International Physicians for the Prevention of Nuclear War (IPPNW) reported in August 2012 on some sleuth work by its affiliate in Germany that turned up documentation of a short-term spike 200--500 higher amounts of radioactive gases being released from the Gundremmingen reactor site in Southern Germany. The investigators established that this rise was associated with the opening of the reactor vessel, as is routinely done for reactor refueling and inspections. Further, the group reported that the elevation of radioactive pollution persisted for the next week, well above usual levels during ongoing operations.
The numbers for concentrations of noble gases reported by IPPNW are: 3 Bq/m3 for usual operations; the spikes were 700 Bq/m3 increasing to a peak of 1470 Bq/m3 in the initial hours after the vessel was opened, then tapering down to an average of 100 Bq/m3 for the next week.
Every reactor generates radioactive gases during normal operation, including noble gases, tritium, carbon-14, iodine and small amounts of volatile cesium and strontium. Reactor vessels are not designed to capture the gases that are present in the core prior to opening for activities like refueling or maintenance and inspections. When the core is opened, these gases escape.
The IPPNW's Reinhold Theil points out that these airborne emissions are of particular risk for women and pregnant women in the vicinity since women are at elevated risk for cancer, and the embryo and fetus suffer the greatest impacts from radiation exposure during gestation; the female fetus is at the highest risk. Tritium has the potential to cross the placental barrier to enter the fetus directly. Gamma emissions from noble gases are also a threat since these inert elements, if inhaled, are likely to be stored in fat deposits of the mother, typically near to the abdomen.
This situation has remained secret, or at the least invisible for the last six decades of reactor operation worldwide because the regulators allow self-reporting of emissions rather than publicly available real-time monitoring, and because regulations allow averaging over the reporting period. Since the NRC requires only annual reports, that allows the US reactor operators to hide these 500 times higher spikes above "usual" by leveling it in the typically lower levels of release.
Source:
http://www.ippnw-europe.org/print/en/nuclear-energy-and- security.html?expa nd=707&cHash=8752881e4a