askST: Is it safe to travel to Japan after the Fukushima accident?

Reader John Davies wrote in to askST: "Is it safe to travel to Japan after the Fukushima incident, especially for women trying to get pregnant?"

Travel Correspondent Lydia Vasko answered the question.

The short answer is Yes.

It has been six years since the massive 9 magnitude Tohoku earthquake and subsequent tsunami along Japan's northeastern coast on March 11, 2011.

The event triggered a series of equipment failures and nuclear meltdowns at Fukushima Daiichi Nuclear Power Plant in what has become the world's worst nuclear disaster since the one at Chernobyl, Ukraine, in 1986.

For fear of radiation poisoning, more than 100,000 people have not been allowed to return to their homes inside a roughly 20km exclusion zone around the power plant. Whether these fears are well founded is currently a topic of debate among some nuclear scientists who say that the emotional trauma of families being uprooted from their ancestral homes is far worse than the effects of minimal radiation there.

Fukushima made headlines again recently when it was reported that robots had measured unprecedented levels of radiation, 530 sieverts, inside one of the nuclear reactors.

To put this into perspective, one dose of one sievert of radiation can cause radiation sickness and nausea; but exposure to five sieverts would kill half of those exposed to it within a month, and a person exposed to a single dose of 10 sieverts would be dead within weeks.

In this context, 530 sieverts is a very scary number. However, it is important to remember that the 530 sieverts was measured inside the nuclear reactor itself, and does not reflect the levels of radiation found in the rest of Japan.

Safecast, a global data-gathering organisation, has been using citizen volunteers to collect data on radiation and air quality around Japan since the Fukushima Daiichi disaster, when people felt that the Japanese government was not making accurate radiation information publicly available.

Volunteers use radiation detecting devices which record location and radiation and ping the data to Safecast every few minutes. Over 50 million readings have been collected to date, and members of the public can track the data on at Safecast.org, where radiation maps are published. People can search the maps by location to learn real time radiation levels in their area. They can even see where the sensor is located.

Because one sievert is a very large amount, radiation exposure is usually measured in millisievert (mSv) or microsievert (µSv) which are one-thousandth or one millionth of a sievert.

As of Thursday afternoon, May 25, the radiation level in the Roppongi district of Tokyo was 0.083 μSv/h, that is less than one millionth of a sievert per hour. In Kyoto, levels were slightly higher at 0.13 µSv/h, while in Fukushima prefecture, near the banks of Lake Inawashiro, levels were 0.111 μSv/h.

At the same time in Singapore, the National Environment Agency reported local radiation levels were normal at 0.1 μSv/h, the same levels as in Fukushima.

According to the International Atomic Energy Agency, a United Nations organisation to promote the safe, secure and peaceful use of nuclear technologies, on average, we are naturally and safely exposed to around 2.4 mSv of radiation every year. This could be higher, depending on one's lifestyle and where one lives. Radiation comes from building materials, particles in the air, food we eat, long-haul flights and the very earth beneath our feet.

There are, in fact, a handful of naturally occurring radioactive sites around the world. On beaches along a 800km stretch of Brazil's Atlantic coast, from north of Rio de Janeiro to the region south of Bahia, the sand was formed from local rocks which contain radioactive metals uranium and thorium.

On the beaches around Guarapari, a city of over 100,000 people and a popular tourist destination, up to 175 mSv of background radiation have been measured per year.

In Ramsar, Iran, a seaside vacation resort on the southern coast of the Caspian Sea famed for its medicinal hot springs, people live happily in areas which have radiation readings of around 250 mSv per year, one of the highest levels of natural background radiation on Earth.

In short, all this information means that travellers to Japan do not have to worry about radiation poisoning. The extreme levels of radiation are currently contained within Fukushima Daiici Nuclear Power Plant, and it is highly unlikely that exposure of less than one millionth of sievert of radiation per hour you will receive outside of the exclusion zone will cause any harm.

The Ministry of Foreign Affairs also does not have any travel warnings or advisories for Singaporeans travelling to Japan, either. So feel free to start planning your next trip to what is still one of the world's most mesmerising destinations.