III.1.5.1. General

Since HTO is the most frequently used water tracer and, in addition, applied in the highest quantities per injection (in becquerels), it is used here as an example on discussion of the environmental impact of such operations.

Sea water contains low concentrations of practically all radioactive nuclides present globally. The radionuclide [1]H is also present in sea water. In the North Sea, the concentration of 3H is in the order of 1 Bq/L. During injection, there will normally be no release of tracer into the sea from offshore installations. However, in case of an abnormal situation arising involving spillage of tracer, then the spilt tracer will be dispersed into the sea. The impact on the environment caused by this type of tracer discharge therefore has to be evaluated.

111.1.5.2. Impact of an accident during injection

(a) Worst case from radioactive tracer discharge into the sea

The worst case impact on the environment will occur if a whole portion of tracer has to be discharged into the sea.

(b) Impact on the European population from HTO discharge

The following is an example on how this has been evaluated for a typical North Sea situation.

The report NRPB-R109 from the British National Radiological Protection Board, A Model to Calculate Exposure from Radioactive Discharges into the Coastal Waters of Northern Europe, contains a suitable model for calculations of dose commitments to the people in the region.

111.1.5.3. Dose commitment from 3700 GBq of HTO

From the NRPB-R109 report, it is possible to calculate that a discharge of 1 GBq in one year gives a collective intake of 57.07 Bq over a period of 50 years. From this, 2000 GBq of HTO gives a collective intake of 211 159 Bq. A discharge of 50 MBq HTO gives a dose commitment equal to 1 mSv. Thus, the collective intake of 211 160 Bq originating from a discharge of 2000 GBq gives a dose commitment of 4.2 x 10-6 mSv.