A MODEL FOR LOW VOLTAGE BREAKDOWN OF THE INSULATORS OF THE REACTOR’S WIRING SYSTEM

Operational Safety Dept., National Center for Nuclear Safety

The important deterioration phenomenon for the insulators is electrical damage to its surface

in the presence of high humidity and contamination, possibly aggravated by high radiation

doses. A model has been developed which predicts, the probability of an electrical breakdown

for different temperatures and protective measures. In this model, breakdown proceeds in

three steps: (i) breakdown current which determines the irreversible onset of breakdown, (ii)

average leakage current, i.e., time averaged and experiment averaged for each essential

parameter combination, and (iii) the probability of complete breakdown which is the ratio of

average leakage current to breakdown current. Expressions for each of these steps have been

introduced. In part of the experiments, a protective enclosure with a small weepholes has been

provided for the insulating terminal blocks of the wiring system of the reactor. The

experimental breakdown probabilities for protected and for unprotected terminals have been

calculated.