Confirmatory Thermal-Hydraulic Analysis To Support Specific Success Criteria in the Standardized Plant Analysis Risk Models–Duane Arnold: Chapters 1 – 8, Appendices A – C (NUREG-2236, Volume 1)

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Publication Information

Manuscript Completed: May 2019
Date Published: October 2020

Prepared by:
S. Campbell,1 S. Dennis,1 D. Helton,1 L. Kozak,1 J. Pires,1 F. Sock1
M. Khatib-Rahbar,2 A. Krall2
R. Buell3

U.S. Nuclear Regulatory Commission1

Energy Research, Inc.2
P.O. Box 2034
Rockville, MD 20847

Idaho National Laboratory3
P.O. Box 1625
Idaho Falls, ID 83415

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Availability Notice


This report extends the work documented in NUREG-2187, "Confirmatory Thermal-Hydraulic Analysis to Support Specific Success Criteria in the Standardized Plant Analysis Risk Models— Byron Unit 1," issued January 2016, to the Duane Arnold Energy Center. Its purpose is to produce an additional set of best estimate thermal-hydraulic calculations that can confirm or enhance specific success criteria for system performance and operator timing found in the agency's probabilistic risk assessment tools. Along with enhancing the technical basis for the agency's independent standardized plant analysis risk (SPAR) models, these calculations are expected to be a useful reference to model end users for specific regulatory applications.

This report first describes major assumptions used in this study. It then discusses the major plant characteristics for the Duane Arnold Energy Center, in addition to the MELCOR model used to represent the plant. Finally, the report presents the results of MELCOR calculations for selected initiators and compares these results to SPAR success criteria, the licensee's success criteria, or other generic studies.

The study results provide additional timing information for several probabilistic risk assessment sequences, confirm many of the existing SPAR modeling assumptions, and give a technical basis for a few specific SPAR modeling changes, including the following potential changes:

  • Degraded high-pressure injection and relief valve Criteria (non-anticipated transient without scram): A single control rod drive pump injecting at the postscram increased injection rate is sufficient for reactor pressure vessel (RPV) water inventory makeup. Additionally, two control rod drive pumps injecting at the postscram injection rateprovide enough makeup to the RPV to facilitate a cooldown of the RPV to cold shutdown conditions. This increased injection is currently not queried in the SPAR models but could be added.

  • Mitigating strategies usage: If diverse and flexible coping strategies (FLEX) are not available, success of long-term cooling for these scenarios is only possible with both anticipatory venting and condensate storage tank (CST) availability. Currently, CST availability is not queried in the SPAR models. This could be added for scenarios for which no alternate injection is available. For loss-of-offsite-power scenarios, FLEX injection led to success in all scenarios that gave FLEX credit. Given the ability of FLEX to prevent core damage, this confirms that the SPAR models should have FLEX equipment added.

  • Emergency core cooling system injection following containment failure or venting: Depending upon the size of containment failure, wetwell and drywell pressure will fall, potentially to the point of allowing high-pressure injection restart following its loss. This action could be added to the SPAR models.

  • Safe and stable end-state considerations: If the CST is unavailable, the long-term availability of high-pressure injection is questionable at best. CST should be queried when high-pressure injection systems are the source of long-term makeup. Additionally, increased postscram control rod drive hydraulic system injection is adequate for makeup. This increased injection is a candidate for inclusion in the SPAR model. Depressurizing when reaching the heat capacity limit curve is important, since the rate of seal leakage, as well as the rate of injection, is pressure dependent. This depressurization is a candidate for consideration in the SPAR models.

Page Last Reviewed/Updated Wednesday, March 24, 2021