NUREG-0800

U.S. NUCLEAR REGULATORY COMMISSION

STANDARD REVIEW PLAN

BRANCH TECHNICAL POSITION 3-4

POSTULATED RUPTURE LOCATIONS IN FLUID SYSTEM PIPING INSIDE AND OUTSIDE

CONTAINMENT

REVIEW RESPONSIBILITIES

Primary - Organization responsible for Mechanical Engineering reviews

Secondary - None

A. BACKGROUND

This position on pipe rupture postulation is intended to comply with the requirements of
10 CFR Part 50, Appendix A, General Design Criteria (GDC) 4 for the design of nuclear power
plant structures, systems and components (SSCs). It is recognized that pipe rupture is a rare
event that may only occur under unanticipated conditions, such as those which might be caused
by possible design, construction, or operation errors; unanticipated loads; or unanticipated
corrosive environments. The staff’s observation of actual piping failures has indicated that they
generally occur at high stress and fatigue locations, such as at the terminal ends of a piping
system at its connection to the nozzles of a component. The criteria of this position are
intended to utilize the available piping design information by postulating pipe ruptures at
locations having relatively higher potential for failure, such that an adequate and practical level
of protection may be achieved.

Subject to certain limitations, GDC 4 allows dynamic effects associated with postulated pipe
ruptures to be excluded from the design basis when analyses reviewed and approved by the

Revision 2 - March 2007

USNRC STANDARD REVIEW PLAN
This Standard Review Plan, NUREG-0800, has been prepared to establish criteria that the U.S. Nuclear Regulatory Commission
staff responsible for the review of applications to construct and operate nuclear power plants intends to use in evaluating whether
an applicant/licensee meets the NRC's regulations. The Standard Review Plan is not a substitute for the NRC's regulations, and
compliance with it is not required. However, an applicant is required to identify differences between the design features, analytical
techniques, and procedural measures proposed for its facility and the SRP acceptance criteria and evaluate how the proposed
alternatives to the SRP acceptance criteria provide an acceptable method of complying with the NRC regulations.
The standard review plan sections are numbered in accordance with corresponding sections in Regulatory Guide 1.70, "Standard
Format and Content of Safety Analysis Reports for Nuclear Power Plants (LWR Edition)." Not all sections of Regulatory Guide 1.70
have a corresponding review plan section. The SRP sections applicable to a combined license application for a new light-water
reactor (LWR) are based on Regulatory Guide 1.206, "Combined License Applications for Nuclear Power Plants (LWR Edition)."
These documents are made available to the public as part of the NRC's policy to inform the nuclear industry and the general public
of regulatory procedures and policies. Individual sections of NUREG-0800 will be revised periodically, as appropriate, to
accommodate comments and to reflect new information and experience. Comments may be submitted electronically by email to
NRR_SRP@nrc.gov.
Requests for single copies of SRP sections (which may be reproduced) should be made to the U.S. Nuclear Regulatory
Commission, Washington, DC 20555, Attention: Reproduction and Distribution Services Section, or by fax to (301) 415-2289; or by
email to DISTRIBUTION@nrc.gov. Electronic copies of this section are available through the NRC's public Web site at
http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0800/, or in the NRC's Agencywide Documents Access and
Management System (ADAMS), at http://www.nrc.gov/reading-rm/adams.html, under Accession # ML070800008.
Commission demonstrate that the probability of fluid system piping rupture is extremely low
under design basis conditions. These analyses are commonly referred to as “leak-before-
break” (LBB) analyses. The application of LBB to piping system design is reviewed in
accordance with SRP Section 3.6.3.

In the ABWR and System 80+ design certification FSERs, the staff accepted an exemption to
10 CFR 100, Appendix A that the design of all safety-related SSCs consider operating basis
earthquake (OBE) loads. In SECY 93-087, the staff recommended that the Commission
approve the approach to eliminate the OBE from the design of SSCs.

Furthermore, the Staff concluded that no replacement earthquake loading should be used to
establish the postulated pipe rupture and leakage crack locations once the OBE is eliminated
from the design and that the criteria for postulating pipe ruptures and leakage cracks in high-
and moderate-energy piping systems should be based on factors attributed only to normal and
operational transients. However, for establishing pipe breaks and leakage cracks due to fatigue
effects, the Staff concluded that calculation of the cumulative usage factor should continue to
include seismic cyclic effects.

B. BRANCH TECHNICAL POSITION

A. High-Energy Fluid Systems Piping

(i) Fluid Systems Separated From Essential Systems and Components. For
the purpose of satisfying the separation provisions of plant arrangement
as specified in B.1.a of Branch Technical Position (BTP) 3-3, a review of
the piping layout and plant arrangement drawings should clearly show
that the effects of postulated piping breaks at any location are isolated or
are physically remote from essential systems and components.1 At the
designer's option, break locations as determined from 2A(iii) of this
position may be assumed for this purpose.

(ii) Fluid System Piping in Containment Penetration Areas. Breaks and cracks need
not be postulated in those portions of piping from containment wall to and
including the inboard or outboard isolation valves, provided they meet the design
criteria of the ASME Code, Section III, Subarticle NE-1120, and the following
additional design criteria:

(1) The following design stress and fatigue limits should not be exceeded:

For ASME Code, Section III, Class 1 Piping

(a) The maximum stress range between any two load sets (including
the zero load set) should not exceed 2.4 Sm and should be
calculated2 by Eq. (10) in ASME Code, Section III, NB-3653.

1
Systems and components necessary to shut down the reactor and mitigate the
consequences of a postulated pipe rupture without offsite power.
2
For those loads and conditions for which Level A and Level B stress limits have been
specified in the design specification (including the operating basis earthquake).

BTP 3-4-2 Revision 2 - March 2007

 If the calculated maximum stress range of Eq. (10) exceeds
2.4 Sm, the stress ranges calculated by both Eq. (12) and Eq. (13)
in Paragraph ASME Code, Section III, NB-3653 should meet the
limit of 2.4 Sm.

(b) The cumulative usage factor should be less than 0.1.

(c) The maximum stress, as calculated by Eq. (9) in ASME Code,

Section III, NB-3652 under the loadings resulting from a
postulated piping failure beyond these portions of piping, should
not exceed 2.25 Sm and 1.8 Sy, except that following a failure
outside containment, the pipe between the outboard isolation
valve and the first restraint may be permitted higher stresses
provided a plastic hinge is not formed and operability of the valves
with such stresses is ensured in accordance with the criteria
specified in SRP Section 3.9.3. Primary loads include those
which are deflection-limited by whip restraints.

For ASME Code, Section III, Class 2 Piping

(d) The maximum stress ranges as calculated by the sum of Eqs.(9)

and (10) in Paragraph NC-3653, ASME Code, Section III,
considering those loads and conditions thereof for which level A
and level B stress limits have been specified in the system's
design specification (i.e., sustained loads, occasional loads, and
thermal expansion), including an OBE event (if applicable), should
not exceed 0.8(1.8 Sh + SA). The Sh and SA are allowable
stresses at maximum (hot) temperature and allowable stress
range for thermal expansion, respectively, as defined in Article
NC-3600 of the ASME Code, Section III.

(e) The maximum stress, as calculated by ASME Code, Section III,

NC-3653, paragraph Eq. (9) under the loadings resulting from a
postulated piping failure of fluid system piping beyond these
portions of piping, should not exceed 2.25 Sh and 1.8 Sy.

Primary loads include those which are deflection-limited by whip

restraints. The exceptions permitted in (c) above may also be
applied, provided that when the piping between the outboard
isolation valve and the restraint is constructed in accordance with
the Power Piping Code ANSI B31.1, the piping should either be of
seamless construction with full radiography of all circumferential
welds or all longitudinal and circumferential welds should be fully
radiographed.

(2) Welded attachments, for pipe supports or other purposes, to these

portions of piping should be avoided, except where detailed stress
analyses, or tests, are performed to demonstrate compliance with the
limits of 2.A(ii)(1).

(3) The number of circumferential and longitudinal piping welds and branch
connections should be minimized. Where guard pipes are used, the

BTP 3-4-3 Revision 2 - March 2007

 enclosed portion of fluid system piping should be seamless construction
and without circumferential welds unless specific access provisions are
made to permit inservice volumetric examination of the longitudinal and
circumferential welds.

(4) The length of these portions of piping should be reduced to the minimum
length practical.

(5) The design of pipe anchors or restraints (e.g., connections to

containment penetrations and pipe-whip restraints) should not need
welding directly to the outer surface of the piping (e.g., flued integrally
forged pipe fittings may be used), except where such welds are 100%
volumetrically examinable in service and a detailed stress analysis is
performed to demonstrate compliance with the limits of 2.A(ii)(1).

(6) Guard pipes provided for those portions of piping in the containment
penetration areas should be constructed in accordance with the criteria of
the ASME Code, Section III, Subsection NE, Class MC, where the guard
pipe is part of the containment boundary. In addition, the entire guard
pipe assembly should be designed to meet the following criteria and
tests:

(a) The design pressure and temperature should not be less than the
maximum operating pressure and temperature of the enclosed
pipe under normal plant conditions.

(b) The Level C stress limits in, ASME Code, Section III, NE-3220
should not be exceeded under the loading associated with
containment design pressure and temperature in combination with
the safe shutdown earthquake.

(c) Guard pipe assemblies should be subjected to a single pressure

test at a pressure not less than its design pressure.

(d) Guard pipe assemblies should not prevent the access necessary
to conduct the inservice examination specified in 2.A(ii)(7).
Inspection ports, if used, should not be located in that portion of
the guard pipe through the annulus of dual barrier containment
structures.

(7) A 100% volumetric inservice examination of all pipe welds should be

conducted during each inspection interval as defined in ASME Code,
Section XI, IWA-2400.

(iii) Postulation of Pipe Breaks in Areas Other Than Containment Penetration

(1) With the exceptions of those portions of piping identified in 2.A(ii), breaks
in Class 1 piping (ASME Code, Section III) should be postulated at the
following locations in each piping and branch run:

BTP 3-4-4 Revision 2 - March 2007

 (a) At terminal ends.3

(b) At intermediate locations where the maximum stress

range2 as calculated by Eq. (10)and either Eq. (12) or
Eq. (13) xceeds 2.4 Sm.

(c) At intermediate locations where the cumulative usage factor

exceeds 0.1.

As a result of piping reanalysis, the highest stress locations may be

shifted; however, the initially determined intermediate break locations
need not be changed unless one of the following conditions exists:

(i) The dynamic effects from the new (as-built) intermediate

break locations are not mitigated by the original pipe-whip
restraints and jet shields.

(ii) A change is necessary in pipe parameters such as major

differences in pipe size, wall thickness, and routing.

(2) With the exceptions of those portions of piping identified in 2A(ii), breaks
in Class 2 and 3 piping (ASME Code, Section III) should be postulated at
the following locations in those portions of each piping and branch run:

(a) At terminal ends.

(b) At intermediate locations selected by one of the following criteria:

(i) At each pipe fitting (e.g., elbow, tee, cross, flange, and
nonstandard fitting), welded attachment, and valve. Or,
where the piping contains no fittings, welded attachments,
or valves, at one location at each extreme of the piping run
adjacent to the protective structure.

(ii) At each location where stresses are calculated2 by the

sum of Eqs. (9) and (10) in NC/ND-3653 of ASME Code,
Section III, to exceed 0.8 times the sum of the stress limits
given in NC/ND-3653.

As a result of piping reanalysis, due to differences

between the design configuration and the as-built
configuration, the highest stress locations may be shifted;

3
This is defined as the extremities of piping runs that connect to structures, components
(e.g., vessels, pumps, valves), or pipe anchors that act as rigid constraints to piping motion and
thermal expansion. A branch connection to a main piping run is a terminal end of the branch
run, except where the branch run is classified as part of a main run in the stress analysis and is
shown to have a significant effect on the main run behavior. In piping runs that are maintained
pressurized during normal plant conditions for only a portion of the run (i.e., up to the first
normally closed valve), a terminal end of such a runs is the piping connection to this closed
valve.

BTP 3-4-5 Revision 2 - March 2007

 however, the initially determined intermediate break
locations may be used unless redesign of the piping
resulting in a change in pipe parameters (diameter, wall
thickness, routing) is necessary, or the dynamic effects
from the new (as-built) intermediate break locations are
not mitigated by the original pipe-whip restraints and jet
shields.

(3) Breaks in seismically analyzed non-ASME Class piping are postulated

according to the same criteria as for ASME Class 2 and 3 piping above.4

(4) Applicable to (1), (2), and (3) above:

If a structure separates a high-energy line from an essential component,

that separating structure should be designed to withstand the
consequences of the pipe break in the high-energy line which produces
the greatest effect at the structure, irrespective of the fact that the above
criteria might not need such a break location to be postulated.

(5) Safety-related equipment should be environmentally qualified in

accordance with SRP Section 3.11. Appropriate pipe ruptures and
leakage cracks (whichever controls) should be included in the design
bases for environmental qualification of electrical and mechanical
equipment both inside and outside the containment.

(iv) The designer should identify each piping run it considered in order to postulate
the break locations pursuant to 2.A(iii) above. In complex systems such as those
containing arrangements of headers and parallel piping running between
headers, the designer should identify and include all such piping within a
designated run in order to postulate the number of breaks pursuant to these
criteria.

(v) With the exceptions of those portions of piping identified in 2.A(ii), leakage
cracks should be postulated as follows:

(1) For ASME Code, Section III, Class 1 piping, at axial locations where the
calculated stress range2 by Eq. (10) in NB-3653 exceeds 1.2 S(m).

(2) For ASME Code, Section III, Class 2 and 3 or nonsafety-class (not ASME
Class 1, 2, or 3) piping, at axial locations where the calculated stress2 by
the sum of Eqs. (9) and (10) in NC/ND-3653 exceeds 0.4 times the sum
of the stress limits given in NC/ND-3653.

(3) Nonsafety-class piping that has not been evaluated to obtain stress
information should have leakage cracks postulated at axial locations that
produce the most severe environmental effects.

4
Note that, in addition, breaks in nonseismic (i.e., non-Category I) piping should be taken into
account as described in Section II.2.k, "Interaction of Other Piping with Category I Piping," of SRP
Section 3.9.2.

BTP 3-4-6 Revision 2 - March 2007

B. Moderate-Energy Fluid System Piping

(i) Fluid Systems Separated from Essential Systems and Components. For the
purpose of satisfying the separation provisions of plant arrangement as specified
in B.1.a of BTP 3-3, a review of the piping layout and plant arrangement
drawings should clearly show that the effects of through-wall leakage cracks at
any location in piping designed to seismic and nonseismic standards are isolated
or physically remote from essential systems and components.

(ii) Fluid System Piping in Containment Penetration Areas. Leakage cracks need
not be postulated in those portions of piping from containment wall to and
including the inboard or outboard isolation valves, provided 1) they meet the
criteria of the ASME Code, Section III, NE-1120, and 2) the stresses calculated2
by the sum of Eqs. (9) and (10) in ASME Code, Section III, NC-3653 do not
exceed 0.4 times the sum of the stress limits given in NC-3653.

(iii) Fluid Systems in Areas Other Than Containment Penetration.

(1) Leakage cracks should be postulated in piping located adjacent to

structures, systems, or components important to safety, except:

(a) Where exempted by 2.B(ii) or 2.B(iv),

(b) For ASME Code, Section III, Class 1 piping, where the
stress range calculated2 by Eq. (10) in NB-3653 is less
than 1.2 S(m), and

(c) For ASME Code, Section III, Class 2 or 3 and

nonsafety-class piping, where the stresses calculated2 by
the sum of Eqs. (9) and (10) in NC/HD-3653 are less than
0.4 times the sum of the stress limits given in
NC/ND-3653.

(2) Leakage cracks, unless the piping system is exempted by (1) above,
should be postulated at axial and circumferential locations that result in
the most severe environmental consequences.

(3) Leakage cracks should be postulated in fluid system piping designed to

nonseismic standards as necessary to satisfy B.3.d of BTP 3-3.

(iv) Moderate-Energy Fluid Systems in Proximity to High-Energy Fluid Systems.

Leakage cracks need not be postulated in moderate-energy fluid system piping
located in an area in which a break in high-energy fluid system piping is
postulated, provided such leakage cracks would not result in more limiting
environmental conditions than the high-energy piping break. Where a postulated
leakage crack in the moderate-energy fluid system piping results in more limiting
environmental conditions than the break in proximate high-energy fluid system
piping, the provisions of 2.B(iii) should be applied.

(v) Fluid Systems Qualifying as High-Energy or Moderate-Energy Systems.

Through-wall leakage cracks instead of breaks may be postulated in the piping

BTP 3-4-7 Revision 2 - March 2007

 of those fluid systems 5 that qualify as high-energy fluid systems for only a short
operational period but qualify as moderate-energy fluid systems for the major
operational period.

C. Type of Breaks and Leakage Cracks in Fluid System Piping

(i) Circumferential Pipe Breaks

The following circumferential breaks should be postulated individually in

high-energy fluid system piping at the locations specified in 2.A of this position:

(1) Circumferential breaks should be postulated in fluid system piping and

branch runs exceeding a nominal pipe size of 1 inch, except where the
maximum stress range2 exceeds the limits specified in 2.A(iii)(1) and
2A(iii)(2), but the circumferential stress range is at least 1.5 times the
axial stress range. Instrument lines, as well as 1 inch and less nominal
pipe or tubing size, should meet the provisions of Regulatory Guide 1.11.

(2) Where break locations are selected without the benefit of stress
calculations, breaks should be postulated at the piping welds to each
fitting, valve, or welded attachment.

(3) Circumferential breaks should be assumed to result in pipe severance

and separation amounting to at least a one-diameter lateral displacement
of the ruptured piping sections unless physically limited by piping
restraints, structural members, or piping stiffness as may be
demonstrated by inelastic limit analysis (e.g., a plastic hinge in the piping
is not developed under loading).

(4) The dynamic force of the jet discharge at the break location should be
based on the effective cross-sectional flow area of the pipe and on a
calculated fluid pressure as modified by an analytically or experimentally
determined thrust coefficient. Limited pipe displacement at the break
location, line restrictions, flow limiters, positive pump-controlled flow, and
the absence of energy reservoirs may be taken into account, as
applicable, in the reduction of jet discharge.

(5) Pipe whipping should be assumed to occur in the plane defined by the
piping geometry and configuration and to initiate pipe movement in the
direction of the jet reaction.

5
The operational period is considered "short" if the fraction of time that the system operates
within the pressure-temperature conditions specified for high-energy fluid systems is about 2% of the time
that the system operates as a moderate-energy fluid system (e.g., systems such as the reactor decay heat
removal system qualify as moderate-energy fluid systems; however, systems such as auxiliary feedwater
systems operated during PWR reactor startup, hot standby, or shutdown qualify as high-energy fluid
systems).

BTP 3-4-8 Revision 2 - March 2007

(ii) Longitudinal Pipe Breaks

The following longitudinal breaks should be postulated in high-energy fluid

system piping at the locations of the circumferential breaks specified in 2C(i):

(1) Longitudinal breaks in fluid system piping and branch runs should be
postulated in nominal pipe sizes 4-inch and larger, except where the
maximum stress range2 exceeds the limits specified in 2.A(iii)(1) and
2.A(iii)(2), but the axial stress range is at least 1.5 times the
circumferential stress range.

(2) Longitudinal breaks need not be postulated at terminal ends.

(3) Longitudinal breaks should be assumed to result in an axial split without

pipe severance. Splits should be oriented (but not concurrently) at two
diametrically opposed points on the piping circumference such that the jet
reactions cause out-of-plant bending of the piping configuration.
Alternatively, a single split may be assumed at the section of highest
tensile stress as determined by detailed stress analysis (e.g., finite
element analysis).

(4) The dynamic force of the fluid jet discharge should be based on a circular
or elliptical (2D x ½D) break area equal to the effective cross-sectional
flow area of the pipe at the break location and on a calculated fluid
pressure modified by an analytically or experimentally determined thrust
coefficient as determined for a circumferential break at the same location.
Line restrictions, flow limiters, positive pump-controlled flow, and the
absence of energy reservoirs may be taken into account, as applicable, in
the reduction of jet discharge.

(5) Piping movement should be assumed to occur in the direction of the jet
reaction unless limited by structural members, piping restraints, or piping
stiffness as demonstrated by inelastic limit analysis.

(iii) Leakage Cracks

Leakage cracks should be postulated at those axial locations specified in 2.A(v)

for high-energy fluid system piping and in those piping systems not exempted in
2.B(iii)(1) for moderate-energy fluid system piping.

(1) Leakage cracks need not be postulated in 1-inch and smaller piping.

(2) For high-energy fluid system piping, the leakage cracks should be
postulated to be in those circumferential locations that result in the most
severe environmental consequences. For moderate-energy fluid system
piping, see 2.B(iii)(2).

(3) Fluid flow from a leakage crack should be based on a circular opening of
area equal to that of a rectangle one-half pipe diameter in length and
one-half pipe wall thickness in width.

(4) The flow from the leakage crack should be assumed to result in an
environment that wets all unprotected components within the

BTP 3-4-9 Revision 2 - March 2007

 compartment, with consequent flooding in the compartment and
communicating compartments. Flooding effects should be determined on
the basis of a conservatively estimated time period necessary to effect
corrective actions.

C. REFERENCES

A. 10 CFR Part 50, Appendix A, General Design Criterion 4, "Environmental and

Dynamic Effects Design Bases."

B. American Society of Mechanical Engineers. Boiler and Pressure Vessel Code,

Section III, “ Rules for Construction on Nuclear Power Plant Components,” and
XI, “Rules for Inservice Inspection of Nuclear Power Plant Components.”New
York, NY American Society of Mechanical Engineers.

C. Regulatory Guide 1.11, "Instrument Lines Penetrating Primary Reactor

Containment."

D. U.S. Nuclear Regulatory Commission. SECY-93-087, "Policy, Technical, and

Licensing Issues Pertaining to Evolutionary and Advanced Light-Water Reactor
(ALWR) Designs," Washington, DC. April 2, 1993; SRM-93-087 issued on
July 21, 1993.

PAPERWORK REDUCTION ACT STATEMENT

The information collections contained in the Standard Review Plan are covered by the requirements of 10 CFR Part 50 and
10 CFR Part 52, and were approved by the Office of Management and Budget, approval number 3150-0011 and 3150-0151.

PUBLIC PROTECTION NOTIFICATION

The NRC may not conduct or sponsor, and a person is not required to respond to, a request for information or an information
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BTP 3-4-10 Revision 2 - March 2007