Sampling FFT data and converting to files

Hi to  whom it may concern, 

I am an amateur in the GNU Radio SDR project and would like to learn more for my work as a ground station Engineer from Singapore  working in a tertiary institution. I would like to learn how to convert FFT signals(500 sample points) to data streams and csv files as I need these data to be logged into a database .

The attached is the flowgraph . Unfortunately I am unable to upload the .csv file as it is too large . 

Regards,

CZ Chen,