Commenced in January 2007
Frequency: Monthly
Edition: International
Paper Count: 30127
Considering Aerosol Processes in Nuclear Transport Package Containment Safety Cases

Authors: Andrew Cummings, Rhianne Boag, Sarah Bryson, Gordon Turner

Abstract:

Packages designed for transport of radioactive material must satisfy rigorous safety regulations specified by the International Atomic Energy Agency (IAEA). Higher Activity Waste (HAW) transport packages have to maintain containment of their contents during normal and accident conditions of transport (NCT and ACT). To ensure containment criteria is satisfied these packages are required to be leak-tight in all transport conditions to meet allowable activity release rates. Package design safety reports are the safety cases that provide the claims, evidence and arguments to demonstrate that packages meet the regulations and once approved by the competent authority (in the UK this is the Office for Nuclear Regulation) a licence to transport radioactive material is issued for the package(s). The standard approach to demonstrating containment in the RWM transport safety case is set out in BS EN ISO 12807. In this document a method for measuring a leak rate from the package is explained by way of a small interspace test volume situated between two O-ring seals on the underside of the package lid. The interspace volume is pressurised and a pressure drop measured. A small interspace test volume makes the method more sensitive enabling the measurement of smaller leak rates. By ascertaining the activity of the contents, identifying a releasable fraction of material and by treating that fraction of material as a gas, allowable leak rates for NCT and ACT are calculated. The adherence to basic safety principles in ISO12807 is very pessimistic and current practice in the demonstration of transport safety, which is accepted by the UK regulator. It is UK government policy that management of HAW will be through geological disposal. It is proposed that the intermediate level waste be transported to the geological disposal facility (GDF) in large cuboid packages. This poses a challenge for containment demonstration because such packages will have long seals and therefore large interspace test volumes. There is also uncertainty on the releasable fraction of material within the package ullage space. This is because the waste may be in many different forms which makes it difficult to define the fraction of material released by the waste package. Additionally because of the large interspace test volume, measuring the calculated leak rates may not be achievable. For this reason a justification for a lower releasable fraction of material is sought. This paper considers the use of aerosol processes to reduce the releasable fraction for both NCT and ACT. It reviews the basic coagulation and removal processes and applies the dynamic aerosol balance equation. The proposed solution includes only the most well understood physical processes namely; Brownian coagulation and gravitational settling. Other processes have been eliminated either on the basis that they would serve to reduce the release to the environment further (pessimistically in keeping with the essence of nuclear transport safety cases) or that they are not credible in the conditions of transport considered.

Keywords: Aerosol processes, Brownian coagulation, gravitational settling, transport regulations.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.3461958

Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 66

References:


[1] IAEA Safety standards for protecting people and the environment, Regulations for the safe transport of radioactive material. 2018 Edition.
[2] BS ISO 12807:2018. BSI Standards Publication, Safe transport of radioactive materials - Leakage testing on packages. 2018.
[3] S. Friedlander. Smoke, dust, and haze, fundamentals of aerosol dynamics. Oxford Univeristy Press, Second Edition, 2000.
[4] M.R.R. Williams and S.K. Loyalka. Aerosol science theory and practice with special applications to the nuclear industry. Pergamon Press, First Edition, 1991.
[5] M.R.R. Williams. Some topics in nuclear aerosol dynamics. Progress in Nuclear Energy, 17:1–52, 1986.
[6] F. Cousin, M.P. Kissane, and N. Girault. Modelling of fission-product transport in the reactor coolant system. Annals of Nuclear Energy, 61:135–142, 2013.
[7] T. Haste, F. Payot, and P.D.W. Bottomley. Transport and deposition in the Ph´ebus FP circuit. Annals of Nuclear Energy, 61:102–121, 2013.
[8] M. Schwarz, G. Hache, and P. von der Hardt. PHEBUS FP: a severe accident research programme for current and advanced light water reactors. Nuclear Engineering and Design, 187:44–69, 1999.
[9] H.J. Allelein, A. Auvinen, J. Ball, S. Guntay, L. Herranz, A. Hidaka, A.V. Jones, M.P. Kissane, D. Powers, and G. Weber. State-of-the-art report on nuclear aerosols in reactor safety. Technical Report NEA/CSNI/R(2009)5, Nuclear Energy Agency - Committee on the Safety of Nuclear Installations, 2009.
[10] S. Chatzidakis. Stress corrosion cracking aerosol transport model summary report. Technical Report ORNL/SPR-2018/1072, Oak Ridge National Laboratory (ORNL), 2018.
[11] C.F. Clement. Aerosol penetration through capillaries and leaks: theory. Journal of Aerosol Science, 26(3):369–385, 1995.
[12] D.A. Morton and J.P. Mitchell. Aerosol penetration through capillaries and leaks: Experimental studies on the influence of pressure. Journal of Aerosol Science, 26(3):353–367, 1995.
[13] M. Tian, H. Gao, X. Han, Y. Wang, and R. Zou. Experimental study on the penetration efficiency of fine aerosols in thin capillaries. Journal of Aerosol Science, 111:26–35, 2017.
[14] R. Martens, F. Lange, W. Koch, and O. Nolte. Experiments to quantify airborne release from packages with dispersible radioactive materials under accident conditions. EuroSafe Conference, 2005.
[15] W. Koch, F. Lange, R. Martens, and O. Nolte. Determination of accident related release data. 14th International Symposium on the Packaging and Transportation of Radioactive Materials PATRAM, 2004.
[16] W.C. Hinds. Aerosol technology: Properties, behavior, and measurement of airborne particles. John Wiley and Sons, Second Edition, 1999.
[17] S.H. Park, F.E. Kruis, K.W. Lee, and Fissan H. Evolution of Particle Size Distributions due to Turbulent and Brownian Coagulation. Aerosol Science and Technology, 36:419–432, 2002.
[18] A.M. Shahub and M.R.R. Williams. The importance of collision efficiency in the coagulation of nuclear aerosol particles. Nuclear Technology, 86:80–86, 1989.
[19] A.M. Shahub and M.R.R. Williams. Brownian collision efficiency. Journal of Physics D; Applied Physics, 21:231–236, 1998.
[20] M.R.R. Williams. On the modified gamma distribution for representing the size spectra of coagulating aerosol particles. Journal of Colloidal Interface Science, 103:516–527, 1985.
[21] J.F. van de Vate. Investigations into the dynamics of aerosols in enclosures as used for air pollution studies. Technical report, Netherlands Energy Research Foundation Report ECN-86, 1980.