The first European self-sustaining <a href="https://en.wikipedia.org/wiki/Nuclear_chain_reaction" id="mwAVI" rel="mw:WikiLink" title="Nuclear chain reaction">nuclear chain reaction</a> is initiated within the <a href="https://en.wikipedia.org/wiki/Soviet_Union" id="mwAVM" rel="mw:WikiLink" title="Soviet Union">Soviet Union</a>'s <a href="https://en.wikipedia.org/wiki/F-1_(nuclear_reactor)" id="mwAVQ" rel="mw:WikiLink" title="F-1 (nuclear reactor)">F-1 nuclear reactor</a>.<sup about="#mwt186" class="mw-ref reference" data-mw='{"name":"ref","attrs":{},"body":{"id":"mw-reference-text-cite_note-35"}}' id="cite_ref-35" rel="dc:references" typeof="mw:Extension/ref"><a href="./December_25#cite_note-35" id="mwAVU" style="counter-reset: mw-Ref 35;"><span class="mw-reflink-text" id="mwAVY">[35]</span></a></sup>
<span class="mw-reference-text" id="mw-reference-text-cite_note-35"><cite about="#mwt183" class="citation web cs1" id="mwCYs"><a class="external text" href="http://nuclearweaponarchive.org/Russia/Russreac.html" id="mwCYw" rel="mw:ExtLink nofollow">"The World's Oldest Operating Reactor: The Russian F-1"</a>. <i id="mwCY0">The Nuclear Weapon Archive</i><span class="reference-accessdate" id="mwCY4">. Retrieved <span class="nowrap" id="mwCY8">7 September</span> 2021</span>.</cite><span about="#mwt183" class="Z3988" id="mwCZA" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=unknown&amp;rft.jtitle=The+Nuclear+Weapon+Archive&amp;rft.atitle=The+World%27s+Oldest+Operating+Reactor%3A+The+Russian+F-1&amp;rft_id=http%3A%2F%2Fnuclearweaponarchive.org%2FRussia%2FRussreac.html&amp;rfr_id=info%3Asid%2Fen.wikipedia.org%3ADecember+25"></span></span>