Evaluation of Safety Margin for Advanced Natural Circulation Reactor
A. Srivastava1,a, H. G. Lele1,b, A. K. Ghosh1,c and H. S. Kushwaha2
1Reactor Safety Division, BARC, Trombay, Mumbai 400 085, India.
aabhisri@barc.gov.in
bhglele@barc.gov.in
cccss@barc.gov.in
2Health, Safety & Environment Group, BARC, Trombay, Mumbai 400 085, India.
kushwaha@barc.gov.in
ABSTRACT
A natural circulation vertical pressure tube type boiling light water cooled and heavy water moderated reactor design is advanced in terms of safety philosophy. One of the important passive design features of this reactor is that the heat removal is achieved through natural circulation of primary coolant at all power level with no primary coolant pumps. The core of the reactor consists of 452 channels lying vertically in the pool of cold moderator. The inlet feeder feeds the subcooled liquid from ring inlet header to individual channel. Safety requirements of this reactor are specified in terms of limits on clad surface temperatures, system pressure etc.
This paper analyses Design Basis Accident (DBA) scenario i.e. postulated 200% break in inlet header to estimate safety margin for future power up rating. The present work involves first best estimate analysis with actual conditions which provides us Peak Cladding Temperature (PCT) for the nominal case. Further, a conservative evaluation of LBLOCA is done with various conservative boundary and initial conditions. This predicts a high PCT value. Then uncertainty analysis for the Large Break LOCA has been carried out for the PCT, based on the response surface technique followed by Monte Carlo method. The input uncertain parameters for the uncertainty analysis have been decided based on their importance to LBLOCA scenario and its impact on PCT. The finding of Best Estimate Plus Uncertainty (BEPU) is much lower compare to conservative PCT value. This provides us some safety margin, which can be further used for power up rating as desired.
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