Two weeks after the earthquake and tsunami, Japan's crippled Fukushima Daiichi nuclear power complex continues to spread both radiation and distrust of nuclear power as the plant's situation lurches from hopeful to harrowing and back again.

This week, Tokyo Electric Power restored grid power to much of the plant's equipment, bringing instrumentation back to life and, in a few cases, restoring cooling to overheated reactors and spent fuel pools. But on Wednesday, Japan's Nuclear and Industrial Safety Agency reported that black smoke from Fukushima Daiichi's reactor unit 3 and a spike in radiation around reactor 2 had forced workers to temporarily abandon work to restart the cooling systems.

The struggle to regain control at Fukushima Daiichi has made the global nuclear industry jittery. Italy's cabinet has decided to put its plans for a return to nuclear energy on hold for one year. Earlier this week, U.S. utility NRG Energy and Japan's Toshiba said they were slowing plans to build new reactors at NRG's Bay City, Texas, nuclear plant next year. Their reasons for the delay were the possibility of shifting requirements from the U.S. Nuclear Regulatory Commission (NRC) and uncertainty over Tokyo Electric Power's ability to take a planned stake in the project.

The International Atomic Energy Agency in Vienna says it has yet to identify any "significant risk to human health." But in Japan there have been reports of radiation in fresh foods and water, and Tokyo residents with infants were warned by municipal authorities Wednesday not to use tap water after radioactive iodine at roughly double Japan's safety limit for infants was detected at a Tokyo water treatment plant.

Meanwhile, radiation trackers have measured the fission products over North America to reveal the extent of radiation released by the Fukushima accident. The measurements showed that in the first four days following the March 11 quake and tsunami, Fukushima Daiichi released Iodine-131 packing 4x1017 Becquerels of radiation, says Gerhard Wotawa, a radiation tracker at the Central Institute for Meteorology and Geodynamics in Vienna. His team generated the estimates using data from the global detectors installed to enforce nuclear weapons test bans.

Wotawa says Fukushima Daiichi released about one-fifth as much Iodine-131 as the 1986 Chernobyl accident. Iodine-131 is short-lived, with a half-life of just eight days, but the resulting carcinogenesis plays out over decades. Elevated thyroid cancer rates linked to Chernobyl's radioactive iodine have yet to decline 25 years later, according to a U.S. National Cancer Institute study published last week.

Fukushima Daiichi released over 3x1016 Becquerels-worth of Cesium-137 in the incident's first four days—about half as much as Chernobyl,  according to Wotawa. Cesium-137 has a half-life of 30 years; land contaminated by it forced the permanent relocation of more than 100,000 residents from around Chernobyl.

The relatively high level of Cesium-137 is one of several factors suggesting that loss of cooling water protecting spent nuclear fuel in pools above Fukushima Daiichi's reactors caused some of the radioactive releases. Spent fuel contains little Iodine-131, which quickly breaks down once fuel is pulled from a reactor, but it retains lots of Cesium-137.