ML20127P213
| ML20127P213 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 11/28/1992 |
| From: | Robinson W PORTLAND GENERAL ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9212020133 | |
| Download: ML20127P213 (6) | |
Text
_ _
1 o
t
,em '
Pae!
yi Portland General Electric Company James E Cross Vice President and Chief Nuclear Officer November 28,1992 Trojar. Nuclear Plant Docket 50 344 License NPF-1 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington DC 20555
Dear Sir:
Supplemental information Regarding License Chnge Application (LCA) 222 The purpose of this letter is to transmit additional information as discussed in a telephone conference held on November 27,1992, between the Nuclear Regulatory Commission and
- Portland General Electric concerning LCA 227, LCA 227 proposes to defer the unscheduled steam gcnerator inservice inspection required by Technical Specification 4.4.5.3.c.1, inspection Frequencies.
The attached information includes further discussion of the use of the heat affected zone criterion for determining adequacy of steam generator tube stress relief, Also ateched ic information which clarifies the heater positioning criteria.
Sincerely, Cff
.jp
(
W. R. Robinson for
~
J. E. Cross
/ '*achments c:
Mr. John B. Martin Regional Administrator, Region V U. S, Nuclear Regulatory Coinmission Mr. David Stewart-Smith Late of Oregon Department of Energy _
Mr. R. C. Barr NRC Resident Inspector y g g,;
_ Trojan Nuclear Plant
-9212020133 921128 F.
I
'PDR ADOCK 05000344
,. 4' P-PDR z
g-121 SW Saimon Street, Portland, OR 97204 503/464-8897
Trojan Nuclear Plant Document Control Desk Docket 50-344 November 28,1992 License NPF-1 Attachment Page 1 of 4 SUPPLEMENTAL INFORMATION REGARDING LICENSE CllANGE APPLICATION 227 i
Additional informnion Recarding IIcater Position Acceptance Criteric Corrosion and metailurgical evaluations perfo med on the freecpan kinetic weldjoints of tube support plate sleeves for 'i/8" OD tubes have shown that a stress relief temperature in the tube of 1275"F to 1525"F for 5 to 12 minutes will adequately relieve stress without adversely affecting j
tube properties. (Ref: Section 6.6, p. 6-90, BAW-2094PA, Rev.1, " Recirculating Steam Generators Kinetic Sleeve Qudifiestion for 7/8 inch OD Tubes"). The stress relief heaters were designed to produce these temperatures with ti e heater coil's centerlines positioned up to 1/4
below the centerline of the kinetic weld expansion. This was done to allow a positionmg
)
tolerance for the stress relief process in field applications (ibid, p.6 91).
The tube leak in Steam Generator "B" Row 25 Column 17 (B25-17) reulted from gross j
mispositioning of the stress relief heater at a location just below and outside the sleeve itself l
such that neither the upper nor lower kinetic weldjoints received any stress relief. Eddy current examiaztion of the tube sleeves in each steam generator has confirmed that this was the or.ly instance of gross mispositioning. I.i contrast to this for the other sl; eves the heaters were positioned within the sleeves and stress relief occurred at both the upper and lowerjoints. Each of these sleeve / tube assemblies has been evaluated for the acceptability of stress relief vis-a-vis the above time and temperature ranges.
One criterion developed for determining stress relief acceptability is ;he degree of mispositioning of the stress relief heater within the sleeve. Following the tube leak event at Trojan, heater misposition tests were performed to determine the relationship between the extent of heater misposition verses time at temperature of the t:.be OD. These tests were performed in 9 sleeved tube samples. In 5 of these samples the sleeves were centered about the tube support plate. To evaluate the effect of sleeve easition on heater performance,4 of the 9 samples were located la hw relative to the support plate when t" heater mispositioning tests were p rformed.
To simi. e in situ steam generator conditions, all samples were surrounded by eight oxidized 7/h" tubes and a black enciasure.' Thennoccuples were mounted on the samples at the apex and
!/2" either side of th apex of both the upper and lower kinetic weld expansions. These locations encompas, the limits of the stressed areas of sleeved tubes.
The heaters were positioned at 0" and then mispositieed 1/8",1/4",1/2" and 3/4" low in the 5 samples that were centered about the support plate. Tin heaters were positioned at 0" (two times) and then mispositioned 1/8" and 1/4" low for the 4 samples located'1" low relative to the support plate centerline.
The results of this testing are shown in Table 1. Acceptable stress relief was obtained in the tubes fo, heaters mispositioned up to 1/2"ir sleeves centered about the tube support plate. For
= Trojan Nucleat Plant Deument Control Desk.
Docket 50-344 November 28,1492
- If ase NPF-1 Attachment Page 2 of 4 sleeses located I" low relatie e to the support plate, acceptaole stress relief was obtained in the tubes for both the 1/8" and 1/4" cases of heater mispositioning. Based on these test results, it was concluded that acceptele stress reliefis assured when the heater physical hardstop is mispositioned up to 1/4" below the bo; tom of the sleeve when the sleeve is positioned up to 1" from the centerline of the tube support plate.
T he specification for the hardstop positioning indication states that when the system indicates that the hardstop is against the bottom of the sleeve, the actual heater hardstop position can be no more than 1/8" from the bottom of the sleeve. This ensures proper heater coil positioning with respect to the kinetic weld expansion joints.
When the heater was designed, an additional margin of safety was built-in. As discussed above, the design of the heater allows the coils to be mispositioned 1/4" and still achieve the required temperatures and times on the OD of the tube behind the sleeve. Thus, even though the specification on the tooling requires 1/8" accuracy on detection of achieving hardstop, the heater can actually withstand 1/4" mispositioning and still perform its function.
Addhional Information Regardine the IIcal Affected Zone HI AZ) Criterion The HAZ Criterion is based on seeing a " perm" line 1.65" or greater above the centerline of the lower weld. The value of 1.65" is based on laboratory tests with a configuration where the sleeve is nominally centered about the centerline of the tube support plate. With this configuration, and the heater mispositioned no more than 1/4", a perm line located 1.65" or greater above the centerline of the lower weld indicates appropriate stress relieving in the sleeve.
In other words, this contiguration results in a temperature profile at the i;be that starts out at 1275"F, or higher, in the weld area and drops to 950 F-1050 F at 1.65" or greater from the centerline of the weld as one moves upward from the lower weld. However, as discussed below measurements less than 1.65" may also be acceptable. If the sleeve is posinoned high (the lower weld moves closer to the tube support plate), the relatively large heat sink of the tube support plate changes the temperature profile such that the " perm" line is now closer to the heat stress relieved weid area and the 1.65" is no longer a valid measurement (the measurement would be less than 1.65"), however the wetd area is still properly stress relieved ( temperature renter than 1275"F) and the temperature drop to 950*F-1050 F occurs over a shorter distance due :a the closer proximity to the heat sink of the tube support plate. Items which affect heat transfer, including proximity to the tube support plate are discussed below:
Proxi.mity to Tube Support Plate Dbplacemen' of the sleeve in the upper direction brings the lower HAZ that much closer to the tube support plate. Since this area is being heated by conduction, the presence of a large mass will reduce the length above the weld that can be heated This will affect the location of the HAZ.
p' m Trojan Nuclear Plant Document Control Desk Docket 50-344 November 28,1992 License NPF-1 Attachment i
Page 3 of 4 Yaription in IIcal Transfer Conditions whhin the Tube and Steam Generator Since the majority of the heat is conducted radially outward in the weld area, small changes in heat transfer conditions in the tube and steam generator will change the tube temperature in the area of the HAZ. Variation in the fit between the tube and the sleeve, for example can change the conduction path.
11 eater Cell Temperature Differences The heater has thermocouples in both areas and the computer picks the colder thermocouple to control the heating cycle. The process allows there to be as much as a 100"F difference in temperature between the upper and lower heater coils. Wiiile this difference does not affect the ability to achieve the prcper temperature in the weld area,it can affect the length of tube that is heated by conduction.
Intal Cycle Time Some tubes w.e longer to get to temperature ( the five minute hold time only applies once the heater gets to the target temperature). After the required time at temperature, the tube is allowed to cool down by natural convection Significantly different times (1-2 minutes difference) are seen from tube to tube in the amount of time it takes to cool down. The length of the HAZ is going to be affected by the total amount of time any part of the tube is at or above 950-1050 F.
Exan1ple of Criteria Am11kalha As mentioned above, the sleeve in D23-66 at the fifth tube support plate is an example of a sleeve positioned high in the tube support plate. Since hardstop pressure readings were not logged for this sleeve, Criterion I could rot be applied. This sleeve was positioned approximately 1.65" high. This placed the lower weld area close enough to the heat sink of the tube support plate that the signai repr ating the perm line was not discernable'. During the process verification test (PVT), the upper coi' on the heater used in this tube reached 1947*F, and the lower coil teached 1966"F. During the stress relief with the same heater in D23-66, the upper coil was at 1966'F, and the lower coil was at 1947'F. This passes Criterion 3a, since mispositioning a heater low would result in an increase of the lower coil temperature.. The -
decrease in the temperature of the lower coil over the PVT is' consistent with it being closer to
. the tube support plate _which acts as a heat sink In addition, the lower coil temperature only D23-6d,05H, was reported as "NHZ" (no penn hne) at the lowerjoint with an associated numerical entry of-1.36". His value was inadvenently processed and yielded an incorrect perm line value of 0.59". The lower perm line, given the confi mration of this sleeve is not discernable.
t
Trojan Nuclear Plant Document Control Desk
. Docket 50-344 November 28,1992
^
Licunse NPF-l Attachment Page 4 of 4 changed 19"F between the PVT run and the run in D23-66, therefore Criterion 3b which requires no greater than a 30 F change between runs was satisfied.
In summary, the testing perfonned on mispositioned heaters showed that the H AZ measurement of 1.65" or greater showed that the heater was positioned within 1/8" of the hardstop. Various conditions not sc :cifically measured or controlled can cause the length of the zone to be less, while the stress ulief process is still completed acceptably. This prompted the development of additional criteria for determining the acceptability of the stress rei.ef of the installed sleeves.
-~
-T,rojan Nuclear Plant Document Control Desk Docket 50-344 November 28,1992 Licerrse NPF-1 Page1of1 Table 1 CORRELATION TUBE THERMOCOUPLE DATA Time Minimum Time Maximum Max Co'd Max Tube TC > 1275F TC > 1275F TC Temp, F Temp, F Upper Lower Upper Lower Upper Lower Upper Lower Run Mi on Expan.
Expan.
Expan.
cxpan.
Expan.
Expan.
Expan.
Expan.
inches 3-2 0
9:35 9:40 10:15 10:05 1391 1401 1444 1417 3-3 1/8 8:50 8:25 9:15 9:20 1400 1394 1436 1444 3-4 1/4 8:30 8:20 9:30 9:40 1355 1364 1430 1439-3-5 1/2 6:50 5:45 10:25 10:33 1287-1300 1442 1433 3-6 3/4 0
0 9:50 10:15 1168 1246 1417 1424 3 19 0
9:10 8:25 10:00 10:05 1350 1356 1412 1444 3-22 0
8 45 9:05 9:45 9:50 1386 1443 1454 1483 3-20 1/8 8:50 9:00 9:05 9:40 1359 1424 1387 1442 3-21 1/4 7:20 7:45 l
9:25 9:45 1308 1368 1416 1470