ML20058P344
| ML20058P344 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 08/15/1990 |
| From: | Wigginton D Office of Nuclear Reactor Regulation |
| To: | Barkhurst R ENTERGY OPERATIONS, INC. |
| References | |
| IEB-88-011, IEB-88-11, TAC-72180, NUDOCS 9008160217 | |
| Download: ML20058P344 (3) | |
Text
_
E (jo nac4,j
'g'
- UNITED STATES
- i
, NUCLEAR REGULATORY COMMISSION i
WASHING TON, D. C. 20555 '
~ _ A.. + y o
Aug'ust' 15,J 1990 ;.
n L
q Docket No. 50-382 Mr. Ross P. Barkhurst Vice President, Operations.
Entergy Operations, Inc.
Post Office Box B q
Killona, Louisiana 70066 1
1
Dear Mr. Barkhurst:
SUBJECT:
NRC BULLETIN NO. 88-11. " PRES $URIZER S11RGE LINE THERMAL' l
STRATIFICATION" - EVALUATION OF COMBUSTION ENGINEERING OWNERS-GROUP;
-l BOUNDINGANALYSIS_(TACNO.72180);
1 By letter dated August.'28,1989,- Louisiana Power and Light Company (LP&L) responded to Item 1.b of NRC Bulletin No. 88-11. " Pressurizer Surge Line-Thermal-.-
i Stratification." 'The letter stated that LP&L supported the bounding. analysis-performed by the Combustion' Engineering Owners Group (CEOG) for which.
1 Waterford 3 is applicable. The analysis; indicated that the: integrity of the pressurizer-surge line (PSL) satisfies the ASME-Section III Code criteria for.
the life of the plant, taking into account the effects of themal stratification.
The staff has completed its review of the CEOG' bounding analysis and finds that-j although sufficient infomation hes been provided-to justify continued plant.
operation until Waterford 3 completes, its final report in accordance with the schedule delineated by the Bulletin, adequate bases have not:been provided for 1
the staff to conclude that the PSL meets all. appropriate Code-limits for-40-year plant life. A copy of the evaluation which was sent to the CEOG'is enclosed for your information. ' Also enclosed is the staff's evaluation of CE's response to items discussed during a September 1989-audit at CE's office.
Entergy 0)erations, Inc. may work collectivelyithrough the CEOG effort to address t1e issues: identified in the evaluation,.but Entergy Operations,JInc.
is responsible to ensure-that the: Bulletin: requested actions.are fully -imple--
mented at Waterford 3.
l 1
q n
1 bg(v(
l 9008160217 900815 E
.PDR ADOCK 05000382
- The staff will assess the conformance~ of the PSL to applicable Codes and f
regulatory requirements for.40. year plant life when the CEOG report regarding l
I Item 1.d of the Bulletin is submitted.
Sincerely,-
Original signed by David L. Wigginton, Project Manager Project Directorate IV.1-Division of Reactor Projects. III, IV, Y and Special Projects Office-of Nuclear Reactor Regulation g
Enclosure:
As stated cc w/ enclosure:
See next page DISTRIBUTION
.DocketJ11e M*
NRC & Local PDRs PD4-1 Reading DCrutchfield BBoger LBerry DWigginton 0GC(MS15B18)
EJordan(MNBB3701)
ACRS(10)(P315)
PD4-1 Plant File PD4 1 Reading File FC
- PD4-1/LA
- PD4 P
- PD4-1/(A)PD :
AME :LBerryk.
l)
- DW ton :TQuay %
ATE:08/lh/90
- 08/[f90
-2 c.
The staff will assess the conformance of the PSL to applicable Codes and regulatory requirements for 40-year plant life when the CEOG report regarding Item 1.d of the Bulletin is submitted.
Sincerely, C
David L. Wi g nton, Project Manager Project Directorate IV-1 Division of Reactor Projects - III, IV, V and Special Projects Office of Nuclear Reactor Regulation
Enclosure:
As stated cc w/ enclosure:
See ne.v.t page
m
.cy v
b Mr. Ross P..Barkhurst-
.Waterford 3" Entergy Operations. Inc.
- I z
. W.;Malcolm Stevenson, Esq.-
Regional Administrator. Region IV.
- Monroe & Leman U.S. Nuclear Regulatory Commission H
201 S;. Charles Avenue, Suite 3300
' Office of Executive Director forL
. New Orleans, Louisiana 70170-3300
. ' Operations
- 611 Ryan Plaza Drive, Suite 1000 J
Mr. E. Blake Arlington, Texas 76011
-Shaw, Pittman, Potts & Trowbridge 2300 N Street, NW LMr.. William H. Spell, Administrator Washington, D.C.
20037-Radiation Protection Division-1 Department of Environmental Quality l
- Resident' Inspector /Waterford NPS Post Office Box 14690 1
President, Parish Council
- Mr. Geral' W. Muench d
- St.1 Charles Parish Vice President,-Operations Hahnville, Louisianae 70057 Support-EntergyLOperations,=Inc.-
Mr; Donald-C. Hintz
.P..D. Box 31995 Executive Vice President and Jackson, Mississippi:'39286.
Chief Operating Officer Entergy Operations,-Inc.
' William A. Cross
- P. O.-Box 31995 Bethesda Licensing Office i
Jackson, Mississippi 39286 3 Metro: Center '
(
' Suite:610'-
[
Chairman Bethesda,~ Maryland' 20814 1
Louisiana Public Service Commission One American. Place, Suite 1630 Mr. Robert B. McGehee-Baton Rouge,-Louisiana 70825-1697 Wise', Carter, Child &. Caraway P.'O.sBox:6511
?
Mr. R. F. Burski, Director-Jackson, Mississippi =39205 d
Nuclear Safety j
Lntergy Operations, Inc.
Mr.- J.:R.-.McGaha, Jr.
317 Baronne Street General; Manager 1 Plant Operations New Orleans, Louisiana. 70112 Entergy, Operaticns, -. Inc. -
j P. O. Box B:
Mr. L. W. Laughlin, Site Licensing Killona, Louisiana: 70066 Support Supervisor- _
Entergy Operations, Inc.
Mr..Jerrold G. Dewease:
P. 0. Box B Sr.:Vice President ~
Killona, Louisiana '70066 Planning & Assurance j
Entergy Operatior,s','Inc.
Post Ofice Box.31995 l
Jackson, Mississippi-- 39286-1995
. i
l v
Page 1 of 7 i
i
[
ENCLOSURE 1 i
RKVIEW 0F i
COMBUSTION ENGINE lR. NG QWNERS GROUP (CEOG) 1 j-
_ PRES $URllER 5 URGE Llh ;
-,0W 5TRATIFICAT ON, ; VALUATION j
CEH 317-P JULY 1189 J
INTRODUCTION The pressurizer surge line (PSL) in the pressurized water reactors I
4
.(PWRs),isastainlesssteelpipe,connectin(Ithebottomofthe pressurizer vessel of the hot le(l of the coo ant loop. The out flow of.
the pressurizer water is general y warmer than the hot leg flow. Such
)
i temperature differential I, delta T) varies with plant operational activities and can be as high as 320*F during the' initial plant'heatup.
Thermal stratification is the separation of the hot / cold flow stream in-Q the horizontal portion of the PSL resulting in temperature differences at
~
the top and bottom of the pipe. Since thermal stratification is the direct result of the difference in densities between the pressurizer and the Iot leg water, the potential for stratification.is increased as system celta T increases and as the insurge or outsurge flow decreases.
Strat fication in PSLs was found recently and confirmed by data measured from teveral PWR plants.
Original design analyses did not include any stratified flow loading conditions.
- nstead it assumed complete sweep of fluid along the line during insurges or outsurges'resulting in uniform thermal loading at any particular piping location. Such anslyses did not. reflect' PSL' actual thermal condition and potentially may overlook undesirable line deflection and its actual stresses may exceed design limits. In i
addition, the striping phenomenon, which is the oscillation of the hot and cold stratified boundary, may induce high cycle fatigue' to-the inner-pipe wall, needs also to be analyzed. Thus assessment of stratification i
i effects on PSLs is necessary to ensure piping integrity and ASME Code Section !!! confotu nce.
STAFF EVALUATION Since stratification in PSL is a generic concern to all PWRs, an NRC Information Notice 88-80 was issued'on October 7,1998 and then an NRC Bulletin 88-11 for the same concern was also issued on December 20 1988. Combustion Engineering on behalf of. the Conbustion Engineering OwnersGroup(CEOG),hasperormedagenericboundingevaluationreport, d
CEN 387-P (Reference 1), which documents the results of the PSL stratification effects. The following is the staff's evaluation.of the Combustion Engineering efforts and information provided in the report.
M A
Page 2 of 7
,A )
Plant r tjtering and update of desien transients.
As a result of the INPO Safety Evaluation Report, which was issued in September 1987 and identified concerns associated with the stratified flow in the PSL, the CEOG initiated surge line temperature collection data at the San Onofre Unit 3.
Concurrently with this effort Baltimore Gas and Electric initiated efforts also for the collection of, temperature data on PSL at the Calvert Cliffs Unit 1.
This was later folded into the CEOG effort.
In addition. Omaha Public Power District also collected similar data for the Fort Calhoun plant, after the CEOG Task " Reduction and analysis of Pressurizer Surge Line data collected from CE0G plants
- had commenced, and submitted them to Combustion Engineering for review and comparison with the data already collected from the first two CE06 plants.
With the exception of the Calvert Cliffs Unit, which was able to retain the temperature distribution data only after the bubble was formed in the pressurizer, the other two plants were able to retain the temperature distribution data during heatup and until normal operation.
Fort Calhoun obtained displacement readings also, in addition to temperature.
The Owners Group is going to decide on a proposed task to collect data during the next cooldown at both Calvert Cliffs Unit I and San Onofre Unit 3.
The staff request.s that monitoring should continue for a full cycle. Data should be obtained and evaluated to determine whether the observd thermal transients are bounded by the transients assumed.
Due to similar design features of all the CE06 plants (10 plants,15 units), the data obtained were deemed adequate and CE0G met with NRC staff on February 13, 1989, to discuss the scope of the " Task" and how the Bulletin's requirements will be addressed.
All CEOG PSLs are similar in layout. They consist of a ?2" (except for the Fort Calhoun which is a 10") stainless steel scheduie 160 pipe, with a vertical drop from the pressurizer to the horizontal run of pipe and a verticaldroptothehotlegnozzle(exceptforMaineYankeewhichisat a 60' vertical angle drop).
A review of the data, which measures pipe wall outside temperature variation with time, indicated that the largest surge line top to-bottom temperature differentials were similar for the three plants and caused either by an insurge or an outsurge of the pressurizer. Therefore emphasis was given to these transients for evaluation. Surge line i
movements in Fort Calhoun plant, were calculated and compared to actual pipe movements measured at three locations.
The deflections predicted by the analysis model were based on a stratified flow model with a pipe top-to-bottom delta T=320'F. The actual measured data collected at Fort Calhoun, were obtained during a pipe top-to-bottom delta T=181'F and when the fluid inside the pipe approximated a uniform temperature distribution model. Even though the l
i l.
i Page 3 of 7 analysis model predicted the same general shape as the measured data, the fluid conditions inside the pipe were not similar. The staff feels that further investigation and/or comparisons are required to predict PSL displacement behavior.
The data obtained from all three plants recorded outside pipe wall surface temperature distribution about the longitudinal and circumfer:ht141 axis of the pipe.
In order to determine fluid conditions for the design basis events at the inside surface of the pipe wall, a 2-D finite element heat transfer analysis of the pipe cross section was performed.
Two bounding analytical heat transfer models with various inside fluid conditions were developed, with an attempt to reproduce the recorded outside pipe wall surface temperature distribution.
- 1) A stratified flow model i
- 2) A uniform temperature gradient mof'21 The stratified flow model assumed the hot (pressurizer temperature) fluid in the upper half of the pipe, and the cold-(hot leg temperature) fluid i
in the lower lealf of the pipe, with a sharp interface in between. During the outsurge it was assumed that flow occurred in the upper portion of the pipe only, while during the insurge it was assumed that flow occurred in the lower portion of the pipe only.
For a given transient, a flow rate was calculated based on the pressurizer level change vs. time plots, and a heat transfer coefficient was then determined.
For the uniform temperature gradient model, the pipe cross sectional area was divided into a finite number of water layers to approximate a continuous temperature gradient. The uppermost layer was considered the hot fluid (pressurizer temperature), and the 10 wast layer was considered the cold fluid (hot leg temperature), with the intermediate layers having a uniform temperature gradient.
It was assumed that flow occurs at the full pipe cross section during an oucsurge or an insurge. During a given transient, a flow rate was calculated based on the pressurizer level change vs. time plots and a heat transfer coefficient was then determined.
Basedontheabovecoefficients,andusingthein-houseCEMARCcomputer code, a 2-D finite element model was deve oped to determine the inside pipe wall temperature distribution for both the stratified flow and the uniform temperature gradient models.
The temperatures at selected nodes wete calculated and compared with the thermocouple data. The uniform temperature distribution model more closely approximated the measured results. This indicates that it does not appear to be a sharp hot / cold inter
- ace, and it is more likely that there is some mixing of the hot and cold fluids with a uniform temperature gradient from top to bottom of pipe. Changes were made to the stratified flow model to better match the measured data. These changes tended to better match the measured data for the outside pipe wall temperature distribution, but CE could not explain why these would be valid assumptions. Since a unique solution could not be derived, assumptions were used for the thermal striping, stress and fatigue evaluations utilizing the stratified flow model, i
Page 4 of 7 M
ASME Code compliance for Stress and Fatigue.
1)
Code Compliance in Stress (Inelastic Analysis).
Each plant specific surge line was reanalyzed by the SUPERPIPE computer code using a bounding generic stratified flow loading.
Elastic analyses were performed on the plant specific piping layout an support configuration for each plant, considering that the maximum delta for a pipe. given transient, occurs along the entire horizontal length of These results were used to choose a specific surge line for the bounding inelastic analysis.
intensity levels in excess of the 35The elastic analyses predicted stress allowable limit of the ASME Code Section 111 was performe. NB-3600, equation 12.
d as per N8-3228.4 Thus an inelastic shakedown analysis to determine if af ter a few cycles of However, the PSL nozzle moments were calculate analysis.
c ASME Code stress indices were used for each pipe t wponent for the specific elastic analyses.
Finite Element shell model and, therefore, the stress indices were inherently included in the analysis.
The $UPERPIPE computer code was used to performed the initial elas analysis, which considered thermal effects of the stratified flow over t entire horizontal length of pipe, for delta T=32'F, delta T*90'F and delta T=320'F.
For each structural model loading and a stratified flow loading were, applied.a uniform fluid temperature stratified flow effects were investigated.
Three types of a)
Local stress due to temperature gradient in the pipe wall b)
Thermal gradient stress across pipe wall due to transient condition c)
Thermal pipe bending moment generated by the restraining effects o supports.
motion, beyond which springu will act as rigids. Actual supp ng based on delta T=320'F, pipe top to bottom stratified flow The maximum movement calculated for Calvert Cliffs Unit 2 and Palisades plants, both at
, was location H2.
The staff feels that since no plant specific support data and displacement Itmitations were considered further evaluations are required to justify the Palo Verde inelas, tic analysis as the worst case in addition it is the staff's opinion that the assumption on spring motion may n,ot be conservative in that which ev.ceeds it's travel range, will cau,se the spring to unload andupward redistribution of stresses will occur.
l i
1 1
l Page 5 of 7 The Palo Verde PSL configuration was chosen for the inelastic evaluation, since it predicted the highest stress levels undar the elastic analysis, While each line will behave differently under a given stratified flow t
icading, it was concluded that the surge line with the highest elastic stresses will provide an upper bound for all other lines. This was verified by the fact that the most highly stressed region is the same location for both the elastic and the inelastic evaluation.
For this line, the elbow under the pressurizer was determined to be the most l
critical location.
i Material properties as T=650'F were used considering the strain hardening behavior of the material. The stress strain curve used was developed by Combustion Engineering based on the ASME code minimum yield stress value and plastic strain.
Three complete cycles of heatup, steady state and cooldown were analyzed.
for fatigue evaluations, the maximum principal strain range values were i
calculated from the maximum and minimum principal strains.
The maximum positive principal strain was calculated for three cycles and extrapolated to be less than 2% after 500 heatup/cooldown cycles, based on the decreasing rate of strain increases with additional cycles. The analysis results demonstrated that the first cycle undergoes significant 4
permanent strain with subsequent cycles having smaller accumulation. The strain range from the first two cycles was considered in the fatigue analysis with the strain range from the third cycle used for the remaining 498 cycles.
Review of Fig. 3.6.2-8 and Fig. 3.6.2-9 of the report could not clearly demonstrate that strains were stabilized after the three heatup/cooldown cycles and that progressive distortion does not exist.
Changes in plastic strains showed some decrease with each cycle but the staff concluded that additional investigation was required to demonstrate that the decreasing rate of plastic strain will approach zero. Since there are no maximum strain limits prescribed in the ASME Section !!!
code, the value of 2% was obtained from the High Temperature Code Case N47 and it was used as a guide for the maximum positive principal strain limit. The staff concludeo that the use of 25 strain limit in this case needs further justification.
O Code Compliance in Fatigue.
To determine stresses at the inside face of the pipe wall due to fluid oscillation at the interface of the hot to cold boundary (strping), a 1-D finite element analysis was performed. The input assumptions used in this analysis were based on the measured data from the CEOG plants, and other information available in the public domain. The thermal striping
i
]
Page 6 of 7 model considered the hot fluid at the Prassurizer temperature, the cold fluid at the Hot Leg temperature, and a sharp interface with no mixing of i
the hot and cold fluid. A sawtooth fluid oscillation was assumed to occur across the interface region.
Results indicated that fatigue damage due to striping is insignificant when compared to all the other causes of fatigue damage. (i.e. static thermal stratification,thermaltransientsetc.). The CE report indicated that based on the stress levels calculated, an infinite number of allowable cycles exist, and thermal striping is not a concern. Since maximum stress due to striping occurs at the act/ cold interface, which is near the horizontal axis of the pipe, and maximum stress due to fatigue occurs at the top and bottom of the pipe, these stresses do not occur at the same location and are not additive. The staff feels that further investigation should be provided for the use of a fraction of the striping amplitude.
In addition, data based on measurement outside the pipe may be inconclusive l
for the purpose of defining the striping phenomena.
Analysis for cyclic operation (fatigue) was performed, in addition to the shakedown analysis. Using the results of the inelastic analysis, the maximum principal total strain range which occurs from shakedown analysis was multiplied by one half the elastic modulus to determine the equivalent alternatingstress,asperNB-3228.4(c). This saximum strain range occurs after cycle 3, and this value was assumed for the remaining cycles.
For the first two heatup-cooldown cycles, the larger of cycle 1 and 2 strain range was used.
The cumulative usage factor for this generic bounding analysis was determined to be 0.21 for the Palo Verde unit.
The maximum cumulative usage factor, when the effect of the :t 2" displacement limitation was i
considered, was 0.36 for Main Yankee. The staff feels that further evaluation is required to justify the Palo Verde inelastic analysis is l
the worst case.
I CONCLUSION Based on our review, we conclude that the information provided by l
Combustion Engineering in References 1 and 2 is not adequate to justify continued operation for the 40 year plant life.
However, the staff l
believes that there is no innediate or short term safety concerns associated with the stratification effects for continued plant operation until final resolution of the Bulletin 88-11 is issued. This is scheduled to be completed by the end of 1990 and should also address the Code acceptance criteria of ASME NB-3600.
2 Concerns that the staff has are the following:
a)
The ASME code acceptance criteria of Section NB-3600 Equations 9-14 i
need to be satisfied as applicable.
l i
i i
1 1
l, Page 7 of 7 1
i b)
A11' supports, including pipe ship restraints, be considered for the l
. effects of providing any additional constraints to the Surge Line, in the plant specific or the bounding pipe stress evaluation.
l c)
All supports, including pipe whip restraints, require plant specific confirmation of their capabilities, including clearances, and that they fall within the bounds of the analysis.
j i
d)
Justify the Palo Verde inelastic analysis as the worst case for j
stress and fatigue for all CE06 plants, including Maine Yankee.
e)
Justify PSL displacement bahavior predicted by the analysis model and the use of a fraction of the striping amplitude.
REFERENCES i
1.
Combustion Engineering Report CEN 387-P (Proprietary). " Combustion' Engineering Owners Group pressurizer surge line flow stratification i
t evaluation." July 1989.
l 2.
Draft meeting minutes of the NRC audit on September 25 and 26 1989 regarding the CE06 Report CEN 387-P MPS-89-1048, dated October 17, l
1989.
?
i l
l 1
i l
1 I
h v
-. _..,,.i......,--....
.u-
1 l
3 i+
Page 1 of 3 l
ENCL 050RE 2 l
Staff review of the CK responses regarding the'NRC Audit onsenember 15 and 26.
989 4
Ref CEDG teport G 'N-357-P MPU-59-1048 l
[
dated Ocf ol>er L7. 1989.
i Section 2.0-l T
1)
The staff. requests that monitoring should continue for a full fuel t
cycle. Data. should be obtained and evaluated to determine whether the observed thermal transients are bounded by the transients assumed.
l i
2)
The staff feels'that further investijation is required to predict PSL 1
displacement behavior, considering tae stratification effects. The-1 deflection predicted hy the analysis'model were based on a stratified.
i flow model with a pipe top to bottom delta T=320'F. The actual measured data collected at Fort Calhoun were obtained during a pipe top-to-bottom delta T=181'F and when the fluid inside the pin approximated a uniform i
temperature distribution model.- Even though tie analysis model predicted the same general shape as the measured data, the fluid conditions inside the pipe were not similar.
3)
Closed.
4)
Closed.
5)
- Closed, i
1 6)
Closed.
7)
Closed.
8)
The staff requests that further investigation is required to demonstrate I
that strains were stabilized after the'three heatup/cooldown cycles and-that progressive distortion does not exist.
It is required.to demonstrate l
that the decreasing rate of plastic strain will. approach zero and the l-peak value will not exceed a maximum strain acceptance criteria of 288.
The staff feels that the _ inelastic analysis will be accepted as-Justification for Continued Operation and that the ASME Code acceptance.
criteria of section NB-3600 equations g-14 need to be satisfied, as r
required by the Bulletin.
a
.'f
-1
- _ _. _ _, _. _ _ _.. _......... _.. ~...
.., - -.. _.... _ - - - _. ~.,,.
l' l,
Page 2 of 3 l
g)
Closed.
- 10) Closed.
- 11) The staff feels that all supports, including pipe whip restraints.
(
be considered for the effects of providin additional constraints in the plant specific or the bounding eva untion.
- 12) The staff feels that all supports, including pipe whip restraints, require plant specific confirmation of their capabilities, including clearances, and that they fall within the bounds of the analysis.
't Section 3.0 1)
Closed.
2)
Closed.
3)
Closed.
4)
Closed.
5)
Closed.
6)
- Closed, i
Table 2.7-1. Closed Table 3.2.2-4. See response of Section 2.0 Item 2.
Table 3.4.3-2. Closed.
l l
Table 3.6.2-1. Closed.
Table 3.6.3 2. The staff feels that further evaluation is required to s
justify the Palo Verde inelastic analysis as the worst case. The r,aximum cumulative usage factor for Maine Yankee.is 0.36 when the effects of the 2" displacement limitations are considered.
L Figure 3.1.2 5.
Closed.
l l-i
+
o.
e
.. + + -,,. -,..,
,.c.
,..------n
-- - - +.. ~. - ~ ~
\\
e Page 3 of 3=
1 l
l Section 4.0
)
{
i l
1).
No specific review was performed.
l i
l-2)
See response of Section 2.0 Item 8.
3)
No specific review was performed, l
i l
Questions durino meetine.=
1
- Closed, j
i I
l s
i I
I 1
i P
l P
P i
n i
i
<I
....