Paris, 10 April 2000
The OECD Nuclear Energy Agency (NEA) announces the publication of a new report, entitled Prediction of Neutron Embrittlement in the Reactor Pressure Vessel, which provides guidance on the best calculation methods for simulating the effects of radiation on structural materials and predicting the subsequent damage to nuclear reactor components, especially pressure vessels.
With an increasing number of nuclear power reactors world-wide approaching the end of their design lives, decisions must be taken with regard to final shutdown or possible plant life extension. Accurately characterising the structural integrity of reactor components is of highest importance if correct decisions are to be taken regarding the validity of a reactor design over time, safety margins and potential plant lifetime extension, and to avoid judgements that might lead to shutting down prematurely nuclear power plants that are still operational. Thus this issue is important for both safety and economic reasons.
For over twenty years, calculation methods with a precision of about 20% have been the principal means of predicting the impact of fast neutrons, responsible for the radiation damage to reactor pressure vessel walls. The uncertainties in these calculations were mainly due to the approximations used in treatment of the problem (two-dimensional geometry).
The new NEA report shows that a more refined (three-dimensional geometry) treatment of the same problem gives significantly better predictions. Accuracy of the order of ± 10% can routinely be obtained and the agreement between "high-precision" calculations is reported to be better than ± 5%.
The report gives results from both approximate and more refined calculations performed by different research groups in NEA member countries. These results are then compared with experimental data from the VENUS reactor at the SCK-CEN nuclear research centre in Mol, Belgium, to draw conclusions on the precision of the calculations.
The recent improvement in computing techniques and the availability of powerful computers has made it possible to reduce significantly the long computing times required for these complex three-dimensional calculations. Even the "high-precision" calculations can now be carried out on a routine basis.
Further decreasing the uncertainty to 5 % in the prediction of radiation damage to reactor components paves the way for more confidence in, and improved safety margins and better economics for, the current generation of nuclear power plants, as well as future designs.
Prediction of Neutron Embrittlement in the Reactor Pressure Vessel Venus-1 and Venus-3 Benchmarks
OECD, Paris, 2000 - ISBN 92-64-17637-3 - 268 pages