Sodium and NaK do, however, ignite spontaneously on contact with air and react violently with water, producing hydrogen gas. This was the case at the Monju Nuclear Power Plant in a 1995 accident and fire. Sodium is also the coolant used in the Russian BN reactor series and the Chinese CFR series in commercial operation today. Neutron activation of sodium also causes these liquids to become intensely radioactive during operation, though the half-life is short and therefore their radioactivity does not pose an additional disposal concern.