ML20044B539
| ML20044B539 | |
| Person / Time | |
|---|---|
| Issue date: | 06/23/1992 |
| From: | Johnson G Office of Nuclear Reactor Regulation |
| To: | Hawthorne J MATERIALS ENGINEERING ASSOCIATES, INC. |
| References | |
| NUDOCS 9207080216 | |
| Download: ML20044B539 (1) | |
Text
if N
J.R. Hawthorne j g 8 0 1992 Materials Engineering Associates 9700-B Martin Luther King Highway Lanham, Maryland 20706
Dear Mr. Hawthorne:
In a telecon on June 9, 1992, you requested background information on reactor vessels that are projected to be below the 50 ft-lb Charpy upper shelf energy (USE) criteria in Appendix G, 10 CFR 50 or are projected to be above the pressurized thermal shock (PTS) screening criteria in 10 CFR 50.61.
Enclosed is a memorandum identifying plants with reactor vessels most susceptible to having their Charpy USE reduced below 50 ft-lb. This memorandum has been made available publicly in Commission paper SECY-91-220.
The reactor vessels in'this memorandum contain weld material fabricated by B&W using Linde 80 flux; In addition to the plants listed, the licensee for Oyster Creek has reported that a plate in its reactor. vessel.could be susceptible to having its Charpy USE reduced below 50 ft-lb..-
As a result of information provided in submittals by licensees,.thre b b tor l
vessels are projected to be:above the PTS screening criteria at the expiration of their licenses.
They are Beaver Valley Unit 1, Palisades, and.Calvert~.
Cliffs Unit 1.
The licensee for Zion Unit I has reported that thesreactor vessel may exceed the screening criteria at the end of its design. life, which l
corresponds to 32 effective full power years (EFPY) of-plant operation..
However, the Zion Unit I vessel ~is projected by the licensee'toLbe-below the l
screening criteria at the expiration of its licens.e (25 EFPY).
The licensees' submittals for Beaver Valley Unit 1, Palisades, Calvert Cliffs Unit 1, and Zion Unit I have been placed,in the PDR.
v omGrNALSIGNED BYf. a George Johnson, Acting Chief...
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- . Materials and Chemical Engineering Branch Division of Engineering Technology l
Enclosure:
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As stated o
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Distribution:
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EMCB RF BElliot KWichman GJohnson i
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September 24, 1987
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MEMORANDUM FOR: Thomas E. Murley, Director Office of Nuclear Reactor Regulation THRU:
Richard W. Starostecki, Associate Di or for Inspection and Technical Assessment FROM:
Lawrence C. Shao, Director Division of Engineering and Systems Technology l
SUBJECT:
REACTOR VESSELS MOST SUSCEPTIBLE TO HAVING THEIR CHARPY UPPER SHELF ENERGY REDUCED BELOW 50 FT-LB i
In response to your request we are providing a list of reactor vessels that as-a result of neutron irradiation are most susceptible to having their Charpy-upper shelf energy (USE) reduced below 50 ft-lb. Table I of the enclosure.
contains the requested list. Susceptibility is greatest for vessels containing high copper welds made with Linde 80 weld flux, characteristic of many early vessels fabricated by Babcock and Wilcox Co. The initial upper i
shelf energy was low, because of the flux, and the copper content makes them susceptible to neutron embrittlement. High fluence is of ' course a' factor.-
-l and'this is a characteristic of some Westinghouse-reactors, such as those which
.l i
1ead the susceptibility list.-
(
'l Table I contains the list of 17 PWRs having high copper, Linde-80, welds,.
which we believe are the reactor vessels most susceptible to having their Charpy USE fall below 50 ft-lb. The table identifies,the calculated Charpy.
USE for the limiting' reactor vessel. beltline' weld on January 1, 1986 and at the end of the plant s license. The calculation was performed using the methodology recosinended in Proposed Regulatory Guide 1.99, Rev. 2.
The calculation indicates that as a result of neutrcn irradiation, several PWR
- 't reactor vessels had weld metal with Charpy USE at'or less
- than 50 ft-1b on'-
January 1, 1986. The table indicates the licensees that have'taken action to resolve this concern.
Licensees for Point Beach and Ginna have not instituted a program to resolve this issue. These Itcensees should be infonned that based on the calculation methods in Proposed Regulatory Guide 1.99, Rev. 2, the Charpy USE for their limiting reactor vessel welds are predicted to be less'than 50 ft-1b. Based on this calculation, the-licensees paragraph V.C.
This aresubjecttotherequirementsofAppendixG,10CFR50[2)materialstestsand-paragraph requires:' (1) inspection for beltline flaws, (3) analyses of vessel integrity to see. if "... lower values of upper shelf energy will provide margins of safety'against-fracture equivalent to those required by' Appendix G of the ASME Code." The licensees should within one year of receipt of the staff letter, provide the staff with a plan for implementing the requirements of Appendix G,10 CFR 50, paragraph V.C.
j l
In addition, as more reactor vessel material surveillance data becomes i
available the NRC staff and licensees should evaluate whether the effect of i
' neutron irradiation-on the Charpy USE of Linde 80 weld metal and other
Contact:
B. Elliot, EMTB/NRD X-27895 g-p f-,,
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confidence rather than using bounding values.
Origitul Signed by L C. shao l
Lawrence C. Shao. Director Division of Engineering and. Systems Technology
Enclosure:
As stated cc:
J. Sniezek R. Starostecki F. Miraglia J. Richardson C. Y. Cheng B. Elliot K. Wichman W. Hazelton N..Randall i
DISTRIBUTION:
- Central File EXT 5 RF EMTB PF N
RStarostecki
- (See next page for concurrences).
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~ OFFICIAL RECORD COPY (5520 DOCUMENT NAME: ELLIOT,USE)
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i Enclosure Charpy Upper Shelf Energies l
for Reactor Yessel Materials l
.)
Rebulatory Backcround Appendix G,10 CFR 50, specifies fracture toughness requirements for reactor-l vessel beltline materials to provide adequate margins of safety during normal-
.i operation, including anticipated operational occurrences and system hydrostatic tests, to which the vessel may be subjected over its service lifetime. 'Section.
!Y.A.1 of Appendix G states, in part, that reactor vessel beltline materials -
d must maintain Charpy upper-shelf energy (USE) throughout the life of the vessel-no less than 50 ft-lb, unless it is demonstrated in a manner approved by the Director, NRR, that lower values of upper shelf energy will provide margins of safety against fracture equivalent to those required by Appendix G of the ASME Code.
NUREG-0744 Rev. I dated October 1982 provided an engineering method, based on-elastic-plastic fracture mechanics-for analyzing reactor vessel beltline-materials with Charpy USE below 50 ft-1b to determine whether they have adequate resistance to fracture. The NUREG did not specify the_ criteria for
('
acceptability for various plant conditions. These criteria are being reviewed -
by an ASME code subcoenittee, in which 'the staff has been actively involved.
The effect of neutron irrediation on a material's Charpy U$E. can be predicted using figure 2 in Regulatory Guide (R.G.) 1.99. This figure indicates that as the amounts of copper in the weld: and neutron fluence increase the Charpy USE -
decreases. This regulatory guide is undergoing a change from revision 1 to 2.
However, figure 2 has not changed.
Discussion Susceptibility for reducing Charpy USE below 50 ft-Ib is greatest for material with high copper.10w unirradiated Charpy USE and high neutron fluence. Weld-metals fabricated _by Babcock & Wilcox (B&W) using a submerged arc weld process with Linde 80 flux appears to be the materials'most susceptible to having their Charpy USE reduced below 50 ft-lhe Other vessel fabricators such as Combustion Engineering (CE) and Chicago Bridge and' Iron (CSI) used weld metal with high l
upper shelf energies. Hence, welds in CE'and CSI fabricated vessels are less susceptible to having their Charpy USE reduced below 50 ft-lb than welds.
fabricated by B&W.
In addition to vessels for their own NS$5 design. B&W _.
supplied reactor vessels' for SWR's and Westinghouse N555 designs. 8WR reactor j
vessels receive significantly less neutron fluence than either Westinghouse or-B&W reactor vessels. Hence. BWR reactor vessels with Linde 80 flux welds are less susceptible to having their Charpy USE reduced below 50 ft-lb than:PWR l
reactor vessels. We have not made an exhaustive survey of USE characteristics of all plate materials in reactor vessel' beltlines. However, plate materials, l
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typically have higher unirradiated Charpy USE than Line 80 weld metal..Hence, they are less susceptible to having their Charpy USE reduced to 50 ft-lb than Linde 80 weld metal.
Table I lists the PWR reactor vessels, which contain Linde 80 weld metal fabricated by B&W. The table identifies the calculated Charpy USE for the limiting reactor vessel beltline weld on January 1,1986 and at the end of the plant's license. The calculation for Charpy USE at end of license was performed using the methodology recommended in Proposed R.G.1.99, Rev. 2.
This Guide recomends that the calculation be perfonned using a line drawn parallel to the existing trend curves and bounding all the data when credible surveillance data is available. This method, although conservative, is necessary when plant specific data is sparse and scattered. When credible surveillance data was not available, the calculation was performed by linear interpolation between trend curves contained in figure 2 of the guide based on the copper content.
The calculation for Charpy USE on January 1,1986 was performed using the methodology recomended; (1) by Comonwealth Edison Co. (Ceco) for Zion, Unit 1 and 2; (2) by the B&W Owners Group for B&W plants participating in their owners group; and (3) in Proposed R.G.1.99 Rev. 2 for the rest of plants. Both methods (1 and 2) provided "best estimates" for when plants woulo reach 50 ft-lb. Ceco combined data from Units 1 and 2 surveillance program to estimate when the limiting beltline weldment would reach 50 ft-lb. The Zion surveillance program I
contains weld metal samples that are equivalent to the limiting beltline weldment.
The Zion surveillance program has produced 5 credible surveillance data points with very little data scatter. Based on tu number of credible surveillance data points and the limited amount of scatter, the Zion procedure is an acceptable alternative to R.G. 1.99 Rev. 2 method for calculating when Charpy USE will reach 50 ft-lb. Ceco estimates Zion Units 1 and 2 will reach 50 ft-Ib no earlier than 1994. The B&W Owners Group perfonned a statistical analysis of all the existing surveillance Linde 80 weld metal.
The staff considers a statistical analysis of all surveillance data points an acceptable alternative to the R.G.1.99 Rev. 2 method for calculating when Charpy USE will reach 50 ft-lb. The owners group procedure indicates all B&W plants will reach 50 fc-lb no earlier than 1997. The B&W plants are identified in Table 1.
Ceco and B&W Owners Group procedures for calculating Charpy USE were not used for estimating the Charpy USE at the end of the plants licenses because there is insufficient surveillance data at end-of-license neutron fluences.
Yankee Rowe and Byron-1 have been included on the list as vessels containing Linde 80 weld metal. However, since both of these vessels have low copper Linde 80 welds, they are less susceptible to having their Charpy USE reduced by neutron irradiation than the other PWR reactor vessels.
Florida Power & Light (FPL) Company has recognized that the Turkey Point -3,
-4 reactor vessel welds are susceptible to having their Charpy USE reduced below 50 ft-lb.
FPL has provided a fracture mechanics analysis to demonstrate that lower values of upper shelf energy will provide margins of safety against fracture equivalent to those required by Appendix G of the ASME Ccde. This analysis is under review by the staff.
I s
3 Since the Charpy USE for reactor vessel welds in Point Beach -1, -2 and Ginna are calculated, in accordance with R. G' 1.99, to be less than 50 ft-lb, the licensees are subject to the requirements of Appendix 6,10 CFR 50, paragraph V.C. which requires: (1) inspection for beltline flaws, (2) materials tests and (3) analyses of vessel integrity to see if "...lewer values of upper shelf energy will provide margins of safety against fracture equivalent to those required by Appendix G of the ASME Code." (App. G,10 CFR 50, paragraph IV.A.1).
The exact nature of the materials tests and analyses required by the regulation in general terms has been the subject of research for several years. The question was addressed in USI A-11, and a final report (NUREG 0744) was issued in October 1982. However, the fortnulation of acceptance criteria that satisfied critics in the industry and the fracture consnunity was not coInpleted.
Instead, a question was sent to the chairman of the Subcomittee on Nuclear Inservice Inspection of the ASME Boiler and Pressure Vessel Code (Section XI) for help on that issue. The final report of the Working Group on Flaw Evaluation to whom it was assigned is not out yet, partly because there is continued evolution in the technology of elastic-plastic fracture analysis. The tentative criteria for normal operation and anticipated operational occurrences (Levels A and B loading, in Code language) are that crack instability shall not occur at pressure of 1101 of Design with a safety factor of 2.0 on pressure stresses and 1.0 on thermal stress. Simplified analyses have been made from time to time which confirmed our belief that safety margins against low-energy ductile fracture were adequate for materials having Charpy USE values in the 40 - 50 ft-lb range. This is the principal reason that we have been willing to wait for development of-the fracture analysis techniques before pursuing this issue further. Another reason is that there are no known, accident scenarios that overpressure the reactors much beyond the setpoint of the safety (10 CFR 50.62) requires certain hardware 110% of Design). The ATW5 Rule systems installations to minimize the frequency and severity of ATWO transients. The other accident scenarios that have been identified stress the vessel in the transition temperature range and are analyzed by linear elastic fracture mechanics methods.
Recommendations Point Beach and Ginna should be infomed:that based on the calculative methods in Proposed R. G.1.99, Rev. 2, the Charpy USE for their limiting reactor vessel beltline welds are predicted to be less than 50 ft-lb. Based on this calculation, the licensees are subject to the requirements of Appendix G, 10 CFR 50, paragraph V.C.
The licensees should within one year of receipt of the staff letter, provide the staff with a plan for implementing the require-ments of Appendix G,10 CFR 50, paragraph V.C.
As more reactor vessel material surveillance data becomes available, the NRC staff and licensee should evaluate whether the effect of neutron irradiation on the Charpy USE of Linde 80 weld metal and other materials such as plate can i
be predicted with statistical engineering confidence rather than using bounding values.
j
Table I Calculated Charpy Upper Shelf Energies (USE) for PWR Reactor Vessels with Linde 80 Weld Metal Charpy USE at Charpy USE on End of License Jan. 1, 1986 PWR Plant End of License (ft-lb)
(ft-lb)
Point Beach -2 W) 2013 34 39 Point Beach -1 W) 2010 38 43 Turkey Point -3 W) 2007 40 44*
Turkey Point -4 W) 2007 40 44*
Ginna B )
2006 42 47 Arkansas One -1 (B&W) 2008 44
>50**
Rancho Seco (B&W) 2008 44
>50**
Crystal River -3 (B&W) 2008 44
>50**
THI-1 (B&W) 2008 44
>50**
Oconee-1 (B&W) 2013 44
>50**
Oconee-3 (B&W) 2014 44
>50**
Surry-2
)
2008 46 51 Zion-1 2008 47
>50***
Zion-2
)
2008 49
>50***
l.
Oconee-(B&W) 2013 49
>50**
Surry-1 g) 2008 53 57 Davis Besse (B&W) 2011 56
>50**
Yankee Rowe 1997 Low Copper Welds Byron-1 LW) g) 2024 Low Copper Welds a
Florida Power & Light Company has provided analyses to demonstrate that the weld metal in these reactor vessels have adequate margin.
nn B&W Owners Group has provided analysis to demonstrate that the Charpy USE for these reactor vessel welds will reach 50 ft-1b no earlier than 1997.
Att Commonwealth Edison Co. has provided analyses to demonstrate that the Charpy USE for these reactor vessel welds will reach 50 ft-Ib no earlier than 1994.
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