Thermal safety of Cirus graphite reflector under transient conditions

Full text: The 40 MW (th) research reactor Cirus uses graphite as reflector which is air-cooled. To ensure safety of the irradiated graphite reflector having stored Wigner energy, thermal analysis was required for confirming adequacy of the graphite cooling under any design basis transient including an unlikely event of an accidental release of Wigner energy based on the measurements of Wigner energy and its release rate from irradiated graphite samples of Cirus by differential scanning calorimetry (DSC) studies and the observed graphite temperatures under various steady state and transient conditions, thermal analysis of the irradiated graphite reflector were carried out using finite element method (FEM). The present paper details results of thermal safety analyses by FEM based thermal model along with its predicting capability and observations made during high power reactor operations. It also presents measures taken for detailed temperatures monitoring of the graphite reflector and reliable cooling of the reflector towards safe reactor operation after refurbishment