This blog posted on June 3 that the Nuclear and Industrial Safety Agency revealed tellurium-132 had been detected 6 kilometers from the plant on the morning of March 12, before the venting of the Reactor 1.
Well, that Yomiuri Shinbun article in that post was incomplete, to say the least. It turns out that it was not only one location in Namie-machi where radioactive tellurium was detected but also at 3 other locations: one more location in Namie-machi, one location in Okuma-machi, and one location in Minami-Soma City.
Moreover, the same air radiation survey done by Fukushima Prefecture detected more volatile iodine-131 at half as much as tellurium, but it hardly detected any cesium-137 except at one location.
It's not supposed to happen that way, if what we've been told about the circumstance is correct, as a Kyoto University professor says in the article in Tokyo Shinbun, below.
(I'll go look for the information at NISA, and update if I find more data.)
Tokyo Shinbun (6/5/2011; emphasis added) reports the puzzling detection of tellurium-132 on March 12:
東日本大震災の発生翌日、福島第一原発で爆発が起きる前に福島県が行ったモニタリング調査で、金属性で飛散しにくい放射性のテルルが原発から約七 キロ離れた同県浪江町などで検出されていたことが分かった。拡散しやすい揮発性の放射性ヨウ素より多く検出されており、早い段階で金属性の放射性物質が広 く飛散していた。テルルはレアメタル（希少金属）の一種で、放射性同位体のテルル１３２の半減期は三日余り。主にベータ線を出す。
It has been revealed that radioactive tellurium, a metal that is hard to disperse in the atmosphere, was detected on the next day [March 12] of the earthquake in Namie-machi, 7 kilometers from the plant, and other locations according to the result of the monitoring survey done by Fukushima Prefecture before the explosion at Fukushima I Nuclear Power Plant that day. More tellurium was detected than more volatile radioactive iodine. It shows that metallic radioactive materials [like tellurium] dispersed wide from an early stage [of the accident]. Tellurium is a rare metal, and tellurium-132 has a half-life of about 3 days, emitting beta rays.
The data was revealed on June 3 evening by the Nuclear and Industrial Safety Agency. The monitoring survey of the air was done from March 12 morning till March 13 night, and the most of the data had been withheld until June 3. Tellurium-132 was detected from the morning till the early afternoon on March 12 at 2 locations in Namie-machi, and Okuma-machi and Minami-Soma City. The concentration was between 23 to 119 becquerels per cubic meter, exceeding the safety limit of 20 becquerels per cubic meter.
At that time, there was no air escaping the reactor building as the air exchange system had stopped. The venting to release the steam was done in the afternoon of March 12, and a hydrogen explosion [in the Reactor 1] happened after the venting.
TEPCO thinks that tellurium came from the Reactor 1 whose fuel core was most damaged, and explains, "As the pressure inside the Containment Vessel rose, tellurium, along with hydrogen, may have escaped from the joints [on the Containment Vessel]. The pressure inside the reactor building also rose, and then tellurium leaked outside the building and was carried by the wind and spread wide."
However, volatile and therefore more easily dispersed iodine-131 was detected at half the amount of tellurium. Cesium-137 was detected in one location in Namie-machi in the amount exceeding that of tellurium; however, at other locations, it was detected in only minute amount.
Associate Professor Toshihiro Yamamoto of Kyoto University Research Reactor Institute (reactor physics) says "Under the circumstance that we have understood so far, it is hard to believe that tellurium would spread far."
Well it apparently did, Mr. Yamamoto. Now what?