TO EVALUATE THE ESBWR DESIGN AND RELATED MATTERS

we discussed the applicability of TRACE thermal-hydraulic system analysis code to evaluate the Economic Simplified Boiling Water Reactor (ESBWR) design and related matters. Our Subcommittee on Thermal-Hydraulic Phenomena reviewed these matters on February 27, 2009. During these meetings, we had the benefit of discussions with representatives of the NRC staff and of the documents referenced. CONCLUSIONS AND RECOMMENDATIONS 1. TRACE is applicable for confirmatory analyses of the blowdown and gravity driven cooling system (GDCS) injection phases of ESBWR loss-of-coolant accidents (LOCAs). Its applicability to cases in which noncondensables may be trapped in the GDCS lines, as well as long-term cooling, has not been demonstrated. 2. The capability of TRACE to predict the effect of trapped noncondensables in the GDCS and the resulting collapsed liquid level in the reactor pressure vessel should be assessed. 3. The adequacy of TRACE and other analysis methods, such as MELCOR, used for confirmatory analyses of long-term cooling phase of ESBWR LOCAs should be evaluated. 4. TRACE should be assessed for applicability to analyses of coupled neutronic and thermal-hydraulic phenomena important to safety, such as instabilities and anticipated transient without scram (ATWS), in the ESBWR design. 5. Ongoing work to demonstrate that TRACE is adequate for confirmatory analyses of LOCAs and other safety-significant thermal-hydraulic phenomena in the new pressurized water reactor (PWR) designs should be completed in a timely fashion to allow application in the design certification process