DEVELOPMENT OF RISK INFORMED METHODS FOR ESTIMATING RADIATION RELEASE FROM CABLE FIRES AT HIGH ENERGY PHYSICS FACILITIES

Abstract: CERN operates the Large Hadron Collider (LHC), the world’s largest and most powerful particle accelerator. The LHC was built to advance the state of knowledge in particle physics by increasing the energy of colliding particles to the TeV range. With this increase in capability comes increased fire safety challenges, including the need for more accurate assessment of fire-induced release of radioactive materials. Through normal operation of particle accelerators, some materials used in the facility structure and equipment are made radioactive through a process called proton activation. Electrical cables are susceptible to proton activation; therefore, a cable fire can potentially result in liberation of radionuclides to the environment. This thesis elevates the state of knowledge and refines methods for estimating fire-induced radiation release from burning cables through (1) development of a more accurate framework for modelling cable fire sequences and quantitatively estimating cable fire frequencies and (2) development of quantitative methods for estimating the portion of radioactive isotopes released into the smoke plume of fires involving activated electrical cables. Improved modelling of cable fire sequences was accomplished by applying electrical engineering principles to categorise and refine cable fire sequences within a fault tree format. Ignition source frequency weighting factors are then applied to associated sequences in the fault tree to produce greater precision in the determination of cable fire risk with respect to configuration, location, operating mode, and prevailing conditions. Proof-of-concept case studies confirm that the methodology is viable for “real-world” applications and can substantially improve cost-benefit analysis for risk mitigation strategies. Conservation of mass principles were used to quantitatively analyse fractional release of radionuclides from burning cables. Mass balance inventory of pre-fire and post-fire radionuclides allowed assessment of activity levels contained in residual char, soot, and gaseous combustion products. Proof-of-concept case studies demonstrate that fractional release calculations are viable but several key influence parameters require further study to ensure accurate application.