Results from pre-tests on liquid metal embrittlement

The possible risk for liquid metal embrittlement (LME), solid metal induced embrittlement (SMIE) and liquid metal corrosion (LMC) caused by lead metals on nuclear materials was raised due to an event at a power plant where radiation shields were unintentionally left on the outer surface of the primary circuit for one operation period (-1 year). The shields were removed at the following outage and the surfaces were cleaned and the cleanliness was evaluated by analysing the outer surface using a portable x-ray analyser. The compositions and melting points of the radiation shields were also determined and found to be below the temperature of the primary circuit outer surface. Based on the literature review evidence of lead causing embrittlement on steel was found, with the pre-requisite that a wetting is achieved and the steel is free from an oxide layer. Before performing LME investigations on nuclear materials, test set-up verification was performed, repeating tests found in the literature, consisting of a series of high temperature tensile tests with and without exposure to lead. The reduction of area was almost similar on exposed and non-exposed tests, while the literature reported a clear reduction. The reason for the difference may be the flux. However, further tests on nuclear materials are not feasible using this test set-up, but would require more extensive studies. The results from the tests performed and reported here as well as from parts of the literature, together with the cleaning procedures performed at the plant, the shielding effect of the oxide layer, and the expected low stresses at the outer surface, indicate a very low risk for lead induced embrittlement on the outer surface of the primary piping with temperature below the melting point of the lead shield.