and 43% of the schools are located in Yokohama City alone.
From Asahi Shinbun (3:02AM JST 8/11/2011):
放射性セシウムに汚染された疑いのある牛肉を給食に使っていた学校や幼稚園が１２都県の２９６施設に上ることが、文部科学省の調 査で分かった。うち２校では国の暫定基準値を超えるセシウムを検出。健康に影響はないとみられるが、文科省は食材の出荷制限などの情報に注意するよう学校 現場に呼びかけている。
The survey by the Ministry of Education and Science has revealed that 296 schools in 12 prefectures have used beef from cows suspected of radioactive cesium contamination. 2 schools used the beef whose cesium level exceeded the provisional safety limit. It is not considered the level of cesium in the meat will affect health, but the ministry is telling the schools to pay attention to information on shipping restriction on food items [due to radiation].
文科省によると、９日現在で、汚染され た稲わらを食べた可能性のある牛の肉は、東北から中国、四国にかけての２０市町の小中高・特別支援学校２７８校と幼稚園１８園の給食で、カレーや牛丼、肉 じゃがなどに使われていたことが判明。横浜市で１２７校、岐阜市で５３校・園、宮城県の４市町では３０校・園に上る。東日本が主だが、三重、島根、香川の 計４市４０校・園でも使われていた。
According to the ministry, as of August 9, the meat from the cows that may have eaten radioactive rice hay was used in school lunches in 278 elementary schools, junior high schools, high schools, and special education schools, and 18 kindergartens, in 20 cities and towns in Japan. 127 schools in Yokohama City used it, so did 53 schools and kindergartens in Gifu City [in Gifu Prefecture], and 30 schools and kindergartens in 4 cities in Miyagi Prefecture. The schools are mostly located in eastern Japan, but 40 schools in 4 cities in Mie, Shimane, Kagawa Prefectures also used the meat.
在庫の肉を検査できた約３０施設のうち、放射性物質が 検出されたのは８施設。うち宮城県の特別支援学校と千葉県の小学校の計２校では、国の暫定基準値（１キロあたり５００ベクレル）を超える１２９３～６４９ ベクレルが検出された。ただしいずれの自治体も、１人あたりの肉の使用量は少なく、健康への影響はないとしている。
30 schools were able to test the remaining meat, and radioactive materials were detected at 8 schools. Of the 8 schools, two schools - a special education school for students with disabilities in Miyagi Prefecture and an elementary school in Chiba, had the meat that exceeded the provisional safety limit (500 becquerels/kg of radioactive cesium), testing 1,293 to 649 becquerels/kg. The municipalities say the amount of contaminated beef per person is small, and it won't affect the health.
In the meantime, the Food Safety Commission under the Cabinet Office is soliciting public comments (in Japanese alone please, says the Commission) on their detailed justification for their decision to set 100 millisieverts for life-time allowable radiation exposure for the Japanese. If you read their conclusion, you would think there would be no problem with any of the nuclides that have been released from the broken nuclear power plant in Fukushima. (More later.)