For participants from abroad, it will take 80 minutes or so from the Narita airport to the Wako-shi station, depending on the connection. (you can find connections and time in http://www.jorudan.co.jp/english/ )

The following is the information for the access from the Narita airport to the RIKEN campus. 

From the airport to the RIKEN campus;
http://www.riken.jp/engn/r-world/riken/campus/wako/index.html

Although there are several options to come to RIKEN, one way I usually do is;

Stations                     : Company etc.                   :  Notes
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Narita --> Nippori      : Keisei, Narita skyliner     :  Using Narita skyliner ( http://www.keisei.co.jp/keisei/tetudou/skyliner/us/ ) needs to buy a ticket for a seat at a place shown in http://www.keisei.co.jp/keisei/tetudou/skyliner/us/findus/index.html

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Transfer to the Yamanote Line (a line colored with green in http://www.jreast.co.jp/e/info/map_a4ol.pdf ) at the platform 11 of the JR Nippori station (Map of Nippori Station; http://www.jreast.co.jp/e/stations/e1184.html )
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Nippori --> Ikebukuro : JR, Yamanote (inner track) : Ikebukuro is the sixth stop

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Transfer to the Tobu-Tojo line (Map of the Ikebukuro station; http://www.jreast.co.jp/e/stations/e108.html ) All the trains except "TJ Liner" stop at the Wako station ( http://www.tobu.co.jp/foreign/tobulineguide/pdf/tobutojoline.pdf )
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Ikebukuro --> Wako-shi   : Tobu-Tojo                             

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Wako-station has only one place of the ticket gates. After going through it, please turn to the left. Then, you are facing towards to the direction to the RIKEN campus (south). After that, please follow the middle inset of the first figure in http://www.riken.jp/engn/r-world/riken/campus/wako/index.html .
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