ML24004A285

(CN 96-020) 10 CFR Guidance: Definition of Leak-Before-Break Analysis and Its Application to Plant Piping Systems

ML24004A285
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Issue date:	09/26/1996
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CN 96-020
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 NRC INSPECTION MANUAL EMCB PART 9900: 10 CFR GUIDANCE

LBBGUIDE. CFR AND ITS APPLICATION TO PLANT PIPING SYSTEMS DEFINITION OF LEAK-BEFORE-BREAK ANALYSIS

A. PURPOSE To provide guidance application for the evaluation of nuclear power plant piping systems. on the definition of Leak-Before-Break (LBB) analysis and its

B. BACKGROUND licensees, licensee submittal It has come to the attention of the staff through recent discussions with s, and internal staff discuss i"ons that licensees may be performing analyses purported to be "LBB analyses" for purposes not approved and requires NRC review and approval. This directive discusses the existing by the NRC. LBB is an analysis procedure with a limited scope of applicability this area. regulatory positions related to this issue and provides inspection guidance in

C. DISCUSSION The NRC undertook a plan to assess the applicability of LBB analyses to nuclear power plant piping systems with the establishment of the Piping Review Committee and the Pipe Break Task Group during the early 1980s. The work of the Pipe Break Task Group culminated in the publication of NUREG-1061. Vol. 3 in November 1984.

which delineated the staff's assessment of LBB applicability. Subsequently. the NRC amended the scope of General Design Criteria 4 (GDC-4) of Appendix A to Title 10 Code of Federal Regulations Part 50 (10 CFR Part 50) to include the use of LBB analyses to allow the removal of pipe whip restraints, jet impingement barriers, and related equipment designed to address the dynamic effects of postulated ruptures in pressurized water reactor coolant system (RCS) piping (2). Further amendment of the ru 1 e extended LBB app 1 i cabil i ty to the high energy piping of a 11 50 as follows: reactor types (3). This is stated in the current (1996) revision of 10 CFR Part

However. dynamic effects associated with postulated pipe ruptures in analyses reviewed and approved by the Corrmission [emphasis added] nuc 1 ear power uni ts may be exc 1 uded from the design basis when demonstrate that the probability of fluid system piping rupture is the piping. extremely low under conditions consistent with the design basis for

• Issue Date: 09/26/96 - 1 - 9900 LBB Analysis Finally, a new draft Standard Review Plan (SRP) Section 3.6.3 was developed to analyses. The limitations on the application of LBB analyses are comprehensively include guidance on the evaluation of licensee submittals with respect to LBB addressed in references Cl) through (3) below, as well as draft SRP Section

• 3.6.3.

As noted above, the NRC-accepted removal of components designed to mitigate the dynamic effects of high energy application of LBB analysis was tailored to the effects which could be excluded under the modifications of GDC-4 in references (pressure > 275 psi or temperature > 200 °F) pipe ruptures. Those dynamic (2) and (3) included:

(a) missile generation, (b) pipe whipping, (c) pipe break reaction forces, Cd) jet impingement forces, Ce) d~compression waves within the ruptured pipe, and Cf) dynamic or nonstatic pressurization of cavities, compartments. or subcompartments (not performing a containment function) as a result of the pipe rupture.

of the postulated pipe break. These are as opposed to global effects such as In general, the considerations listed above can be summarized as local effects gross containment pressurization, rises in area temperatures and/or humidity, radiation release, and fluid inventory loss. Reanalysis as a result of the use of LBB of the magnitude of these global effects and their influence on the design of emergency core cooling systems, containment boundaries, and/ or the envi ronmen ta l qualification of electrical and mechanical components is not allowed by the regulations.

Therefore, if a licensee has received an SER from the Commission noting which sections of the facility's piping have been approved for the application of LBB

• analysis modifications such as the following may be undertaken:

(a) The removal of pipe whip restraints and jet impingement shields.

Cb) The removal of snubbers whose only design function is the mitigation of thrust loads on steam generators and reactor coolant pumps (c) Temporary or blowout shielding designed to protect the integrity of associated with the pipe break.

the reactor pressure vessel bioshield during design basis loss of Cd) The elimination of pressure and temperature conditions for the design coolant accident events may be replaced with permanent shielding.

of subcompartments associated with the break of a line (but only if the subcompartment itself does not provide a containment related Ce) The installation of permanent refuelling pool seals. function).

D. CON CL US ION If the inspector identifies a situation in which a licensee proposes to apply LBB analysis for any purpose, the inspector should:

1. Verify that the licensee has received NRC review and approval for the LBB analysis for the piping system under consideration and possesses an NRC SER.

9900 LBB Analysis - 2 - Issue Date: 09/26/96

2. Examine the modification which is being proposed to establish that the purpose for the application of LBB is appropriate given the information provided in this Inspection Guidance and references (1) through (4) below.

3. licensee's actions. the item should be sent via TIA to NRR for If the inspector is unable to verify the appropriateness of the

• assessment and interpretation.

E. REFERENCES The guidance provided in this directive was extracted from the following:

1. NUREG-1061. Volume 3. Report of the U.S. Nuclear Regulatory Review Committee, Evaluation of the Potential for Pipe Breaks. November 1984. Commission Piping

2. Federal 'Register Vol. 51. No. 70. April 11. 1986.

3. Federal Register Vol. 52. No. 207. October 27. 1987.

4. Draft Standard Review Plan (NUREG-0800) Section 3.6.3.

END

Issue Date: 09/26/96 - 3 - 9900 LBB Analysis