Radioactive Substances Committee Thematic Assessment

The input of radioactive substances to the marine environment

The main contributions to the pressure that results from inputs of radioactive substances to the marine environment are the authorised discharges from the nuclear sector and the oil and gas sub-sector. The intensity of these discharges varies across the five OSPAR Regions, with the highest intensity in Region II (Greater North Sea) and Region III (Celtic Seas). Discharges from the nuclear sector have shown progressive and substantial reductions, while discharges of radioactive substances from the oil and gas sub-sector have mostly remained unchanged. A further contribution to this pressure comes from historic discharges from the same activities, as well as from other events such as the Chernobyl accident and fallout from nuclear weapons testing in the 1950s and 1960s.

¹ - Relative for the OSPAR Maritime Area and based on discharge data reported to OSPAR up to 2018 and published in the Fifth Periodic Evaluation. Although there are no direct discharges from the nuclear sector to OSPAR Region V, discharges from the nuclear sector to other OSPAR Regions can be transported by ocean currents to OSPAR Region V. The relative intensity for OSPAR Region V is therefore based on expert judgement in relation to the intensity of the pressure of discharges from the nuclear sector to the other OSPAR Regions.
² - Trends since the QSR 2010 are based on the assessments carried out by OSPAR in the Fifth Periodic Evaluation, with the exception of OSPAR Region V which is based on expert judgement (see footnote 1).
³ - Expected trends to 2030 consider the type and number of facilities, and whether facilities are operational or undergoing decommissioning activities. Expected trend for OSPAR Region V is based on expert judgement (see footnote 1).
⁴ - Relative for the OSPAR Maritime Area and based on discharge data reported to OSPAR up to 2018 and published in the Fifth Periodic Evaluation.
⁵ - Trends since the QSR 2010 are based on the assessments carried out by OSPAR in the Fifth Periodic Evaluation.

Input of radioactive substances

There are ongoing pressures from the discharge of radioactive substances as a result of the normal operation of nuclear facilities, oil and gas platforms and some other non-nuclear industries as well as from medical uses.

Input of radioactive substances from the nuclear sector

Radionuclides present in liquid effluents from nuclear power stations vary depending upon the type of reactor. However, in general, these effluents contain quantities of fission products such as caesium-137 (Cs-137), and activation products such as cobalt-60 (Co-60) (which are beta/gamma emitters). Sometimes, they also contain very low levels of alpha-emitting radionuclides such as plutonium-239 and plutonium-240 (Pu-239,240). In addition, nuclear power stations are a significant contributor to discharges of tritium (H-3), a weak beta emitter. The sources of these discharges include the reactor, the coolant and associated systems, and the fuel storage ponds. Effluents are typically routed via treatment plants to reduce the levels of radioactivity before discharge.

Nuclear fuel reprocessing results in authorised discharges to the environment from a range of sources such as fuel storage ponds, reprocessing plants and associated downstream plants, and legacy waste management and decommissioning. The radionuclides discharged include H-3, carbon-14 (C-14), beta-gamma emitters such as Co-60, strontium-90 (Sr-90), technetium-99 (Tc-99), ruthenium-106 (Ru-106) and Cs-137, and alpha emitters such as Pu-239,240 and americium-241 (Am-241).

Liquid discharges from the nuclear fuel fabrication and enrichment sub-sector largely consist of uranium isotopes and their decay products, as well as other radionuclides such as Tc-99 if certain types of feed material, such as uranium from reprocessing, have been used.

Liquid discharges from the nuclear research and development sub-sector are typically lower than the other sub-sectors. In some cases, the range of individual radionuclides reported is relatively large, but the principal radionuclides tend to be those found in discharges from the nuclear power sub-sector.

OSPAR has carried out assessments of indicators for each nuclear sub-sector (for individual Contracting Parties where discharges from these sub-sectors occur to the OSPAR Maritime Area and the sum of all such discharges) as well as for the nuclear sector as a whole (the sum of all such discharges from all sub-sectors). From the assessments carried out by OSPAR on data for the period 1995 to 2018 there is clear evidence that in the majority of cases for the nuclear sector there have been progressive and substantial reductions in discharges. Further, it should be noted that no assessments revealed any actual increase in discharges across the nuclear sector.

Input of radioactive substances from the non-nuclear sector

The main source of radionuclides from the oil and gas sub-sector to the marine environment is through the discharge of produced water. Produced water is a by-product of the extraction of oil and gas that can comprise a mixture of formation water (i.e. water found naturally in the same formation as the oil or gas) and seawater that has been injected into the reservoir to maintain reservoir pressure. The radioactive content of produced water arises from naturally occurring radionuclides contained in the reservoirs and includes lead-210 (Pb-210), radium-226 (Ra-226) and radium-228 (Ra-228).

From the assessments carried out by OSPAR on data for period 2005 to 2018 for the oil and gas sub-sector there is evidence of some progressive and substantial reductions in discharges. However, in most cases discharges of radioactive substances from this sub-sector have remained unchanged. Further, none of the assessments carried out for individual Contracting Parties revealed any actual increase in discharges.

For the medical sub-sector, the main radionuclide discharged is iodine-131 (I-131), with a half-life of eight days. The use of decay tanks in some countries has notably reduced the discharge of I-131. Due to uncertainties associated with the reported data and the amount entering the marine environment, OSPAR has agreed not to carry out any assessments of the discharges from this sub-sector at present. However, OSPAR is continuing to review the work of individual Contracting Parties on the issues surrounding the discharge of this radionuclide.

Several Contracting Parties report data to OSPAR for a number of other non-nuclear sub-sectors. From the data reported for the university and research centre sub-sector, it is reasonable to conclude that this sub-sector is not a significant contributor to total beta (excluding tritium) or tritium discharges and that there are no alpha discharges.

Radiochemical production is carried out in several Contracting Parties, but the discharges from this sub-sector are in some cases included with those from the nuclear research and development sub-sector due to co-location of sites. Discharges of naturally occurring radionuclides have been reported by some Contracting Parties for phosphate production, titanium dioxide pigment manufacture, primary steel manufacture and rare earth mineral production. From the data reported to OSPAR it is reasonable to conclude that these sub-sectors are no longer a significant contributor to total alpha and total beta (excluding tritium) discharges.

Other inputs and factors controlling the level of radioactive substances in the marine environment

Radionuclides that are soluble in seawater are typically dispersed away from their discharge points by tidal and prevailing ocean currents. Radionuclides that are less soluble typically bind to sediments in the areas around their discharge points, where they can accumulate over time. The process by which such radionuclides bind to sediments can be dynamic, meaning that these radionuclides can be released or remobilised back into the overlying seawater. Through such processes, radionuclides that have accumulated in sediments as the result of previous higher discharge levels can act as a significant source of these radionuclides over time, particularly where discharge levels have subsequently been reduced.
It is important to note that not all radionuclides present in the environment are the result of authorised discharges from the nuclear and non-nuclear sectors. There have been a number of accidents and events, such as the Chernobyl accident in 1986 and fallout from atmospheric nuclear weapons testing in the 1950s and 1960s, which resulted in the introduction of radionuclides to the marine environment. Indeed, any accident situation in the future involving the release of radioactive substances may lead to increased levels of radionuclides in the marine environment over and above those resulting from current discharges.

Other industrial activities have also released radionuclides into the marine environment as a consequence of their processes. In many cases, the additional sources of radionuclides from these historical accidents and events are still detectable today and will generally be indistinguishable from past and contemporary discharges of radionuclides. For this reason, monitoring data for environmental concentrations of radioactive substances reflect the sum of contributions from historical accidents and events and past and contemporary discharges of radionuclides. In addition, environmental concentrations of naturally occurring radionuclides by definition will also contain natural background levels of these radionuclides.

Table P.2: Statement on confidence assessment for conclusions on the pressure from discharges of radioactive substances from the nuclear sector and the oil and gas sub-sector⁶

⁶ - Confidence assessments are based on trends since the QSR 2010 (see summary table) as these are based on discharge data reported by Contracting Parties and assessments carried out by OSPAR in the Fifth Periodic Evaluation. Conclusions made by OSPAR as to the progressive and substantial nature of any reductions in discharges are based on the statistical significance of the relevant assessment methodologies.