The reactor at Three Mile Island was a so-called light water reactor of a relatively early design. The capacity was 852 MW.
More about the accident can be seen here.
As a natural thing the reactor was protected by reactor containment.
Such a reactor containment, which usually is an about 2 meters thick reinforced concrete shell, is the last defense against the release of radioactive waste.

Here it proved to stand up to the test:
People within a radius of 15 km from the reactor were exposed to an average dose of 8 millirem (0.08 mSv).
Highest measured dose was 100 millirem (1 mSv).
This should be seen in the context of the natural background radiation, which we are all exposed to, is about 200 millirem (2-3 mSv) per year.

Such a core meltdown can under no circumstances evolve into just something towards a “nuclear explosion”.
It will require both highly enriched uranium and a very special “initiator”.
Yet it was not long before half of the American population had been convinced that such a threat was imminent.
A small crowd of journalists who perhaps had waited for some horror stories.
They had to go home disappointed.
As so often both Greenpeace and the lawyers were buissy.

Radioactive contamination

It is estimated that US coal burning in 1982 released 155 times as much uncontrolled radioactivity to the atmosphere as the Three Mile Island incident.

Evacuations and claims

There were some panicky evacuations and many claims for compensation.
Most, if not solely, for loss of income as a result of the unnecessary evacuations.
The private, but compulsory Price Anderson Act’s savings, covered as far as it can be seen all these costs.
These costs came to $ 70 million, of which 41% were “legal expenses”.
To put this amount in perspective I will mention that the US nuclear power plants annually pay $ 375 million to this private insurance-fund.

It may be worth mentioning that it was the first and the only time where a nuclear accident resulted in this form of payment.
When the savings accumulated in the Prince-Anderson “money tank” (0,01 US-cent/kWh) reached astronomic proportions, further payments has been suspenderet.

But the cleanup was expensive

On this link it is stated that the cleanup lasted 11 years and cost about
USD 1 billion.
This long time: 11 years is probably explained by a desire to wait until the worst radioactivity had subsided.