Reactivity accidents analysis during natural core cooling operation of ETRR-2

One of the main features of Egypt Test and Research Reactor Number 2 (ETRR-2), MTR type, is a continuous steady-state operation at low power level, <=400 kW, with core cooling by natural water circulation. Two ¯apper valves mounted on the return core cooling pipe lines and long chimney encloses the reactor core and assure natural convection phenomena through the reactor core and reactor pool. Many tests and experiments are carried out during this state of operation. A possible occurrence of reactivity insertion accidents (RIA) may be expected over this operation. The present work studies two types of possible RIA: 1-fast reactivity insertion accident (FRIA) with rate 1.04$/s and 2-slow reactivity insertion accident (SRIA) with rate 0.023$/s which may occur due to fast/slow withdrawal of a control rod or sudden cooling of the core inlet water temperature. Failure or success of the reactor scram system during the transient operation is considered. A computer code TRAP22 is developed for such analysis. It is veri®ed against CONVEC code and commissioning tests for steady state opera- tion. The results of veri®cation show good agreement. The study demonstrates that the reactor can be scrammed safely due to either FRIA or SRIA, whenever the maximum expected hot channel HC clad temperature lies within the range 70.73±71.85 C. While, in case of failure of scram system the maximum (HC) clad temperature reaches the burn out value at time 1.175s for FRIA and at 46.36s for SRIA. At the burn out point the clad surface heat ¯ux exceeds its design critical value which results in partial fuel melt.