[Mephisto]

A fusion reactor will not explode IIRC. To keep the plasma at the required temperature of several million ° Celsius you have to keep up a high degree of pressure. The moment the magnetic fields are distorted the pressure is released and the fusion reaction ceases. The temperature of the plasma declines dramatically. You get no explosion whatsoever and only the plasma may damage the reactor and the vicinity. But as I already said, with the magnetic field gone the plasma cools down imminently to the point were it isn't harmful any more to the reactor.
The BT rule crew was even aware of it but kept the catastrophic damage event in the rules for “eye candy” (it’s written somewhere in the rules).