WASHINGTON (AP) — An unpublished study says key members of the Air Force's nuclear missile force are feeling "burnout" from what they see as exhausting, unrewarding and stressful work.

The study by researchers for RAND Corp. was provided to The Associated Press in draft form.

Its finding adds to indications that trouble inside the nuclear missile force runs deeper and wider than officials have acknowledged.

The study also cites heightened levels of misconduct like spousal abuse. It says court-martial rates in the nuclear missile force in 2011 and 2012 were more than twice as high as in the overall Air Force.

These indicators add a new dimension to an emerging picture of malaise and worse inside the intercontinental ballistic missile force.