NRC Generic Letter 1987-11
v
- - .~ S
e^UNITED STATES
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D. C.20555 June 19, 1987 TO ALL OPERATING LICENSEES, CONSTRUCTION PERMIT HOLDERS AND APPLICANTS FOR
CONSTRUCTION PERMITS
SUBJECT: RELAXATION IN ARBITRARY INTERMEDIATE PIPE RUPTURE REQUIREMENTS
(GENERIC LETTER 87- 1]
The NRC has finalized a revision to Branch Technical Position MEB 3-1 of Standard Review 'Plan S~ection 3.6.2 In NUREG-0800 (Enclosure 1). The revision eliminates all dynamic effects (missile generation, pipe whipping, pipe break reaction forces, Jet impingement forces, compartment, subcompartment and cavity pressurizations and decompression waves within the ruptured pipe) and all environmental effects (pressure, temperature, humidity and flooding) resulting from arbitrary intermediate pipe ruptures. This action allows the elimination of pipe whip restraints and Jet impingement shields placed to mitigate the effects of arbitrary intermediate pipe ruptures,, and other related changes.
Licensees of operating plants desiring to eliminate previously required effects from arbitrary intermediate pipe ruptures may do so without prior NRC approval unless such changes conflict with the license or technical specifications. In the case of a conflict, a license amendment should be requested before any changes are made. In either case, the licensees' updated FSARs should reflect eliminated hardware associated wit'h arbitrary intermediate pipe ruptures.
Arbitrary intermediate pipe ruptures, which previously were specified in B.1.c.
-(l)(d) of MEB 3-1 for ASME Code Class 1 piping and in B.1.c.(2)(b)(ii) of MEB
3-1 for ASME Code Class 2 and 3 piping, are now no longer mentioned or defined in MEB 3-1. Besides the relaxation in requirements relating to arbitrary intermediate pipe ruptures, the revised Standard Review Plan Section 3.6.2 updates the citations to the ASME stress limits to achieve consistency with'
current practices, and introduces other minor changes. However, requirements for postulated terminal end pipe ruptures, postulated intermediate pipe ruptures at locations of high stress and high usage factor and for leakage cracks are retained in the revision to MEB 3-1.
Frank J a. r.
Associate Director for Projects cL eOffice of Nuclear Reactor Regulation Enclosure: Revised MEB 3-1 of SRP 3.6.2 I
~~pghl L5b o
BRANCH TECHNICAL POSITION MEB 3-1 POSTULATED RUPTURE LOCATIONS IN FLUID SYSTEM
PIPING INSIDE AND OUTSIDE CONTAINMENT
A.
BACKGROUND
This position on pipe rupture postulation is intended to comply with the requirements of General Design Criterion 4, of Appendix A to 10 CFR Part 50 for the design of nuclear power plant structures and components. It is recognized that pipe rupture is a rare event which may only occur under unanticipated conditions, such as those which might be caused by possible design, con- struction, or operation errors; unanticipated loads or unanticipated corrosive environments. Our 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 compon- ent. The rules 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.
B. BRANCH TECHNICAL POSITION
1. High-Energy Fluid Systems Piping a. 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)
ASB 3-1, a review of the piping layout and plant arrangement draw- ings should clearly show the effects of postulated piping breaks at any location are isolated or physically remote from essential systems and components. At the designer's option, break locations as determined from B.1.c. of this position may be assumed for this purpose.
b. 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 isola- tion valves provided they meet the requirement of the ASME Code, Sec- tion III, Subarticle NE-1120 and the following additional, design re- quirements:
Systems and components required to shut down the reactor and mitigate the con- sequences of a postulated pipe rupture without offsite power.
3.6.2-10 Rev. 2 - June 1987
(1) The following design stress and fatigue limits should not be exceeded:
For ASME Code,Section III, Class I Piping (a) The maximum stress range between any two loads sets (including the zero load set) should not exceed 2.4 Sm.,
and should 'be calculated2 by Eq. (10) in NB-3653, ASME
Code, Section.III.
If the calculated maximum stress range of Eq. (10) exceeds
2.4 Si. the stress ranges calculated by both Eq. (12) and Eq. (13) in Paragraph NB-3653 should meet the limit of
2.4 S
(b) The cumulative usage factor should be less than 0.1.
(c) The maximum stress, as calculated by Eq. (9) in NB-3652 under the loadings resulting from a postulated piping I -.
failure beyond these portions of piping should not exceed the lesser of 2.25 SM and 1.8 S, 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 assured in accordance with the requirements 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 as calculated by the sum of Eqs. (9)and
(10) in Paragraph NC-3652, ASME Code,Section III, con- sidering 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 should not exceed 0.8(1.8 Sh + SA). The 5h and 5A
^- 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
-2 - III.
2For those loads and conditions in which Level A and Level B stress limits have been specified in the Design Specification (including the operating basis earthquake).
3.6.2-11 Rev. 2 - June 1987
(e) The maximum stress, as calculated by Eq. (9) in NC-3653 under the loadings resulting from a postulated piping failure of fluid system piping beyond these portions of piping should not exceed the lesser of 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 con- structed in accordance with the Power Piping Code ANSI
B31.1 (see ASB 3-1 B.2.c.(4)), the piping shall either be of seamless construction with full radiography of all cir- cumferential welds, or all longitudinal and circumferential welds shall 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 B.L.b.(1).
(3) The number of circumferential and longitudinal piping welds and branch connections should be minimized. Where guard pipes are used, the enclosed portion of fluid system piping-should be seamless con- struction and without cfrcumfergnjtTal 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 con- tainment penetrations and pipe whip restraints) should not require welding directly to the outer surfdce of the piping (e.g., flued integrally forged pipe fittings may be used) except where such welds are, 100 percent volumetrically, examinable in service and a detailed stress analysis is performed to demonstrate compliance with the limits of B.1.b.(1).
(6) Guard pipes provided for those portions of piping in the containment penetration areas should be constructed in accordance with the rules of Class MC, Subsection NE of the ASME Code,Section III, where the guard pipe is part of the containment boundary. In addition, the entire guard pipe assembly should be designed to meet the following requirements 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.
3.6.2-12 Rev. 2 - June 1987
I
(b) The Level C stress limits in NE-3220, ASME Code, Sectionl
- I I .
III, should not be exceeded under the loadings associated
- ' + with containment design pressure and temperature in com- bination with the safe shutdown earthquake.
i (c) Guard pipe assemblies should be subjected to a single pressure test at t-'pressure not less than its design pressure.
(d) Guard pipe assemblies should not prevent the access re- quired to conduct the inservice examination specified in B.1.b.(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 IWA-2400, ASME Code,Section XI.
c. Postulation of Pipe Breaks In Areas Other Than Containment Penetration
(1) With the exception of those portions of piping identified in B.l.b, breaks in Class I piping (ASME Code,Section III) should be postulated at the following locations in each piping and branch run:
(a) At terminal ends 3
2 (b) ,At intermediate locations where the maximum stress range as calculated by Eq. (10) exceeds 2.4 S
(c) At intermediate locations where the cumulative usage factor exceeds 0.1.
As a result of -piping reanalysis due to differences between the design configuration and the as-built configuration, the
- highest stress or cumulative usage factor locations may be
.3.
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 inthe stress analysis and is shown to have a significant pres- effect on the main run' behavior. In piping runs which are maintained (i.e., up surized during normal plant conditions for only a portion of the run to the first normally closed valve) a terminal end of such runs is the piping connection to this closed valve.
Rev. 2 - June 1987
. .-
3.6.2-13
shifted; however, the initially determined intermediate locations need not be changed unless one break conditions exists: of the following
(1) The dynamic effects from the new (as-built)
break locations are not mitigated by the original intermediate I
whip restraints and jet shields. pipe (ii) A change is required in pipe parameters such as major dif- ferences in pipe size, wall thickness, and routing.
(2) With the exceptions of those portions of piping identified in B.L.b.,
breaks in Class 2 and 3 piping (ASME Code,Section III) should be postulated at the following locations in those piping and branch run: portions of each (a) At terminal ends.
(b) At intermediate locations selected by one of the following criteria:
(1) At each pipe fitting (e.g., elbow, tee, cross, nonstandard fitting), welded attachment, and valve.flange, and the piping contains no fittings, welded attachments, Where valves, at one location at each extreme of the or adjacent to the protective structure. piping run
(11) At each location where stresses calculated 2 by Eqs. (9) and (10) in NC/ND-3653, ASME Code, the sum of exceed 0.8 times the sum of the stress limits Section III,
NC/ND-3653. given in As a result of piping reanalysis due to differences between the design configuration and the as-built configuration, the highest stress locations shifted; however, the initially determined may be intermediate break locations may be used unless a redesign piping resulting in a change in pipe parameters of the wall thickness, routing) is required, or (diameter, effects from the new (as-built) the dynamic intermediate break locations are not mitigated by the original restraints and jet shields. pipe whip
(3) Breaks in seismically analyzed non-ASME
Class according to the same requirements for ASME piping are postulated Class 2 and 3 piping above 4
4Note that in addition, breaks in non-seismic, are to be taken into account as described in that is, non-Category I piping, Other Piping with Category I Piping" of SRP 3.9.2.Section II.2.k. "Interaction of
3.6.2-14 Rev. 2 - June 1987
(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 require such a break location to be postulated.
(5) Safety-related equipment must be environmentally qualified in accordance with SRP 3.11. Required pipe ruptures and leakage cracks (whichever controls) must be included in the design bases for environmental qualification of electrical and mechanical equipment both inside and outside the containment.
d. The designer should identify each piping run he has considered to postulate the break locations required by B.1.c. above. In complex systems such as those containing arrangements of head- ers 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 required by these criteria.
e. With the exception of those portions of piping identified in B.L.b, leakage cracks should be postulated as follows:
(1) For ASME Code,Section III Class 1 piping, at axial lo- cations where the, calculated stress range2 by Eq. (10)
in NB-3653 exceeds 1.2 Sf
(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 stress 2 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 which has not been evaluated to obtain stress information should have leakage cracks postulated at axial locations that produce the most severe environmental effects.
2. Moderate-Energy Fluid System Piping a. Fluid Systems Separated from Essential Systems and Components For the purpose of satisfying the separation provisions of plant arrangement as specified in B.L.a. of BTP ASB 3-1, a review of the piping layout and plant arrangement drawings
3.6.2-15 Rev. 2 - June 1987
should clearly show that the effects of through-will leakage.
.cracks at any location in piping designed to seismic and noh- seismic standards are isolated or physically remote from essen- tial systems and components.
b. 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 they meet the requirements of the ASME Code,Section III, NE-1120, and the stresses cal- culateO2 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.
c. 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 B.2.b. or B.2.d.0
(b) for ASME Code, Section IlI, Class 1 piping, the stress range calculated2 by Eq. (10) in NB-3653 is less than 1.2 Sm.
(c) for ASME Code,Section III, Class 2 or 3 and nonsafety class piping, the stresses calculated 2 by the sum of Eqs. (9) and (10) in NC/ND-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 con- sequences.
(3) Leakage cracks should be postulated in fluid system piping designed to nonseismic standards as necessary to satisfy
8.3.d. of BTP.ASB 3-1.
d. 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 breakin
3.6.2-16 Rev. 2 - June 1987
high-energy fluid system Piping is.postulated, provided such leakage cracks wouId 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 B.2.c. should be applied.
e. Fluid Systems Qualifying as High-Energy or Moderate-Energy Systems Leakage cracksinstead of breaks ... may. be postulated in the piping ofl those fluid systems that qualify as high-energy fluid systems for
-only short operational period5 but, qualify as moderate-energy fluid systems for the major operational period.
3. Type of Breaks and Leakage Cracks in Flui'd System Piping a. Circumferential Pipe Breaks The following circumferential breaks should be postulated individually' in high-energy fluid system piping at"'the locations specified in B.1 of this position:
(1) Circumferential breaks should be postulated in .'fluid system piping'and branch'runs exceedinga intoinal pi-pe tize-Of I Inch, except where the maximum stress range- exceeds'-.the limitsl specified in B.l.c.(1) and B.l.c.(2) but the circumferential stress range is at least 1.5 times the axial- stress range.
Instrument lines, one 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 shoul'd be: postulated at the piping welds to each fitting, valve, or welded attachment.
5Tfieoperational period is considered'"short"1 if the fraction of time that thel system operates'wi.thin the pressure-temperature.conditions specified for high- energy fluid systems is about 2 percent. of the ti'me thatasthe system operates as a moderate-energy fluid system (e.g., systems such the reactor decay heat removal system qualify-Aas modetate-energy fluid systems; however, systems such as auxiliary feedwater systms operated curing PWR reactor startup, hot standby, or shUtdown qualify as high-energy fluid systems).
. . . I t : .. - , . . . - ..
I
3.6.2-17 Rev. 2 - June 1987
(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.gi.,.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 the pipe and on a calculated fluid pressure as modifiedarea of by an analytically or experimentally determined thrust coefficient.
Limited pipe displacement at the 'break location, line restrictions, flow limiters, positive pump-controlled flow, the absence of energy reservoirs may be taken into account, andas applicable, in the reduction of Jet discharge.
(5) Pipe whipping should be assumed to occur 'inthe plane defined by the piping geometry and configuration, and to initiate pipe movement in the direction of the Jet reaction.
b. Longitudinal Pipe Breaks The following longitudinal breaks should be postulated in high-enery fluid system piping at the locations of the circumferential breaks specified B.3.a'.:
(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 range exceeds the limits specified in B.1.c.(1) and B.1.c.(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- plane 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 1/2D) 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
3.6.2-18 Rev. 2 - June 1987
- t J
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.
c.- Leakage Crack Leakage cracks should be postulated at those axial locations specified'in B.1.e for high-energy fluid system piping and in those piping systems not exempted in B.2.c.(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 B.2.c.(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 diam- eter 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
-- compartment, with consequent flooding in the compartment and
'communicating compartments. Flooding effects should be deter- mined on the basis of a conservatively estimated time period-re- quired to effect corrective actions.
C. REFERENCES
1. 10'CFR Part 50, Appendix A, General Design Criterion 4, 'Environmental and Missile Design Basis."
2. ABoiler and Pressure Vessel Code," Sections III and XI, American Society
2 of Mechanical Engineers, 1986 Edition'. S e
3. Regulatory Guide 1.11, "Instrument Lines Penetrating Primary Reactor Containment."
3.6.2-19 Rev. 2 - June 1987
LIST OF RECENTLY ISSUED GENERIj LETTERS
Generic Date of Letter No. Subi ect Issuance Issued To GL 87-10 IMPLEMENTATION OF 10 CFR 06/12/87 ALL POWER
73.57, REQUIREMENTS FOR FBI REACTOR
CRIMINAL HISTORY CHECKS LICENSEES
GL 87-09 SECTIONS 3.0 AND 4.0 OF THE 06/04/87 ALL LIGHT
STANDARD TECHNICAL WATER REACTOR
SPECIFICATIONS ON THE LICENSEES AND
APPLICABILITY OF LCO AND APPLICANTS
SURVEILLANCE REQUIREMENTS
GL 87-08 IMPLEMENTATION OF 10 CFR 73.55 05/11/87 ALL POWER
MISCELLANEOUS AMENDMENTS AND REACTOR
SEARCH REQUIREMENTS .LICENSEES
GL B7-07 INFORMATION TRANSMITTAL OF 03/19/87 ALL FACILITY
FINAL RULEMAKING FOR REVISIONS LICENSEES
TO OPERATOR LICENSING-1OCFRS5 AND CONFORMING AMENDMENTS
GL 87-06 TESTING OF PRESSURE ISOLATION 03/13/87 ALL OPERATING
VALVES REACTOR
LICENSEES
GL 87-05 REQUEST FOR ADDITIONAL 03/12/87 LICENSEES OF
INFORMATION-ASSESSMENT OF OR'S,
LICENSEE MEASURES TO MITIGATE APPLICANTS FOR
AND/OR IDENTIFY POTENTIAL OL'S, AND
DEGRADATION MKI HOLDERS OF
MARK I
CONTAINMENTS
GL 87-04 TEMPORARY EXEMPTION FROM 03/06/87 ALL POWER
PROVISIONS OF THE FBI CRIMINAL REACTOR
HISTORY RULE FOR TEMPORARY LICENCES
WORKERS
GL 87-03 VERIFICATION OF SEISMIC 02/26/87 ALL LICENSEES
ADEQUACY OF MECHANICAL AND NOT SUBJECT TO
ELECTRICAL EQUIPTMENT IN USI A-46 OPERATING REACTORS, USI A-46 REQUIREMENTS
GL 87-02 VERIFICATION OF SEISMIC 02/19/87 ALL HOLDERS OF
ADEQUACY OF MECHANICAL AND OPERATING ^.
ELECTRICAL EQUIPMENT IN LICENSES NOT
OPERATING REACTORS (USI A-46) REVIEWED TO
CURRENT, J
LICENSING
CRITERIA ON
SEISMIC
QUALIFICATION
OF EQUIPMENT