Workers refueling Exelon's Peach Bottom unit 2 were exposed to low levels of radiation following a steam leak Tuesday.

Peach Bottom nuclear plant. Source: NRCThey had been disassembling the reactor head vent when steam escaped from a flange at about 1 a.m., according to a report filed with the Nuclear Regulatory Commission. Radiation was contained to the building, where it was detected by monitors.

Speaking to the York Daily Record, an NRC spokesman said that 51 of 138 people working in the area did not immediately clear radiation monitors. Seven then cleared them after changing clothes and showering. Seventeen recorded doses less than 10 millirems and 27 recorded doses above 10 millirems, with one worker receiving a dose of 173 millirems. The exposure limit for nuclear workers is 5,000 millirems per year.

The NRC spokesman indicated workers encountered higher-than-expected levels of water, which flashed to steam when contacting a steam dryer. The unit near Lancaster, Pa., is a General Electric Type 4 boiling water reactor first licensed in 1973, according to the agency.