An international working group bringing together two CEA teams is determining the quantity of methane released into the atmosphere in September 2022 by leaks from the Nord Stream gas pipelines. Estimated at 465,000 tonnes, or 0.1% of annual anthropogenic emissions of this powerful greenhouse gas, this is the largest quantity of methane ever measured for a single transient event.
In September 2022, the Nord Stream pipelines carrying natural gas from Russia to Germany suffered explosions. The leaks caused released a large quantity of methane, a powerful greenhouse gas, into the atmosphere, raising questions about the climate impact of this event.
In parallel with the first estimates, largely underestimated and obtained on the basis of atmospheric measurements, the United Nations Environment Program (UNEP) set up an international working group to determine more precisely the quantity of methane released. in the environment. Bringing together around twenty research teams, including two from the CEA, it delivers results which agree on a volume of 465,000 tonnes (+/- 20,000). This is the largest methane emission ever measured for a single transient event; unique event comparable to the annual traffic emissions of 8 million vehicles!
Modeling the temporal evolution of the leak flow rate
Previously, various studies have tried to quantify the quantities of gas released from atmospheric or satellite measurements, without however achieving results consistent with the estimates of methane initially stored in gas pipelines. “ On the one hand, it turns out that the atmosphere does not detect the first hours of emissions due to leaks even though they are the most intense », indicates Antoine Berchet of LSCE (CEA/CNRS/UVSQ).
On the other hand, the main difficulty lay in estimating the temporal evolution of the leak rate, which was then unknown. This is why a team from the CEA Energy Department (DES) is part of this UNEP project, with its Cathare software, developed since 1979 in partnership with EDF, Framatome and IRSN for reactor safety studies. nuclear. “ This code can in particular predict the outgoing flow through a circuit breach based on geometric characteristics and initial thermohydraulic conditions. Its modeling capabilities were extended to many fluids including methane, which allowed its use for this study. », Explains Raphaël Préa from CEA-Isas to DES.
Using the geometric data of the gas pipelines (length, diameter, etc.) and the initial conditions at the time of the breaches (pressure and temperature of the gas), his team calculated the changes in the methane flow rates resulting from the leaks (consequently estimating the quantity of dispersed methane).
-Monitor the transport of the methane plume into the atmosphere
At the same time, an LSCE team used readings from stations in the European observation network Icos which continuously measure atmospheric concentrations of greenhouse gases including methane. It turns out that the plume of methane from the leaks was transported into the atmosphere on winds around the Baltic Sea where it could be detected by the nearest stations. “ Based on the French chemistry-transport model Chimere, we were able to monitor the methane plume and thus calculate another estimate of the quantity of methane released by the “Nord Stream” gas pipelines during breaches. The estimates from the two approaches are very consistent, which supports the results. », specifies Antoine Berchet.
Indeed, all the results were compared with those of other research groups having used aerial, underwater or even satellite measurements. They underline the importance of means of detection and quantification of methane emissions, and the relevance of the use of varied and complementary techniques.
Illustration legend: ESA credit
Références : »Methane emissions from the Nord Stream subsea pipeline leaks. » Nature : s41586-024-08396-8
Source CEA – Article original
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