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GOOD SCIENCE VS UNCERTAIN REGULATORY GUIDANCE OR HOW CHI/Q AFFECTS NUCLEAR SAFETY

GOOD SCIENCE VS UNCERTAIN REGULATORY GUIDANCE OR HOW CHI/Q AFFECTS NUCLEAR SAFETY. Ken Evans Illinois Department of Nuclear Safety 1035 Outer Park Drive Springfield, Illinois 62704 217-558-0499 evans@idns.state.il.us. Introduction. X/Q Calculations used to be simple

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GOOD SCIENCE VS UNCERTAIN REGULATORY GUIDANCE OR HOW CHI/Q AFFECTS NUCLEAR SAFETY

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  1. GOOD SCIENCE VS UNCERTAIN REGULATORY GUIDANCE OR HOW CHI/Q AFFECTS NUCLEAR SAFETY Ken Evans Illinois Department of Nuclear Safety 1035 Outer Park Drive Springfield, Illinois 62704 217-558-0499 evans@idns.state.il.us

  2. Introduction • X/Q Calculations used to be simple • As a result of tracer studies more realistic models were developed • Regulatory Guidance has not always followed the best science

  3. Development of ARCON-96 • Regulatory Guide 1.145 recognized the existence of plume meander and building wake • There was no attempt to develop an accurate model of these two terms • NUREG/CR-5055 was a first attempt to develop a more realistic model • ARCON-95 was the first realistic model to predict the effects of plume meander and building wake.

  4. ARCON-96’s Results • The results of the new X/Q are spelled in on page 44 of ARCON-96 • “…there are numerous instances where ARCON-96 predicts concentrations that are more than a factor of 10 lower than the Murphy-Campe model predictions.”

  5. The Source Term Issue • NUREG-1465 Published in 1995 • It received much attention because source terms were known to be overly conservative. • Conservatism in X/Q’s not as well understood

  6. Clinton’s RAST Team • Clinton Power Station decided to form a team to evaluate the new source term. • The Revised Accident Source Term (RAST) team’s mission was to look for economic benefits. • The RAST Team also evaluated the effect of ARCON-95

  7. First Case • The timing aspects of the new source term only were used. • Other aspects of the new source term such as chemical species and accident analysis were more difficult to calculate. • In 1996 it was not clear what methodology the NRC would approve for revised design basis calculations.

  8. Results For Timing Only • Reduction in dose less than a factor of 2. • Did not produce enough benefit to pursue further.

  9. New X/Q Case • Take credit for Suppression Pool Scrubbing • Calculate new X/Qs using ARCON-95 • Use current Reg Guide 1.3 Source Term • Results Approximately a factor of 10 reduction

  10. Control Room X/Q • The Clinton calculations for Control Room were reduced by a factor of 4 for occupancy. • The new guidance in DG-1111 allows a factor of 10 for Clinton’s design of air intakes.

  11. Reg Guide 1.183 • Reg Guide 1.183 provides guidance on use of new source term • It is silent on use of ARCON-96 for other than control room dose • Defense in Depth must be maintained, i.e charcoal trains can not be eliminated.

  12. SUMMARY AND CONCLUSIONS • ARCON-96 as well as the NUREG 1465 Source Term result in lower dose when performing design basis calculations. • The design of nuclear plants has been based on conservative analysis • The regulatory dilemma becomes recognizing improvements in the science without obviating the required safety systems that are now in place.

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