made for seismic re-evaluation. Static and response spectrum analysis has been performed to evaluate the stresses due to dead weight, imposed load, thermal load and seismic loads. The stresses due to various loadings and their combinations have been compared against the allowable stresses as per ASME Section III Division 1 and found within the limit.

Keywords: Seismic, Decoupling, Floor response spectra, Response spectrum.