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Assigning Tolerances to J-Values used in Safety Analysis

Assigning Tolerances to J-Values used in Safety Analysis. James Kearns (2 nd Year PhD Student) Supervisor : Professor Philip Thomas School of Engineering and Mathematical Sciences City University, London EC1V 0HB. The J-Value Method.

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Assigning Tolerances to J-Values used in Safety Analysis

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  1. Assigning Tolerances to J-Values used in Safety Analysis James Kearns (2nd Year PhD Student) Supervisor: Professor Philip Thomas School of Engineering and Mathematical Sciences City University, London EC1V 0HB Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  2. The J-Value Method • An objective method of assessing appropriate levels of expenditure on safety systems. • Ensures consistency when making decisions which affect human life. Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  3. The J-Value & Input Parameters • ε: Coefficient of Risk Aversion • δVN: Cost of protection system (£) • N: Population affected by hazard • G: GDP per person per year (£/y) • δXd: Change in life expectancy (y) Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  4. The J-Value & Input Parameters • If J > 1: - The safety scheme is too expensive. • If J < 1: - The safety scheme represents good value for money. • J = 1 represents the maximum reasonable cost. Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  5. J-Value Analysis: AP1000 Rejected Safety Systems Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  6. Assigning Tolerances and Investigating Sensitivities • Recent work has focused on obtaining accurate evaluations of J-value input parameters and their tolerances. • Sensitivity analyses have also been performed to test assumptions of the J-Value model. Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  7. Assigning Tolerances and Investigating Sensitivities • The assumptions tested for sensitivity were: • Population distribution (steady state vs actual observed). • Work-time fraction distribution (rectangular vs actual observed). • Variation over time (parameters projected to 2080). Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  8. Population Distributions Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  9. Work-Time Fraction Distributions Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  10. J Case-Independent Case-Dependent G ε N δXd δVN GDP nPop w0 θ nsv Ts y X GDP COE MI gw(a) pw(a) p(a) S(a) Uncertainty Propagations • ~20 Input Parameters which contribute to the J-Value uncertainty. Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  11. Results: Risk Aversion • Variances: 0.4% (all). • Changing from actual p(a) to steady state increases ε by 0.001. • Changing v(a) from actual to rectangular increases ε by 0.001 – more risk averse. Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  12. Results: Risk Aversion Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  13. Results: J-Value • Test case with J = 1 for both actual distributions. σG = 0.75%. • Here assumed σδX = σδV= σN=0. • Variances: 2 % for all. Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  14. Summary • “Internal Accuracy” of J-value is within 2% • J-value model is very insensitive to initial assumptions. • Simplified assumptions reduce uncertainties, give slightly more conservative J-values, and reduces the complexity of the J-value model. • This justifies the use of such assumptions. • Slow time variation. Universities Nuclear Technology Forum, April 14-16, 2010, Salford

  15. Thank You! • Further Information: • Thomas, P., Jones, R. and Kearns, J., 2010, “The Trade-Offs Embodied in J-Value Safety Analysis”, Process Safety and Environmental Protection, in press, doi: 10.1016/j.psep.2010.02.001 • Thomas, P., Jones, R. and Kearns, J., 2009, "Measurement of parameters to value human life extension", XIX IMEKO World Congress, Fundamental and Applied Metrology, September 611, 2009, Lisbon, Portugal • Thomas, P. and Stupples, D., 2007, "J-value: a new scale for judging health and safety spend in the nuclear and other industries", Nuclear Future ,Vol. 03, No. 3, May/June Universities Nuclear Technology Forum, April 14-16, 2010, Salford

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