High concentration of radioactive materials with very short half-life, iodine-133 (half-life 21 hours) and xenon-133 (half-life 5.2475 days), was detected in the cooling water inside the Reactor Pressure Vessel (RPV) of the Reactor 2 at Tsuruga Nuclear Power Plant run by Japan Atomic Power Company (JAPC).
The amount of iodine-133 doubled from a week ago, and the amount of xenon-133 was 750 times as much as a week ago.
JAPC suspects there are minute holes in the cladding, through which the radioactive materials are leaking.
Tsuruga Nuclear Power Plant is part of what is dubbed as "Nuke Power Ginza" in Fukui Prefecture. There are 5 nuclear power plants in the region with total 14 reactors.
From the company's press release on May 2:
"The Reactor No.2 at Tsuruga Nuclear Power Plant (PWR, 1,160,000 kilowatt) was tested for iodine and noble gas during the regular operation on May 2, 2011 in the cooling water that circulates around the fuel rod clusters; xenon-133 and iodine-133 were found to be exceeding the previous test result of April 26 as follows:
5.2 Bq/cm3 (cubic centimeter) (April 26) to 3,900 Bq/cm3 (May 2)
2.1 Bq/cm3 (April 26) to 4.2 Bq/cm3 (May 2)
"Based on this result, we have determined that there is a possibility of a leak of radioactive materials from the fuel rod clusters, and we have decided to monitor the radiation level of the cooling water [by monitoring it every day, instead of once a week - the footnote No. 2 in the original document].
"Further, in order to identify the leaking fuel rods, we may shut down the reactor.
"There is no leak of radiation in the environment as the result of this event."
The Reactor 2 at Tsuruga Plant is in its 18th Cycle (of power generation) that started on July 12, 2010.