In 2012 a leakage of radioactive tritium to soil was discovered at the High Flux Reactor (HFR) in Petten. NRG, the HFR-operator, took countermeasures to stop the leakage into the soil. RIVM investigated the radiological consequences for residents in the vicinity of the reactor. Even in very unfavourable scenarios, the exposure of local residents remains limited to a dose that is generally considered insignificant, namely less than 10 microsievert per year. To put things into perspective, this is less than 0.4% of the average amount of radiation that people in the Netherlands are exposed to per year from sources that are largely present in the environment (www.rivm.nl/stralingsbelasting). The leakage of tritium to the soil appears to have stopped, but the concentrations at the edge of the site could increase to higher levels than previously estimated. Continuation of a monitoring programme is therefore deemed advisable.
The above conclusions were the result of an investigation carried out by RIVM for the Authority for Nuclear Safety and Radiation Protection. The investigation was based on the soil analyses carried out by NRG and the modelling of the groundwater flows by the Sweco firm of consulting engineers.
RIVM has studied 20 reports submitted on the matter (up to and including October 2016) and supports the conclusion that the concentration of tritium in the groundwater on the edge of the site in or after 2018 could possibly exceed the threshold value of 100 Bq/L that was set previously. RIVM also estimates that the total amount of contamination still remaining is probably greater than the amount indicated by Sweco and NRG. However, the maximum concentration at the edge of the site is expected to remain below a few thousand Bq/L. For tritium contamination of drinking water, the World Health Organisation (WHO) applies a guideline of 10,000 Bq/L, which is considerably higher than the estimated maximum concentrations in the groundwater at the edge of the site. Even in the most unfavourable scenario, the exposure of local residents remains limited to a maximum of 10 microsievert per year.
Measures As the managing authority of the HFR, NRG has taken measures to stop the leakage and control the contamination. Based on the available information, RIVM has concluded that there are no indications that the leakage is still continuing. NRG has considered various options for further limiting the concentrations at the edge of the site. As the concentrations are already low and no effects are to be expected on the health of the local residents, these measures would appear to have little extra effect. However, RIVM recommends that NRG continues monitoring concentrations at the site, as it has proven difficult to provide adequate predictions of the groundwater flows at the site. In addition, RIVM recommends monitoring the levels of contamination just outside the edge of the site, for example in the neighbouring ditch.
Tritium Tritium is a radioactive compound that results from nuclear reactions in a water-cooled nuclear reactor. The compound also exists in nature, as a result of reactions of solar particles with our atmosphere. Tritium is used in emergency lighting in aeroplanes and as a light source in military equipment. The radiation released by tritium is very weak and cannot penetrate the skin. It can only contribute to the exposure of humans to radiation if it is absorbed into the body, especially after swallowing or inhalation. Tritium decays very slowly; after 12 years, half of the original amount still remains.