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The Blind Spots In the Nuclear Test Monitoring System
Lasrick writes The International Monitoring System managed by the Comprehensive Nuclear-Test-Ban Treaty Organization relies on detecting one or more of four distinct signatures from a nuclear explosion. Seismic detectors continuously listen for the shock waves passing through the earth from underground nuclear tests. Hydro-acoustic monitors listen for sound waves in the oceans from underwater tests. Infrasound detectors scan for pressure waves in the atmosphere. The fourth kind of signal involves radioactive gases generated by a nuclear explosion and released into the atmosphere. Ulrich Kuhn and Michael Schoeppner describe the system in detail, and point out that there are blind spots, particularly in the area of noble gas detection: "Our research has found that the noble gas detection part of the International Monitoring System is unlikely to work as it should because of the limited distribution of noble gas stations, neglect of important meteorological patterns in some areas, and the radionuclide background from emissions from the commercial production of medical isotopes." Kuhn and Schoeppner go on to describe possible fixes, and call on the 183 states that have signed the Comprehensive Nuclear-Test-Ban Treaty and the CTBTO to provide the resources to build extra monitoring stations where they are required and to curb activities that might limit the global capability to monitor possible nuclear tests.
Evidently the behavior of nuclear weapons is fairly well quantified neutrino wise - you get 1.3e23 MeV neutrinos per kiloton yield spread over 4pi steradians of a sphere.
The sub-GeV neutrino-nucleon cross section is about 1e-44m^2. At the Super-K neutrino detector presents a detection volume that contains roughly 3e31 nucleons, which means we need about 3 neutrinos to pass through a square .55 micrometers on a side to hit the cross section it presents to get 3 counts at once and sound the alarm.
The result is, "damn that miserably small cross section" because the result is that a ~10kt Little Tinpot's First Nuke would only register to Super-K if it were within 100km or so. I haven't run numbers for Icecube but it's not promising because range scales as the square root of detector size since neutrino flux dilutes as the square of distance but target count is only proportional to volume.