ML20244E522
| ML20244E522 | |
| Person / Time | |
|---|---|
| Issue date: | 12/18/1986 |
| From: | Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Ward D Advisory Committee on Reactor Safeguards |
| Shared Package | |
| ML20149C371 | List:
|
| References | |
| NUDOCS 8612230109 | |
| Download: ML20244E522 (17) | |
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u-A EMC.LOSURE 3
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UNITED STATES
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7 Mr. David A. . Ward, Chairman Advisory Committee on Reactor Shfeguards
- U. S. Nuclear Regulatory Comission Washington, DC
- 20555 ~
Dear Hr. Ward:
U
SUBJECT:
ACRS COMMENTS ON REY. SRP 3.6.2 " DETERMINATION OF RUPTURE LOCATIONS
M 'AND DYNAMIC EFFECTS' ASSOCIATED WITH THE POSTULATED RUPTURE
~~ OF '
PIPING, DATED 10/2/86
- The staff has; considered the recommendation made in your letter of November 12, 1986 on retaining. nonmechanistically, the effects of an eliminated postulated
- arbitrary intermediate pipe rupture for the purpose of establishing compartment
. and subcompartment pressure buildup, particularly outside containment. While we do not agree with revising Standard Review Plan (SRP) 3.6.2 to address the Comittee recommendation, the staff would be pleased to meet with appropriate
- Committee members to discuss their concerns and see if they can be accommodated in.other ways.
We disagree with your recommendation to retain in part the effects of an eliminated postulated: pipe rupture for a number of reasons. The regulatory analysis performed in'accordance'with Comission policy did not identify differential pressurization as an important contributor to the values and 3-impacts associated with the elimination of arbitrary intermediate pipe rupture.
The regulatory analysis to support the elimination of arbitrary intermediate pipe' rupture focused on the removal of pipe whip restraints and jet impingement barriers which were identified as tue prime contributor to the values and impacts. obtained via this revision. The results of the regulatory analysis do not. justify _ the retention of differential pressurization. In addition to the
- regulatory analysis results, there are other supplemental reasons reinforcing a
. decision not to accept your recommendation; specifically, (1) retention-of
- certain nonmechanistic effects related to an event which has been eliminated.
- has ' caused undue confusion to both staff and industry in past situations and
- .is, therefore, not recommended; (it would be preferable to directly address the structural design bases of compartments and subcompartments if the Committee
.-perceives:some weakness in those design bases due to the elimination of this loading effect.- even though this fact is not supported by the regulatory analysis),'(2) differential pressurization due to tenninal end pipe ruptures,
~ due to intermediate pipe ruptures at high stress and high usage factor locations and'due to leakage cracks are still required and this effectively covers the great majority uf compartment /subcompartment designs, (3) in terms of event- .
. frequency of occurrence, double ended pipe ruptures at piping system terminal !
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ends are rare events and are still retained, double ended pipe ruptures at intennediate locations in a piping ' system are very rare events and are still retained; however, double ended pipe ruptures at the selected arbitrary (low l stress) intermediate locations are extremely rare events with a frequency of occurrence well below most other design basis events and therefore are being proposed as candidates for elimination in their entirety.
Sincerely, Original signed by, Victor Stellop_
Victor Stello, Jr.
Executive Director for Operations Distribution Centrol Files E. Beckjord T. Speis DSR0 Chron. C. Heltemes B. Sheron EIB R/F R. Fraley T. Novak PPAS J. Snfezek <
F. Miraglia V. Stello J. Davis OR.enero H. Denton J. Murray G. Arlotto R. Vollmer D. Mossburg (86-643) J. Richardson R. Hernan EDQ + M 2Jc7 3
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- Westinghouse Electric Corporation Power Systems .87 JAN 22 A9:09 P%.. " , . . . . '
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6/ M fMM - January 16, l a NS-NRC-87a-3 K" 0mmAx 3, gpu
-Mr. Michael Lesar, Acting Chief /
Rules and Procedures Branch Division of Rules and Records U.S. Nuc, lear Regulatory Commission Room 4000, Maryland National Bank Building 7735 Old Gea'getown r Road Bethesda, Maryland 20014 r.
Dear Mr. . Lesar:
In the Federal Register, Volume 51, No. 232, dated December 3, 1986 the U.S.
Nuclear Regulatory Commission posted a proposed revision to Branch Technical Position ME83-1 of Standard Review Plan Section 3.6.2 in NUREG-0800. The revision would change requirements relating to postulated arbitrary intermediate pipe ruptures in Class 1, 2 and 3 piping as specified in 8.1.c(1)(d) and 8.1.c(2)(b)(ii) of Branch Technical Position MEB3-1.
Pursuant to the solicitation for comments on this proposed revision, Westinghouse Electric Corporation offers the following:
A. Class 1 Piping not in containment penetration area:
The proposed Standard Review Plan revisions to the stress threshold for pipe breaks in Class 1 systems is not technically justified and will lead to a large number of unnecessary postulated intermediate break locations in PWR piping. The July 1981 version of the SRP specifies break locations when both Equation 10 and Equation 13 exceed 80% of their Code allowables or when both Equation 10 and Equation 12 exceed 80% of their Code allowables. The proposed SRP revision specifies break location when Equation 10 exceeds 80% of its Code
" allowable". Westinghouse recommends retaining the combinations of Equations 10 and 12 and Equations 10 and 13. The Code permits Equation 10 calculated stresses f ar in excess of the Code " allowable",
and the actual Code stress limits are based on Equations 12 and 13.
Thus the use of Equation 10 only is unduly conservati'/a.
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.~ B ; Seismically analyzed non-ASME Class piping not in containment penetration area:
The' proposed-Standard fieview Plan changes require that break locations in ANSI /ASML'831.1 (l) piping systems be determined by the. stress i Equations,(or:ASME C16ss 2/3 piping. This will lead to unnecessary.
additional analytical ~ effort and possibly unnecessary. intermediate B break. locations. A more direct approach which utilizes 831.1 Equations.12 and 13 in place of Class 2/3 Equation 9 and 10 should be pe rmi-t ted .
-(II
References:
"ASME Code for Pressure. Piping, 831 An American National Standahd", American Society.o'f Mechanical Engineers, 1986.
[ Westinghouse appreciates the opportunity to submit these comments and the consideration.they will be given by the staff.
Sincerely, Id w 2. n]
W. At>nson, Mg .
Nuclear Safety Department t
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Duxe Powen GOMPANY
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Jsnuary.19, 1987 n
' r. Michael Lesar, ' Acting Chief M 7 /kdY
-Rules and Procedures' Branch 8,gh 3, Division of Rules and Records fe,[PT U.S.. Nuclear Regul,atory Commission g' , /
Bathesda,-Maryland ~200.14 s l
Subject:
Revision to Branch Techni..a1 Position
'MEB 301
. Duke Power Company' Comments
(
? .Dsar Mr. Lesar:
c-In the Federal Register dated December 3,1966, the Nuclear Regulatory Commission published for com ent a revision to Branch Technical Position MEB 301 of Standard Review Plan section 3.6.2 in }"JREG-0800. This would change requirements relating to' postulated arbitrary intermediate pipe rupture in Class 1, 2, and 3 piping as specified in B.I.c. (1gd) and B.i .c. (2)(b)(ii) of Branch Technical Position MEB 3-1.
The following is Duke Power Corpany's comment on the revision:
NUREG-1061 recommended the elimination of all Arbitrary Intermediate Breaks without specifying class of piping. In addition to Class 1, 2, and 3 piping, Arbitrary Intermediate Breaks have been postulated in ANSI B 31.1 piping which.was seismically designed and stress analyzed to the requirements of Class 2 and 3 piping. For clarity, the proposed revision to MEB 3-1 should be worded so as not to exclude any class of piping in which Arbitrary Intermediate Breaks have been postulated.
Duke Power appreciates the opportunity to comment on this revision and requests
' the Commission give consideration to the above item prior to finalization.
- Vsry truly yours.
O d /$ M
.Hal B. Tucker p9
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Etat.LOSORE 5
[7590-01]
L NUCLEAR.RtGULATORY COMMISSION h
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. Standard Review Plan; Issuance L ' The Nuclear Regulatory Commission (NRC) has finalize'd its revision of Branch Technical Position MEB 3-1 of .' Standard Review Plan (SRP) Section 3.6.2 'in NUREG-0800. The revision is effective immediately. Public commerit on this
. revision .was solicited in a' Federal Register notice published on December 3
-1986 (51 FR 43695). Two public conrnent letters were received which raised
< -three issues as described below. The comment letters did not overtly support nor oppose the proposed revision, but instead offered tuggested improvements or. raised questions.
Issue 1. The revised MEB 3-1 actually increases conservatism for po-stulated intermediate pipe ruptures determined by stress in Class 1. piping.
The former requirements should be retained.
NRC Response:
The revised version of MEB 3-1 now requires only that the stress range in ASME Code,Section III, NB-3653, Equation (10) exceed 2.4 S,in order that a rupture be postulated in Class I piping. Formerly, to postulate a pipe rupture, the stress range in either Equation (12) or (13) would, in additio.n, need to exceed
6
[7590-01]
2.4 S,. This apparently could lead to more postulated pipe ruptures, since now only one condition must be satisfied (as opposed to two conditions L formerly), for a pipe rupture to be postulated. The NRC changed its position p
relating to stress-determined intermediate pipe ruptures in Class 1 piping
.because the linear thermal gradient stress term was removed from Equation (10) since the ' July 1981 version of MEB 3-1 was published. The new requirement i
- would have minimal impact, since it will apply only to piping in Class 1 future designs where demonstration of leak-before-break is expected to be
, successful in many situations. Such a successful demonstration will eliminate all pipe ruptures, including those postulated at intermediate locations by high stress.
Issue 2. For seismically analyzed non-ASME piping, the requirements to use ASME Class 2 and 3 rules poses unnecessary additional analytical effort and possibly unnecessary intermediate pipe ruptures.
NRC Response:
Formerly B.I.c.(3) of PEB 3-1 referred to breeks in nonnuclear class piping.
The revised PEP 3-1 in B.I.c.(3) refers instead to seismically analyzed non- I ASME Class piping. Breaks are only postulated in seismically analyzed piping in the revised FEB 3-1. Because seismic stresses are available for all pipinc
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2
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[7590-01]
1 covered, the ' staff has decided to utilize ASME Class 2/3 piping rules for determining break locations and number, even if the piping was designed by ANSI B31.1. This will not impose, in the staff's view, any significant additional analytical effort for licensees and applicants, but will result in more real-istic criteria for postulating pipe breaks.
Issue 3. Arbitrary intermediate pipe breaks should be eliminated 'in
~~
seismically analyzed piping designed by ANSI B31.1.
NRC Response:
B.1.c.(3) - of . the revised MEB 3-1 states that " Breaks in seismically analyzed non-ASME Class piping are postulated according to the same requirements for 3
Since arbitrary intermediate pipe ruptures are AStiE Class 2 and 3 piping."
eliminated in Class 2 and 3 piping, they are also eliminated in seismically analyzed non-ASME Class piping (that is, ANSI B31.1 designed piping).
The staff is issuing a Generic Letter advising all licensees and applicants of this revision to MEB 3-1. The Generic Letter will also distribute the revised Branch Technical Position MEB 3-1. The revised MEB 3-1 is available for inspection at the Commission's Public Document Room,1717 H Street NW., Wash-ington, DC. Individual copies may be obtained from John A. O'Brien, Telephone
-(301)443-7854, 3
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s f7590-01' l
Dated at Rockville, Maryland this day of 1987
,/-
For the Nuclear Regulatory Commission Eric S. Beckjord, Director Office of Nuclear Regulatory Research 4
m i H'.. ENC.LOSURE G fo urg'o,,
UNITED STATES
/p o NUCLEAR REGULATORY COMMISSION
.h k ' WASHINGTON, D. C. 20555
- / January 27, 1987
- ses TO ALL OPERATING LICENSEES, CONSTRUCTION PEPMIT HOLDEPS AND APPLICANTS
- .FOR CONSTRUCTION PERMITS
SUBJECT:
RELAXATION IN ARBITRARY INTERMEDIATE PIPE RUPTURE RE0VIREMENTS (GENERIC LETTER 87-XX)
The NRC has finalized a revision to Branch Technical Position MEB 3-1 of Standard Review Plan Section 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 pressurization and decompression waves within the ruptured pipe) and all environmental effects. (pressure, temperature, humidity and flooding) resulting from -aribtrary intermediate pipe ruptures. 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 reauested before any changes are made.
Arbitrary intermediate pipe ruptures which previously were specified in B.I.c.(1)(d) of MEB 3-1 for Class 1 piping and in B.1,c.(2)(b)(ii) of MEB 3-1 for 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 ar.d 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 re-vision to MEB 3-1.
Harold Denton, Director Office of Nuclear Reactor Regulation
Enclosure:
Revised MEB 3-1 of SRP 3.6.2
,'., ENO.LO50 RE 7 F .
BRANCH TECHNICAL POSITION MEB 3-1 POSTULATED RUPTURE LOCATIONS IN FLUID SYSTEM PIPING INSIDE AND OUTSIDE CONTAINMENT A. BACKGR0t'ND 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 u,tilize the available piping design information by postulating pipe ruptures at locations having relatively higher potential for failure, such that an adeouate 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.I.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.1 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 teet the requirement of the ASME Code, Sec-tion III, Subarticle NE-1120 and the following additional design re-quirements:
I Systems and c mponents 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 - February 1987 I 1_ ___ __ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ . _ . }
a .
t (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 loads sets (including the zero load set) should not exceed 2.4 S,,
2 and should be calculated by Eq. (10) in NB-3653, ASME -
Code,Section III.
If the calculated maximum stress range of Eq. (10) exceeds 2.4 S,, the st) . ranges calculated by both Eq. (12) and Eq. (13) in Pam uph 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 h under the loadings resulting from a postulated piping failure beyond these portions of piping should not exceed I the lesser of 2.25 S, and 1.8 Sy except that following a g 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 fomed 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 themal expansion)).The including g S h and San OBE y
event should not exceed 0.8(1.8 Sh+SA A 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.
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 - February 1987 y
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'(e) The' maximum stress.: as calculated by Eq. (9) in NC-3653 under the' loadings resulting from a postulated piping
- failure ofi fluid system piping beyond these portions of .
piping should not exceed the lesser of 2.25 Sh and 1.8 Sy . l Primary loads include those which are deflection limited E 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- 4 structed in accordance with the Power Piping Code ANSI
' i 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 1 welds shall be fully radiographer.
'(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.I.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 circumferential welds unless specific- access provisions are made to permit inservice volumetric examination of the longitudinal and circumferential welds.
'i4) 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 surface of the piping (e.g., flued integrally forged pipe fittings may be ' red) 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.I.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 i entire guard pipe assembly should be designed to meet the following requirements and tests: 1
)
i (a) The design pressure and temperature should not be less than the !
o maximum operating pressure and temperature of the enclosed pipe under , normal plant conditions.
l 3.6.2-12 Rev. 2 - February 1987 f
Im a - _
I i
s (b) The Level C stress limits in NE-3220, ASME Code Section III, should not be exceeded under the loadings associated ,
with containment design pressure and temperature in com-bination 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.
4 (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 definad 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.I.b, breaks in Class 1 piping (ASPE Code,Section III) should be postulated at the following locations in each piping and branch run:
3 (a) At tenninal ends 2
(b3 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 in the stress analysis and is shown to have a significant effect on the main run behavior. In piping runs which are maintained pres-surized 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 runs is the piping connection to this closed valve.
I ;
Rev. 2 - February 1987 l 3.6.2-13 1
1 I
- i shifted; however, the initially determined intermediate break locations need not be changed unless one of the following I conditions exists:
(1) 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 required in pipe parameters such as major dif- 4 ferences in pipe size, wall thickness, and routing.
(?) With the exceptions of those portions of piping identified in B.1.b., y 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 t_erminal 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. 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 calculated2 by the sum of Eos. (9) and (10) in NC/ND-3653, ASME Code,Section III, 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; however, the initially determined intermediate break locations may be used unless a redesign of the piping resulting in a change in pipe parameters (diameter, wall thickness, is required, or the dynamic effects from therouting) 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 requirements for ASME Class 2 and 3 piping 4
above .
4 Note that in addition, breaks in non-seismic, that is, non-Category I piping.
- are to be taken into account as described in Section II.2.k. " Interaction of Other Piping with Category I Piping" of SRP 3.9.2.
3.6.2-14 Rev. 2 - February 1987
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(4) Applicableto(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.I.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.I.b. leakage cracks should be postulated as follows:
(1) For ASME Code,Section III Class 1 piping, at axial lo-2 cations where the calculated stress range by Eq. (10) in NB-3653 exceeds 1.2 Sg .
(2) Fcr 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 by the sum of Eqs. (9) and (10) in 2
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.1.a. of BTP ASB 3-1, a review of the piping layout and plant arrangement drawings 3.6.2-15 Rev. 2 - February 1987 l
\~c __ - _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
l l
should clearly show that the effects of through-wall leakage ;
, cracks at any location in piping designed to seismic and non-seismic standards are isolated or physically remote from essen- .
' tial systems and components. j i
- 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 q outboard isolation valves provided they meet the requirements of the ASME Code,Section III, NE-1120, and the stresses cal-culated2 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 Systenis 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., !
(b) for ASME Code.Section III, Class 1 piping, the stress range calculated 2 by Eq. (10) in NB-3653 is i less than 1.2 S,,
(c) for ASME Code.Section III, Class 2 or 3 and 2
by nonsafety class p(iping, the stresses calculated 9) and (10) in the sum of Eqs.
than 0.4 times the sum of the stress lir.its 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 B.3.d. of BTP ASB 3-1.
- d. Moderate-Energy Fluid Systems in Froximity to High-Energy _
Fluid Systems Leakage cracks need not be postulated in moderate-energy h j
fluid system piping located in an area in which a break in 3 l
l 3.6.2-16 Rev. 2 - February 1987 i
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LY__-__________-____:_____ _ _ _ _ _ _ . _ _ .
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 systeg piping, the provisions of B.2.c. should be applied.
- e. Fluid Systems Oualifying as High-Energy or Moderate-Energy Systems Leakage cracks instead of breaks may be postulated in the piping of h those. fluid systems that qualify as hich-energy fluid systems for
- only short operational period 5 but qualify as moderate-energy fluid systems for the major operational period.
- 3. Type of Breaks and Leakage Cracks in Fluid 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 exceeding a nominal pipe size of 1 inch, except where the maximum stress ran bxceeds the limits specified in B.I.c.(1) and B.I.c.(?) ge but the circumferential 5 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 should be postulated at the piping welds to each fitting, valve, or welded attachment.
I 5
The operational period is considered "short" if the fraction of time that the g system operates within the pressure-temperature conditions specified for high-energy fluid systems is about 2 percent 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).
3.6.2-17 Rev. 2 - February 1987
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t (3) Circumferential breaks should be assumed - to result in pipe severance and separation amounting to at least a one-diameter lateral displace;nent 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).,
under loading . a plastic hinge in the piping is not developed (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.
i
- b. Longitudinal' Pipe Breaks The' fellowing longitudinal breaks should be postulated in high-energy fluid s:ystem piping at the locations of the circumferer.tial breaks specif"ed in B.3.a.:
(1) Longitudinal breaks in fluid system piping and branch runs shtuld be postulated in nominal pipe sizes 4-inch and larger, excapt where the maximum stress range 2 exceeds the limits 3 spe:ified in B.1.c.(1) and B.I.c.(2) but the axial stress range B is it least 1.5 tirnes 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 elementanalysis).
(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 i
3.6.2-18 Rev. 2 - February 1987 F-
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analytically or experimentally determined thrust coefficient as I determined for a circumferential break at the same locatinn. l
, 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. ,
t (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 Lenkage cracks should be postulated at those axial locations specified in B.I.e for high-energy fluid s piping systems not exempted in B.2.c.(1.) forystem moderate-energy piping andfluid in those 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 conse For-moderate-energy fluid system piping, see B.2.c.(2)quences. .
(3) Flyid flow from a leakage crack should be based on a circular opening of area ecual 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 cMck should be assumed to result in an environment that wets ali unprotected components within the compartment, with consecuent flooding in the compartment and connunicating compartments. Flooding effects should be deter-mined on the basis of a conservatively estimated time period re- .
quired to effect corrective actions. l C. REFERENCES
- 1. 10 CFR Part 50, Appendix A, General Design Criterion 4, " Environmental and Missile Design Basis."
- 2. " Boiler and Pressure Vessel Code " Sections III and XI, American Society of Mechanical Engineers, 1986 Edition.
- 3. Regulatory Guide 1.11 " Instrument Lines Penetrating Primary Reactor Containment."
3.6.2-19 Rev. 2 - February 1087
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