ML17251A533
| ML17251A533 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 05/31/1989 |
| From: | Mecredy R ROCHESTER GAS & ELECTRIC CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-011, IEB-88-11, NUDOCS 8906070196 | |
| Download: ML17251A533 (7) | |
Text
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REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
ACCESSION NBR:8906070196 DOC.DATE: 89/05/31 'OTARIZED: NO FACIL:50-244 Robert Emmet Ginna Nuclear Plant, Unit 1, Rochester G
AUTH.NAME
'UTHOR AFFILIATION.
MECREDY,R.C.
Rochester Gas
& Electric Corp.
RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
SUBJECT:
Forwards justification for continued operation re pressurizer surge line stratification.
DISTRIBUTION CODE:
A001D COPIES RECEIVED:LTR ENCL SIZE:
TITLE: OR Submittal:
General Distribution NOTES:License Exp date in accordance with 10CFR2,2.109(9/19/72).
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<Zsit>ZZ ROCHESTER GAS AND ELECTRIC CORPORATION o 89 EAST AVENUE, ROCHESTER, N.Y. 14649-0001 May 31, 1989 TELEPHONE ARE* CODE 7ld 546-2700 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.
20555
References:
- a. License No. DPR-18 (Docket No. 50-244)
- b. Justif ication for Continued Operation Regarding Pressurizer Surge Line Stratification Gentlemen:
Attached is the Justification for Continued Operation regarding pressurizer surge line stratification which was referred to in the RG&E to NRC letter dated March 6,
- 1989, "Alternate Schedule for Evaluation of Pressurizer Surge Line Thermal Stratification".
Very truly yours, Robert C. Mecre General Manager Nuclear Production RWEK042 Attachments xc:
Allen R. Johnson (Mail Stop 14D1)
Project Directorate I-3 Washington, D.C.
20555 U.S. Nuclear Regulatory Commission Region I 475 Allendale Road King of Prussia, PA 19406 Ginna Senior Resident Inspector 8906070 198 89053 1 PDR ADDCK 05000244
- t. P, PDC
JUSTIFICATION FOR CONTINUED OPERATION REGARDING PRESSURIZER SURGE LINE STRATIFICATION R.E. Ginna Back round.
It was first reported in INPO SER 25-87 that temperature measurements at a German PWR indicated thermal transients different than design.
Recent measurements at several domestic PWRs have indicated th'at the temperature difference between the pressurizer and the hot leg results in stratified flow in the surge line, with the top of the flow stream 'being hot (pressurizer temperature) and the bottom being colder (hot leg temperature).
The top-to-bottom temperature difference can reach 250'F to 300'F in certain modes of operation, particularly Modes 3,
4, or 5 during heatup and cooldown.
Surge line stratification causes two effects:
Global bending of the pipe is different than that predicted in the original design.
0.Fatigue life of the piping could be reduced due to the global and local stresses from stratification and striping.
More recently, the NRC has issued Bulletin 88-11, "Pressurizer Surge Line Thermal Stratification", December 20, 1988, identifying actions to be taken by licensees.
a)
Conduct visual inspection walkdown b) Update stress and fatigue analysis to account for stratification and striping c) Obtain monitoring data, as necessary.
The Bulletin encourages licensees to perform actions b) and c) above through collective efforts with other plants.
In October 1988, Rochester Gas and Electric Corporation and other members of the Westinghouse Owners Group (WOG) authorized a program to perform a generic evaluation of surge line stratification in Westinghouse PWRs that will address portions of Bulletin 88-11.
The WOG program is designed to benefit from the experience gained in the performance of several plant specific analyses on Westinghouse PWR surge lines.
These detailed analyses included definition of revised thermal transients (including stratification) and evaluations of pipe
- stress, fatigue usage
- factor, thermal
- striping, fatigue crack
- growth, leak-before-break, and support loads.
The overall analytical approach used in all of these analyses has been consistent and has.been reviewed, in detail, by the NRC staff.
Ps of March 1989, plant-specific analysis have been performed on five domestic Westinghouse PWRs.
In addition, twelve Westinghouse plants have completed or are currently performing an interim evaluation of surge line stratification which includes finite element structural analysis of their specific configuration under stratified loading conditions.
WOG Pro ram Status Surge line physical and operating data has been collected and summarized for all domestic Westinghouse PWRs (55 units).
Information relating to piping layout, supports and restraints, components,
- size, material, operating
- history, etc'.,
has been obtained.
This data has been evaluated in conjunction with available monitoring data and plant-specific analyses performed by Westinghouse.
Based on this evaluation, the WOG has developed several observations and conclusions, regarding the effects of thermal stratification at Westinghouse PWRs, which form the basis of the following justification for continued operation.
JUSTIFICATION FOR CONTINUED OPERATION A. Stratification Severit Thermal stratification
( h.T
> 100'F) has been measured on all surge lines for which monitoring has been performed and which have been reviewed by the WOG to date (eight surge lines).
The amount of stratification measured and its variation with time (cycling) varies.
This variation has been conservatively enveloped and applicability of these enveloping transients has been demonstrated for plant-specific analyses.
Various surge line design parameters were tabulated for each plant.
From this, four parameters judged. to be relatively significant. were identified.
A. Pipe inside diameter B. Piping slope (average)
C. Entrance angle of hot leg nozzle D. Presence of mid-line vertical riser These parameters were used in a
grouping evaluation which resulted in the definition of 10 monitoring groups corresponding to various combinations of these parameters at Westinghouse PWRs.
Approximately 40% of the plants fall into one group for which a
large amount of monitoring data has already been received and for which the enveloping thermal transients, discussed.
- above, are applicable.
The remaining 60%
of Westinghouse PWRs are divided among the other. nine additional groups.
Although monitoring data has not yet been received representative of all these groups, in general, the combination of significant parameters of these nine groups is expected to decrease the severity of stratification below that of the enveloping transients.
This conclusion is also supported by a comparison of available monitoring data.
B. Structural Effects Significant parameters which can influence the structural effects of stratification are:
- a. Location and design of rigid supports and pipe whip restraints
- b. Pipe layout geometry and size
- c. Type and location of piping components Although the material and fabrication techniques for Westinghouse surge lines are reasonably consistent and of high
- quality, the design parameters listed above vary among Westinghouse PWRs.
This variation in design is primarily a result of plant-specific routing requirements.
A preliminary evaluation, comparing the ranges of these parameters to those of plants for which plant-specific analysis and interim evaluations are available (approximately 20-o of Westinghouse PWRs) has been performed.
This comparison indicates a high degree of confidence
- that, from a
combined transient severity and structural effects standpoint, the worst configuration has most likely been evaluated.
This conclusion is supported by plant-specific analyses covering five plants and interim evaluations of six additional plants (interim evaluation is in progress on six more plants as of March 1989).
These analyses and evaluations have included various piping layouts, pipe sizes, support and restraint designs and piping components.
Although the full range of variation in these parameters has not been evaluated, experience gained from these evaluations indicates that further evaluations will not result in a more limiting configuration than those already evaluated.
C.
eratin Procedures The WOG currently has available the surveys of operating procedures performed in support of existing plant-specific analyses.
Experience indicates that heatup and cooldown procedures have a significant effect on stratification in the surge line.
All conclusions reached by the WOG to date have assumed a steam bubble mode heatup and cooldown procedure which may result in a temperature difference between the pressurizer and reactor coolant system (RCS) hot leg of more than 300'F.
In many
- cases, individual plant Operating Procedures and Technical Specifications provide limits on this value.
It is also known that some procedures utilize nitrogen, during at least part of the heatup/cooldown cycle, as a means of providing a
pressure absorbing space in the pressurizer.
Based on information currently available to the
- WOG, a high confidence exists that the steam bubble mode heatup, assumed to date, is conservative with respect to Westinghouse PWRs.
D. Remainin Life All plant-specific analyses performed as of March 1989 have demonstrated compliance with applicable ASME Codes and a surge line fatigue life in excess of a 40 year plant life.
Review of plant-specific fatigue calculations indicates that the surge line fatigue life is primarily dependent on the number of heatup and cooldown cycles, rather than years of operation.
Considering the worst case years of operation (28.5 years) in combination with the worst case number of heatup/cooldown cycles (75, at a different plant) at any Westinghouse PWR, and assuming a 40 year life for all surge lines, it is estimated that no more than approximately 50-o of the fatigue life has been used at any Westinghouse plant to date.
For a design life considering 200 heatup/cooldown cycles (used in plant-specific analyses),
this would indicate approximately 100 remaining cycles.
This number of remaining cycles far exceeds the postulated worst case number for the two year time frame needed to resolve the stratification issue.
E. Leak-Before-Break All the plant-specific analyses performed to date that have included the loadings due to stratification and striping have'alidated the "leak-before-break" concept and have substantiated a
40 year plant life.
Fatigue crack growth calculations, performed as part of these plant-specific
- analyses, have demonstrated that any undiscovered crack as large as 10: of the wall thickness would not grow to cause leakage within a 40 year plant life.
Nevertheless, any postulated through wall crack propagation would most likely result in "leak-before-break" and thus permit a safe and orderly shutdown.
F. Ins ection Histo The NDE inspection history at R.E. Ginna, as well as all other domestic Westinghouse designed
- PWRs, has not revealed any service induced degradation in the surge line piping that has been attributed to thermal stratification.
A visual examination of the pressurizer surge line, prior to the removal of the insulation was performed on March 22, 1989.
The results of this inspection did not indicate any gross discernable distress or structural damage to the surge line.
Following the removal of the insulation, visual, surface and volumetric examinations were performed on each of the welds.
A visual examination was performed on the one spring hanger.
The pipe segments between the welds were visually examined as a part of the adjacent weld examination.
All of the welds and the spring hanger were determined to be acceptable and showed no evidence of any degradation attributable to thermal stratification.
~'
Summa of Conclusions from WOG Pro ram Based on information assembled on surge lines for all domestic Westinghouse
- PWRs, and evaluation of that information in conjunction with plant-specific and other interim evaluation
- results, the WOG concludes that:
4 A high degree of confidence exists that further evaluation will confirm that the worst combination has already been evaluated for stratification severity, structural effects and
.operating procedures.
4 All plant-specific analyses, to date, have demonstrated a 40 year life of the surge line.
Assuming that.
further evaluation leads to the same conclusion for the remaining Westinghouse
- PWRs, the worst case remaining life is approximately 100 heatup/cooldown cycles.
4 Through wall crack propagation is highly unlikely, however, "leak-before-break" would permit a safe and orderly shutdown if a through wall leak should develop.
NDE inspection history demonstrates the present day integrity of Westinghouse PWR pressurizer surge lines.
While additional monitoring,
- analyses, and surveys of'.
operating procedures are expected to further substantiate the above conclusions, the presently available information on surge line stratification indicates that Westinghouse PWRs may be safely operated while additional data is obtained.
Overall Conclusion Based on the above discussions, Rochester Gas and Electric Corporation believes it is acceptable for R.E.
Ginna to continue power operation for at least ten additional heatup/cooldown cycles.
Rochester Gas and Electric Corporation has committed to address the requirements of Bulletin 88-11 by January 1991.