ML19261B223

Final Rept on Suppl Metallurgical Studies for Chemical Cleaning of Dresden 1. Discusses Corrosion Tests in Dow Solvent NS-1 & Effectiveness & Corrosion Effects of Use of Dow Dilute Copper Rinse During Chemical Cleaning

ML19261B223
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Site:	Dresden
Issue date:	01/24/1979
From:	DOW CHEMICAL CO.
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References
DNS-D1-029, DNS-D1-29, NUDOCS 7902140257
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Text

e 9

THIS DOCUMENT EONTAINS POOR QUALITY PAGES Final Report on Supplemental Metallurgical Studies for the Chemical Cleaning of Dresden-1 DNS-D1-029 January 24, 1979

[A 9

Prepared for Commonwealth Edison Company by Dow Nuclear Services The Dow Chemical Company Midland, Michigan 48740 B-600-024-79 c

9o2i CO257

1 LEGAL fl0TICE This report was prepared as an account of work performed by The Dow Chemical Company ("Dou") and sponsored by the Commonwealth Research Company (CRC).

fleither CRC nor Dow nor any person acting on behalf of either:

a.

Makes any warranty or representation, expressed or implied, with respect to accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may rot infringe privately-owned rights; or b.

Assumes any liability with respect to the use of, or for damages resulting from the use of, any information, apparatus, method or process disclosed in this report.

t

Table of Contents 4

Page ABSTRACT i

Section 1 - Corrosion Tests in Dow Solvent US-1

• Sub-Section I-A - Galvanic Corrosion of Bimetallic Couples in Dow Solvent HS-1.

1 Appendix 1.A.1 -

Corrosion Rate Foraula and Precision of Data 5

Appendix 1.A.2 -

Figures and Tables 7

• Sub-Section 1-B - Stress Corrosion Testing on Highly Irradiated Type 304 Stainless Steel in Dow Solvent fG-1 15 Appendix 1.B -

Figure, Table, and Photographs 23

• Sub-Section 1-C - Corrosion Testing of Type 410 (Ha rdened) S tainless Steel in Dow Solvent HS-1 36 Appendix 1.C.1 -

Certification of Heat Treatment of Corrosion Test Specimens 42 Appendix 1.C.2 -

Tables, Photographs, and Figures 44 Section 2 - Effectiveness and Corrosion Effects of the Use of the Dou Dilute Copper Rinse During the Dresden-1 Chemical Cl ea n i ng 51

• Sub-Section 2-A - Effectiveness and Corrosion Effects of the Dow Dilute Copper Rinse 52 Appendix 2.A.1 -

Figures 59

• Sub-Section 2-B - Effect of the Dow Dilute Copper Rinse Solution on Copper Washers in Dresden-1 65

• Sub-Section 2-C - Corrosion Rate of Silver in the Dow Dilute Copper Rinse Solvent 67

ABSTRACT A feasibility study has been completed for chemically cleaning the primary system of the Dresden-1 Nuclear Power Plant.

The results of this study were documented in June,1977 in a report entitled, "Technica1 Study for the Chemical Cleaning of Dresden-1" (DNS-DI-016).

f major component of this docu-ment was a description of the laboratory testing of the corro-sion effects of Dow Solvent NS-1 on the materials of con-struction of the Dresden-1 system.

An ongoing review of data presented in that report has taken place by personnel f rom Commonweal th Edison Company, the United States Nuclear Regulatory Commission, and private consultants.

This review process gave rise to questions concerning the effectiveness and potential effects on various materials of construction of the Dow Solvent NS-1 ana the Doi Dilute Copper Rinse.

Previous reports and/or correspondence have addressed certain of these questions.

This report presents test procedures, test results, and conclusions relative to six specific areas of concern which have not previously been addressed by testing.

These concerns are grouped and addressed in the body of the report, as follows:

Section 1 - Corrosion Tests in Dow Solvent NS-1 Su b-S ec tio n 1 A.1 - Galvanic Corrosion of Bimetallic Couples in Dow Solvent NS-1 Sub-Section 1.B.1 - Stress Corrosion Testing on Highly Irre.diated Type 304 Stainless Steel in Dow Solvent NS-1

Sub-Section 1.C.1 - Corrosion Testing of Type 410 (Hardened)

Stainless Steel in Dow Solvent NS-1 Section 2 - Effectiveness and Corrosion Effects of the Use of the Dow Dilute Copper Rinse During the Dresden-1 Chemical Cleaning Sub-Section 2-A - Ef-fectiveness and Corrosion Effects of the Dow Dilute Copper Rinse Sub-Section 2-B - Effect of the Dow Dilute Copper Rinse Solution on Copper Washers in Dresden-1 Sub-Section 2-C - Corrosion Rate of Silver in the Dow Dilute Copper Rinse Solvent Each sub-section contains a brief description of the specific concern, a description of the tests used to answer the concern, and conclusions based on the experimental findings.

Significant findings of the experimental work described in this report are, as follows:

1)

General corrosion in Dou Solvent NS-1 of various heats of low-alloy and carbon steels found coupled to AISI 304 Stainless Steel in the Dresden-1 primary system is less than 20 mils during the planned ex-posure interval.

Corrosion penetrations of this magnitude are not expected to cause operational problems during the cleaning operation or during subsequent plant operations.

ii

2)

Following exposure to Dow Solvent NS-1, highly irradiated specimens of AISI 304 Stainless Steel removed from the core area of the Dresden-1 showed:

(a) no significant degradation in mechanical proper-tiesand(b)noinitiathonofstresscorrosion cracking.

From this testing, it can therefore be assumed that exposure to NS-1 will not cause any significant deleterious effects to the highly irradiated 304 Stainless Steel portions of the Dresden-1 system.

3)

Highly stressed samples (85% yield) of AISI 410 (Hardened) Stainless Steels show relatively high corrosion rates upon exposure to Dor Solvent NS-1.

However, samples of AISI 410(H) exposed to the maximum expected stress level (<20% yield) antici-pated in the Dresden-1 system displayed corrosion penetration of 15 mils during the planned cleaning interval.

This is considered to be a negligible percentage of thickness and should not pre;ent operational problems during the cleaning operation or during subsequent plant operation.

4)

Use of the Dou Dilute Copper Rinse Solvent is an effective way to renove the amount of replated copper anticipated in the Dresden-1 systen following the Dow Solvent flS-1 cleaning.

5)

The general corrosion rates of the Dou Dilute Copper Rinse Solution on alloys AISI 1018 carbon steel and AST!! A336 low-alloy steel were measured and found to be 5 mpy and 7 mpy, respectively.

I! hen the usage and iii

configuration of these materials in Dresden-1 is con-sidered, these corrosion rates are not considered to pose an operational problem during or after the rinsing step.

6)

The Dow Dilute Copper Rinse Solvent does not induce stress corrosion cracking on either sensitized or unsensitized samples of Inconel 600 or AISI 304 Stainless Steel under the planned operating conditions.

7)

The Dow Dilute Copper Rinse will have a negligible J

corrosion effect on the metallic copper washers found in the Dresden-1 reactor recirculating pumps.

8)

The Dow Dilute Copper Rinse will have a negligible corrosion effect on the silver plating of the reactor pressure vessel head gasket.

Based on these findings, the six outstanding items addressed in this report are considered to be resolved.and are not con-sidered to present any significant unresolved operational concerns either during or af ter the proposed cleaning opera-tions.

iv

O m

SECTION 1 CORR 0SI0t1 TESTS IN D0W SOLVEllT NS-1 G

h D

GALVANIC CORROSION OF BIMETALLIC COUPLES IN DON S0LVENT NS-1 (Sub-Section 1-A)

The major objective of this test program was to evaluate the corrosion behavior of carbon and low alloy steels galvanically coupled to AISI Type 304 Stainless Steel, in the Dresden-1 chemical cleaning environment.

Effect of cathode to anode area ratio on corrosion rate and heat to heat variation were also to be investigated.

Test Procedures Three heats each of a ;oys A336-F1, A335-P1, A302-8 and A105, and two heats of A106-B were obtained from the General Electric Company.

The Tabl e 1. A.1 (Appendix 1.A.2) sunnarizes the chemical composition of each heat (based on the original mill certifications and G.E. data).

The test specimens of rectangular shape and nominal dimension, 1.5" x 1.0" x 0.25" with a 21/ 64" hole at the center, were f abricated from the sample stocks by saw-cutting and milling.

No further surface inish was applied.

The specimens were pre-pared for corrosion testing as recommended by ANS G80 (ASTM G1-72).

The corrosion test was conducted in the Dow Dynamic Test Loop.

This equipment simulates the fluid notion of the cleaning process.

The specimens were exposed to Dow Solvent NS-1 at 1

250 F + 5 F for 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />.

The carbon and low-alloy sv a1 specimens were galvanically coupled to AISI type 304 plates at stainless steel to test alloy area ratios of 1, 2, 5, 10, and 20.

The bimetallic couples were electrically i olated from the remainder of the loop by Teflon

• shoulder washers.

Two excep-tions were made in the specimen placement outlined above.

Some low-alloy and carbon steel specimens were not electrically coupled to Type 304 in order to represent zero area ratio.

Some low alloy and carbon steel specimens were electrically coupled to the loop in order to simulate an infinite area ratio.

All tests were run using triplicate specimens for each area ratio placed at random locations in the test vessel.

Drawings and photographs of the loop are shown in Figures 1.A.1 and 1.A.2 of Appendix 1.A.2.

Test Results Five runs of the dynamic loop were completed.

The conditions varied somewhat from run to run.

They were, however, more severe than conditions expected to exist during the Dresden-1 cleaning operation.

The final Fe concentration of the " spent" NS-1 ranged from 2,000 to 3,000 ppm as compared to 1,200 ppm limit to be followed during the Dresden-1 operation.

The metal surface area to NS-1 solution volume ratio was also in excess of twice the value estimated for the Dresden system.

During the loop runs, both the pressure rise of the system (presumably due to accumulation of H from the corrosion of 2

Fe) and the Fe concentration of the solvent were recorded.

Both parameters remained substantially linear with time, 2

indicating that the corroJion rate was constant during the 100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> period.

Following the exposure to NS-1 in the loop test, visual exum-inations of the coupons were made.

The tested coupons, especially low alloy steels coupled to high area ratio of 304 Stainless Steel, had very ragged surface.

No metallographic analysis was conducted.

Corrosion rates were calculated from the weights of coupons before and after NS-1 exposure, according to the formula ex-plained in Appendix 1.A.I.

Visual examination of the coupons did not reveal evidence of pitting or localized corrosion attack.

Therefore, the final data are expressed in terms of thickness of corrosioi. loss in mils per 100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> cleaning cycle and listed in Table 1.A.2 (of Appendix 1.A.2).

Conclusions The Table 1.A.3 shows the range of values of corrosion loss over different heats of alloys and different runs, wherever applicable.

Within the scope of the present test program, the follouing conclusions may be drawn:

1.

Galvanic effect on corrosion of low alloy and plain carbon steel is an important factor in NS-1 cleaning solvent.

2.

Low alloy steel, as a class, shows higher corrosion rates (approximately tuice) than those of plain carbon steel at all area ratios.

~

3

3.

Ilithin each class (low alloy steel or plain carbon steel) alloy-to-alloy variations seem to have less effect than heat-to-heat variations on corrosion rates.

Heat-to-heat variations are significant.

4.

The greate.t corrosion on alloy heats included in this test (and which are part of the Dresden-1 system) is about 10 to 20 mils of thickness loss during 100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> exposure to NS-1.

5.

The corrosion rate is constant for up to 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />, showing no induction time or a critical variation.

6.

A listing of carbon steel and low alloy steels con-tained in the Dre,. den-1 system was prepared in letter format on October zu, 1976 (DIS File Number EQ-01-006).

The predominant application of these materials was in components, valves, and piping which (for the mest part) were subsequently clad with 304 Stainle:

Steel.

In these cases, the thickness of the base metal would, in our opinion, not be substantially reduced during the Dresden-1 chemical cleaning.

Work has been carried out by General Electric Company to measure the corrosion effect of NS-1 on low-alloy and carbon steel base materials clad with 304 Stainless Steel with simulated cladding cracks.

Results of these tests have been previously reported by General El ec tric.

(Report 509.ATR-17, W. L. Walker, December 6, 1978)

This work indicates that accelerated cracking of carbon and/or low-alloy base metals does not occur following NS-1 ex-posure in a simulated cladding crack configuration.

~

4

d APPEllDIX 1.A.1 CORROSION RATE FORiiULA AND PRECISI0t1 0F DATA a

e 5

The corrosion rate in mils per year was calculated from the initial weight (Wi) and the final weight (llf) in grams, by the formula:

c.r. (mpy) = K (Mi - Wf)/Wf Where K is a constant given by 3

K = [(3451 10 ). Vo] / (T *S )

g in which Vo is the nominal volume (cm )

2 So is the nominal surface area (cm )

and T is the length of test (hours).

The corrosion loss per 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> was obtained by dividing:

c.r.

(mpy) by 87.66.

The coefficient of variation of the corrosion rate data from triplicate samples had the median; 8%, mode; 9%, and mean; 13%.

Three quarters of all rate data had less than 10% standard deviation.

6

APPEl1 DIX 1.A.2 FIGURES AIID TABLES 7

Figure 1.A.1 Views of Dynamic Loop o

p ~ y gy;

.,sr lT _ l,,

. t t-

'.)l

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k l'

ll ',

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(AISI 304 Construction)

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11

Table 1.A.1 Chemical Composition of Test Material Alloy Heat No.

C Cr Cu Mn Mo Ni P

Si S

V A336 F-1 210832

.26

.10

.08

.70

.57

.07

.011

.27

.013

.054 43563

.24

.12

.07

.76

.48

.16

.018

.24

.031

.002 45716

.23

.13

.06

.75

.45

.17

.017

.22

.024

<.001 A335 P-1 Z3263

.16

.14

.11

.57

.51

.09

.011

.26

.009

.006 Z3582

.17

.10

.10

.57

.53

.07

.010

.27

.007

.006 814950

.15

.08

.12

.67

.54

.10

.008

.28

.022

.002 A302B A5923

.23

.09

.09 1.42

.58

.08

.010

.15

.011

.003 A5933

.21

.10

.15 1.37

.58

.13

.009

. 2 5'

.011

.003 A2529

.23

.08

.09 1.25

.55

.05

.010

.24

.015

.005 A106 B 66549

.26

'c

.11

.81

.05

.11

.012

.19

.028

<.005 66402

.26

.11

.86

.05

.11

.011

.21

.031

<.005 A105H 38875

.34

.03

.08

.82

.01

.05

.008

.19

.017

.03 2748

.35

.05

.13

.99

.01

.04

.016

.26

.051

.04 44331

.36

.05

.13

.99

.01

.04

.014

.28

.051

.04

Table 1.A.2 Corrosion Loss Data (mils per 100 Hours)

AREA RATIO (304/ alloy) l 1 (or 2) l 5

l 10 ll 20 (or =)

0 ASTM HEAT Run. Number ALLOY NU4BER 1

2 3

4 5

1 2

3 4

5 1

2 3

4 5

1 2

3 4

5 1

2 3

4 5

A336 F-1 213832 0.2 (4.0L2 5.6 5.7 A336 F-1 43563 0.8 3.0 7.4 15.7 6.5

( 12.3 )2 A336 F-1 45716 0.3 4.2 4.8 6.5( 10.7)2 A335 P-1 Z3263 0.3 2.1 3.7 3.5 5.2 4.4 (8.2 )2 A335 P-1 Z3582 0.4 2.2 5.8 5.5 8.6 A335 P-1 814950 0.7 3.0 7.2 7.6 12.5 A302 B A5923 0.4 2.2 5.4 4.6 5.7 7.3 A302 B A5933 0.7 3.1 6.2 10.2 A302 B A2529 0.3 10.0 10.1 A106 B 66549 0.3 1.8 2.7 2.9 3.5 3.4 (4.2 )2 A106 B 66402 0.2 1.3 4.6 6.5 A105 H 38875 0.1 1.8 3.2 3.2 3.9 3.9 (4.9 )'

A105 H 2748 0.3 1.5 4.3 7.0 A105 H 44331 0.3 1.7 5.0 8.6 I

NOTE:

2 Data from single run and sing'le heat tests.

Table 1.A.3 Range of Corrosion Loss (mils per 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />) i A STil i

AREA RATIO 304/ ALLOY) iALLOYS 0

1 or 2) 5 10 20

=

I A336 0.43 1 0.26 3.5 + 0.5 7.5 + 4.2 (6.5)2 8.8 + 2.8 A335 0.47 + 0.17 2.4 + 0.4 5.611.6 7.8 1 3.4 (8.2)2 A302 0.47 + 0.17 2.7 + 0.5 6.4 + 1.9 8.8 + 1. 5 (10.1)2 5

A106 0.20 + 0.08 1.6 + 0.2 3.3 + 0.7 4.6 i 1.3 4.1 1 0.5 I

A105

0.30 _+ 0.0 1.6 _+ 0.1 4.7 _+ 0.4 7.8 + 0.3 NOTE

2 Data f rom single run and single heat tests.

STRESS CORROSION TESTING ON HIGHLY IRRADIATED TYPE 304 STAINLESS STEEL IN D011 S0LVENT NS-1 (Sub-Section 1-B)

Previous corrosion testing in preparation for the Dresden-1 decontamination involved the testing of metal coupons that had not been exposed to radiation.

A corrosion test was devised to provide data on the effects the decontamination would have on highly irradiated structural components.

Type 304 Stainless Steel was chosen as the test material since a majority of the primary system was constructed from this alloy.

Four charpy V-notch containers (provided by General Electric Company) made of Type 304 were chosen for testing.

These cans were exposed to 20 2

fluence levels on the order of 10 neutron /cm These were the most representative samples availabic to simulate the exposure history of the 304 materials in the core region of Dresden-1.

A total of 26 tensile specimens were fabricated for stress cor-rosion testing.

Eight highly irradiated tensile specimens were stressed to their unirradiated 0.2% yield strength and tested in "used" Dow Solvent NS-1 for a typical cleaning cycle. In addition, six other highly irradiated tensile specimens were transferred to Battelle llemorial Institue and pulled for mechanical prop-erties.

Four of these specimens had been exposed to a typical cleaning cycle in Dow Solvent NS-1; two specimens were tested as received.

No stress cor ssion resulted from the constant stress tests and the mechanical properties of irradiated 304 did not change upon exposure to Dow Solvent NS-1.

15

Test Procedures Material Four "charpy V-notch" containers were used to fabricate a total of 26 tensile coupons.

The coupons were notched at one end to maintain container idt tity.

Charpy Container Number of Number of Number Notches Coupons 6

3 8

47 2

6 20 1

6 5

0 6

All four cans had been inserted in the Dresden-1 reactor during the 1964 refueling outage.

Cans 5, 6, and 47 were in racks on the core perip.hery in positions 50/13, 50/13, and 50/11, respectively.

Can number 20 was located in a dummy fuel element at ;osition 58/25.

Cans 5 and 6 were removed from the reactor in February of 1967, and cans 20 and 47 were removed from the reactor in April of 1968.

The flux wires from these cans were never subjected to analysis and subsequently were discarded to hot scrap, so an accurate calculation of the dose the cans received during their exposure may not be possible from our records.

However, a reasonable estimate can be made from the general flux at 12 2

the core periphery (1.5-2.5 X 10 n/cm /sec; E>l Mev) and a factor of 0.77 (correction f actor for actual full power operating days).

Based on this approach, cans 5 and 6 20 2

received an exposure of approximately 1.2 X 10 n/cm ; E>l flev and cans 20 and 47 received an exposure of approxi-20 2

mately 1.5 X 10 n/cm ; E>l Mev.

No mill certifications 16

are available for the can materials themselves, because they were never intended to be part of a test program.

Drawings for the f abrication of the cans (General Electric Drawing 923C101) specified ASTM A167 Type 304 Stainless Steel.

This represents the only documentation of the can material.s as 304 Stainless Steel.

Specimen Fabrication The tensile specimens were milled out of the charpy con-tainers into tensile " dog-bone" specimens.

Figure 1.B.1 (of Appendix 1.8) shows the dimension of the specimens.

Random checks of the coupon gauge centers indicate a width of 0.250 + 0.003 inch.

Specimen Loading Conotant stress loading jigs were fabricated from Type 304 Stainless Steel to test the specimens.

The jigs were made of 304 Stainless Steel to eliminate galvanic effects.

Photographs 1.B.1 show a typical jig.

The jigs were de-signed so the specimens could be inserted and stressed remotely, using mechanical arms.

Two specimens from each "charpy" container were loaded in constant stress jigs to 53,257 psi.

This value was chosen as the test s tress using the following reasoning:

A search of General Electric 's material records on 30 different heats of Type 304 indicate the mean 0.2%

17

yield strength value as 42,133 psi with a standard deviation of 5,562 psi.

To have a 95% confidence level of stressing at yield requires 42,133 psi plus 2 sigma or 53,257 psi.

This is considered a conservative value since the 304 material at Dresden would not be loaded to yield.

Mechanical Properties Determination Six irradiated specimens were transferred to Battelle Memorial Institute in Columbus, Ohio.

Four of the speci-mens were exposed to NS-1 in a typical cleaning cycle (250 F for 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />) while the two remaining specimens were tested as received.

All irradiated tensile specimens were tested at room tem-perature.

The tensile properties determined were 0.2%

offset yield strength, ultimate tensile strength, reduction of area, and total elongation.

The reduction in area was calculated from pre-test and post-test specimen measurements made wi th a blade micrometer.

The total elongation was determined from the increased distance between two gauge marks scribed on the specinen prior to testing.

Due to problems arising frca inconsistent specimens synmetry and high irradiation levels, the pretest gauge narks were placed 1.44 inches apart.

This slightly longer gauge section extended out of the gauge section and thereby gives a slightly lower calculated total elongation.

18

The tensile tests were conducted on a 20,000-lb. capacity, screw drive Instron testing machine.

A nominal crosshead speed of 0.005 in/ min was used through yield to a post-yield strain of approximately 0.75 percent, then increased to 0.05 in/ min until failure.

The specimen deformation was measured to approximately 0.5 percent beyond general yield, using an Instron, Class B1, 1 inch, 1 percent strain gauge extensometer.

The strain gauge extensometer senses the differential movement of two extension arms attached to the specimen gauge section at a separation of 1 inch.

Prior to reaching the extensometer limit, the Instron strip chart recorder was changed to time and record the load time to failure.

Calibration traceable to the National Bureau of Standards is done on the Instron load cell annually.

Prior to testing, a standard electric short calibration is performed on the load measuring system.

The extensometer was calibrated before testing using an Instron high-magnification drum-type extensometer calibrator.

The edges of all specimens were burred, especially in the region of the gauge length, making placement of the clip gauge extensometer very dif ficul t.

Attempts were made to deburr the edges, but were only partially successful, due to the hardness of the naterial.

Consequently, the clip was installed in the best nanner possible.

19

Specimen Exposure to Dow Solvent NS-1 Eight " dog-bone" specimens were prestressed to 53,257

+ 200 lbs/in and exposed to a " simulated used" NS-1 cleaning cycle (250 F for 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />).

The " simulated used" solvent contained 1200 ppm ferric ion as ferric ammonium sulfate, and 650 ppm nickelous ion as nickel sul fate.

The "used" solvent was the test medium since the presence of fron and nickel might be expected to in-crease the prcbablity of sone deleterious effect.

In addition, the major portion of the cleaning cycle will involve exposure to NS-1 containing these elements.

The tests were carried out in air with the solvent being air saturated initially and with no replenishment of air or sol-vent.

All tests took place under isothermal, static con-ditions.

Test Results and Conclusions Mechanical Proerty Determination The mechanical properties calculated from the six specimens tested are tabulated in Table 1.B.1.

Note that variations in properties exist, but this is due to several factors:

1.

The " dog-bone" specimen is under a biaxial state of stress, where a normal tensile rod is under uniaxial stress.

2.

The edges of all specimens were burred, especially in the region of the gauge length, makin; place-ment of the clip gauge extensometer very difficult.

20

Attempts were made to deburr the edges, but these attempts were only partially successful, due to the hardness of the material.

3.

It is possible that each of the four "charpy" containers came from different heats of 304, so

~it is only reasonable to compare specimens cut from the same can.

From Table 1.B.1, specimens labeled 0 notch and 2 notches are present in both the "as received" condi tion (contaminated) and the decontaminated condition.

The 2 notch specimen 20 was exposed to a fluence of approximately 1.5 x 10 nyt and 20 specimen 0 notch to a fluence of 1.2 x 10 nyt.

A direct comparison can be made on the average of two pairs of these specimens:

Ave. 0.2%

Ave. UTS Ave.

Ave.

Of f set Yield PSC RA %

TE %

Decontaminated 72,257 103,304 51.2 30.9 Group (0 notch, 2 notches)

Contaminated 73,859 103,434 51.2 27.5 Group (0 notch, 2 notches)

From these data, it seems apparent that no significant change in mechanical properties has occurred due to ex-posure to solvent.

The property of greatest significance to corrosion results is ultimate tensile strength.

It can be seen that the average values for cleaned and un-cleaned sanples are very close, indicatir] no effect.

It 21

should be noted that a larger difference in the percent elongation was observed in these paired samples.

However, a statistical evaluation of this difference was made by means of a T-test.

The difference was not significant, at a 0.2 level, where conventionally, differences greater than 0.1 l evel in this tests are not considered significant.

A post-test photograph of the two types of specimens contaminated and decontaminated, is shown in Photograph 1.B.2.

Constant Stress Testing The eight tensile specimens used in the constant stress tests, were highly activated, giving a dose rate of 30-50 Rem /hr per specimen on contact.

Because of the high dose rate, the only practical way to examine the specimens following testing was optically through a lead window.

Photographs of all the specimens were taken after exposure and while they were under load.

(See Photographs 1.B.2 to 1.B.10).

No failure could be detected in this manner.

If any small crack had developed in any of the specimens the stress would have increased drastically, causing a rapid propagation to failure.

Since all specimens remained intact, it is not likely that stress corrosion was initiated.

22

APPENDIX 1.B FIGURE, TABLE, AND PHOTOGRAPHS 23

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Table 1.B.1 Mechanical Properties of Contaminated and Decontaminated 304 Stainless Steel Specimens Speciuen Specimen 0.2% Yield UTS RA TE Group Iden t ifica tion psi psi I ")

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1(#)

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2 Notches 74,489 101,444 46.8 26.4 1(a )

3 Notches 68,100 103,226 57.2 34.0 2( )

0 Notch 72,356 103,125 48.4 25.0 2(b) 2 Notches 75,362 103,744 53.9 29.9 (a ) Decontaminated Specimens (b) Contaminated Specimens

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CORROSION TESTIllG 0F TYPE 410 (llARDEllED) STAIllLESS STEEL Ill D0ll SOLVEllT flS-1 (Sub-Section 1-C) In the primary system of Dresden-1, AISI Type 410H (ASTit-276-55) Stainless Steel is present as various parts of the core support systen (see Table 1.C.1 of Appendix 1.C.2). The vendor record shous that the naterial had been hea t-treated to 3/4 naxinun hardness (Rockwell C hardness value of about 35). Since the ecrlier naterials test progran for Dresden-1 did not include any heat-treated Type 410, a supplenental corrosion test on Type 410H uas undertaken. A prelininary test using tensile dog-bone specinens indicated that the corrosion rate of heat-treated Type 410 can be very high under certain severe con-dition: namely: 1. Binetallic coupling to very large area of AISI Type 304 Stainless Steel and also, possibly, to carbon steel or lou-alloy steel. 2. Tensile stress level approaching yield. 3. Severe cold-working. The prinary objective the Type 410H corrosion test was to deternine whether or not the heat-treated Type 410 stainless steel is susceptible to stress cracking, particularly of hydro-gen type, under the Dou Solvent flS-1 cleaning environnent. In addition, the effects of heat-treatnent, tensile stress level, galvanic effect and cold-working were also to be studied. 36

Test Procedures Twenty flat coupons, 4.00" x 0.50" x 0.075", of AISI Type 410H (J&L HT 30148), were sent to a commercial firm for heat treatment to approximately 3/4 hard condition. As documented in the letter attached (Appendix 1.C.1), the coupons were heat-treated according to the following schedule: 1. 1825 F for 30 minutes in a nitrogen atmosphere. 2. Air quench. 3. Tempered at 1025 F for four hours. Hardness of coupons after the treataent Rc 37.0 to 37.5. The 0.2% offset yield strength was determined by testing three of the heat-treated coupons on a 20,000 lb. capacity Instron testing machine, according to the method ANSI / ASTM E8. The mechanical properties determined were: 1. Yield Strength (0.2% of fset) (14313 )KS1 (Strain at Yield - 0.65%) 2. Ul timate tensile strength (166 1 2)KS1 6 3. Tensile modulus (33 1 1) x 10 psi Some test coupons were pickled prior to exposure to NS-1. Specimens were loaded in pairs in a bent-beam fashion using a loading-block fabricated by welding two pieces AIST Type 304 round rod, 0.50 inch in diameter (Photograph 37

1.C.1; Appendix 1.C.2). The bent-beam assembly was loaded ~ by compressing both ends simultantously by means of a vise at each end until the curvature corresponding the desired strain at the outer fiber was obtained. The specimens were loaded at two levels, i.e., 85% and 20% of yield stress, corresponding strain values at the out fiber being 0.40% (9.3" radius of a curvature) and 0.09% (42" radius of curvature), respec tively. The loaded coupons were placed in covered glass liners containing 200 ml each of NS-1 (without addition of simu-lated corrosion products). The glass liners were lined with 100 mesh wire cloth of AISI Type 3G4 Stainless Steel, to sinulate galvanic coupling which exists in the Dresden .1 core support systen. Flat coupons of AISI Type 405 Stain-less steel (which also exist in the core support systen) were placed in the glass liners in order to sinulate the condition cf Dresden-1 as closely as possible. Each glass liner was then placed in a steel jacket consisting of an end-cap / bull-plug aseembly to fora a sealed bonb. A total of eight bombs were olaced in an oven and maintained a t the anticipa ted opera ting tempera ture. The NS-1 exposure was conducted for 111.5 hours with temperature fluctuating between 250 F and 2f6 F. Test Resul ts After conpletion of US-1 exposure the bent-beam specinens were visually observed for any sign of deformation (such 38

as loosening or kinking) which would have resulted from -imen cracking. The specimens were cleaned thoroughly to remove corrosion products and examined under 70X stereo-microscope. No cracks were observed on any of the 15 coupons. Typical samples (stressed to 20% and 85% of yield) were selected for metallography. The resulting photomicrographs are shown in Photographs 1.C.2 and 1.C.3 of Appendix 1.C.2. These photomicrographs illustrate the increased surface corrosion as the level of stress in the saraples was varied from 20% to 85% of yield (at 165X and 410X magnification). Corrosion rate was also determined by the weight loss of each test coupon. The rate in mils per year is compiled in Table 1.C.2. For comparison, corrosion rate data on (b) annealed 410 stainless steel coupons and (c) a round rod dog-bone sanple, as used during preliminary testing has been included in Tabl e 1.C.2. Conclusions The follouing observations can be made on the basis of the resuits obtained. 1. AISI Type 410H coupons prepared as described previously did not crack under the anticipated NS-1 cleaning con-dition. 2. Heat-treatment is the major factor in high corrosion rate of AISI Type 410H in NS-1. 39

3. Galvanic effect on the corrosion rate of Type 410H is also evident from the data but is less important than the heat-treatment. Unstressed Type 410H of about 3/4 hardness may corrode at the rate of 300 mils per year (or 3 to 4 mils per 100 hour cleaning cycle) when galvanically coupled to AISI Type 304. If a galvanic couple to Type 405 also exists (as in the case of Dresden-1 core support system) the corrosion rate may be reduced to about one half. 4. The effect of stress level on the corrosion rate of Type 410H seems to be very significant. By combining the corrosion rates obtained earlier using round rod loaded in pure tension and the rate obtained in the present test using the same rod unloaded, a tentative stress versus corrosion rate curve is obtained as shown in Figure 1.C.1. [It is to be noted that rates obtained from bent-beam tests do not provide good information on the stress-dependence of the corrosion rate. Theoretically, the average internal stress of a bent beam is close to zero. Therefore, these in'ernal stresses may be relieved significantly as the corrosion associated weight loss of the specimen takes place.] The curve of Figure 1.C.1 suggests that the corrosion rate of alloy 410H could be as high as 3,000 rd l s per year or 40 mils per 100 hour cycle, provided that the stress level is as high as yield. 40

However, there is not a reliable record concerning the stress level on the AISI Type 410H parts in the Dresden core support system. The best estimates calculated from the design torque limits and the norma's engineering practices at the time of construction range from 15% to 20% yield stress of the ma terial. At this low stress level, the corrosion rate of 410H is ex-pected to be less than about 15 mils per 100 hour cleaning cycle. This is not considered to present a problem during the cleaning cycle or during subsequent plant operations. 41

4 APPEllDIX 1.C.1 CERTIFICATI0ft 0F HEAT TREAT!1EilT OF CORR 0SI0ft TEST SPECII-1 Ells 42

? S. K. S. Heat Treating Company, Inc. ?m. (7H E ".' A L TREATINO SPEClALISTS G* FLINT 234 3412 ur,. cca,.tm are os,.

m, t 0 I 6 M E R RI L L S T R E E T SAGINAW 777 0270 u, ca sin FLINT, MICHIGAN -48503 November 21, 1978 Mr. Tag Young floon Larkin Laboratory 1691 Swede Road Midland, Michigan-48640

Dear Tag:

The following data should cover the information you requested relative to the heat treating of twenty AISI 410 stainless steel tensile bars. 1. The parts were processed in a nitrogen protective atmosphere. The cycle was 30 minutes at heat 1825 F and air quench. 2. The parts vere tenpered four hours at heat 1025 F. 3. lia rdnes s : R/C 37.0 to R/C 37.5. The parts were suspended vertically in a fixture to ainil.ize distrotion. If you need more information or any other form of certification, please contact me. Yours truly, ..s -..-s- ,,, y.,f/f'

't,

ws> c Donald L. Christiansen Chief Engineer o.C/ei (~) r: d# !?15 s i 'u :sM y)qm ~ ) 43

APPEllDIX 1.C.2 TABLES, PHOT 0GRAP51S, AtlD FIGURE 44

Tabi ? 1.C.1 AISI 410H in Primary System at Dresden-1 (From DNS-D1-016, Technical Study for the Chemical Cleaning of Dresden-1) ASTM Component Piece Location A-276-55 C-2 Hex Cap Socket Screw Core Support A-276-55 C-2 Hex Head Bolt Core Support A-276-55 (410H) C-2 Locator Pin Core Support A-276-55 (410H) C-2 Special Cap Screw Core Support A-276-55 (410H) C-2 Set Screw Core Support A-276-55 (410H) C-2 Dowel Core Support A-276-55 (410H ) C-2 Bolting Diffuser Basket A-?76-55T C-2 Bolt Thimble A-276-55 C-2 Hex Head Bolt Top Head Closure ^-276-55 C-2 Hex Head Nut Top Head Closure A-276-53 (410H) C-2 Soc. Head Shoulder Sc. Top Grid 108M2 Valves Disc Vent and Drain Valves 108M2 Disc Nut Vent and Drain Valves 108.12 Yoke Bushing Vent and Drain Valves A-182-Gr. F6 MV-10 Valves Stem M0-130 A-182-Gr. F6 MV-10 Valves Protective Ring M0-130 A-182-Gr. F6 MV-10 Valves Thrust Ring M0-130 400 Series Mark 110 Valves Stem Drain in Feedwater Line 400 Series Mark 110 Yoke Bushing Drain Valves in Feedwater Line

Table 1.C.2 Corrosion Rate of AISI Type 410 in Dow Solvent NS-1 (100 Hours at (258 1 8) F Galvanically Corrosion Rate Stress Level Coupled to (Mils per Year) (a) Heat-Treate (RC 37) 85% Yield Str. None 126 1 2 85% Yield Str. 304 and 405 145 1 2 85% Yield Str. 304 247 1 5 20% Yield Str. None 121 1 3 g 20% Yield Str. None 185 1 4 20% Yield Str. 304 and 405 159 1 3 20% Yield Str. 304 320 1 9 No Stress S04 and 405 160 (b) Annealed Condition Yield Stress 304 4.8 1 0.1 No Stress None 3.0 (c ) Hea t-Trea ted (RC 36) Round Dog-Bone No Stress 304 285

Photographs 1.C.1 Specimen Loading Procedure ~ m I*/f k' s- ,,i e;i 1 5-y s _,3 E < A M..._a 7 - "'[ O m 5Ab> ~ mas w p. e bM 72 + n, .I s,..u Yi s'agww;-:cza-ei ^ ^

Photographs 1.C.2 Post-Test Photomicrographs (410H, 20% Yield Specimen) AISI 410H specimens stressed to 20% of yield and exposed to Dow Solvent NS-1 for 111 hours at -250 F. 1. 165X flagnifica tion 1 ~ 2. 410X Magnification f, No tes : Ko */o Wof (a) Lighter area is metal, darker area is mounting resin (DER 320) (a) No etching was applied (c) Samplec polished with 1.0 pm diamond

Photograph 1.C.3 Post-Test Photomicrographs (410H, 85% Yield Specimen) AISI 410H specimen stressed to 85% of yield and exposed to Dow Solvent NS-1 for 111 hours at ~250 F. 1. 165X Magnification f (: I f. 2. 410X Magnification i i-0#% ddf Notes: (a) Lighter area is metal, darker area is mounting resin (DER 320) (b) No etching was applied (c) Samples polished with 1.0 pm diamond

Figure 1.C.1 Ef fect of Stress on Corrosion flate of AISI 41311 (ItC 37) in Dou Solvent (15-1 % of Yield Stress 0 20 40 60 80 100 /' Galvanically coupled to / m AISI 304 of infinite / area ra tio ,/ ,/ x / L m / / o W / / 5 /' f' 2 e e m E L o .. ~ l l l 0 0 50 100 Tensile Stress (KS1) 50

SECTI0ft 2 EFFECTIVEf1ESS AtlD CORROSI0ft EFFECTS OF Ti1E USE OF T11E D0ll DILUTE COPPER RIfiSE DURIf1G Tile DRESDEll-1 CHEF 1ICAL CLEAfilflG 51

EFFECTIVENESS AND CORROSION EFFECTS OF TiiE D0U DILUTE COPPER RIUSE (Sub-Section 2-A) In the course of the Dresden-1 corrosion test progran, it was shown that the copper present in the scale and sludge of the primary systen may plate out fron Dou Solvent NS-1. This copper plating could occur throughout the systen surface as a non-collectible, light deposit or " flash" of copper. This was reported in the earlier Dou report entitled, " Technical Study f or the Chemical Cl eaning of Dresden-1," (DNS-NS-016). A nethod had been devised to prevent the " copper flashing" in which electrolytic filtration was used to keep the concentra-tion of copper ion at a sufficiently lou value (less than 10 to 15 ppn), so that no plating can occur. This nethod was demonstrated earlier and was reported on in the Dow report en ti tl ed, "The Chenical Cleaning of the Corrosion Fatigue Loop at Dresden-1" (DNS-D1-019). However, an alternative which is econonically more favorable is to let the copper plate out during the 100 hour US-1 con-tac t and to subsequently redissolve the copper flash during the first water rinse by cheuical neans. A copper rinse solution, containing residual US-1 from the chenical cleaning stage was formulated and proven to be effec-tive in dissolving the copper in the systen and keeping it in 52

solution. This rinse solution consisted of a residual quantity of NS-1 (it is estimated that 5% of the Dresden-1 system volume ~ will remain as a residual during the initial draining), 0.25% (w) of H 0 and NH 0H sufficient to raise the pH to 9.5. This 22, 4 f ormul a tion is designated as the Dow Dilute Copper Rinse Solution (Copper Rinic)g By the end of 1977, however, an objection to the use of hydro-gen peroxide was raised by a consultant for the Commonwealth Edison Company due to the possibility of causing stress cracking of 304 Stainless Steel. General Electric Company conducted an intensive stress corro-sion cracking (SCC) test, using this proposed rinse composition to resolve the issue. During the time, Dow's effort was re-directed toward finding an alternative rinse composition. The General Electric tests, however, concluded and showed that SCC caused by the H 0 system is improbable. This finding was 22 reported in a General El ectric Report enti tled, "Dresden-1 Radiation Level Program Corrosion Tests Progress Report", (PME transmittal number 78-509-42; dated March, 1978). The Dou Dilute Copper Rinse Systen is planned to be used as the first rinse of the Dresden-1 cleaning operation. The objectives of the Dou work on the copper rinse were: 1) To show that the proposed rinse solvent will dissolve metallic copper without allowing significant anounts of copper to replate on cleaned metal surfaces; 53

2) to determine the corrosion rates of carbon steel and low alloy steel in the copper rinse solvent; and 3) to evaluate the possibility of stress corrosion cracking of the materials of construction, par-ticularly 304 Stainless Steel upon exposure to the copper rinse. The best estinate of the amount of copper present (based on r e p r e s e n ta t i y e s c a l_ e__a nillyse s_)__i.n 0 roc der.-1-i s-betwww a nd -~~ ~~-- 50 pounds. This quantity will be less than 100 ppm when completely dissolved in the total volume of the system. Test Procedures and Results A total of three runs were made in the Dou Dynamic Loop. All three runs were nade at a constant temperature of 120 F using the Dou Dilute Copper Rinse Solvent of the following composition: 1. NS-1 5.0% (w) 2. H0 0.25% (w) 22 3. NH 0H to raise pH value to 9.5 4 (-0.5% of 30% agua ammonia) The loop, has a total volune of about 25 gallons and a total surface area of about 50 square feet. The material of construction of the loop is AISI 304 Stainless Steel. A schematic drawing of the loop is shown in Figures 2.A.1. 54

Six specimen racks were suspended in the volume tank. A description of each of the three runs follows: 1. Run #1 A qualitative preliminary test was run using copper-plated AISI 1018 carbon steel coupons mounted on the specimen racks. The purpose of this run was to de-termine if the copper rinse solvent was capable of dissolving metallic copper and keeping it in solution. .A _n_u m b.e r._ of_ mp l a t e d_ A I S L i n 18..nr h a n t.te e !..ar, d -A s-T-;; A336 low-alloy steel specimens were also placed in the loop to evaluate corrosion rates and replating of copper. The results of this run were, as follows: a. Plated copper dissolved very rapidly - within about thirty minutes of contact time. b. Very small patches of undissolved copper metal remained on the coupons in the tight crevices between the pecimen rack and the carbon steel coupons. The location of these " patches" was predominantly in the downstream side of the mount-ing bolts. c. The corrosion rate of AISI 1018 carbon steel was negligible. The A336 alloy steel corroded at a rate 8 mils per year (mpy) during the first sixty minutes and an average rate ~of 4 mpy 'or the total duration of eighteen hours. d. No replating of copper was observed. 55

2. Run #2 In order to simulate spent NS-1, 1200 ppm Fe++ and 600 ppm Ni++ were added. Metallic copper which was dissolved in this run was in the form of fine mesh 2 wire cloth of surface area 50 cm /g. Plated corrosion samples (similar to the Run #1) were also placed in the loop. Oxidation-reduction potential of the solution was followed using a platinum electrode versus a saturated calomel electrode. The results of this run were, as follows: Ilith the addition of Fe++ and Ni++, copper dissolved a. 2 at fairly constant rate of about 3 ng/cm /hr. At the end of two and a half hours, the Cu++ level in solution reached 700 ppm (see Figure 2.A.2). No replating was observed. b. The corrosion rate of AISI 1018 carbon steel was about 5 mpy and A336 alloy steel about 7 upy. c. The variation of oxidation-reduction potential does not allow clear interpretation, probably because of the chemical complexity of the system. (Figure 2.A.3) 3. Run #3 This run was identical to Run #2, but the follouing doubie U-bend specinens were placed on the soecimen racks to evaluate stress corrosion cracking: 1) Sensitized INCONEL 600 5 sets (50 hours at 1200 F) 56

2) Unsensitized IllCONEL 600 5 sets ~ 3) Sensitized 304 Stainless 5 sets Steel (50 hours at 1200 F, air-cooled and descaled in ammonium citrate) 4) Unsensitized 304 Stainless 5 sets Steel The results of this run were, as follows: a. This runs is basically a repeat of the Run #2, except that the copper level exceeded 2000 ppm level (Figure 2.A.4). The dissolution rate diminished abruptly from that point, U-bend samples showed formation of dark precipitate, which probably consisted of oxides of iron and/or copper. However, no replating of copper occurred. No stress corrosion cracking was revealed in any of the U-bend specimens under microscopic investi-

gation, b.

The oxidation-reduction potential followed the same pattern as in the Run #2 (Figure 2.A.5). In all the runs above, samples of solvent taken at regular intervals during the test were analyzed for iron and copper by atomic absorption methods. Conclusions 1) Copper metal dissolved very rapidly in the dilute copper rinse solvent. 2) No replating of the dissolved copper from the solvent tool place during the test runs. 57

3) The solvent remains clear and free of any solid particles, unless very high level of Cu++ (>2000 ppm) is present in the system. 4) The oxidation-reduction potential may not be a useful parameter to be monitored. It is suggested that the best method for the determination of residual H022 activity should be the standard thiosulfate titration of iodine liberated from iodide by H 0 2 2* 5) Based on these data, the Dou Dilute Copper Rinse is an effective and practical way to remove plated copper following the application of Dow Solvent NS-1 to the Dresden-1 Primary Sys tem. W 58

APPEtlDIX 2.A.1 FIGURES 59

J b 1 Figure 2.A.1 e";; i::; .o a. Perspective View ? E of f 'u,- .-? i e j s - gi f n! k .r .h" h N / +:/5. 4 /j' 2 .i .- v ' M., s- = ~~ xr e se m A\\. 'g*/\\-[ n!!$ .\\\\ t. J i i!; i ?

E l e 5

\\ 2 o, \\ un s u e / i g s spi i 9-s, e + 0' Q Oh5

.U Y

n. 0 .s s 8, n / ', 2_so 4 ./' ?, 1) s 1, e ~,, m 5\\ / Y i. _ _.. '."_ M.'s'A\\ \\ ,.1~/ Ai s f. / c \\\\ y// /ff/ // - pW j cy - /,/ e, N L / J l 5 9 U f A 60

Figure 2.A.2: Dissolution of Copper (Run #2) in the Dow Dilute Copper Rinse (Fe++ and fli++ Added) O 700 l ,0 I / / i O 1 / / 600 \\ l / / I ,0 500 O --eaa v 400 et d O /2 ++ 300 3 U O 200, 51oc I t / l / i O ,/ 100 O '; s r t 'i---- -~..I___.... _ _.,__ _ l.,__,_. __L,,,,___[ t 0 0.5 1.0 1.5 2.0 2.5 Time (Ilou rs) 61 e.

Figure 2.A.3 Redox Potential of Dow Dilute Copper Rinse Solution During Run #2' e .-. / ::: :, "I & 3 _s Pt. Electrode vs. S.C.E. i' '- m. 100 L. O 1 O ~ ~ 0, //o -100 f I / O O O -206 -300 m -l I ( [ [ 0 0.5 1.0 1.5 2.0 2.5 Time (Hour) 62

Figure 2.A.4 Dissolution of Copper During Run #3 O p 0 / 2000 O t ii / / 1500 / / l r / / 10t '0 / Il /l t / O //l 500 l s i J D O e, O C i .C C_-._.____...___. _..J...____.____._'_.______ _3 _ _. L_ _ o 1 2 3 4 5 Time (Ilours) 63

Figure 2.A.5 Redox Potential of Dow Dilute Copper Rinse Solution During Run #3 Pt. Electrode vs. S.C.E. 100 O9 / / O O - - - - - - - - - - - - - - - - ~ ~ ~ - - ~ ~ O r 70~ O 's / v I of N \\ O i 5 \\ I / \\ / -100 g \\ / 1 / \\ / \\ / \\ / \\ / / -200 ~ I 1 t i 1 0 1 2 3 4' 5 Time (Ilou rs ) 64

EFFECT OF THE DOW DILUTE COPPER RIllSE SOLUTION ON COPPER WASHERS IN DRESDEN-1 (Sub-Section 2-B) Copper washers are present in the main recirculation pumps of the Dresden-1 primary system. Since the Dow Dilute Coppar Rinse Solution was designed to dissolve replated metallic copper film, the copper washers will be affected by the copper rinse process. Although the washers may be readily replaced after chemical cleaning, excessive loss of metal during the solvent contact may consitute an operational problem. A study was undertaken to estimate the loss of washer material during this stage and to provide engineering data for the evaluation of the risk, d Test Procedures Three pieces of test specimen, ueasuring 3-29/32" by 5/16" x 0. 0 25" thick were fabricated from a sheet of copper gasketing material (very soft copper). Each specimen was sandwiched between a piece of 304 Stainless Steel and a piece of 316 Stainless Steel which were 1/16" oversized in dimension so that the copper piece was recessed under stainless steel pieces by 1/32" all around. This siuulate the actual configuration in the punp. Each sandwiched piece was then inmersed into 200 ml of the copper rinse solution (prepared as described in Sub-Sec tion 2. A. ; Run #1). 65

The bottles con taining 200 nil of the solvent and the test specimen assembly were placed in a shaker-incubator at 120 F (51'C) for a net total exposure time of 16 hours. Test Resul ts The weight loss data of the four specimen pieces were as follows: Corrosion Rate Coupon Net Ut. Loss (g)_ (mils per year) X 0.0047 70 Y 0.0028 42 Z 0.0031 46 Mean 53 + 12 mpy The corrosion rate is based on the estimated exposed sur-2 face area of 0.2F inches Conclusions The redcction in linear diaension at the edge of the washer will be about 0.1 to 0.2 mils during the total period of the copper rinse stage presently planned for 24 hours. Since the thickness of the copper washers in the main recirculation penps is a pproxima tely 1-1/2 inches, a loss of 0.2 nils is cansidered negligible and should not in-dica te any oper. tional problems. 66

CORR 0SION RATE OF SILVER Ill THE D0ll DILUTE COPPER RINSE SOLVENT (Sub-Section 2-C) Silver-clad 304 Stainless Steel o-rings are found in the Reactor Pressure Vessel head gasket of the Dresden-1 system. Since silver is similar in electrochemical behavior tc copper, it is important to know the corrosion rate of silver in the Dow Dilute Copper Rinse Solvent. If the corros:on rate of silver is appreciable in this solvent, a leak during the rinse stage could resul t (since these o-rings are wetted and constitute a pressure boundary). Test Results and Conclusions Two different alloys of silver were subjected to a simulated copper rinse stage for 24 hours at 120 F (51 C), to deter-mine the corrosion rate of silver. The results were: a. Refined silver (such as ASTri 13413, 99.90%) corroded at a rate of 0.2 nils per year, about 0.01 micron per day. b. Silver Electrical Contac t Alloy (such as ASTf1 B617) containing 10% Cu corroded at a rate of 5 nils per year, or less than 0.5 micron per day. If the o-rings are clad uith pure silver, there should be no concern for corrosion induced leakage during the dilute copper rinse. 67

If the o-rings contain more than a few percent of alloying metals, further study aay be in order. The plating of the RPV head gasket is considered to be of pure silver, there-fore, no r. rational problems are expected during applica-tion of this copper rinsing step. h e a 9 68}}