We, Tokyo Electric Power Company, have been observing the water level of 
the spent fuel pool of Fukushima Daiichi Nuclear Power Plant Unit 4 since
April 22nd, 2011. In the course of the observation, we collected 150ml 
pool water on April 28th.
As a result of nuclide analysis of radioactive materials contained in the
pool water on April 29th, radioactive materials were detected as shown in
the appendix. 
We will further evaluate the matter in detail. 

Appendix: Results of analysis of spent fuel pool water of Fukushima 
          Daiichi Nuclear Power Plant Unit 4 (Update) (PDF 10.2KB)