ML20044C593
| ML20044C593 | |
| Person / Time | |
|---|---|
| Issue date: | 03/24/1993 |
| From: | Bagchi G Office of Nuclear Reactor Regulation |
| To: | Norberg J Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19342A692 | List: |
| References | |
| NUDOCS 9304080205 | |
| Download: ML20044C593 (4) | |
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MEMORANDUM FOR: James A. Norberg, Chief Mechanical Engineering Branch Division of Engineering FROM:
Goutam Bagchi, Chief Civil Engineering and Geosciences Branch Division of Engineering
SUBJECT:
PROPOSED REVISION TO CRITERIA FOR POSTULATING INTERMEDIATE PIPE BREAXS
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INTRODUCTION For ASME Code Class 1 piping, the staff position for postulating pipe breaks are delineated in the Branch Technical Position MEB 3-1 of the SRP 3.6.2.
Prior to issuance of Revision 2 of BTP MEB 3-1 in June 1987, breaks were postulated at intermediate locations between terminal ends of a pipe run if one of the following conditions exists:
(1) if the maximum stress range as calculated by Eq.(10) > 2.4 SJ and either by Eq.(12) or Eq(13) > 2.4 S,, or (2) if the fatigue cumulative usage factor (CUF) > 0.1.
For piping in the containment penetration area, breaks need not be postulated if the stress ranges and CUFs can be designed under the same limits stated above. The criteria stated above were implemented in many plants operating today.
In Rev.2 of BTP MEB 3-1, the same criteria are maintained for break exclusion in the containment penetration areas. However, for other areas, the criteria were revised requiring breaks be postulated at any intermediate locations when only Eq.(IS) exceeds 2.4 $,.
The use of Eq.(12) and Eq.(13) was eliminated.
The Advanced Reacters Engineering Section of the Civil Engineering and Geoscience Branch reviewed the impact of BTP MEB 3-1 Revision 2.
We find that the Rev.2 criteria are inconsistent in that they allow higher limits in the containment penetration areas than in other areas.
It would appear that the break exclusion area should provide a margin greater than (or at least equal to) the margin for areas outside the break exclusion area.
In addition, the Rev.2 criteria will result in a significant increase in the number of postulated pipe breaks, which may be counter productive in terms of enhancing plant safety.
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1 IMPACT OF REV.2 CRITERIA Recently, information obtained by us and from various independent sources verify our assumptions about a significant increase in postulated pipe breaks resulting from SRP Rev.2 criteria.
The information consists of the following:
1.
On December 16, 1992, the staff (D. Terao and S. Hou) and its consultant (P. Chen) from ETEC visited TVA at the Watts Bar Nuclear plant (a PWR) site.
Samples of data from recently completed piping reanalysis for the Watts Bar plant were reviewed, which consisted of pipe rupture analysis results of nine piping subsystems.
The plant used SRP 3.6.2 Rev.1 criteria. The staff found a large number of piping node points exceeded the Eq.(10) limit, but were less than the pipe break limit of both Eq.(12) and Eq.(13).
For example, in Run #1, 5 nodes have fatigue CUF <
0.1 and have Eq.(10) > 2.4 S.
However, among these 5 nodes, 4 have both Eq.(12) and Eq.(13) bel,ow the 2.4 S limit and breaks need not be postulated at these 4 locations.
Thisobservationwouldindicatethat the Rev. 2 criteria, which require a pipe break to be postulated when Eq.(10) alone is exceeded, would result in a significant increase in number of postulated pipe breaks from the criteria in Rev.1 of the SRP.
2.
On February 11, 1993, the same team of staff and its consultant visited Sargent & Lundy's office in Chicago. Samples of pipe rupture analysis results of 15 ASME Class 1 subsystems in the La Salle plant (a BWR) were reviewed.
The plant used SRP 3.6.2 Rev.1 criteria. The staff found that for 19 intermediate locations having the maximum stress range in Eq.(10) exceeding 2.4 S,14 also have both Eq.(12) and Eq.(13) within the limits of 2.4 s.
Thus pipe breaks need not be postulated at these 14 locations in ac,cordance with SRP 3.6.2 Rev.1, otherwise would be postulated if SRP 3.6.2 Rev.2 was used.
3.
During the visit to Sargent & Lundy, we were also informed that the Rev.2 criteria were used in the Ulchin Nuclear plant (a PWR) in South Korea and in portions of the Hope Creek plant (a BWR) in United States.
After comparing similar plants using Rev.1 criteria, the Yung-Gwan plant in South Korea and other GE plants in U. S., it was found in both cases that the use of Rev.2 criteria resulted in a significant increase in the number of postulated pipe breaks.
4.
Rev.2 of SRP 3.6.2 was issued in June 1987, following the revision of the ASME Code in which the thermal gradient term was removed from Eq.(10). The ters was included in Eq.(10) during the period when the Rev.1 criteria was in effect. The facts stated in item 3 above indicate that the effect of not using Eq.(12) and Eq.(13) outweight the effect of the specific ASME Code revision.
5.
We have discussed the potential impact of Rev.2 criteria with EMEB staff (M. Hartzman and J. Fair) and the RES staff (J. O'Brien). Opinions of R. Bosnak and the NRC staff consultant E. Rodabaugh were also solicited.
It appears that a unanimous consensus was reached that the current pipe break criteria should be revised.
The RES staff, which originated the Rev.2 criteria also indicated that it was not their intent for the new criteria to result in a significant increase in pipe breaks.
RECOMMENDED. ACTIONS Although there are some differences in piping design criteria between conventional LWR plants and the ALWR plants, we believe the information and conclusions reached above are applicsole in establishing some general trends that are relevant to ALWR plants.
It is our recommendation that the Rev.1 criteria related to allowing the use of Eq.(12) and Eq.(13) be reinstated for the postulation of intermediate pipe breaks in ASME Code Class 1 piping systems. We are taking steps to implement the revised criteria discussed above for standardized ALWR plant designs. The EMEB should take the necessary actions to revise the SRP 3.6.2 accordingly.
Goutam Bagchi, Chief Civil Engineering and Geosciences Branch Division of Engineering
Enclosure:
The marked-up page of SRP 3.6.2 Revision 2 cc:
L. C. Shao A. Murphy J. O'Brien T. Chan M. Hartzman J. Fair I
I
O En c los u re e
(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.
(d) Guard pipe assemblies should not prevent the access re-quird to conduct the inservice examination specified in B.I.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.
Postulation of Pipe Breaks In Areas Other Than Containment Penetration j c.
(1) With the. exception of those portions of piping identified in 8.1.b. breaks in Class 1 piping (ASME Code,Section III) should be postulated at the following locations in each piping and branch run:
3 (a) At terminal ends 2
(b) At intermediate locations where maximum stress range as calculated b
_xceed 4S-er eg. un) er Eq"'03 P an es (c) At intennediate locations care the cutulative 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 3Extremities of piping runs that connect to structures, components (e.g., l 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.
3.6.2-13 Rev. 2 - June 1987
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