Thermo-hydrodynamic design and safety parameter studies of the TRIGA MARK II research reactor

Abstract

The PARET computer code was used to analyse important thermo-hydrodynamic design and safety parameters of the 3 MW TRIGA MARK II research reactor at Atomic Energy Research Establishment (AERE), Savar, Dhaka, Bangladesh. The study involves the determination of the departure from nucleate boiling (DNB) value and studying its effect over the thermo-hydrodynamic design of the reactor. In the process the temperature profile, heat flux and pressure drop across the hottest channel of the TRIGA core were evaluated. The DNB ratio (DNBR), which is defined as the ratio of the critical heat flux to the heat flux achieved in the core, was computed by means of a suitable correlation as defined in PARET code. Over the length 0.381 m of the hottest channel the DNBR varies, starting from 3.8951 to 5.4031, with a minimum of 2.7851. The peak heat flux occurs at the axial centre of the fuel elements; therefore the DNBR is minimum at this location. The reactor core should be designed so as to prevent the DNBR from dropping below a chosen value under a high heat flux transient condition for the most adverse set of mechanical and coolant conditions. The loss-of-flow accident (LOFA) scenario of the reactor has also been studied to ensure that the existing design and procedures are adequate to assure that the consequences from this anticipated occurrence does not lead to a significant accident. The loss-of-flow transient after a trip time of 4.08 s at 85% of loss of normal flow for the TRIGA core shows a peak temperature of 709.22 °C in the fuel centreline and 131.94 °C in the clad and 46.63 °C in the coolant exit of the hottest channel. The transient was terminated at 15% of nominal flow after ∼48.0 s and the time at which the reversal of coolant flow starts is ∼67.0 s.