Worlds deadliest weapons!

Satan II
Effects radii for 40 megaton airburst* (smallest to largest): ▼

Fireball radius: 4.23 km (56.1 km²)
Maximum size of the nuclear fireball; relevance to lived effects depends on height of detonation. If it touches the ground, the amount of radioactive fallout is significantly increased. Minimum burst height for negligible fallout: 3.8 km.

Radiation radius (500 rem): 4.67 km (68.5 km²)
500 rem radiation dose; without medical treatment, there can be expected between 50% and 90% mortality from acute effects alone. Dying takes between several hours and several weeks.

Air blast radius (20 psi): 9.65 km (292 km²)
At 20 psi overpressure, heavily built concrete buildings are severely damaged or demolished; fatalities approach 100%. Optimal height of burst to maximize this effect is 6.22 km.

Air blast radius (5 psi): 23.8 km (1,780 km²)
At 5 psi overpressure, most residential buildings collapse, injuries are universal, fatalities are widespread. Optimal height of burst to maximize this effect is 10.7 km.

Thermal radiation radius (3rd degree burns): 56 km (9,840 km²)
Third degree burns extend throughout the layers of skin, and are often painless because they destroy the pain nerves. They can cause severe scarring or disablement, and can require amputation. 100% probability for 3rd degree burns at this yield is 13.5 cal/cm2.

That's a 'very' nasty weapon, look at that 23.8kms 'RADIUS' and most buildings knocked over.  That's beyond madness.  It's also highly improbable that anywhere in Australia would be a high enough priority for such a weapon, even if they built 100 of them [unlikely].