ML20073H145

Study of MITR-II Core Tank Aging for Relicensing Consideration

ML20073H145
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Site:	MIT Nuclear Research Reactor
Issue date:	12/09/1992
From:	Hwang J MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE
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4 A SBJDY OF MITR--II CORE TANK AGING FOR RELICENSING CONSIDERATION l

d by JYH-TZONG HWANG ,

i Course 22.39

" Nuclear Reactor Operations And safety "

i i

December 9,1992 1

Massachusetts Institute of Technology 9410050134 940929 PDR ADOCK 05000020 P PDR l'

• Abstract A program to upgrade and to obtain approval for extending the operating life of the Massachusetts Institute of Technology Research Reactor (MITR) is undergoing. In order to extend the life of the reactor, it is essential to predict the remaining life of various ,

components of the plant. Each components and systems of the reactor plant play their i particular role in the safety and/or mliability function of the plant. They am also subject to the age-related degradation for the service environments. The structure integrity of the com ,

tank is essential for ensuring that the reactor core will remain stable during normal >

operation, anticipated transient, and emergency and faulted condition. The purpose of this ]

report is to assess, based on currently available experimental information, the suitability of ,

the reactor core tank for extended operation at higher power level 2

l l

. Table of Contents l 1

1 Abstract I i

List of Figures ]

List of Tables I Introduction ,

II Description of MITR--II III Aluminum 6061 Alloy Aging Mechanisms IV Evaluation of MITR--II Core Tank Suitability for Extended Operation V Conclusions and Recommendations References 4

i A

l 3

• List of Figures Figure 1 View of M.I.T. Research Reactor Figure 2 Verticalcross-section MITR-II Figure 3 Aging characteristics of 6061 aluminum alloy  :

Figure 4 Dark field micrograph of precipitate reflections showing Mg2 Si Pitci itation P at grain boundary and in grains Figure 5 Tensile curves at two temperatures Figure 6 Tensile properties of the irradiated and defilmed HFIR hydraulic tube  :

Figure 7 Effect of thermal to fast flux ratio on the mechanicalproperties of type 6061 T-6 aluminum Figure 8 Typical corrosion curves for weight gain of aluminum exposed in water Figure 9 Total plastic energy versus fatigue life Figure 10 Stress amplitude versus fatigue life Figure 11 Radial and axial mesh: Standard model core section of MITR-II Figure 12 Azimuthal mesh: Enlarged model core section of MITR-II Figure 13 Thermal and fast fluence at core tank.

Figure 14 Core maximum thennal and fast fluence Figure 15 Reduction in ductility Figure 16 Increase in tensile strength e

4 h

List of Tables Table 1 6061 Aluminum alloy chemical composition limit Table 2 Typical mechanical propenies of wrought heat-tmatable aluminum-magnesium-silicon alloy Table 3 Physical, thermal, and mechanical properties of aluminum and its alloy Table 4 Tensile propenylimits Table 5 Summary of data on HFBR irradiation of Al-6061-T6 Table 6 Neutron flux from CITATION Table 7 MirR-IIaxialmesh: Standard Model Table 8 MITR II radial mesh: Standard Model Table 9 MITR II azimuthal mesh: Enlarged Model Table 10 Summary of data 5

-4 I Introduction A program to upgrade and to cbtain approval for extending the operating life of the Massachusetts Institute of Technology Research Reactor MITR)is undergoing. In order to extend the life of the reactor, it is essential to predict the remaining life of various components of the plant. Each components and systems of the reactor plant play their panicular role in the safety and/or reliability function of the plant. Rey are also subject to the age-related degradation for the service environments. Aging of components and materials refers to the variation of their propenies with time, the propenies ofinterest being those related to the safety function of the component or material. .

The structure integrity of the core tank is essential for ensuring that the reactor core will  !

remain stable during normal operation, anticipated transient, and emergency and faulted l condition. De reactor core tank is subject to age-related degradation for the reactor coolant environments, particularly from neutron irradiation. De purpose of this repon is to assess, based on currently available experimental information, the suitability of the reactor 1 core tank for extended operation at higher power level. Section H of the report provides i general description of the Massachusetts Institute of Technology Research Reactor.

Section IH will discuss the aging mechanisms of the core tank material (aluminum 6061 alloy), and Section IV will evaluate the suitability of the core tank for extended operation.

Finally, the conclusions and recommendations will be presented in Section V. l i

H Description of MITR-H  ;

ne original Massachusetts Institute of Technology Reactor, MITR-I, was both heavy-water moerseed and cooled with an open array of plate-type fuel elements. His original j core attained criticality in July 1958 and operated at power levels of up to five megawatts until 1974. De present core, MTIR--H, is a heavy-water reflected, light-water cooled and moderated nuclear reactor which utilizes flat, plate-type, fmned, aluminum-clad fuel elements highly enriched ( 93% ) in U-235. De reactor is designed to operate at power  :

I levels of five megawatts. The operating temperature and pressure are 40 to 53 *C and i

atmospheric with hydrostatic pressure from twelve inches of H20, respectively. A venical cross-section of the MTIR-H depicting both major components and experimental facilities is shown in Figure I and 2 [1].

The reactor core is centered within three concentdc metal vessels each of which provides protection to the core against loss of coolant and can be considered as a containment barrier. The outermost tank, which is made of steel, serves as a liner between the biological shield and, moving radially inward, a two feet thick graphite annulus that functions as a reflector. Both the concrete shield and graphite reflector contain penetrations ,

for various experimental facilities such as the beam ports, the fast blanket, the medical room shutters etc.

l The reflector tank, which is four feet in diameter, is used to maintain the heavy water at f the level necessary for reactor operation. The D2O system includes a pump and heat i exchanger to dissipate heat generated in the heavy water and a dump tank for rapid l

reduction of reactivity by lowering the D2O level. 'Ihis capability serves as a backup  ;

emergency method for reactor shutdown. The heavy-water reflector is a closed system.

This is important so as to avoid both the degradation of the heavy water and the release of tritium which is formed whenever a neutron is absorbed by deuterium oxide. The D2O j reflector tank is constmeted of high purity aluminum 6061 alloy. The lower part of this j tank has an inside diameter of 47.25 inches with a wall thickness of 0.375 inches. It i expands at the top to an inside diameter of 54.75 inches. Its overall height is 122 inches . .

i The innermost of the three tanks is constructed of high purity aluminum 6061 alloy  ;

vessel of varying diameter that is referred to as the core tank. It contains the light water that !

cools and moderates the reactor core. The bottom section of the tank has three diameter i transitions. The bottom portion has an inside diameter of twenty-inches. It then widens to an inside diameter of forty-five inches with a wall thickness of 0.25 inches and finally to an [

inside diameter of fifty inches with a wall thickness of one inch. An elevated support ring, which supports the core support housing assembly and the core shroud, is welded to the  :

bottom of the forty-five inch diameter section. Immediately below the top flange of the core tank is the eight-inch primary coolant inlet pipe that leads to the inlet plenum. The over all height of the core tank bottom section from the dished bottom to the top flange, is 102.375 inches. 'Ihe tank's design pressure is 24 psig. 'Ihe top section of the core tank .

I has an inside diameter of forty-four inches with a wall thickness of 0.75 inches and overall height of fifty inches. Its diameter matches that of the top flange of the bottom section of the tank.

. Surrounding the tank, nineteen inches below the top lip, are six penetrations, sixty .

- degrees apart, for the shim blade ddve mechanism and one penetration for the irgulation r 7 i

rod drive, he regulation rod is on the center-line of the thermal column. Penetrations also exist for the tank level probe and pressure taps.

Energy released by the fission of U-235 is removed by forced convection. The light-water coolant that enters the tank from the inlet plenum is directed to the annulus formed by the flow shroud and the tank's inner wall. It then flows downward through this annulus, under the suppon ring, and through another annulus formed by the core tank and housing until reaching the bottom of the fuel assemblies. It is then directed upward through the fuel elements and into the large outlet plenum above the core. The energy removed from the core is transferred through three heat exchangers to the secondary coolant system whereupon it is dumped to the atmosphere via two cooling towers. He use of a secondary coolant system is imponant as it allows the reactor's heat to be dissipated while maintaining the slightly radioactive primary coolant in a closed loop.

Two anti-syphon valves are positioned at the upperjunction of the flow shroud and the core tank. Dese, together with four natural convection valves that are located on the support ring are held closed by primary pump pressure and will open automatically if flow is lost. He fonner are intended to prevent siphoning of water out of the core tank should a primary inlet pipe rupture. He function of the latter is to promote natural circulation cooling if both the normal and emergency electric power supplies should be lost. .

III Aluminum 6061 Alloy Aging Mechanisms Aluminum 6061 alloy is an age-hardenable alloy. Figure 3 shows the aging characterisocs c,f the alloy [3]. De chemical composition limits of aluminum 6061 alloy used in nuclear reactor applications is shown in Table 1 [2]. He typical physical, thermal, and mechanical properties are shown in Table 2 and 3 [3,4]. He general requirement of tensile strength limits as Whd in ASME CODE (1989 ) is shown in Table 4. From the ,

survey of current technical papen, there are three main aging mechanisms in aluminum 6061 alloy, that is, irradiation aging, corrosion and low cycle fatigue as discussed in the following.

8 4

l. Irradiation aging i

Irradiation effects on aluminum alloys are relatively light. No drastic changes in e mechanical properties and dimensional stability have been observed during tests in high flux res 2. cb mactors. The threshold-integrated neutron fluences (both fast and thermal  :

11uence) to wuse aluminum alloy to loss of ductility was estimated to be in the order of  !

1012 n/cm2 [4),

Aluminum has a transmutation cross section of 0.23

• 10-24 cm2 for neutrons of.025 eV energy to produce silicon from the reaction 27Al(n,7)28Al, followed by the # decay to 28Si [5,6]. Irradiation with thermal neutrons triggers a novel phase instability in aluminum-based alloys. As such, a reactor with a relatively high thermal flux may readily produce 1% or more silicon by transmutation of aluminum atoms. Silicon is relatively insoluble in aluminum based alloys, and in this case precipitated out as a fine dispersion of

'(Mg2 )SiParticles as seen in Figure 4 [5]. The precipitates are believed to reduce void nucleation and growth by acting as sites for enhanced recombination of vacancies and interstitials and by retarding the climb of dislocations, which in turn reduces the rate at t which dislocations absorb interstitials [5]. [

Farrell et al. [6), have studied the effects of irradiation of 6061-T6 aluminum in the >

High Flux Isotope Reactor (HFIR). Bey observed that the microstructure of the material from the unirradiated end of the hydraulic tube consisted of a very finely dispersed, acicular precipitate of Mg2Si and the usual population of inclusions found in commercial alloys.

Here were also some isolated dislocations that were probably introduced after heat treatment during bending or straightening of the tube. Irradiation caused two obvious .

changes. One, it induced considerable precipitation of transmutation-produced silicon, l especially heavy at grain boundaries. Elemental silicon is less dense than aluminum,2.33 g /cm3 versus 2.7 g /cm3, and the introduction of precipitate of silicon causes the 6061 I I

alloy to swell. De second change in the microstructure, observed only in material irradiated to fast fluences greater than 6

• 1022 n/cm2, was the introduction of cavities. L These cavities were heterogeneously distributed and not associated with the silicort particles, and they seeme'd to be absent from grain boundaries except at some inclusions that lay on the boundaries. Deze was no direct evidence that helium and hydrogen from (n, a) and (n.p) reactions were involved in fracture and ductility loss. De irradiation ]

effects on tensile properties change are shown in Figure 5. neir results also show that, at a fast to thermal flux ratio of 0.6, a gradual increase in tensile strength and loss in ductility 9

l I

I begins at a fast (E > 0.1 MeV) fluence of 1021 n/cm2, but that the ductility loss appears to saturate above a fast fluence of 1022 n/cm2, as shown in Figure 6. r i

More recently, Weeks et al. [7, 8], studied the inadiation effects on 6061-T6 aluminum of control rod drive follower (CRDF) tubes in the High Flux Beam Reactor (HFBR) which is operated at a temperature of approximately 333 *k. Table 5 shows the summary data on .

HFBR irradiation of Al-6061-T6. Their msults show that:

(1) The original Mg2Si recipitates P were mplaced with a high concentration of 8 nm diameter, amorphous particles rich in silicon. The changes in mechanical properties are  !

attributed to the development of the silicon-rich precipitates. -

(2) 6061-T6 is a fully age-hardened alloy,it contains a massive network ofinternal sub-critical nuclei of magnesium silicide (Mg2Si) so that little additional strengthening and loss in ductility were anticipated to be caused by fast neutrons. A high fast fluence may have the beneficial effect of randomizing the locations of the silicon atoms and therefore seducing their effects on mechanical properties of the alloy. '

(3) Increase in tensile strength and decrease in ductility primarily fmm the thermal fluence.

'Ihe higher the fast to thermal fluence ratio at the same thermal fluence, the less increase in tensile strength and the less decrease in ductility,~as shown in Figure 7. Since, at high the: mal to the fast fluence ratio will induce a high concentration ofinsoluble silicon 1

per unit atomic displacement and, hence, a high degree of supersaturation and profuse nucleation of silicon-rich precipitates.

(4) The effects appear to be saturating at above approximately 1.8E23 n/cm2 thermal 4

fluence. 'Ihe ductility appears to reach a minimum value of approximately 9%.

John Weeks et al. also proposed the equations that fit the experimental data for CRDF tubes tensile strength and elongation changes [8], as presented in the followmg. -

i T.S. = 50 + 24.5 * ( 4th *10-23).5 in ksi, or

= 345 + 170* ( 4 th *10-23).5 MPa,

% E = 10.7 - 0.69*(4th *10-23) 4th : "Ihermal Fluence in n/cm2 ,

a 10

a *

-2. Corrosion i

Aluminum alloys have excellent corrosion resistance to air and water coolant (pure water and its vapor). The oxidation corrosion resistance of aluminum alloys lies in the fact .

that aluminum and oxygen have a high chemical affinity to form such oxides as Al2O3 The protective oxide film is tightly adherent on the metal surface that prevents or minimizes further attacks by free oxygen existing in most aqueous media.

Aluminum corrodes uniformly in the coolant water of thermal research reactors up to l about 220 *C [4]. At higher temperatures, hydrogen atoms produced by the radiation decomposition and corrosion reaction H2O -+ H + OH 2Al + 3OH -+ Al2O3 + 3H -

H + 3H -+ 2H2 diffuse into the metal and combine as molecular hydrogen. 'Ihis can accelerate the corrosion rate during the development of corrosion products and gas blisters spread on the metal surface. Figure 8 [4] shows the typical corrosion curves of aluminum plate l specimens exposed in water at various temperatures under atmospheric pressure.

r

'Ihe corrosion rate of aluminum as a function of pH has been relatively sparsely l studied. The rate was found to depend logarithmically on the pH [26], different  ;

dependencies being noted on either side of the pH at which the corrosion is a minimum ,

(close to 6). This value of pH is also close to that of the minimum solubility of various ,

hydrated aluminas which may form as conosive product films. Ambat et al. [27], studied the influence of pH on the corrosion of several aluminum alloys (not include Al-6061 ,

alloy). Their results show that the corrosion rate is negligible for pH value between 5 to 8.

3. Low cycle fatigue Y. S. Chung et al. [10), performed axial strain-controlled tests on five aluminum alloys !

(1200,5083,6061,6351, and 7005) to provide information on their cyclic behavior. The experimental results are shown in Figure 9 and 10. They also conclude that the precipitation i alloys,7005,6351, and 6061, show cyclic hardening followed by cyclic softening and the cyclic hardening generally increases with the strain amplitude and with the ratio of ultimate  ;

tensile stress to yield stress.

I1

- - ,y. _ _ ,, . , . . a . , ,. . - . . ,

IV Evaluation of MITR--II Core Tank Suitability for Extended Operation

1. Irradiation aging consideration As discussed in the section III, the primary concern ofirradiation damage on MITR--II core tank is the degradation of structure integrity due to tensile propenies change. Them is no specific MITR-II com tank material (aluminum 6061 alloy) experimental data available to examine the mechanical propenies change under irradiation. The formulas, proposed by Weeks et al., will be used to evaluate the suitability for extended operation of the core tank. ,

The flux used in this calculation was obtained from 4-8-92 CITATION run [11]. Table 6 shows the corresponding flux infonnation. The mesh point shown in the table refers to the core model in the John Bernard's thesis [12]. Figure 11,12 and Table 7,8, and 9 show the location and composition of each mesh points.

Since energy cutoff of the neutron flux in CITATION is not the same as those to be used in the formulas, the flux data from CITATION should be revised. The assumptions and formulas used in flux and fluence calculation are li.cted in the followings.

(1) MITR--II:

- Accumulated fission energy as of 9-20-92 : 291,120.25 MWH [11].

- Reactor operated at 4.9 MW,200 days per year, during 9-20-92 to 5-7-%.

(2) MITR-III:

-- Reactor operated at 10 MW,300 days per year,20 years operation.

(3) FluxlevelforMITR-III:

-- Two times that of MITR--II.

(4) Empirical formulas to evaluate fast flux (E 20.1 Mev) and corrected thermal flux (2200 m/sec) from CITATION [14]:

raa ra.

4(E)dE - 2.25

• 4(E)dE 4 0.t Mev . IMev

- r-4(E)dE - 3.04

• 4(E)dE s3 Kev . IMev 4, = O.(293.6p,p 2 313 12

-- F: group 3 flux from CITATION

-- assuming 40 'C @ core tank

-- % 2200 m/see thermal flux ne elongation and tensile strength at the end of each year are summarized in Table 10.

Figure 13,14 show the trend of cumulative thermal and fast fluence, while Figure 15,16 show the trend of the elongation and the tensile strength. He figures and the table also show the trend of the fluence and properties change at the maximum flux point of the core. i nis is proposed to be a reference case for more conservadve esumation purpose. De thermal to fast fluence ratio of MITR-II or III at core tank is approximately 1.8 which is well below the value of HFBR (Figure 7). The results should be conservative, assuming ,

all others to be the same. De corresponding elongation and tensile strength at core tank after additional 20 years operation of MITR--III are 9.995 % E and 74.76 ksi, respectively.

If the maximum flux of the core is used instead of flux at core tank, the elongation and >

tensile strength are 9.909 % E and 76.23 ksi, respectively. Although, the elongation is ,

slightly smaller than specified 10 % E in ASME CODE (1989)* at the end of 20 years operation of MITR--III, operated at 10 MW, it is still well above 5 % E as recommended by John Weeks [15]. He 10 % limit in elongation in ASME CODE may be interpreted as  !

an uni radiated limit but, this should be clarified.

• MITR Code compliance: ASME section II,1968 (But, not available to the author up to the report time). l

2. Corrosion consideration l The Al-Mg-Si (6000 series) alloys have excellent corrosion resistance in all natural atmospheric environment. As shown in Figure 8, at relatively low temperature,200 *C to l 250 *C, the corrosion rate is small and constant with exposure time. He operating I temperature of MITR-IIis 40 *C to 53 *C which is well below 200 *C, The pH value of  ;

the coolant system is in the range of 5.5 to 6.5 [1], which is around the value (6) for minimum corrosion rate as dLe-d in Section III. Therefore, the corrosion effect on the '

core tank material is negligible. Suppose the operating pressure, temperature and water  ;

chemistry of MTIR--III ase the same as that of MITR--II, there will be no corrosion damage on the core tank at the end of additional 20 years operation. However, this i assessment is based on typical corrosion resistance characteristics of aluminum alloys, due  ;

to lack of specific experimental data for Al-6061 alloy. De field inspection of the core tank ,

to determine the actual costosion rate is strongly recommended. Besides, the environment of the reflector tank is quite different from that of the core tank, the corrosion rate at the 13 l

.- reDector tank should be examined separately. (Note: No corrosion evidence of the reflector ,

tank was found, based on visual inspection conducted by MITR staff in 1989 [30].) I

3. Fatigue consideration For simplicity, the following formulas [23] am used to evaluate the stress level of the I

core tank.

P*R R a (Pressure stress) = , (- = 40, thin wall fonnula applicable) t t E*a *-AT  :

a (Thermal stress) =

1- v 2 P : Pressure = 0.1 MPa R : Core tank radius = 10 inches, at core region t : Core tank thickness = 0.25 inches 4

a: Linear thermalexpension coefficient = 23.4*10 /C v: Poisson's ratio = 0.28 E : Modulus of elasticity = 6.693*10' MPa I

AT : 50 'C (for conservative evaluation)

The total stress level of the core tank is approximately 60 MPa (neglect discontinuity stress, bending stress and other local factor, if any). As shown in Figure 10, the endurance limit [24] (i.e., the stress level which the material can withstand for an indefinite l number of cycles without failure) of aluminum 6061 alloy is approximately 200 MPa.

'Ihere is, at least, a factor of 3 for the core tank stress level to reach the endurance limit. l l

i V Conclusions and Recommendations  !

1. Irradiarian effects on aluminum alloys are relatively light. No drastic changes in  !

mechanical properties' and dimensional stability have been observed during tests in high flux research reactors.

2. Increase in tensile strength and decrease in ductility are prirnarily from the thermal fluence; that is , transmutation of aluminum to silicon. The higher the fast to thermal fluence ratio at the same thermal duence, the less increase in tensile strength and the l 14 l 4

i l

l

less decrease in ductility.

3. The elongation at com tank after 20 years operation of MITR--III is slightly smaller than specified 10 % E in ASME CODE, but, it is still well above 5 % E as mcommended by John Weeks. The 10 % limit in elongation in ASME CODE may be interpreted as an unirradiated limit but, this should be clarified.

4. The mechanical property tests of the com tank material, mmoved from MITR--II at the end of licensed operation lifetime, are mcommended, if possible, to demonstrate the integrity of the core tank can be maintained during the lifetime of MITR--III.

5. Since CITATION code may not properly predict flux peak at the core interface regions, it is desirable that more precise flux map be provided so as to reduce the uncertainty in the core tanklifetime prediction.

6. The corrosion effect on the core tank structure integrity will be negligible, assuming the same water chemistry for MITR--III. However, the assessment is based on typical corrosion resistance characteristics of aluminum alloys, due to lack of specific experimental data for Al-6061 alloy. The field inspection of the core tank to determine the actual corrosion rate is strongly recommended.

7. There will be negligible cyclic fatigue effect on the core tank, assuming the same operating pressure and temperature for MITR--III.

l 1

15

i References  ;

i

1. MITR Staff, " Safety Analysis Report for the MIT Research Reactor (MITR-II),"

1970.

7

2. ASME CODE Section II,1989. j

3. William F. Smith, " Structure and Properties of Engineering Alloys," 1981.

4. Benjamin M. Ma, " Nuclear Reactor Materials and Applications," 1983.  !

5. K. C. Russell, " Phase Stability Under Irradiation," Progress in Materials Science Vol. 28,1984.

6. K. Farrell and A. E. Richt, " Postirradiation Properties of the 6061-T6 Aluminum High Flux Isotope Reactor Hydraulic Tube," ASTM STP 570,1975.  !

7. John R. Weeks, Carl J. Czajkowski, and Paul R. Tichler, " Effects of High Thermal ,

and High Fast Fluences on the Mechanical Properties of Type 6061 Aluminum on the HFBR," ASTM STP 1046,1990.

8. John R. Weeks, Carl J. Czajkowski, and Paul R. Tichler, " Effects of High Thermal Neutron Fluences on Type 6061 Aluminum," to be published in 1993. -

9. Information Provided by Professor D. D. Lanning.

10. Y. S. Chung and A. Abel," Low Cycle Fatigue of Some Aluminum Alloys," ASTM STP 942,1988. ,

11. Personal Communication with K. Kwok, MITR Staff,9-25-92.

12. John A. Bemard, Jr., " MITR-II Fuel Management, Core Depletion, and Analysis: ,

Codes Developed for the Diffusion Theory Program Citation," M.S. Thesis, MIT Department of Nuclear Engineering,1979.

13. E. F. Sturcken, " Irradiation Effects in Magnesium and Aluminum Alloys," Joumal of i Nuclear Materials 82,1979. ,

14. Susan E. Best, " Characterization of the MIT Research Reactor for Fusion Reactor j Related Studies," M. S. Thesis, MIT,1979.  !

15. Personal Communication with John Weeks, BNL, 10-23-92.

16. M. Victoria, W. V. Green and D. Gavillet, " Nucleation and Growth of Precipitates

i and Helium Bubbles in a High-Purity Al-Mg-Si Alloy Irradiated with 600 MeV Protons," Journal of Nuclear Materials 155-157,1988. .

17. King, R. T., Jostsons, A., and Farrell, K., " Neutron Irradiation Damage in a Precipitation-Hardened Aluminum Alloy," ASTM STP529,1973.

18. S. Abis, et. al., " Investigation of Mg2Si Precipitation in an Al-Mg-Si Alloy by Small ,

Angle Neutron Scattering," Journal of Nuclear Materials 135,1985.

19. T. Kino , et. al., " Effects of Solute Atoms on the Evolution of Structural Damage in 16

, lon Irradiated High-Purity Aluminum Alloys," Journal of Nuclear Matenals 155-157, 1988.

20. B.N. Singh , et. al., " Effects of 600 MeV Proton Irradiation on Nucleation and Growth of Pmcipitates and Helium Bubbles in a High Purity Al-Mg-Si Alloy,"

Joumal of Nuclear Materials 141-143,1986.

21. F. King, " Aluminum and Its Alloys," 1987.

22. S. P. Carfagno and R. J. Gibson, " A review of Equipment Aging Theory and Technology," EPRI NP-1558,1980.

23. Course 22.314J Class Notes.

24. S. H. Crandall, N. C. Dahl, and T. J. Lardner, "An Introduction to the Mechanics of Solids," 1978.

25. " Corrosion in Natural Environments," ASTM STP-558,1974.

26. M. R. Tabrizi et al., " The Long-Term Corrosion of Aluminum in Alkaline Media,"

Corrosion Science, Vol. 32,1991.

27. R. Ambat, E. S. Dwarakadasa, "'Ihe Influence of pH on the Corrosion of Medium Strength Aerospace Alloys 8090,2091 and 2014," Corrosion Science, Vol. 33,1992.

28. Z. Szklarska-Smialowska, " Insight into the Pitting Corrosion Behavior of Aluminum Alloys," Corrosion Science, Vol. 33,1992.

29. E. Hom and H. Diekmann, " Corrosion of Aluminum and Aluminum Alloys in Nitric Acid," ASTM STP 1134,1991.

30. Reflector Tank Inspection Result, MITR Procedum 7.6.1, Provided by MITR Staff, 11-30-92.

l 17

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Figure 7 Effect of thermal to fast flux ratio on the wwhanwal properties of type 6061 T-6 mhuninum.

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1992 '19' 9 8 ' '2 6 0 d ' ' '2 0'S' '20'16 ' ' ' '2016 Year ,

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Thermal Fluence 1.6 E+ 23 -

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1992 1996 2000 2005 2010 2016 Year Figure 14 Core maximum therinal and fast fluence.

=

t Thermal Fluence at Core Tank-Maximum Thermal Fluence --

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1992 1996 2000 2005 2010 2016 Year Figure 15 Reduction in ductility (% Elongation).

Thermal Fluence at Core Tank -

Maximum Thermal Fluence --

80 75-

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1992 1996 2000 2005 2010 2016 Year Figure 16 Incmase in tensile stmngth.

Table 1 6061 ALUMINUM ALLOY CHEMICAL COMPOSITION LIMIT (ASME CODE)

Si Fe Cu Ma Mg Cr Zn Ti OTHER Al

.4.8 .7 .15 .4 .15 .8-1.2 .04.35 .25 .15 .15 remainder Table 2 Typical mechanical properties of wrought inest-trestable alumsinuse-anagnesium-silicon alloyst [3)

Tenale Tensile yield Elon- Hard- Shear Fatigue strength, strength.! gation. ness. strength, limst Ternper pu  % in 2 in Bhnt psi ps 1 Alloy psi 6053 O 16.000 8.000 35 26 Il.000 8.000 T6 37.000 32.000 13 80 23.000 13.000 O 18.000 8.000 25 30 12.000 9.000 6061 35.000 21.000 22 65 24.000 13.000 T4.T451 45.000 40.000 12 95 30.000 14.000 T6.T651 T81 55.000 52.000 15 32.000 59.000 57.000 12 33.000 14.000 T98 T913 67.000 66.000 10 35.000 12.000 18 43 14.000 6066 0 22.000 52.000 30.000 18 90 29.000 T4.T451 12 120 34,000 16.000 T6.T651 $7.000 52.000 10.000 20 35 14.000 9.000 6070 0 21.000 52.000 12 120 34.000 14.000 i T6 57.000 32.000 28.000 15 71 20.000 6101 T6 43.000 17 800 32.000 12.000 6151 T6 48.000 6 15.000 6201 T81 48.000 l

55.000 to 120 35.000 13.000 6262 T9 58.000 27.000 20 60 22.000 13.000 6351 T4 T451 42.000 95 29.000 13.000 ;

T6. T651 49.000 43.000 13 0 16.000 6.000 30 28 11.000 )

6951 i 39.000 33.000 13 82 26.000 T6 t After Ref.1.

3 Ywid strength. 0.2 percent offset. f I 50(Mg load.100 mm ball.

1 Based on 500 million cycles using an R. R. Moure type of rotating-beam machine.

j i

. Table 3 Physical. Thermil, and Mechanecci Propertos of Aluminum and its Alloys [4]

B100 60M SAP Pt OPl R M _ Al . =o Al .uov' AI (alio)i Ialloy b allon 1 Dense 20'C (3:cm's 2699  : ?! 2 'O 27-28 Crystal lattice structure FCC FCC Lattice parameter. 20"C q At 4 049 4 050 Melimg point t'C3 660 645-655 620-650 > 660 Boehng point t *C3 2060 Specinc heat. C,25-100'C (cal,g.'C) 0 226 0 230 0 230 Thermal conductmty 25-100'C ical/cm.sec- Ci 0 5035 052-053 052-053 0 40 linear thermal capansion 20-100'C t 10 * */ 'C i 23 8 23 5 23 4 20 Litimaie sirength annessed Al only akg,cmh 485 900-1680 900-2450 3500 cold-rolied 175h Al skg/cm3 ) 1820 (4 .H i t t 4+T6s Yield sirength q0 2 offset cold rolled Al ekg/cmh 1050 15001.H i 8) 2100s.T66 2500 Elongation annealed Al sheet only I'5) 48 5 35(41 2514)n 10 trode cold-worked Al sheci(H 55 5t-Hit) 12476)

Modulus of elasiscity 100 700 710  ?!0 20'C 508 skg/cm ) 3

~

Poisson s raseo 0 30 0 30 0 28 0 28 Hardness Srinell humber cold. worked Al only 27 23-44 25-73 "1100 At alloy is commercially pure. 6061 Al alloy 40 7 e/o Ms. 0 4 e/o Si). SAP 17-14 =/o Al,O l i Table 4 Tensile property limits [2]

i Seamless Tube Elongatson in 2 in. or 4 x Tensile Strength, kal Yield Strengths Diameter / nun, %

Specified Wall (0.2% OtheO Full-Section Cut-out Temper Theckness,8 in. rnin man min, ksi S(,acimen Specimen Alloy 6061 T4 0.025-0.049 30.0 . 16.0 16 14 0.050-0 259 30.0 16.0 18 16 0.260 4.500 30.0 .. 16.0 20 18 T6 0.025-0.049 42.0 . 35.0 10 8 0.050 4.259 42.0 , 35.0 12 10 0.260-0.500 42.0 . 35.0 14 12 Plate Tensele Strength, ksi Yield Strength (0.2% othet), ksi Elongation in 2 in. nr 4 x Temper Specified Thickness, in. min mas nun mas Diameter min. %

Alloy 6061 T4 0.051-0.249 30.0 16.0 lb T451' O.250-1.000 30.0 16.0 18 1.001-3.000 30.0 16.0 16 T6 0.051-0 249 42.0 35.0 . 10 T651' O.250-0 499 42.0 35 0 10 0 500-a.000 42.0 33.0 P 1.001-2.000 42.0 35.0 B 2.001 4 000 42.0 , 35.0 6 4 001-6 000 40.0 35.0 6

, e .

Table 5 Summary of data on HFBR irradiation of Al-6061-T6 [7).

Flaence. n (m-It nsile Pcrcent Number of Source E > o i NicV t hermal (tretagth. k u 1.li'nc.ition, total Li pcomcin Alcoa Handbook o o 25 i; Chow &

Jones o o 44 J : 20 17 5 : : 5  : ,

ORSL o o 50 s : o s ll o : 1 3 Czajkowski o o at s : 1 10 3 : o 5 4 Surscillance 5 = 10' 7 = 10 ' as : : Is 15 : 1o  :

Surseillance 2 10' I o7 , 10:' 594:o4 17 o  :

Surseillance 1 = 10:' 64= 10" 61 0 : 3o 12  :

CRDF A 6 7.9 x ItP 1.7 = 10' M2.7 : : 3 8:: 16 4 CRDF A-7 2.2 w 10' 49e 103 62.3 : 1M 29.7 : o 7 7 CRDF A4 1.5 x 10" 32x 10' 86 5 : 8 86: 2 6

( A4. ignormg lowest sample) (ss 3 : : 8) (9 0 = 0 3) ($1 l V.15.13 l9x 10" l5 10' 71 6 : 12 lu: : 0 7  :

V.15.17 93x 10" 1.2

• lo" 620:04 11 6 : 14  :

V.15.23'* l 6 = 10' 4 2

• to" 508=2 12 9 : 1.1  :

V.15.8 l.9 x los Io r 10" 55 2 0R 15.7 : 1.9 2 Chow and Jones also mclude data from four specimens from the upper end of the tube, which contained httle mduced actissty, mdicatmg a much lower thermal fluence lhese data were omitted from this evaluation.

• Inches from top of vertical thimble flow shroud.

' The same specimen gase low values of both tenwie strength and percent clongation.

Table 6 Neutron flux from CITATION ( 4 8-92 ).

N FLUX. %GROUF GROUF 2 GROUP 3 GROUP 1 FL FLUX 9em taak 5.869E13 3.352E13 9.092E13, FLUX max 1.557E14 6.249E13 1.021E14

• Energy cutoff (ev) upper energy mean energy Group 1 1E07 5.472E04 Group 2 3E03 3.464E01 Group 3 4E-1 IE 2

• FLUX @ core tank : Maximum flux at core tank

• FLUX max : Maximum flux of the core

• Location of the flux (mesh point ): R: Radial: 6: Azimuthal;Z: Axial 1

. Core tank : Group 1: RI5: 626; Z11 Group 2: R15; O26; Z11 Group 3: R15; O24; Z12

. Core max.: Group 1: R6; O27; Z11 Group 2: R2; O2; Z11 Group 3: R17; O26; Z11

Table 7 f1tTR-I t AXI AL f:ESit: S]_,11:DARD f10 del. ,

-tesh Interval (cm) I.ocation 30.48 Upper llater Plenum 10.16 Crid Plate 2.54 Fuel / Boron-Stainicss Inserts 2.54 Fuel / Boron-S tainless Inserts 5.08 Fuel / Boron-Stainicss Inserts 5.08 Fuel 5.08 Fuc1 5.08 Fuel 5.08 Fuel 5.0o Fuel 5.08 Fuel 5.08 Fuel 5.08 Fuel 5.08 Fuci 2.54 Fuel 2.54 Fuci 1.30 Lower Crid 0.60 Core Structurc/I'rlmary Coolant 1.90 Cure Tank 3.20 IIcavy 11ater/Al uminum 0.60 1.igh t I!ater/Itcavy t-fater 8.225 licavy 11ater/ Reentrant Beam Forts 46.645 llea v-j Ifater iteflector

Table 8 MITR-II RADI AL MESil: STAtiDARD MODEL Mesh Interval (cm) Location 3.552 Inner A-Ring 0.896 Idddle A-Ring 1.893 Outer A-Ring 0.634 llexagonal Spider 1.000 Inner D-Ring 5.200 Idddle B-Ring 1.000 Outer B-Ring 1.000 Inner C-Ring 3.282 Idddle C-Ring 1.000 Outer C-Ring 0.9525 Core Housing 1.080 Regulating Rod 0.635 Control Blades 0.9525 Core Structure / Primary coolant 0.681 Core Tank l.721 licavy Water Reflector 15.435 Heavy Water Reflector 15.435 lleavy Water Reflector 68.030 Ruficctor Tank /Craphite Re flector

Table 9 ntTa-II AzInuTHAT. utsit: c::r. Ar.cr.n "nntt

!!er.h Interval (radians) I.ocation 0.104790 A1, Radial Spider, Regulating Rod 0.397921 A1, B1, Cl 0.265281 A 1, B 1, C 2 0.132640 Al, B2, C2 0.146566 A1, B2, C3 0.104790 A2, B2, C3 0.146566 A2, B2, C3 0.132640 A2, B2, C4 0.265281 A2, 83, C4 0.397921 A2, B3, C5 Repeat the above sequence for the remaining teo triads of the MITR-Il core.

e T

Table 10 Summary of data.

%E %E T.S. ksi T.S. ksi g $f (f $. $.

@ core tank core max. @ core tank core max. @ core tank core max. @ core tank con: max.

1992' 9.2871 E+21 2.4634 E+22 1.6688E+22 1.8739E+22 10.5848523 10.5707023 60.0085045 60.605642 1993 1.0023E+22 2.6585E+22 1.801 E+22 2.0223E+22 10.5757335 10.560463 60.397251 61.0175824 1994 1.0758E+22 2.8536E+22 1.9331 E+22 2.1707E+22 10.5666148 10.5502236 60.7719774 61.414666 1995 1.1493E+22 3.0487E+22 2.0653E+22 2.3191 E+22 10.557496 10.5399843 61.1340991 61.798393 1996 1.18E+22 3.13E+22 2.1203E+22 2.3809E+22 10.5536965 10.5357179 61.2815532 61.9546446 1997  ; 1.4051'E+22 3.7272E+22 2.5249E+22 2.8352E+22 10.5257819 10.504373 62.3108536 63.0453563 1998, 1.6303E+22 4.3244E+22 2.9295E+22 3.2894E+22 10.4978673 10.4730281 63.2604975 64.0516587 1.8554E+22 4.9216E+22 3.334 E+22 3.7437E+22 10.4699527 10.4416832 64.1465356 64.9905605 199%

2000! 2.0806E+22 5.5188E+22 3.7386E+22 4.198E+22 10.4420381 10.4103383 64.9802585 65.8740258 2.3057E+22 6.116E+22 4.1431E+22 4.6523E+22 10.4141235 10.3789934 65.7699658 66.7108494 2001' 2002 2.5308E+2R 6.7132E+22 4.5477E+22 5.1065E+22 10.3862089 10.3476485 66.5219701 67.5077206 2003 2.756E+22 7.3104E+22 4.9523E+22 5.5608E+22 10.3582943 10.3163036 67.2412056 68.2698679 2004' 2.9811E+22 7.9075E+22 5.3568E+22 6.0151 E+22 10.3303797 10.2849587 67.9316158 69.0014701 2005 3.2063E+22 8.5047E+22 5.7614E+22 6.4694E+22 10.3024651 10.2536138 68.5964115 69.7059295 3.4314E+22 9.1019E+22 6,1659E+22 6.9236E+22 10.2745505 10.2222689 69.2382483 70.3860601 2006 3.6565E+22 9.6991 E+22 6.5705E+22 7.3779E+22 10.2466359 10.190924 69.8593523 71.0442211 2007 2008 3.8817E+22 1.0296E+23 6.9751 E+22 7.8322E+22 10.2187214 10.1595791 70.4616116 71.682413 2009 4.1068E+22 1.0894E+23 7.3796E+22 8.2865E+22 10.1908068 10.1282342 71.046644 72.3023502 2010 4.332E+22 1.1491 E+23 7.7842E+22 8.7407E+22 10.1628922 10.0968893 71.6158484 72.905515 4.5571E+22 1.2088E+23 8.1887E+22 9.195E+22 10.1349776 10.0655444 72.1704437 73.4931992 2011 2012 4.7822E+22 1.2685E+23 8.5933E+22 9.6493E+22t 10.107063 10.0341995 72.7115004 74.0665369 1.3282E+23 8.9978E+22 1.0104E+23 10.0791484 10.0028546 73.239964 74.6265303 2013 5.0074 E+22 5.2325E+22 1.388E+23 9.4024E+22 1.0558E+23 10.0512338 9.97150969 73.7566749 75.1740697 2014 5.4577E+22 1.4477E+23 9.807E +22 1.1012E+23 10.0233192 9.94016478 74.262384 75.7099509 2015 5.6828E+22 1.5074E+23 1.0212E+23 1.1466E+23l 9.99540458 9.90881988 74.7577655 76.2348884 2016 2

(f : Fast Fluence (n / cm ), (, : Thermal Fluence (n / cm') @ core tank : Max. Fluence at Core Tank T.S. : Tensile Strength in ksi core max. : Max. Fluence of the Core

% E : % Elongation.

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