By David Owen in Buenos Aires

Tokyo 2020 has sent a letter to IOC members in an attempt to quash concerns about the Fukushima nuclear accidentSeptember 4 - Tokyo 2020 has sent a letter to all 100-plus International Olympic Committee (IOC) members seeking to allay concerns about the Fukushima nuclear accident.

With key Olympic decision-makers gathering here in Argentina's capital to decide the host of the 2020 Olympic and Paralympic Games as part of the most important IOC Session for at least a decade, the persistent, some would say darkening, shadow cast by Fukushima is a leading talking-point.

The letter suggests strongly that, for all the bid's public protestations that life carries on as normal in Tokyo and that they are "totally focused" on delivering a "superb and safe" Games in 2020, bid leaders are privately concerned about the possible impact the issue might have on a very tight race.

The Japanese city is up against Istanbul and Madrid for the honour of succeeding Rio de Janeiro as Summer Games host, with IOC members due to make the decision on Saturday (September 7).

Shinzō Abe has pledged ¥47 billion for an ice wall around the Fukushima nuclear plantShinzō Abe has pledged ¥47 billion for an ice wall around the Fukushima nuclear plant

Word of the letter comes as the Japanese Government announced it was to earmark an estimated ¥47 billion (£302 million/$473 million/€358 million) to build a frozen wall around the stricken plant, which was crippled by the 2011 earthquake and tsunami, to stop leaks of radioactive water.

A spokesman said the Government "felt it was essential to become involved to the greatest extent possible".

Japanese Prime Minister Shinzō Abe is expected to arrive in Argentina shortly and to spearhead the Tokyo delegation's final push in the hours before Saturday's key vote.

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