Will ³⁷Ar emissions from light water power reactors become an obstacle to its use for nuclear explosion monitoring?

³⁷Ar is a promising candidate for complementing radioxenon isotopes as indicators of underground nuclear explosions. This study evaluates its potential anthropogenic background caused by emissions from commercial pressurized water reactors. Various ³⁷Ar production pathways, which result from activation of ³⁶Ar and of ⁴⁰Ca, respectively, are identified and their emissions quantified. In-core processes include (1) the restart of operation and degassing of the primary cooling water after maintenance and refueling shutdown, (2) the replacement of primary coolant water for limiting its tritium concentrations, and (3) the leakage of ³⁷Ar produced from calcium impurities in UO₂ after fuel rod failures. Activation of air and of calcium in concrete within the biological shield are major out-of-core production pathways. Whereas emissions from in-core processes are transient, a rather constant ³⁷Ar source term results from its out-of-core production. Generic atmospheric dispersion simulations indicate that already at moderate distances from the emitter, concentrations of ³⁷Ar caused by routine reactor operations are far below its cosmogenic background in air. The only exception results from an inadvertent reactor re-start without operation of the primary cooling water degassing system for prolonged time. Such an event also causes high emissions of ⁴¹Ar which can be used for discriminating its ³⁷Ar signal from an underground nuclear explosion.