Fire Risks in Using Paraffin as Neutron Radiation Shielding Material

Safety in general and fire safety in particular are key concerns in neutron-based research facilities, and the choice of the material that is used to stop neutron radiation is critical in this respect. Borated paraffin has been used at existing research facilities and could potentially be used at new facilities. However, a literature search resulted in very little information about the fire properties of borated paraffin. This was the motivation for the study discussed in this article. Two types of fire tests were performed. The Cone Calorimeter was used to obtain heat release rate characteristics of regular paraffin and borated paraffin. The results from standard Cone Calorimeter tests on specimens in the horizontal orientation show that borated paraffin with 4.5% boron has a heat release rate per unit area that is a factor of 3–5 lower than regular paraffin. The second type of test involved exposure of a small mock-up of a section of a hollow steel wall filled with borated paraffin exposed on one side to the standard ISO 834 temperature–time curve. During the first 20 min of the test, the borated paraffin in contact with the steel plate on the exposed side melted. Pressure from boiling water in the resulting cavity was relieved by pushing the molten paraffin to the unexposed side, where it exited through cracks in the unexposed surface of the wall section. The test confirmed the hypothesis of pressure release by molten paraffin.