You can refer to the IAEA technical reports concerning Fukushima and Chernobyl

Some information that could help in answering your question.

A lot of media outlets first made the Fukushima-Chernobyl comparison back in April, when the Japanese revised their estimate of the Fukushima accident—rating it a seven on the seven-point international INES scale. A couple of things have changed since those first reports. First, the Japanese doubled their estimate of the radiation released by Fukushima in June to 7.7×1017 Becquerels (Bq). With the new Cs-137 data, we can now directly compare the fallout from Chernobyl to Fukushima. The first thing that you can see is that Chernobyl is indeed quite a bit bigger. In fact, the permanent exclusion zone encompasses most of the Fukushima fallout map. If Fukushima had been a Chernobyl-scale crisis, significant amounts of radiation would have spread all the way up to Iwate Prefecture, and depending on the winds, it’s not inconceivable that Tokyo might have been hit with serious levels of fallout.

But that’s not the whole story. If Chernobyl had happened over Japan, much of its Cs-137 contamination would have ended up in the Pacific. Similarly, a good deal of the Fukushima fallout isn’t seen here because it has blown out into the ocean. Indeed, the total estimate delivered to the International Atomic Energy Agency in June states that Fukushima has released 1.5×1016 becquerels (Bq) of Cs-137—about a fifth of the Cs-137 from Chernobyl. The total radioactive release from Fukushima is currently estimated at about 5.5% of Chernobyl, which spewed an incredible 1.4×1019Bq.

The Fukushima fallout is notable for what it doesn’t contain. Some very nasty contaminants like strontium-90, americium-241, and various plutonium isotopes are all absent in any significant quantity because the concrete vessels around the reactors appear to be largely intact. In Chernobyl, the explosion and subsequent fire spewed these extremely dangerous isotopes far and wide.

The bottom line here is that Fukushima and Chernobyl are comparable, and a comparison really helps underscore the differences. Fukushima’s heavy containment vessels limited the spread of some dangerous isotopes, but the coastal location makes marine contamination a much bigger issue than it ever was for Chernobyl. The fallout of radioactive Caesium from Fukushima already rivals Chernobyl. Radioactive caesium and iodine have been deposited in northern Japan far from Fukushima at levels that were classified as highly contaminated after Chernobyl. The readings were taken by the Japanese science ministry, MEXT (Ministry of Education, Culture, Sports, Science and Technology), and reveal high levels of caesium-137 and iodine-131 outside the 30-kilometre evacuation zone, mostly to the north-north-west. Radioactive caesium is one of the main dangers from the Japanese nuclear accident. Over the longer term, the big threat to human health is caesium-137, which has a half-life of 30 years. At that rate of disintegration it takes over 200 years to reduce it to 1 percent of its former level. It is caesium-137 that still contaminates much of the Ukraine area around the Chernobyl reactor which is designated as a dead zone. Caesium-137 mixes easily with water and is chemically similar to potassium. It thus mimics how potassium gets metabolised in the human body and can enter through many food chains, including cows grazing in the countryside and the milk they produce. The relatively low levels as defined in a glass of milk or a bowl of spinach are deceptive because this radioactive contamination is bioaccumulative, especially in mammals, and grows with each additional exposure over long periods of time.

After the 1986 Chernobyl accident, the most highly contaminated areas were defined as those with over 1,490 kiloBecquerels per square metre (kBq/m2) of caesium. Agricultural produce from soil with 550 kBq/m2 was destroyed. People living within 30 kilometres of the Fukushima plant have evacuated or been advised to stay indoors. Since March 18th, MEXT has repeatedly found caesium levels above 550 kBq/m2 in an area some 45 kilometres wide lying 30 to 50 kilometres north-west of the plant. The highest was 6,400 kBq/m2, about 35 kilometres away, while caesium reached 1,816 kBq/m2 in Nihonmatsu City and 1,752 kBq/m2 in the town of Kawamata, where iodine-131 levels of up to 12,560 kBq/m2 have also been measured. [New Scientist]

What About The Plutonium MOX?"

• Reactor 3 suffered significant damage after the quake and the tsunami waves on March 11th;

• The roof of the building was destroyed by a powerful explosion ... caused by an accumulation of hydrogen;

• Reactor 3 raises the most concern since it runs on MOX or Mixed Oxide fuel -- a mixture of plutonium and uranium;

• MOX is far more dangerous than uranium on its own; and

• MOX is two million times more deadly than normal enriched uranium."

"What if the release of elements in the smoke and vapour were not just radioactive iodine, caesium and uranium but a MOX combination including plutonium?

• This would explain why the workers were immediately evacuated given the deadly nature of plutonium;

• Plutonium is extremely difficult to detect because it emits limited gamma rays -- unlike radioactive iodine, caesium and uranium -- and it is deadly;

• Plutonium release would not show up as a radiation spike;

• Plutonium 239 is the deadliest element known to man;

• Half-life of Plutonium-239 in MOX is 24,000 years: Few milligrams of P-239 escaping in a smoke plume will contaminate soil for tens of thousands of years; and

While radioactive iodine and cesium (half-life 8 days and 30 years, respectively) are the most immediate threats to human health, one of the plants is leaking plutonium having a half-life of 24,000 years. The “safe” levels of radiation quoted by authorities are generally what would be experienced standing next to the hot isotopes, but if these are ingested the consequences are much more severe. If one millionth of a gram of plutonium lands in a human lung, the individual gets lung cancer. Plutonium along with other radioactive isotopes is leaking through tunnels to the ocean where it will be distributed locally by currents, concentrated in fish, and distributed world wide by migratory fish.