ML12340A596

From kanterella
Jump to navigation Jump to search
Official Exhibit - RIV000117-00-BD01 - Makoto Higuchi, Takao Nakamura, & Yasuaki Sugie, Development of an Environmental Fatigue Evaluation Method for Nuclear Power Plants in Jsme Code, Journal of Environment and Engineering Vol. 6, No. 2, 2
ML12340A596
Person / Time
Site: Indian Point  Entergy icon.png
Issue date: 06/29/2012
From:
IHI Technology Solutions, Japan Nuclear Technology Institute, Osaka Univ, Japan
To:
Atomic Safety and Licensing Board Panel
SECY RAS
References
RAS 22867, 50-247-LR, 50-286-LR, ASBLP 07-858-03-LR-BD01
Download: ML12340A596 (17)
v • d • e


Text

{{#Wiki_filter:RIV000117 Submitted: June 29, 2012 United States Nuclear Regulatory Commission Official Hearing Exhibit In the Matter of: Entergy Nuclear Operations, Inc. (Indian Point Nuclear Generating Units 2 and 3) ASLBP #: 07-858-03-LR-BD01 Docket #: 05000247 l 05000286 Exhibit #: Identified: Admitted: Withdrawn: Rejected: Stricken: Other: RIV000117-00-BD01 10/15/2012 10/15/2012 Copyright © 2011 by JSME ~n1I1"*O"lment Development of an Environmental Fatigue Evaluation Method for Nuclear Power Plants in JSME Code* Makoto HIGUCHI**, Takao NAKAMURA*** and Yasuaki 8UGIE**** ""IHI Technology Solutions Inc. 1 Shin-nakahara, Isogo-ku, Yokohama, 2358501 Japan E-mail: makoto_higuchi@ihLco.jp """Division of Sustainable Energy and Environmental Engineering, Osaka University 2-1 Yamadaoka, Suita, Osaka, 5650871 Japan Abstract

        • Codes and Standards Division, Japan Nuclear Technology Institute 4-2-3, Shiba, Minato-ku, Tokyo, 1080014 Japan Many examinations concemingthe fatigue life reduction for structural materials of nuclear power plants in simulated LWR coolant have been.performed,and the effects of several parameters on fatigue life reduction have been quantified in the time since the first paper on this subject was recognized in Japan. Based on these results, methods to evaluate fatigue damage for materials exposed to LWR coolant have. been ** developed. The ** MITI Guidelines (2000) and. the. TENPES Guidelines (2002) were issued for evaluating environmental fatigue damage in operating plants. The Environmental Fatigue Evaluation Method (EFEM) for* Nuclear Power Plants (JSME S NFl-2006) was established in the Codes for Nuclear Power Generation Facilities. by the JSME by reviewing the. equations for the environmental fatigue life correction factor, Fen, and the techniques for evaluation based on the. most up-to-date knowledge atthe time. A revised version of the EFEM was drafted. by incorporating updated ** knowledge and issued by the end ** of 2009.

This paper outlines the revised JSME Codes and technical bases, and discusses the effects of several parameters on fatigue life reduction in such enviromnents. Key words: Fatigue, Corrosion Fatigue, Nuclear Power Generation, Nuclear Reactor

1. Introduction Since the first paper (I) was issued regarding the phenomenon that component material fatigue life is reduced in simulated LWR coolant, many studies on this subject have been completed and various factors that can reduce fatigue life have been quantitatively evaluated. The materials covered in the studies include carbon steels, low alloy steels, stainless steels, and nickel chromium iron alloys. Both PWR and BWR enviromnents have been evaluated. Factors tested include strain rote (i [o/<Js]), temperature (T [OC]), dissolved oxygen concentrations (DO

[ppm]), sulfur contents (S [%]), flow rate (WFR [mls]), and strain hold time. In addition, tests were performed with fluctuating parameters assuming actual plant transients and the enviromnental fatigue evaluation method for light water reactors has been developed based on the results of these studies. In September 2000, the Agency for Natural Resources and Energy of the then Ministry of International Trode and Industry (MIT!) issued the "Guidelines for Evaluating Fatigue Initiation Life Reduction in the LWR Environment." (2) These guidelines provided only equations to determine fatigue lives in such enviromnents. Accordingly, the Thermal and Nuclear Power Engineering Society (TENPES) issued the "Guidelines on Enviromnental Fatigue Evaluation for LWR Components" (3) in 2002, which provided the method for applying the enviromnental fatigue evaluation to operoting plants. By reviewing and combining the MIT! and TENPES guidelines, the Japan Society of Mechanical Engineers -I1,mWfl ***

(JSME) established the Environmental Fatigue Evaluation Method (EFEM) for Nuclear Power Plants in its Codes for Nuclear Power Generation Facilities in 2006 (JSME S NFI-2006).(4) A revised version of the EFEM was established by incorporating the most up-to-date information and issued in 2009. This paper summarizes the revised JSME Codes and technical bases concerning the effects of several parameters on fatigue life reduction in LWR environments.

2. Environmental fatigue life correction factor, Fen 2.1 Definition of Fen The environmental fatigue life correction factor, Fe!> is used to evaluate environmental fatigue.

Fell is defmed as the ratio of the fatigue life in air divided by the fatigue life in water at the same strain amplitude, as shown in equation (1). Fen=NAINW (1) In equation (1), NA is the fatigue life in air at room temperature and Nw is the fatigue life in simulated L WR water. NA can be determined from a reference fatigue curve developed using the least-squares method with data obtained from strain-controlled fatigue tests conducted in Japan. The reference fatigue curves for carbon, low alloy, austenitic stainless steels, and nickel chromium iron alloys can be expressed using the following equations, respectively: ea = 25.71N;:*490 +0.113 (Carbon steel) (2) ea = 38.44N;:562 +0.155 ea = 23.0N;:*457 + 0.11 ea = 19.0N: 45o +0.118 2.2 Fen for carbon and low alloy steels 2.2.1 Effects of sulfur content (Low alloy steel) (Stainless steel) (Ni-Cr-Fe alloy) (3) (4) (5) The fatigue life of carbon and low alloy steels in hot water is dependent on the sulfur content within the steels. Figure 1 illustrates the relationship between Fell and sulfur content under the condition of 289°C, DO>O.7 ppm, and 0.001 %/s strain rate (5). The plotted points in Figure 1 represent the average Fell for various levels of sulfur content in order to eliminate biased trends due to an unbalanced number of data points. Data on weld metals were excluded from the plot because those materials are apparently less sensitive to environmental effects. As shown in Figure 1, the logarithm of Fell increases linearly with sulfur content. It was concluded that regarding the effects of sulfur content, there is no significant difference between carbon and low alloy steels, and both data sets were analyzed by a least squares fit.. The resultant line and equation are shown in Figure 1. 2.2.2 Effects of strain increase rate Figure 2 shows the relationship between Fell and strain rate (8) under a 289°C and DO>0.7 ppm environment (5). To eliminate the effects of different sulfur contents in individual specimens, Fell for each specimen was converted to the value of which sulfur content was 0.015% using equation (6). Fen(S=O.015%) = Fen(S) 1 EXP(97.92 x (S-0.015)) (6) The plots represent the average Fell for a given strain rate. As the strain rate decreases, Fell(NI.OIS%) increases almost linearly in double logarithmic plot. There is little difference between carbon and low alloy steels. The resultant line of a least squares fit and equation are shown in Figure 2. Figure 3 shows the relationship between Fell and strain rate for selected heats including data tested at strain rates below 0.0001%/s(5). Data for both carbon and low alloy steels are provided for different environments with higher DO (1-8 ppm) and lower DO (0.2 ppm) For both groups of data, Fell reaches a threshold at lower strain rates. The strain rate threshold for the group with greater DO is 0.0001 o/oIs, and is 0.00040/0Is for the group with a lower DO.

102 10' Carbon & Low-Alloy Steels 0 CS BM Strain Rate=O.OOl%/s L;. LAS BM in BWR Water T=289°C !o, DO>O.7ppm ~ MITI Guideline. to _ - - - - - --0 \\- --~- o--~ -;::0 ""'JSME S NFI-2006/2009 Fon =13.41 EXP(97.92S) lifL-~---L--~--L-~ __ -L~~~~~~~ 0.000 0.005 0.010 0.015 0.020 0.025 Sulfur Content (%) Fig. I Relation of sulfur content to Fen for carbon and low-alloy steels (average values, excluding weld metals) 1~~~~~~~~~~~~~~~~~~~ 102 10* Carbon & Low-Alloy Steels S=0.015% in BWR Water 289°c 00>0.7 ppm /. ~ o CSBM D. LAS BM ~ JSME S NFI-200612009 F =1 496-0*518 ICl',,~'O /'~ MITI Guideline "0 10" L:-'~.u.w:L.....~u.wI~~u.wI-:-,"~.u.ul.~~....... :-,-~.wJ 10.5 10-4 10" 10.2 10.1 10* 10' Strain Rate &(%/5) Fig. 2 Relation of strain rate to F enjS~aOI5%) for carbon and low-alloy steels (average values) 102 c:: u..'" 10' ° I:>. 0 0 10* 'Y 0 10" . 'Y... 'Y. ___...--, *S 1:>.0 D. o '~----iJ"--- [5 i 0 Carbon & Low-Alloy Steels in BWRWater T=289°C S DO CS 0.016% 1*8 ppm "V - - - CS 0.016% 0.2 ppm .*.. LAS 0.021% 1-8 ppm B -**-LAS 0.008% 0.2 ppm -T ---.D. - -, O~'" £1" "V S DO G. -",

  • ° CS 0.016% 1 ppm 0.3%

CS 0.016% 8 ppm 0.6% CS 0.016% 0.2 ppm 0.6% CS 0.016% 0.2 ppm 0.3% LAS 0.021% 1 ppm 0.3% LAS 0.008% 0.2 ppm 0.6% 8 o 10" 10-4 10" 10.2 10.1 10* 10' Strain Rate 6 (%/5) Fig. 3 Relation of strain rate to Fen for carbon and low-alloy steels (saturation at low strain rate) 2.2.3 Effects of temperature Figure 4 shows the relationship between Fel1(S~O.015%) and temperature for carbon and low alloy steels under the conditions of DO>O.7 ppm and 0.001 %/s strain rate. As shown in the figure, for temperatures between 50 and 160°C, a flat line representing Fel1(S~O.015%)=6.0 is assumed; for temperatures above 160°C, the relationship is represented by the equation shown in the figure; and for temperatures below 50°C, a line connecting the point (50°C, Fel1(S~O.015%)=6.0) to the point (O°C, Fel1(S~O.015%;=1.0) is assumed. -Ifj

10 2 10* o CSBM

6.

LAS BM Carbon & Low-Alloy Steels Strain Rate=O.OOHVs in BWR Water S=0.015% DO>O.7 ppm 50 100 150 200 250 300 350 Temperature T ('C) Fig. 4 Relation oftemperature to F en(S~aOIJ%) for carbon and low-alloy steels 2.2.4 Effects of dissolved oxygen concentration Figure 5 shows the relationship between Fell(S~o.OJ5%) and dissolved oxygen concentrations for carbon and low alloy steels under the conditions of 289°C and a strain rate of 0.001 %/s (5). The threshold of Fell(S9I.OJ5%) is assumed to be 53.5 at high DO, which can be derived by substituting i: = 0.001 %/ s in the equation shown in Figure 2. The threshold of Fell(S~o.oJ5%) at low DO is assumed to be 3.28, which is derived by averaging the data on carbon and low alloy steels with DO of 0.01 ppm or less. A line in the transition zone connecting the point (Fell=53.5, DO=O.7 ppm) to the point (Fell=3.28, DO=O.02 ppm) is assumed, as expressed by the equation shown in Figure 5. Carbon & Low-Alloy Steels 0 CS BM in BWR Water

6.

LAS BM Strain Rate=O.OOl%/s $=0.015% 102 T=289'C JSME S NFl-200012009 Fen=70.8(DO/*785 b, 0 'g o 8 ~ '8G "a. ~ ~"~MITI Guideline ~~,,,, Lo. (O.02ppm, 3.28) Dissolved Oxygen Concentration DO (ppm) Fig. 5 Relation of DO to Fen for carbon and low-alloy steels in BWR water 2.2.5 Effects of water flow rate Figure 6 shows the relationship between Fell and water flow rate for carbon steels (5), (6). Fell is highly dependent on the flow rate, under high DO and high sulfur content conditions, and decreases as flow rate increases. However, the flow rate has little influence on Fell for materials with low sulfur content and/or for environment with low DO, in which conditions, Fell is essentially small. Accordingly, it can be concluded that the flow rate has no effect on Fell in the PWR water and has only a minor influence on Fell in BWR feed water, where the DO is around 0.05ppm. Similar trends can be seen for low allow steels. The current Fell equation, which was formulated based on data taken at lower flow rates, consistently results in a conservative evaluation for high flow rate conditions. Therefore, the effects of flow rate are not considered applicable to carbon and low alloy steels for this evaluation.

~I;m~]mllllil

5(%) DO(ppm) S(%) DO(ppm) 1 02 -o-5T5410 0.016 1 . 1' *ST5410 0.006 0.02 - ST5410 0.016 0.2

    • -<J***ST5410 0.006 0.05

-*iJ*-ST5410 0.Q16 0.05

      • O***ST5410V1t.1 0.005 0.05

-*<>***5T5410 0.016 0.01 -**(>--SFVC28 0.004 1 S CartlonSteel 0 &,=0.6% ~ in BWR Water ) .......... Q i=O.OOlo/oI. ~ /f'\\ \\ OT=289"C

~=
:?=~;t;~~

100~~~~~~~~~~~~~~~~~ 10.5 10-2 10-' 100 10' 102 Water Flow Rate (m/sec) Fig. 6 Relation of water flow rate to Fen for carbon steel in BWRs 2.2.6 Effects of material strength The environmental fatigue tests were also performed for representative high strength materials to be used in the pressure boundary of L WRs, including carbon steel STS480 and low alloy steel SQV2B. The test results confirmed that the environmental effects are not significant for these high strength materials. 2.2.7 Equation to calculate Fen for carbon and low alloy steels An equation to calculate Fell for carbon and low alloy steels derived by considering all ofthe above test results, is shown in Table 1 (5). Table 1 Fen equations for carbon and low alloy steels In(Fen )=O.00822(OR2-i$9"PO* s* = 10(2.16) (&>2.16%IS) t* =In(t) (0.0004 St~2_16%ls.DO~0.7ppm) t* = In(O.OOO4) (t< O_oo04%ls,DO ~O.7ppm) s* = Io{sl (0.OOO1*~ s :;:2.16%ls,DO > O.7ppm) s* =10(0.0001) (s < 0.0001%/8,DO > O.7ppm) S*.. 10(12.32}+97.92S T*=D.0358T (T <50°C) T*,,,In(6) (50 ~ T ~ 160°C) T*= In(0.398)+o.017T IT> 160OC} 0" -10(3.28) (DO < 0.02ppm) 0* = In(70.79)+ 0.1853ln{DO) (0.02 ~ DO:;: O.1ppm) 0* = 1o(53.5} (DO>O.1ppm) FeJI =1_0 (&aSO.042%orinthecase of earthquake) 2.3 Fen for stainless steels 2.3.1 Effects of strain increase rate Different equations to calculate Fell are applied to BWR and PWR stainless steel components. Figure 7 shows the relationship.between Fell and strain rate at 289°C in simulated BWR water (5). Materials are classified into Type 316NG, 304, its associated weld metal, and cast stainless steel, and the average Fell values for individual materials are plotted for various strain rates. Data obtained from tests on 316NG, 304 and 304L conducted at high flow rates exceeding 1 mls are plotted separately. As can be seen in the figure, average Fell values for cast steel and those obtained at high flow rates are greater than Fell values for non-cast steels tested in stagnant water. It may be possible to apply separate equations to cast steels and non-cast steels. However, due to difficulties in evaluating the data for high flow rates, all of the data are analyzed as a whole using a least squares fit to determine a trend line. The resultant line and equation are shown in Figure 7. . --.----------.~~~~~~~~~--~~- ---*-----------,-----*~~---------1!ll1~'m* ***

u." 10 o 316NG BM t; 304 BM o Weld Metal o Cast SS Stainless Steel in BWR Water T= 289°C 'V Hi Flow Rate (316NG. 304. 304L) 0.1 '-'-~"""""~",---,"~",---,~_~,",-~wuL~wuL~",", 1~ 1~ 1~ 1~ 1~ lif lif 1~ 1~ Strain Rate 6 (%/s) Fig. 7 Relation of strain rate to Fen for stainless steel in BWRs The relationship between Fen and strain rate is shown in Figure 8 (5) for 316NG and cast stainless steel (both of for which data are obtained at very low strain rates under a simulated BWR environment at 289°C),. In Figure 8, the trend line described in Figure 7 is also shown. Data for 316NG are not saturated at 0.00004o/c/s, however this was determined to be the threshold for strain (the same value as for PWRs). This value was chosen since it is closest to the lowest average strain rate at a transient, and even if it is assumed that the strain rate is saturated at 0.00004o/c/s, it would not significantly influence the result. t: u.'" Stainless Steel in BWRWater 102 T=289°C 10' DO(ppm) e.(%) o SUS316NG BM*l 0.01 0.6 SUS316NG WM 0.01-8 0.6 o SUS316NG BM*2 0.01 0.6 SCS14A 0.01 0.3. 0.6 100 Saturated at O.OOO04%/s(JSME S NF1*2009) _._.- Saturated at 0.OOO4%/s(JSME S NF1*2006) 10" 10-5 10.4 10" 10.2 10" 10° 10' Strain Rate 6 (%/s) Fig. 8 Relation of strain rate to Fen for stainless steel in BWRs (saturation at low strain rate) Figure 9 shows the relationship between Fell and strain rate for stainless steels in a simulated PWR environment at 325°C (5). Materials are classified into Type 316, 304, its associated weld metal, and cast stainless steel and the average Fell values for individual materials at various strain rates are plotted. As shown in this figure, there is no significant difference among the materials, although Fell for SUS304 is slightly higher and that for weld metals is slightly lower. Therefore, the data were analyzed as a whole using a least squares fit to determine a trend line. The resultant line and equation are shown in Figure 9. Figure 10 shows the relationship between Fell and strain rate in a simulated PWR environment for cast and non-cast stainless steels for which test data at very low strain rates have been obtained (5). In FigurelO, the trend line in Figure 9 is also shown. As can be seen in the figure, the threshold for lower strain rates for non-cast stainless steel is 0.0004o/c/s and that for cast stainless steel is 0.00004o/c/s.

Stainless Steel in PWR Water T=325°C 10 o 31BBM t; 304 BM o Weld Metal o CastSS Fon=2.70(ir>"°.254 (JSME S NFl-2006/2009) 0.1 L.....~.L..~wL~uwI...~u.wl.~....wL..o...~oL...~wL.~= 1~ 1~ 1~ 1~ 1~ 1~ lif 1~ 1~ Strain Rate iT (%/s) Fig. 9 Relation of strain rate to Fen for stainless steel in PWRs 10 o 0) o 316 BM t; 304 BM o Weld Metal o Cast SS Stainless Steel in PWR Water T=325°C F on=2.70(ir>"°*254 (JSME S NFl-200B/2009) -Saturated at 0.00004"/ s for Cast

    • ---"Saturated at 0.0004%/s for not Cast 0.1 LL~""-"~woL~,"",-~"""",,-,-~,,--,-~wL.~""'--~"""

1~ 1~ 1~ 1~ 1~ 1~ lif 1~ 1~ Strain Rate &T (%/5) Fig. 10 Relation of strain rate to F", for stainless steel in PWRs (saturation at low strain rate) 2.3.2 Effects oftemperature The relationship between Fell and temperature in a simulated BWR environment is shown in Figure 11 (5). The trend line in Figure 11 was not obtained using a least squares fit of the data, but was derived by connecting the Fell value (9.14), which was obtained by substituting i: = 0.001 %/ s into the BWR trend line at 289°C (shown in Figure 7) to the point, Fell =1 at DoC. The equation for the trend line is shown in Figure 11. 10 Stainless Steel in BWR Water Ii= 0.001 %Is o 316NG 8M o 316NG WM t; Cast SS Temperature T ("C) Fig. 11 Relation oftemperature to Fen for stainless steel in BWRs --.----.----~ ----~---.---.. ------------- ------1II,~~'1m: *** 1

Figure 12 shows the relationship between Fell and temperature in a simulated PWR environment(5). The trend line in Figure 12 is derived by connecting the Fen value (14.76), which was obtained by substituting Ii = 0.001%1 s into the PWR trend line at 325°C (shown in Figure 9) to the point, Fell =1 at O°C. The equation for the trend line is shown in Figure 12. 100 Stainless Steels in PWR Water § c= O.OO1'i/s 10 In(FeJ=0.00B46T u.." 8 El 0 0 0 0.1 '--"'---'----'-...L~--'---'--'---'---I.--'--'L.......'--'__""___' o 50 100 150 200 250 300 350 400 Temperature T (OC) Fig. 12 Relation of temperature to F m for stainless steel in PWRs 2.3.3 Effects of dissolved oxygen concentration The effect of dissolved oxygen concentration on Fen for stainless steels was not clearly seen in either the simulated BWR or PWR environments. Accordingly, it is concluded that the effect of dissolved oxygen concentration on stainless steels is negligible in this evaluation. 2.3.4 Effects of water flow rate Figure 13 shows the relationship between Fen and water flow rate in the simulated BWR environment for three types of stainless steels (5, 6). Contrary to carbon steels, Fell for stainless steels becomes larger at higher flow rates (indicating that the life of stainless steel decreases under higher flow rates). The extent of increase in Fell at high flow rates depends on the material with the largest increase being for SUS304. With a large dispersion in the data it is impossible to quantify a dependency on the flow rate. Therefore, as described in the above section 2.3.1 "Effects of strain increase rate", three averaged Fell values at a strain rate of 0.001 o/w's and a high flow rate exceeding hnJs for the three types of stainless steels are incorporated into the data set This is used to determine the relationship between Fen and strain rate. Stainless Steel in BWR Water -o-SUS316NG, 00=0.05 ppm -"':'-SUS316NG,00=0.2ppm -*-{}*-SUS304. 00=0.05 ppm 100~~~?~~~~~~~~~~~~uW 10.5 10.2 10" 100 10' 102 Water Flow Rate (m/sec) Fig. 13 Relation of water flow rate to Fen for stainless steel in BWRs As shown in Figure 14, Fell is not dependent on the flow rate in the PWR environment (5).

  • --*-*---**----I9l,~1:m* ***

Do ~ 1i --~ -----;----~ ----------~ -og -- Average Stainless Steel in PWR Water &=0.001%18 T= 325°C o SUS316. £.=0.6% '" SUS316. £.=0.3% o SUS304. £ =0.6%. <> SUS304. £.=0.3% 100~~7~~~~~~~~~~~~~~ 10"" 10-2 10-1 100 101 102 Water Flow Rate (m/sec) Fig. 14 Relation of water flow rate to Fen for stainless steel in PWRs 2.3.5 Effects of sensitization There is no significant difference in Fen between sensitized and solution-treated SUS304 base metal in the simulated BWR environment, and thus it is concluded that the sensitization has no effect on Fen in the BWR environment. In addition, the results of many fatigue tests for thennally-aged materials have shown that there is not a significant dependence of thennal ageing on the fatigue life for most of the tested materials. 2.3.6 Equation to calculate Fen for stainless steels An equation to calculate Fell for stainless steels derived considering the above test results, is shown in Table 2 (5). Table 2 Fen equations for austenitic stainless steels In{Fen)=(C~t*)T* C=O.992 (BWR) C=3.910 (PWR) t* =1n{2.69) (BWR :t>2.69%/s) 6* = 1n(49.9) (PWR :.b 49.9%1 s) 6*=ln(6} (BWR :O.OOOO4!>t S2_69%ls) (PWR not Cast: 0_0004 ~ t::;; 49.9%1 s) (PWR Cast : 0.00004 ~ E ~ 49.9%/ s) 6*=ln(ROOO4) (PWR not cast: 6 <O.OOO4%ls) E*=ln(O.OOOO4) (BWR. PWR Cast: &<O.OOOO4%/s) 'r = OJXI0969T (BWR) 'r=O.OOO782T (PWRTS325°C) T" = 0.254 (PWR: T>325°C) Fen =1.0 (sa ::;; 0.11 % or in the case of earthquake) 2.4 Fen for nickel chromium iron alloy 2.4.1 Effects of strain increase rate For nickel chromium iron alloys it is necessary to adopt different Fell equations for the BWR and PWR environments. Figure 15 shows the relationship between Fell and strain rate for nickel chromium iron alloy in a simulated BWR environment at 289°C (5). The data for Alloy 600 conventional, Alloy 600 modified with higher see resistance, and type 182 weld metal are plotted separately in this figure. Since no clear differences were observed in the behavior of these materials, it was detennined that the data could again be analyzed as a whole. Although there is relatively large scatter in the data, the line and equation shown in the figure were derived using a least squares fit. The slope of this line is significantly less than that for other materials, which suggests that the fatigue life of nickel chromium iron alloy is less sensitive to the BWR environment.

trllimldllJ' ***

Ni-Cr-Fe Alloy in BWR Water T= 289°C o 600BM Cony 600BM +Nb o 182WM o 6 10".......... L...~~."-:...~~..L.~~.u.oL~~uuL~~.u..J 10" 10-3 10.2 10" 10* 10' Strain Ratei: (%/s) Fig. 15 Relation of strain rate to Fen for Ni-Cr-Fe alloys in BWRs Figure 16 shows the relationship between F." and strain rate for nickel chromium iron alloys in a simulated PWR environment (5). The data for Alloy 600 base metal, type 132 weld metal, Alloy 690 base metal and type 152 weld metal are plotted separately in the figure. Both Alloy 600 and Alloy 690 are less sensitive to the PWR environment, although there is a slight difference between these materials. It was determined that the data could be analyzed as a single sample set. The line and equation shown in Figure 16 were obtained by analyzing all test data using a least squares fit. The threshold for lower strain rates was set at 0.00004%/s for BWRs and 0.00040/,.Is for PWRs respectively-similar to those of rolled stainless steel since the amount of data was insufficient to perform the analysis. Ni-Cr-Fe Alloy in PWR Water T= 325°C o 600BM 132WM 690BM o 152WM -600/690 10" L....~........,,~~LWL~u..u.wL~~uL..~~L....~......., 1~ 1~ 1~ 1~ 1~ 1if 1d Strain Ratei: (%/s) Fig. 16 Relation of strain rate to Fen for Ni-Cr-Fe alloys in PWRs 2.4.2 Effects oftemperature Figure 17 shows the relationship between Fell and temperature for nickel chromium iron alloys in LWR water at a strain rate ofO.001%/s(5). Since a limited amount of data was obtained from fatigue tests at different temperatures, it is difficult to identify the relationship between Fell and temperature. Therefore, a logarithmic linear relationship between Fell and temperature is assumed (similar to stainless steels), and straight lines connecting the average Fell values at 289°C for BWRs and at 325°C for PWRs to the point (O°C, Fell=I.0) are plotted. The figure also shows the relationship between Fell and temperature for austenitic stainless steel in simulated PWR and BWR environments.

t: u..'" -'-'-' SS PWR

          • SS BWR

./ 10 /). Alloy600/690 PWR /.: - _. 0 Alloy600 BWR Ni-Cr-Fe Alloy in LWR Water i= 0.001%/0 ~ ~ l'> In(Fe) = 0.00233 7(BWR) o 100 200 300 400 Temperature T DC Fig. 17 Relation oftemperature to Fen for Ni-Cr-Fe alloys in LWR water 2.4.3 Effects of dissolved oxygen concentration It has been confrrmed that Fell for nickel chromium iron alloys does not depend on the dissolved oxygen concentration. 2.4.4 Equation to calculate Fen for nickel chromium iron alloys An equation to calculate Fell for nickel chromium iron alloys, derived considering the above test results, is shown in Table 3 (5). Table3 Fen equations for Ni-Cr-Fe alloys In(Fen)=(C-e*)T* C::(U12 (BWR) C=2.94 (PWR) 6*=ln(0.894) (BWR :&>0.894%IS) 6"=ln(19.0) (PWR: &>19.0%/s) s* =In{s) (BWR :0.00004:S:: E :S::0.894%/s) (PWR :0.0004:s;s~19.0%IS) i:* = In(O.OOOO4) (BWR: i < 0.00004 %/ s) e-=ln(O.OOO4) (PWR :e<O_0004%/S) 1'*=O.OOO343T (BWR) 1'* = O.OOO397T (PWR) Fen=1.0(Ea :S;O.11%orin the case of earthquake)

3. Evaluation of Fell during actual transients 3.1 Evaluation of Fen under inconsistent conditions The equations to calculate Fell are provided assuming consistent conditions are maintained.

However, under an actual transient strain rates and temperatures fluctuate. Fell may be calculated for a fatigue test by increasing strain rates in a stepwise manner, as shown in Figure 18, by using an Fe/I equation used in the constant strain rate test according to one of the following three models (Fellcal): (1) Mean strain rate model (2) Time-based integral model Fell weighted with the loading time is integrated. The method, which was proposed by Mehta (8), can be expressed by Equation (7) shown below: Fen.thi = (l / tr.th) f"h {Fen (t)}dt (7) (3) Strain-based integral model

~------19,[¥m *** 1

Fell for individual strain rates weighted with strain gains is integrated. The method, which was proposed by Kishida et al.(9) and Higuchi et al.(lO) can be expressed by Equation (8) shown below. This is called the modified rate approach. (8) t Fig. 18 A sample of strain wave for a 2-step strain rate change fatigue test Calculated results are compared with Fell1est for carbon steels in a simulated BWR environment in Figure 19 (7). The results calculated using the time-based integral model show few variations, even under different conditions. In particular, the calculated results in the range with small strain changes at lower strain rates are excessively conservative. The strain-based integral model shows the best correlation with the test results. The results calculated by the mean strain rate model are located between those calculated using the strain-based or time-based methods. ConSidering these results, the modified rate approach is suitable for calculating Fe!> and the mean strain rate model enables a simplified evaluation and provides conservative results. Similar results have been observed for stainless steels. During a transient at an actual plant, temperatures, dissolved oxygen concentration, and strain rate may change. Several fatigue tests have been conducted in simulated BWR and PWR environments while changing temperatures, strain rates and other conditions (II. 12). Considering the results of these tests, it is concluded that the modified rate approach is suitable for evaluating Fell under any conditions. ~ u..'" 12 t> t> t:. t::. t> t> 10 t> ~ 0 0 0.- 0 0 0.- t:. t>t:. 0 DO d' ().o.- 0 .- 0 8 o o c? 0,,'- 6 o,," CS (STS410) tJ#;.t>o* (;POD ra£1' ~ at " 6 in BWR Water ~ O'o? T =2S!rc 4 0'1;J ~o 0" DO=l-Sppm ~ 0,,% CO ~ ~.n"bi sbi: strain base integral 2 ...:. J;l_~ en, fbi tbi: time base integral UOV 0 F en,a., asr: average strain rate 2 4 6 Fentest 8 10 Fig. 19 Comparison of F en,sbi, Fen,rbi and F en,OS1' for carbon steel in BWRs 3.2 Evaluation of Fen considering the effects of strain holding In the BWR environment, the fatigue life of materials is reduced due to strain holding at the peak stress intensity (local maximum value) (13). The relationship between Fell and strain hold time is shown for carbon steels, low alloy steels, and stainless steels in Figures 20-22,

.-------.-.-~-------------.---.. -- ----.-------------------*-----------IIlI!1lW ****

respectively. In these figures, the test results under the strain holding at the peak, peak minus 0.03% and peak minus 0.06% are also shown. STS41O(S=0.016%) T= 289"(; in BWR Water DO = 1 ppm [] =0.3" without hold' <J B .~......... /(0:0~4~/~)**~*********~***o*~**o****o-***** without hold ~ 0 (O.4"/s)\\ g -0,-,- _. __ Cl. __.l.g._._._._._._._._. __. ___. ___. __._. ___. __._. __ o t(%/s) o 0.4 to. 0.04 o 0.01 t("/s) <> 0.004 "V 0.001 <l 0.0004 Hold at Peak-O.OS" Il Hold at Peak-0.03% Open: Hold at Peak (0.3%) 101 102 Hold lime t (sec) Fig. 20 Relation of hold time to Fen for carbon steel in BWRs SQV2A(S=0.021%) T= 289'c in BWR Water 00= 1 ppm [] = 0.3% 102 without hold II B. (~:0~4"~S\\....... ~ <1 o 0 0 8 0 ~

u. 10' o

without hold H 0

,. 0 (O.4"/s~

0 0 0 (J -'0-'-'- -*-.-.0-.-.-\\-.0.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-..... -.-.-.-'-'-'-" o t("/s) o 0.4 11 0.1 o 0.0 t("/s) <> 0.01 V 0.004 <l 0.001 Hold at Peak-0.06" () Hold at Peak-O.D3" Open: Hold at Peak (0.3") 10' 102 Hold Time t (sec) Fig. 21 Relation of hold time to Fen for low alloy steel in BWRs SUS316NG 6.(") c(%/s) in BWR Water 0 0.6 0.4 T= 289'C 11 0.6 0.04 00= 0.D1 ppm 0 0.6 0.004 0.6 0.0004 0 0 V 0.3 0.004 V 0 ~ 1 0' V without hold 8 0 10* o (0.004%10)" 0 --.- ----------~------------ _____ 1I ________ _ 0 0 10' 0 10 2 II 0 Hold at 0.6-0.06% Hold at 0.6-0.03% Open: Hold.t Peak (0.6") 103 Hold Time t (sec) Fig. 22 Relation of hold time to Fen for stainless steel in BWRs On the plots for carbon and low alloy steels, the dotted lines represents Fell at astrain rate of 0.004o/w's without holding, and the dotted and dashed lines represents Fell at a strain rate of 0.4o/w's without holding. On the plot for stainless steels, the dotted line represents Fell at a strain rate of 0.004o/w's without holding. In each case, Fen increases due to strain holding at the peak. For carbon and low alloy steels, fatigue life reduction becomes negligible at a strain rate of --1M

0.004O/cJs or lower. Conversely, fatigue life reduction is significant for stainless steels even at lower strain rates, and does not become saturated as the strain holding time becomes longer. When the strain rate is maintained slightly below the peak and thermal transients are taken into account, no fatigue life reduction is observed even though tensile stresses corresponding to the yield point remain. It can be concluded that under normal thermal transient conditions, it is not necessary to consider fatigue life reduction due to strain holding. Considering the above results, it was determined that for calculating the reduction in fatigue life due to strain holding, if the peak stress intensity to be used in the fatigue life evaluation is equal to that during operation at rated power output and the strain increases to a peak value and then is retained, the strain rate shall be treated as follows:

  • Carbon and low alloy steels: Strain rates above 0.004O/cJs are treated as a strain rate of 0.004%ls/
  • Stainless steels: The strain rate is set at 0.00004o/cJs.
  • Nickel chromium iron alloys: Reduction in fatigue life due to strain holding is not considered.

No fatigue life reduction due to strain holding was observed under a PWR environment, as shown in Figure 23 (13). 10' SUS316 T= 325'C in PWR Water 00 = 0.005 ppm without hold

6. = 0.6%

(0.0001%10)

    • D***************************************************.... ~.. /.

b, -£>.- __. ___________ - - ______ - ________ - __ b, ________ _ without h011 tOl/o) o (0.001%10) 0 0.4 10' 10 2 Hold Time t (sec) 11 0.001 o 0.0001 10 3 Fig. 23 Relation of hold time to Fen for stainless steel in PWRs

4. Codes for Nuclear Power Generation Facilities - Environmental Fatigue Evaluation Method for Nuclear Power Plants-4.1 General The Codes specify a fatigue evaluation method that accounts for the influence of environmental effects found in structures exposed to light water reactor cooling water, including PWR secondary system water. The Codes apply to materials such as carbon steels, low allow steels, austenitic stainless steels and nickel chromium iron alloys, which are used for light water reactors (and are authorized for use by the JSME Rules on Materials for Nuclear Facilities (JSME S NJl-2008)). The Codes are applicable to a range oftemperature and water chemistry conditions consistent with LWR design and operating conditions. The Codes do not specifically mention at which stage they should be applied (Le., plant design, construction or maintenance).

4.2 Methods to evaluate environmental effects Cumulative fatigue usage factors in the air are calculated using the methods specified in existing Codes. The cumulative fatigue usage factor in the environment, Uetb is expressed by Equation (9) below: n U en = U X Fen = LUi X Fen,;

=1 (9)

trlI!ll.(i1im ***

In Equation (9), U; refers to the cumulative fatigue usage factor in the ith stress cycle out of n total cycles; and F"~i is Fell during the ilh stress cycle and is determined for individual materials as a function of strain rate, temperoture, dissolved oxygen concentration and other parameters. It is known that environmental effects disappear at small strain amplitudes (1,5). Based on this understanding, the threshold of strain amplitude is set at 0.042% for carbon steels, which is equal to the strain amplitude at 106 cycles in the current design fatigue curve. Similarly, the threshold is set at 0.11 % for stainless steels and nickel chromium iron alloys, which is equal to the strain amplitude at the fatigue limit. Below these values, environmental effects need not be considered. Environmental effects disappear at high strain rates, as mentioned in the section regarding the effects of strain rate. Fatigue evaluation of thermal transient events is normally required to consider environmental effects because strain rates are low during such events. However, seismic loading cycles are excluded from the environmental fatigue evaluation because seismic load cycles are characterized by high strain rates of short duration. 4.3 Method to calculate environmental fatigue correction factor Fen To calculate F"I> the range in which strain during a transient increases in a continuous manner is divided into severol time segments, and calculations are performed for each segment. Three methods to determine F"I> are available: (1) Factor multiplication method The factor multiplication method performs the evaluation in the simplest and most conservative manner according to the design conditions of the location subject to the evaluation. In the calculation, the lower threshold of strain rote, maximum service temperoture of the concerned location and expected maximum dissolved oxygen concentration are used. (2) Simplified method To perform an evaluation using the simplified method, F"~Simp.A and F"~Simp,B are calculated respectively for two transients (A and B), which constitute the stress cycle used in the calculation of a fatigue usage factor. As shown in Figure 24, the time segments evaluated for each transient are those where strain is increasing the (binil,-> 8max) ** After defining the strain rote, average strain rate, maximum service temperature and maximum dissolved oxygen concentration in these segments, F.,~simp,A and F"~simp,B are calculated. F...,Simp of a stress cycle is calculated using Equation (10), below. The larger of F"~simp,A and F...,simp,B, is used in the equation. F . = Fen,simp,A x (8max,A -8min,A) + Fen,slm,B x (8max,B -8min,B) en,stmp (& max,A - & min,A ) + (& max.B - & min,B ) (10) (3) Detailed method To perform an evaluation using the detailed method, F.,~simp,A and F,,~simp,B are calculated for two transients (A and B), which constitute the stress cycle used in the calculation of a fatigue usage factor.. As shown in Figure 24, the range where strains continuously increase (8mill-> &max) are divided into m-number segments to be evaluated.. The average strain rate, maximum metal temperature at the wetted section, and maximum dissolved oxygen concentration for each segment are used to calculate Fell,simp,A and Fell,simp,B' F"~det during each transient is calculated using Equation (11) below: m /18 Fen,de, = L Fen,k k k=l Ernax - Emin (11) Although the detailed method is most complicated to calculate F"I> it can reduce excessive conservativeness. The Codes specifY different evaluation methods for vessels, pipes, pumps, valves and core internals. The largest difference between the evaluation methods among the components is the methods used to calculate strain rotes, If the stress analysis according to time. histories is

.-----~-------------------------.

~I,~m~*1I1I1I

performed, strain rates are calculated from the results of the stress analysis. If not, as in the case for pipes, strain rates are calculated according to the following procedure: First, the bending moment term (M) and the temperature difference terms (11Th I1T2, and Ta - Tb) of Equation (12) are evaluated to determine which is dominant. If the M term is dominant, the strain rate is assumed to be equal to the linearized strain rate of the "startup" transient. If one of the temperature difference terms (I1Tj, I1T2, or Ta - Tb) is dominant, the strain rate is obtained based on the assumption that the strains increase linearly from the minimum to the maximum value. In this case, these minimum and maximum strain values are of the most dominant term among the terms I1Tb I1T], and Ta - Tb for the transient being evaluated. K1C1PoDo K2C2M;, K3Eaill.~i i i Eaill.T2i (12) S = + + + K3C3Eab aaTa -abTb + --- p '--- ~ \\ Z; I Ll4-----.J \\ I LJ.J--1 ,--,r-- y- --,r-- P M I1TJ Ta - Tb I1T2 Refer to the article PPB-3532 in the Rules on Design and Construction for Nuclear Power Plants (JSME S NC1) (14) for the defmitions of symbols in Equation (12).

5. Conclusion In its 2006 Codes for Nuclear Power Generation Facilities (JSME S NFl) in 2006, the Japan Society of Mechanical Engineers (JSME) established an Environmental Fatigue Evaluation Method (EFEM) for Nuclear Power Plants describing the methods to evaluate fatigue life of components in contact with L WR cooling water. In 2009, the JSMB S NFl Codes were revised. This paper presents an outline of the Codes and their technical basis.
  • The environmental fatigue life correction factor Fe" is used in the evaluation of environmental fatigue, Fe" is determined for individual materials as a function of different factors.
  • The Codes specifY three types of evaluation methods: the factor multiplication method, the simplified method, and the detailed method. Any of these methods may be selected for use arbitrarily. In addition, conditions which do not require the consideration of environmental effects are specified.
  • For carbon and low alloy steels, Fe" is defined in as a function of strain rate, temperature, dissolved oxygen concentration and sulfur content.
  • For stainless steels and nickel chromium iron alloys, Fe" is defined in as a function of strain rate and temperature.
  • The modified rate approach method is specified to evaluate environmental effects under conditions of changing strain rates, temperatures and dissolved oxygen concentrations.
  • A reduction of fatigue life due to high water flow rates is considered for stainless steels in a BWR environment.
  • A reduction of fatigue life due to strain holding is considered for carbon steels, low alloy steels and stainless steels in a BWR environment References (1) Higuchi, M. and !ida, K, "Fatigue Strength Correction Factors for Carbon and Low-Alloy Steels in Oxygen-Containing High-Temperature Water", Nuclear Engineering and Design Vol. 129 (1991),

pp.293-306 (2) "Guidelines for Evaluating Fatigue Life Reduction in the LWR Environment", (in Japanese), Nuclear and Safety Management Division, Agency for Natural Resources and Energy (2000) (3) "Guidelines on Environmental Fatigue Evaluation for Power Reactors", Thennal and Nuclear Power Engineering Society (2002) (4) Code for Nuclear Power Generation Facilities, Environmental Fatigue Evaluation Method for Nuclear Power Plants (JSME S NFI-2006), Japan Society of Mechanical Engineers (2006) (5) Sakaguchi, K, Higuchi, M., Hirano, A., and Nomura, Y., "Final Proposal of Environmental Fatigue Life Correction Factor (Fen) for Structural Materials in LWR Water Environments", American

Society of Mechanical Engineers, Pressure Vessel and Piping Conference (ASME PVP) 26100, (2007) (6) Hirano, A., Sakaguchi K, and Shoj~ T., Effects of Water Flow Rate on Fatigue Life of Structural Steels under Simulated BWR Environmenf', ASME PVP 26423, (2007) (7) Higuchi, M., Hirano, T. and Sakaguc~ K, "Evaluation of fatigue damage on operating plant components in LWR water", ASME PVP2004-2684,.(2004) (8) Mehta, H. S., "An Update on The EPRIlGE Environmental Fatigue Evaluation Methodology and Its Applications", ASME PVP Vol. 386, pp.l83-193., (1999) (9) Kishida, K, Umakoshi, T. and Asarla, Y., "Advances in Environmental Fatigue Evaluation for Light Water Reactor Components", American Society of Testing and Materials, Special Technical Publications (AS1M SIP) 1298, p. 282., (1997) (10) Higuchi, M., !ida, K and Asada, Y., "Effects of Strain Rate Change on Fatigue Life of Carbon Steel in High-Temperature Water", ASTM STP 1298, pp. 216-231, (1997). (11) Hirano, A. and Sakaguc~ K, "Modified rate approach method to evaluate fatigue life of carbon steel under simulated synchronously changing BWR conditions", ASME PVP2006-94006, (2006) (12) Sakaguc~ K, Nomura, Y., Suzuki, S. and Kan~ H., "Applicability of the Modified Rate Approach Method Under Various Conditions Simulating Actual Plant Conditions", ASME PVP2006-93220., (2006) (13) Higuchi, M., Sakaguchi, K, and Nomura, Y., "Effects of Strain Holding and Continuously Changing Strain Rate on Fatigue Life Reduction of Structural Materials in Simulated LWR Water", ASME PVP-07-26101, (2007) (14) Code for Nuclear Power Generation Facilities, Rules on Design and Construction for Nuclear Power Plants (JSME S NCI-2008), Japan Society of Mechanical Engineers (2008)

~Iiitdl; ***}}

Retrieved from "https://kanterella.com/w/index.php?title=ML12340A596&oldid=5246360"