I doubt very much that any modern equipment uses tunnel diodes. Unlike other semiconductors, they have a limited life because of the very high doping density leading to further diffusion at room temperature.
The effects of RF are, as far is known and can be reproduced, limited to thermal effects. This means that the radar duty cycle (pulse length and time between pulses) comes into play, as does the length of time the exposure happens. For fuel ignition, there is a DEF STAN on the subject.
100 watts into a 20dB gain antenna gives 10kW ERP: however, there is only 100 watts available to heat somebody up.