What are the short-term consequence of a nuclear accident?

The only thing that can be said about the short term effects of a nuclear accident is that there is the possibility that some one might suffer from radioactive poisoning.
There are a number of different types of nuclear accidents, and the only thing they all have in common is the presence of radioactivity. The numbers of different types are probably too numerous to list. Some types include:

Nuclear meltdown
Accidental loss of nuclear waste
Loss in transit of nuclear materials
Accidental distribution of radioactive materials
Accidental exposure to radioactive materials that were improperly disposed of
Accidents in laboratories or hospitals.
Industrial accidents involving radioactive materials.

The International Nuclear Events Scale (link below) rates nuclear accidents according to severity, from 0 (a below scale event of no significance) to 7 (wide spread off site impact).
The Chernobyl Disaster is the only accident so far to have been rated 7.
The Kyshtym Disaster is the only one rated number 6, and it was not at a nuclear power plant, but rather a reprocessing facility.
Two of the three accidents rated 5 were at nuclear power plants (including Three Mile Island). The other, however, happened because radioactive materials were improperly salvaged from abandoned medical equipment, resulting in the deaths of several people, who thought the dust that glowed blue in the dark was pretty and used it as a cosmetic (GoiĆ¢nia accident).
A fair number of the so-called Radium Girls died, but they were not part of an accident that was rated because it preceded the term of the rating system. The short term effects were radiation poisoning, leading tot the deaths of several people.
A case of improper disposal of radioactive materials in New Jersey was also not rated. The materials were discovered because of cases of radiation poisoning leading to the deaths of three people. The site had to be cleaned up, a process on about the same scale as the decommissioning of a nuclear power plant.