ABSTRACT

In this work, the effect of inadvertent control rod withdrawal on the thermal-hydraulic parameters of VVER-1200 type nuclear power reactor has been investigated. Personal Computer Transient Analyzer (PCTRAN) has been used to simulate the transient responses associated with the situation. An attempt has been made to find out the maximum amount of positive reactivity that may be inserted instantaneously without causing serious damage to any of the essential reactor components. Four instantaneous positive reactivity insertion case studies have been performed in the range of 2.5-10% Δk/k in order to identify the limiting condition for ensuring safety of the nuclear facility. Results show that for all the cases, prompt criticality is observed due to positive reactivity insertion higher than 0.66% Δk/k. For positive reactivity insertion up to 7.5% Δk/k, the maximum core thermal power is observed to be less than 160% of the rated core thermal power. The peak cladding temperature is observed to be less than 800oC with no clad failure. However, for 10% Δk/k reactivity insertion, core thermal power has been observed to reach nearly 360% of the rated core thermal power. Also, a 76% probability of cladding failure is recorded due to peak cladding temperature reaching nearly 1400oC. To identify the maximum limit of instantaneous positive reactivity insertion, a “Factor of Safety” based analysis has been conducted. Results from the analysis reveal that maximum limit is around 8.8% Δk/k. This finding is supported by the results from further simulations.

KEYWORDS

Cladding Failure, Core Thermal Power, Positive Reactivity Insertion, Transient Response, VVER-1200.