ML18267A086

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1545 HELB
ML18267A086
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Issue date: 09/24/2018
From: Robert Tregoning
NRC/RES/DE
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High Energy Line Break (HELB)

Limit of CUF = 0.1 Michael L. Benson Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission Gary L. Stevens EPRI Public Meeting on Environmentally Assisted Fatigue Research Rockville, MD September 25, 2018 This presentation was prepared as an account of work conducted by an agency of the U.S. Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third partys use, or the results of such use, of any information, apparatus, product, or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights. The views expressed in this paper are not necessarily those of the U.S. Nuclear Regulatory Commission.

High Energy Line Break Issue (1/2)

  • High energy line break (HELB) Class 1 piping locations in some plants are limited to a cumulative usage factor of 0.1

- Mainly (only?) BWRs

- Documented in FSARs

- Several plants had difficulty meeting CUF < 0.1 for HELB locations for 60 years

- Hatch plant in 2000-2002 time frame

  • HELB was also an identified issue for new plants
  • The NRC intended to investigate this criterion in as part of their EAF research started in 2010 under a joint User Need Request #1 sponsored by NRR and NRO Public Meeting on Environmentally Assisted Fatigue Research 2

High Energy Line Break Issue (2/2)

  • The NRC held an EAF public meeting on January 5, 2012 and discussed HELB

- Meeting summary and all presentations available at ML120120028

- Structural Integrity/EPRI presented work on an Improved Basis and Requirements for Break Location Postulation (EPRI Technical Report 1022873, October 2011, publicly available); that work performed leak probability probabilistic calculations are argued for a revised criterion = 1.0

- The NRC also explained their rationale behind the HELB criteria

  • Subsequently, the industry identified that they had no identified need for HELB issues to be addressed until the 2020s
  • Based on the above, the NRC delayed the HELB work from Under Need Request #1

- It was felt that the Extremely Low Probability of rupture (xLPR) code, when completed, could address this issue

- At that time (~2012), the xLPR code was forecast for completion in 2018, so it would be available for use commensurate with the industrys need

  • Subsequently, in 2014, NRO escalated their need to address the HELB issue; this led to a second User Need Request Public Meeting on Environmentally Assisted Fatigue Research 3

High Energy Line Break User Need #2

  • Issued jointly by NRR and NRO in January 2015
  • Related to Standard Review Plan 3.6.2 on pipe rupture postulation
  • Cumulative usage factor criterion for postulation of pipe rupture: CUF 0.1

- A conservative criterion that may not have a well-understood basis

- Determine/document the basis behind the criterion

- Develop options for revising the criterion

  • Jet force modeling

- Evaluate water jet force models (ANSI/ANS 58.2 and NUREG/CR-2913) against laboratory data and computational fluid dynamics calculations

- Make recommendations for regulatory positions Public Meeting on Environmentally Assisted Fatigue Research 4

General Design Criterion 4

  • components important to safety shall be designed to accommodate the effects ofpostulated accidents.
  • Missile generation, flooding, pipe whip, increased temperature and humidity, and water jet impingement
  • Possible outcome: installation of pipe whip restraints or jet impingement shields
  • SRP 3.6.2 describes methods acceptable to the staff for complying with GDC 4
  • SRP 3.6.2 references the jet force models and Branch Technical Position 3-4 Public Meeting on Environmentally Assisted Fatigue Research 5

History of BTP 3-4

  • BTP 3-4 provides methods acceptable to the staff for determining postulated break locations
  • Many criteria are stress based
  • B.1.(ii)(1)(b) for Class 1 and B.1.(iii)(1)(c) for Class 2 have a cumulative usage factor criterion, CUF0.1
  • Conservative criterion but the technical basis is not well documented Public Meeting on Environmentally Assisted Fatigue Research 6

CUF Criterion

  • Begins with the 1972 Giambusso letter (found in Appendix B of BTP 3-3, ML070800027)
  • Early versions state that the fatigue criterion is only considered when the maximum stress range exceeds a certain value, but that caveat was removed in later versions
  • January 2012 public meeting on fatigue issues (ML120120028)

- EPRI presented a risk-informed approach to postulated break locations (Report 1022873)

- Staff determined conservatism in the 0.1 criterion may be warranted due to environmental fatigue affects

- If environmental effects were accounted for, staff demonstrated willingness to accept 0.4 as a criterion

- The staff was not aware of a compelling reason to update the criterion at that time Public Meeting on Environmentally Assisted Fatigue Research 7

ESBWR Design Certification

  • Economic Simplified Boiling Water Reactor (ESBWR)
  • Adopted 0.4 as CUF criterion when environmental effects were accounted for

- Basis for this decision is not clearly documented, but it has roots in a 1986 memo (Legacy Library 8603060209B)

  • The staff updated BTP 3-4 in July 2016 to include

- For new reactor design certification reviews, the staff has considered a CUF limit of 0.4 to be acceptable when the effects of EAF are considered in the piping design.

Public Meeting on Environmentally Assisted Fatigue Research 8

Other References

  • American Nuclear Society Standard 58.2

- Very similar to BTP 3-4

- Adopts CUF 0.4

- ANS was not able to provide the technical basis for this criterion

  • 1986 Memo with Rodabaugh letter attached

- Derives CUF 0.4 approach

  • S. R. Gosselin and F. A. Simonen, A Risk-Informed Approach to Fatigue Break Criterion for ASME Class 1 High Energy Piping, Proceedings of the 20th International Conference on Nuclear Engineering, July 30 - August 3, 2012, Anaheim, CA, ICONE20-54534.

- A risk-informed approach to the CUF criterion

  • EPRI 1022873, Improved Basis and Requirements for Break Location Postulation, EPRI, Palo Alto, CA, October 2011.

Public Meeting on Environmentally Assisted Fatigue Research 9

Current Status of User Need #2

- Background information gathered and organized

- Draft TLR written but not finalized

- All NRC work on the CUF criterion has ceased due to low priority

  • Jet force models

- RES recently restarted research on jet force calculations

- The focus is to provide conservative modeling guidance for HELB jet force calculations

- Potential work includes updating ANSI/ANS 58.2-1988 standard

- Work performed in RES/DSA, POC: Jason Thompson Public Meeting on Environmentally Assisted Fatigue Research 10

Whats Next?

  • A few questions to ponder:

- Do any PWRs use CUF = 0.1? Why not?

- Why do some BWRs have CUF = 0.1 and others do not?

- How did B31.1 plants address this issue (since these plants do not have CUFs)?

  • Discussion - Whats next?

Public Meeting on Environmentally Assisted Fatigue Research 11

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