The disaster was costly for Soviet Union. The clean-up work and the sarcophagus caused great costs in addition to hundreds of thousands of liquidators are getting ill with many different kinds of cancer. Additionally, their children are very sick and this is a real issue in Ukraine.
The disaster causes issues in other countries as well. The westbound wind aired the fallout to west. Belarus was worst affected, there are still places where man can not live. In Sweden and in Finland huge radiation levels were measured and at last the fallout landed to Central Europe.
The reason and the consequences are still under discussion. No-one seems to know, what really happened and what were the consequences. Some of the facts were faulty, like radiation figures. The basic reason was human error and inadequate technology and lack of professionalism. The biggest reason was perhaps the Soviet bureaucracy. The Soviets could not early enough intervene the missing security and the aftermath of the explosion.
Within the 30 kilometer diameter, the soil is contaminated useless, badly contaminated areas can also be found elsewhere in Ukraine and in neighboring Belarus and Russia. These areas got about 70% of the total radiation. Most of the radiation rained down to earth during that spring. But still these areas are populated with 800 000 inhabitants.
Cesium-137 is most dangerous radioactive substance of this accident. This substance has a half-life of 30 years. The traces can still be seen in Chernobyl and elsewhere, e.g. in game, fish, mushrooms and in berries.
The residents got radiation in their thyroid glands, due to radioactive iodine emissions. The main was inhaled during the first days after the accident, then later the dose was cause by food, mainly milk.
The United Nations estimates about 4000 people will die downright radiation caused cancers. This is contradictory to Greenpeace estimates of over 25 times larger figures. However, the thyroid cancer in children has increased in Ukraine's worst affected areas. 1800 of affected children have fallen ill with cancer already and ten have already died. Most of these cases could have been prevented, had the milk usage been prohibited after the accident and had the iodine pills been spread immediately.
A current Finn gets half of his/her yearly dosage of radiation from Chernobyl. Radiation from the food from the nature is not dangerous even on the worst affected areas in Finland. The radioactive fallout will be responsible for a few hundreds of cancer deaths within next 80 years. In the same time period, a million Finns will die in cancer for other reasons.