ML13333A331
| ML13333A331 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 07/20/1978 |
| From: | Desiree Davis Office of Nuclear Reactor Regulation |
| To: | Mcewen J KMC |
| Shared Package | |
| ML13333A330 | List: |
| References | |
| TASK-03-05.A, TASK-3-5.A, TASK-RR NUDOCS 7812140311 | |
| Download: ML13333A331 (13) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 July 20, 1978 K M C, Incorporated ATTN: Mr. Jack McEwen 1747 Pennsylvania Avenue, N.W.
Washington, D. C. 20006
SUBJECT:
Assessment of Postulated Pipe Breaks Inside Containment for SEP Plants (Topic III-5.A)
Dear Mr. McEwen:
As a followup to our discussion on April 28, 1978, we have drafted an outline (enclosed) of three potential approaches which could be used for postulating pipe break locations inside the containment for SEP plants (SEP Topic III-5.A). With each approach the following two phases of review are involved:
Phase 1 - Evaluation of the effects of the postulated pipe break on the mechanical integrity of the affected piping run and the operability of its components (i.e., would the break postula ted lead to unacceptable degradation of the affected piping system and its components because of reaction loads?).
Phase 2 - Evaluation of the effects of the postulated pipe break on nearby safety-related equipment, structures and systems located inside the containment (i.e., would the break postulated lead to unacceptable degradation of nearby safety-related equipment because of pipe whipping or jet impingement?).
For operating pressurized water reactors, the pipe break effects (described in Phase 1) are presently being considered on a generic basis (NRR's Technical Activity A-2) as discussed in NRC's letter dated January 25, 1978, to licensees. A potential exists to expand this generic concern (Technical Activity A-2) to BWRs. While the scope of this effort is slightly narrower than the SEP effort, we believe that, with only minimal additional effort, it could be expanded to resolve the Phase 1 of the SEP topic described above as well as another SEP topic (VI-2.B Subcompartment Analysis). Therefore, we would propose to integrate much of the output of the generic concern into the SEP, if licensees also believe that a significant amount of effort may be saved.
781.21403(
The assessment of the pipe break effects (described in Phase 2) on safety-related equipment, structures and systems located outside the affected system can, in our opinion, proceed independently of the analytical effort required for Phase 1. Additionally, the consideration of Phase 2 should logically precede Phase 1, since methods to resolve any concern in this area, e.g., additional pipe restraints, may also resolve concerns which could develop in Phase 1.
As we have discussed previously, an efficient way to further develop our Phase 2 approach in resolving this-topic would be to conduct plant visits with selected licensees and assess the application of the aforementioned approaches on several SEP plants.
Don K. Davis, Chief Systematic Evaluation Program Branch Division of Operating Reactors
Enclosure:
As stated cc: Dairyland Power Cooperative MOREam
SYSTEMATIC EVALUATION PROGRA ASSESSMENT OF THE EFFECTS OF POSTULATED BREAKS IN FLUID SYSTEM PIPING INSIDE CONTAINMENT
- 1. INTRODUCTION The purpose of this paper is to provide guidance for selecting the design locations and orientations of postulated breaks in high 1 1/
energy fluid system piping within the reactor containment. Appro priate protection for nearby safety-related equipment from the jet impingement and pipe whipping effects resulting from these postulated breaks would then be assessed.
This technical paper is intended to be used in the Systematic Evaluation Program to assess the effects that postulated breaks in high energy piping systems will have on components of essential systems.
The results of this assessment will be combined with other elements of the Systematic Evaluation Program to determine the staff's overall assessment of the safety adequacy of the operating nuclear power plants.
- 2. DISCUSSION OF POTENTIAL APPROACHES FOR POSTULATING BREAK LOCATIONS Three basic approaches for postulating pipe breaks inside containment are outlined in this paper. The first one is a fully mechanistic approach which utilizes stress analysis for postulating break locations.
The second one is an effect oriented approach which postulates breaks in the immediate vicinity (i.e., most critical locations) of the Definitions of underlined phrases are given in Appendix A to this paper.
--2 safety-related equipment. The third one is a simplified mechanistic approach which postulates breaks at terminal ends, at each pipe fitting (such as elbows, tees, valves and flanges), and at each weld. Also a combination of the three approaches may be utilized if it is justified.
The first approach is an evolution of the current criteria outlined in Regulatory Guide 1.46 and Branch Technical Position (BTP) MEB 3-1.
However, it does not significantly deviate from these criteria. The criteria for this approach are based on the current Mechanical Engineering Branch's (MEB) practice and are extracted from the revised Standard Review Plan(SRP) 3.6.2.
The second approach is an effect oriented approach for postulating break locations which does not require stress analysis.
Its main objective is to provide a basis for protecting safety-related equipment located inside containment from a break anywhere in the piping system.
This approach is based on the current Auxiliary Systems Branch's (ASB) practice for postulating break locations in the mainsteam and feedwater lines outside containment as an alternative to separation.
The criteria for this approach are partially extracted from BTP ASB 3-1.
The third approach is a simplified mechanistic approach which does not require stress analysis. It is also extracted from the revised SRP 3.6.2.
This appraoch will result in a large number of break locations as a trade-off for not performing stress analysis.
-3
- 3. DESCRIPTION OF THE THREE APPROACHES A. Mechanistic Approach This approach postulates breaks at terminal ends of each pipe run and at intermediate locations chosen as follows:
2/
- 1) For seismic Category I, Quality Group A (ASME Code Class 1) piping when either:
a) The stress intensity range (including the zero load set) for the limiting normal and upset plant conditions as cal culated by equation (10) and either equation (12) or (13) of NB-3653 of the ASME Code exceeds 2.4. Sm; or b) The cumulative usage factor derived from the piping fatigue analysis under the loading resulting from the normal, upset and testing plant conditions exceeds (7.1.
- 2) For seismic Category I, Quality Group B (ASME Code Class 2) piping when the stress for the limiting normal and upset conditions as calculated by the sum of equations (9) and (10) of NC-3652 of the ASME Code exceeds 0.8(1.2 Sh + SA).
- 3) For seismic Category I, Quality Group C (ASME Code Class 3) piping when the stress for the limiting normal and upset conditions as calculated by the sum of equations (9) and (10) of ND-3652 of the ASME Code exceeds 0.8(1.2 Sh + SA Section III of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code, "Nuclear Power Plant Components".
-4
- 4)
For seismic Category I, Quality Group D piping when the stress for the limiting normal and upset conditions as calculated by the sum of equations (12) and (13) of 104.8 of ANSI B31.1 exceeds 0.8(1.2 Sh + S
- 5) For non-seismic Category I piping everywhere along the run.
B. Effect Orientated Approach Pipe breaks in each run of a high energy piping system should be postulated at the following locations:
- 1) At the terminal ends of the run; and
- 2) At effect oriented intermediate locations chosen in accordance with the following:
a) A longitudinal pipe break at the point which produces the greatest jet impingement loading on each component of each essential system (typically this would be the point of closest approach); and b) A circumferential pipe break at the point which produces the greatest pipe whip loading on each component of each essential system.
American National Standard Code for Pressure Piping ANSI B31.1, "Power Piping".
-5 C. Simplified Mechanistic Approach This approach postulates breaks at terminal ends, at each pipe fitting (such as elbows, tees, valves and flanges), and at each weld.
A
- 4. TYPES OF BREAKS The following types of pipe breaks should be postulated to occur at the locations determined in Section 3 above:
A. A circumferential break in runs of piping greater than 1 inch nominal size at:
- 1) Each terminal end; and at
- 2) Each of the following intermediate locations:
a) Chosen in accordance with the effect oriented criteria to produce the greatest pipe whip loading on each component of each essential system [3.B.2)b)].
b) Chosen in accordance with the simplified mechanistic approach (3.C.).
c) Chosen in accordance with the mechanistic approach (3.A.).
With the exception of locations chosen based on high usage factor [3.A.l)b)] or on being a non-seismic Category I piping system [3.A.5)], circumferential breaks need not be
-6 postulated when the circumferential stress is equal to or greater than 1.5 times the longitudinal stress.
B. A longitudinal break in runs of piping 4 inch and greater nominal size at each of the following intermediate locations:
- 1) Chosen in accordance with the effect oriented criteria to produce the greatest jet impingement loading on each component of each essential system [3.B.2)a)].
- 2) Chosen in accordance with the simplified mechanistic approach (3.C.).
- 3) Chosen in accordance with the mechanistic approach (3.A.). With the exception of locations chosen based on high usage factor
[3.A.l)b)] or on being a non-seismic Category I piping system
[3.A.5)], longitudinal breaks need not be postulated when the longitudinal stress is equal to or greater than 1.5 times the circumferential stress.
- 5.
EFFECTS OF BREAKS The effects of the above postulated breaks should be calculated based on the following:
A. Circumferential Breaks
- 1) Should be assumed to result in pipe severance and separation amounting to at least a one diameter lateral displacement
-7 of the ruptured piping sections unless physically limited by piping restraints, structural members, or piping stiff ness as may be demonstrated by inelastic limit analysis.
- 2) The dynamic force of the jet discharge at the break location should be based on the effective cross sectional flow area of the pipe.
- 3) Pipe whipping should be assumed to occur in the plane defined by the piping geometry and configuration, and to cause move ment of the pipe in the direction of the jet reaction.
B. Longitudinal Breaks
- 1) Should be assumed to result in an axial split without pipe severance.
a) For break locations selected in accordance with either the mechanistic (3.A.) or simplified mechanistic (3.C.)
approaches, splits should be oriented (but not concurrently) at two diametrically opposed points on the piping circumference such that the jet reaction causes 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.
.*.-8 b) Por break locations selected in accordance with the effect oriented approach [3.B.2)a)], a single split should be oriented such that it produces the greatest jet impingement loading on the component of the essential system.
- 2) The dynamic force of the fluid jet discharge should be based on a circular or elliptical (2D by 1/2D) break area equal to the cross sectional flow area of the pipe at the break location. Alternatively, a smaller split may be assumed where it can be justified using conservative assumptions and methods based on fracture mechanics.
.3) Piping movement should be assumed to occur in the direction of the jet reaction unless physically limited by structural members, piping restraints, or piping stiffness as demonstrated by inelastic analysis.
C. Breaks should be assumed to fully develop instantaneously.
Alternatively, a detailed analysis may be performed to establish a finite opening time.
D. Jet discharges should be assumed to fully develop instantaneously and to sweep the entire arc between the pipe's initial
-9 and final positions. Alternatively, a detailed analysis may.be performed to establish the actual area of jet discharge sweep.
E. The dynamic force of the jet discharge at the break location should be based on a calculated fluid pressure as modified by an analytically or experimentally determined.
thrust coefficient. Limited pipe displacement at the break location, line restriction, flow limiters, positive pump controlled flow, and the absence of energy reservoirs may be taken into account, as applicable, in the reduction of the jet discharge.
F. The environmental effects of changes in pressure, temperature, and humidity should be included.
G. Flooding, if applicable, should be considered in the affected compartment and any communicating compartments. Flooding effects should be determined on the basis of a conservatively estimated time period for corrective action.
H. All unprotected components within the affected compartment should be assumed to be wetted by humidity and indirect spray.
APPENDIX A DEFINITIONS Components of Essential Systems. Components of systems required to shut down the reactor and mitigate the consequences of a postulated piping failure, without offsite power. The specific systems for which protection is necessary will be delineated at a later date.
High-Energy Fluid Systems. Fluid systems that, during normal plant conditions, are either in operation or maintained pressurized under conditions where either or both of the following are met:
- a. maximum operating temperature exceeds 200aF, or
- b. maximum operating pressure exceeds 275 psig.
Normal Plant Conditions.
Plant operating conditions during reactor startup, operation at power, hot standby, or reactor cooldown to cold shutdown condition.
S A. Allowable stress range for thermal expansion as defined in NC-3652 and ND-3652 of the ASME Code and 104.8 of ANSI B31.1.
S h.
Allowable stresses at maximum (hot) temperature as defined in NC-3652 and ND-3652 of the ASME Code and 104.8 of ANSI B31.1.
S M Design stress intensity as defined in Article NB-3600 of the ASME Code.
Terminal Ends.
Extremities of piping runs that connect to large components (such as vessels, pumps) or pipe anchors that act as constraints to piping
-2 movement including rotational movement from static or dynamic loading.
A branch connection to a main piping run is a terminal end of the branch run.
Intersections of runs of comparable size and fixity need not be considered terminal ends when the piping model includes both the run and branch piping and the intersection is not rigidly constrained to the building structure.
Test Plant Conditions. Those plant conditions associated with the production, preservice, and inservice testing of components and systems.
Upset Plant Conditions. Plant operating conditions during system transients that may occur with moderate frequency during plant service life and are anticipated operational occurrences, but not during system testing. The Operating Basis Earthquake (OBE) is considered to be an upset plant condition.