the Square Mile another name for the City of London (= the financial and banking centre of London), used especially in news reports. It is called this because the area of the City is about one square mile.
a nuclear power station in Pennsylvania in the US, where there was a serious accident in 1979. The people in charge managed to prevent a MELTDOWN (= when the nuclear material melts and burns through its containers), but the accident increased opposition to nuclear power in the US and prevented new power stations from being built.