ML20205P793

Boral from Long-Term Exposures at BNL & Brooks & Perkins

ML20205P793
Person / Time
Site:	Vermont Yankee
Issue date:	12/14/1978
From:	Adamson R, Warner R GENERAL ELECTRIC CO.
To:
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ML20205P635	List: ML20205P631 ML20205P793 ML20205Q542
References
78-212-0079, 78-212-79, EWA-EAC80-10, NUDOCS 8704030374
Download: ML20205P793 (35)

Text

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6ENER AL @ ELECTRIC CME TRANSMITTAL

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NUC1. EAR ENERGY DIVISION DR 7 BORAL FROM LONG-TERM EXPOSURES AT BNL AND BROOKS & PERKINS U. E. Wolff ,

EWA EAC80-10 December 14, 1978 APPROVED: 6 R. B. Adamson, Manager Core Materials Testing M

Verified by R. W. Warner

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DISCLAIMER OF RESPONSIBILITY This document was prepared by or for the General Electric Company. Neither the General Electric Company nor any of the contributors to this document:

A. Makes any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this document, or that the use of any information disclosed in this document may not infringe privately owned rights; or B. Assumes any responsibility for liability or damage of any kind which may result from the use of any information disclosed in this document.

8704030374 870331 PDR ADOCK 05000271 P PDR _

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BACKGROUND ,

Boral used for fuel storage racks is exposed for up to 40 years in the fuel pool water. Long-time corrosion resistance in that environment therefore, is of concern. Two types of specimens were investigated which had undergone long-time exposure.

1. Three specimens were obtained from BNL. These are sections of

-inch plugs removed from a 5-foot diameter by 36-incfies high cylinder. The Boral which was clad with stainless steel had been exposed for 19 years to the reactor coolant of the Brook-haven Medical Research Reactor. The reactor ran for 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> a day, 5 days a week, or less, at a temperature of 115 to 136 F.

Over the weekends the temperature dropped to 75 to 80 F. The water had a pH of 6 to 7 and a conductivity of 2pmho/cm (at 25 C).

Specimen #1 had one edge exposed to the water (see Figure la),

Specimen #3 and specimen #6 had no contact area with water (unless seepage had occurred between the cladding and the Boral._)

2. Brooks and Perkins (B&P) have supplied Boral sheet which had been exposed for 360 days. in 100 F water at two different pH levels, i.e. , pH 4.1 and pH 10.4. For details, see (1) (copy attached).

TEST PROCEDURES Figures 1 and 2 show the shapes of the test specimens and indicate the var-ious surfaces examined. The top and bottom surfaces of all specimens are A1. Sandwiched between these is the Boral which consists of BS C particles embedded in a matrix of Al.

The curved surfaces of the BNL plugs (Figure 1) have been produced by a

, core drill; the surfaces cutting the circles in half apparently were rough saw cuts. The only Boral surface in contact with the coolant was the cut-off corner surface of BNL #1. Since that surface was corroded, it had a low conductivity. Therefore, it was coated by sputtering with a thin (ap-proximately 100X) film of Au to make it conductive. The other surfaces and samples were left uncoated.

All 4 surfaces of BNL #1 visible in the sketch Figure la were examined by scanning electron microscopy (SEM). Since the saw cut did not give any meaningful information, only two surfaces of BNL #3 and #6 were examined, i.e., the Al (top in Figure Ib) and the curved core drill cut.

After completion of SEM the samples were cut with a diamond wheel along the planes indicated in Figures Ic and d. The two sections of BNL #1 were mounted and metallographically polished on the two planes marked A and B in Figure lc. Only one half of each of BNL #3 and #6 were mounted and polished on the plane of the cut (arrow Figure id).

One B&P sheet of each pH level was selected at random for examination.

These were:

l No. 6-2 -- pH4 ,

No. 12-3 -- pH10

The samples cut from these sheets are indicated in the schematic, Figure

2. The corner samples were selected at random, the samples marked C were

selected after thorough examination of all four Boral edges in an optical stereomicroscope. The regions around C appeared to exhibit the heaviest corrosion.

SEM was performed on three surfaces of each of the corner samples, i.e.,

the two exposed Boral edges and one of the Al surfaces. On sample C only the exposed Boral edge was examined. The' SEM examination included .

stereo pairs for the corner sample. Maximum visible pit depths in these pairs were measured quantitatively with a Hilger-Watts measuring stereo viewer.

After completion of SEM, metallographic sections A, 8, and C (Figure 2) were prepared for further evaluation of corrosion penetration. Sections C were vacuum-impregnated with mounting material to better distinguish between pits and pores originally open to the surface, and those produced by possible grinding and polishing pull-out.

RESULTS

1. BNL Samples A. BNL #1 A composite SEM micrograph (Figure 3) of most of the outer Al l surface (upper surface in Figure la) shows flakey corrosion l deposits and one or two deeper corrosion pits. However, the '

. depth of these pits appears to be insignificant compared with the thickness of the Al layer (about imm as seen in cross i section). The depth of the pits could not be measured from the SEM micrographs.

The surface exposed to the reactor coolant (front surface in Figure la) is shown in Figure 4. The saw cut (not visible) is at the right edge, the curved core drill cut at left. The vertical parallel grooves belong to the latter surface. The Boral surface exposed to the water is covered with a thin layer of corrosion product which in some places has spalled off the Al layer (bottom edge, Figure 4). Some pits and crack-like features of considerable depth are visible. Because of the tortuous path of these features their depth could not be de-termined from the SEM micrographs.

One such deep crevasse is seen (in the lower left corner of i Figure 4) to have apparently been cut and exposed by the core l drill. The depth of that feature can better be seen on the I

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curved surface, Figure 5. Measuring from the intersection between the corroded surface and the curved core cut to the apparent bottom of the crevasse one determines a depth of at least 1.5m. However, it is-possible this crevasse has been produced or enlarged by the stresses of core cutting (see also Figures 11 and 12). The large shallow, more rounded pit vis-ible in the center of the Boral in both, Figures 4 (left) and 5 (right) is about 0.8m deep and over lam wide. _

The saw cut surface, Figure 6, (right surface in Figure la) does not show any structural details because of the coarse cutting grooves. However, the cross-section through a pit, about 0.5m deep, correlates with a feature on Figure 4-(left of the numeral 7 on micrograph 7914).

The low-magnification micrographs (Figures 7a and b) of the metallographic cross-sections (A and B in Figure Ic) show the BS C distribution in the Boral to be non-unifonn. The section B has been made approximately 20 to 25m (0.4m real distance) j from the right edge of the micrograph in Figure 4. The features

lying along that line are seen in cross-section in F.igures 7b and j -

c. The deep pit in the center curves back toward the surface and is probably part of the long deep crevasse running roughly hori-

! zonta11y through Figure 4. Its maximum depth in Figure 7c is

0. 8m. Two shallower pits are 0.3 ~and 0.2m deep respectively.

1 B. BNL #3 and #6 l No part of the Boral content of the two plugs drilled from  ;

i BNL #3 and BNL #6 had been exposed to the reactor coolant. The Al surfaces (top surface in Figure Ib) of both samples had a A

thin, rather dense, and occasionally spalled corrosion layer (Figures 8 and 9). The microstructure of this layer is shown s

at higher magnification in Figure 10b.

. Part of the curved surfaces of the same samples (left in Figure 1b) are shown in Figures 11 and 12. (In both these figures, the Al surfaces of Figures 8 and 9 are at the bottom.) There is no I

evidence of corrosion on these surfaces. Figure 11 includes the intersection with the sawed surface.. Both figures show '

crevasses similar to those in Figure 5. Since in BNL #3 and #6 the core-drilled and the saw-cut surfaces presumably had not been in contact with water (this is corroborated by the absence

{ of corrosion) it must be concluded that the crevasses have been j produced by the cutting action. :The possibility therefore exists the crevasses in BNL #1 also have a mechanical origin.-

Meta 11ographic cross-sections (Figure id) through both plugs are

, shown in Figure 13. The BuC distribution in BNL #3 is slightly

non-uniform, in BNL #6 it is uniform. Since none of the Boral

! surfaces was exposed to the coolant they were unattacked.

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2. Brooks & Perkins Samples A. pH4, Sheet 6-2 , .

The appearance of one of the Al surfaces is shown in Figure

14. Shallow corrosion pits and a discontinuous residue of a liquid is present. The pit depth and the thickness of the deposit was measured on a stereo pair. Both were..less than the depth of superficial scratches. (See Table 1 for numerical val-ues.) Apart from this one area, the Al surface looked uncor-roded.

The two edges forming one corner of the sheet are seen in Fig-ures 15a and 16a. The Boral portion has a very rough surface while the Al cladding looks nearly unattacked. At higher mag-nification an occasional patch of a corrosion deposit (Figure 16b) is seen. Also there are slightly pitted regions in the Al filler (Figures 15b, c, and 16c). A region adjacent to cut C (Figure 2a) shows more extensive corrosion deposits, espec-ially at the bottom of deeper pits (Figure 17). The deepest local pits of Figures 15 and 16 were measured on stereo pairs (Table 1). It should be kept in mind that these depths do not refer to the original (A1) surface but rather to the difference between highest and lowest point in the limited area of the

1. respective micrograph.

Figure 18 gives the cross sections A and B as marked in Figure 2a. Figure 19 represents section C. The BqC crystals have an enormous size range with some particles as large as 0.5 to

0. 6m . Some of these large particles are pressed deeply into the Al covering leaving in some places only about 0.25m A1 i

cover. The pit depths in both Figures .18b and 19b are about

0. 4m.

B. pH10, Sheet 12-3 On the Al surface (Figure 20) no residues or corrosion products are visible. However, at one place the Al cover is broken and BSC particles are exposed (Figures 20c and d). Such a defect could easily have been produced at a place where the BgC par-ticles nearly penetrate the Al cover. Stereo measurements of the depth of these defects (Table 1) reveal them to be of the magnitude expected from Figure 18, i.e., 0.2m below the Al surface.

The two edges forming the corner of the sheet are shown in Figures 21 and 22. The local pit depths are listed in Table 1.

In addition to the deep pits and crevasses visible in the SEM i micrographs, the Al filler shows small pits (Figure 21c) and part of the Al cladding is covered with a deposit (Figure 22b).

A deep pit on section C (Figure 23) has a very smooth surface.

l This is believed to be the surface of a large BgC particle.

Another deep pit (Figure 24) is completely covered with a cor-rosion deposit with typical " mud crack" surface.

1

a The three cross sections (Figures 25 and 26) are similar to I those from sheet 6-2. Non-uniform distribution of B SC par-ticles of a wide size range is typical. The pit depth meas-ured from the plane of the cut Al cladding to the deepest l

depression in the Boral again is 0.3 to 0.4m. i:e., of the ,

j same order of magnitude as the largest BgC particles.

No differences attributable to the different pH }evels were observed.

E :

DISCUSSION The features observed in all the Boral specimens do not resemble those found inanear11erexamination.(2) In particular:

l. The only BNL specimen surface which had been in contact with the i

coolant is covered with a rather uniform, tightly adhering corro-

! sion product layer. The larger features of the surface, i.e.,

large pits and crevasses may be explained as discussed below for the sheet. The general pitting of the Al filler which was ob-served in (2) is nowhere found here.

i

, 2. The exposed Boral surfaces of the sheets generally give the im-

! pression much more of mechanical than of chemical damage. Again, no pitting of the type seen in (2) is observed. The large pits are of a size comparable to the size of the large BgC particles.

The Boral material is very brittle. When cutting it, it is quite possible (and in fact can be avoided only by great care) to produce

' delamination cracks or " crevasses", and to loose BgC particles near I the surface. The sheet surfaces exposed to the water may originally have been damaged during cutting and the pits and cracks thus pro--

duced may have served as pockets for subsequent corrosion attack.

Whether this view is correct can be determined only by the examina-

• tion of archive material; i.e., the sheet material would have had

to be prepared identically to the corrosion tested sheets, but should not have undergone the corrosion test.

1 SUMARY On the BNL specimens only one surface of BNL #1 had been exposed to reactor ,

coolant, and this surface is covered with a tightly adherent thin corrosion

product. Large pits and crevasses may originally have been caused mechani-

! cally. Their additional corrosion does not appear excessive. The depth of

such pits may have an order of magnitude of 1m.

4

, The edges of the B&P Boral sheets has cracks and pits comparable to the size of the largest BS C particles. Corrosion appears to be minimal; it does not I,

extend significantly below the depth of the pits, i.e., about 0.4m. No sig-I nificant difference between the two pH levels was detected. It is believed )

mechanical damage during specimen preparation may have loosened BgC particles i  ;

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and produced cracks and pits which served as starting locations for fur-ther corrosion. However, the corrosion attack itself appears to be an order of magnitude smaller than the presumed mechanical damage.

REFERENCES

1. Brooks & Perkins, Incorporated, " Storage Module Boral_ Panel Corrosion Testing, Final Report", Report No. 566, April 28, 1978.

2. U. E. Wolff, "SEM Examination of Corroded Boral", CME Trans-mittal No. 78-212-0034, June 26,1978.

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TABLE 1 1

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Pit Depths in Boral Sheet, Measured on Stereo Pairs ,.l l

Mean Individual Specimen SEM Measurements Sigma g Ident. Location Micrographs (m) (m)-

pH4; 6-2 Al Surface 17972/3 0.038 0.05 0.063 M (0.075 scratch)

Beveled Edge 17957/8 0.157 0.218 0.171 0.20 0.284 N

17955/6 0.162

! 0.226

, 0.160 l Other Edge 17949/50 0.143 0.190 O.170 0.165

, 17951/2 0.129 0.03 0.192 1

pH10; 12-3 Al Surface 17975/6 0.209 0.164 0.19

, 0.189 N

, Beveled Edge 17961/2 0.284 2

O.263 0.228 0.275 17963/4 0.291 0.03 0.307 l

Other Ed9e 17969/70 0.230 0.198 0.130 0.205 17967/8 0.223 0.04 0.245 0.206 i

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APPENDIX C BROOKS AND PERKINS Report No. 577

4 .

1, , ,

Report No. 577

, 0T)$ Brooks &Perkins. Incorporated I

Prepare'd by:

g I

Brooks & Perkins, Inc.

, Advanced Structures Div.

12633 Inkster Road l

Livonia, Michigan 48150 L

I.

{ Date: July 21,1978 I

THE SUITABILITY OF

• BROOKS & PERKINS' SPENT FUEL STORAGE MODULE FOR USE IN BWR STORAGE POOL L .

r ..

I

'-wr'/ )ing

/Aci o u y_

i 1 l

i

. /b /"/s  !

4-- m- w

Rsport 577 n .. c LD+p Brooks & Perkins. Incorporated THE SUITABILITY OF BROOKS & PERKINS SPENT FUEL STORAGE MODULE FOR USE IN BWR STORAGE POOL PURPOSE The purpose of this report is to exhibit test results and literature research that illustrates the suitability of the Brooks & Perkins Spent Fuel Storage Module u (SFSM) for use in a boiling water reactor (BWR) storage pool.

BACKGROUND Spent Fuel Storage Module: The SFSM is a slender square-shaped tube with open ends that is used for the' storing and the shielding of one spent fuel assembly in a light water nuclear reactor storage pool. The tube is constructed with the inside and outside coverings being made of type 304 stainless steel. These two stainless steel surfaces are welded together at the top and bottom of the tubsover an inner layer of a thermal neutron shielding material called BORALtm. Boral is a sand-which type panel that has outer surfaces of type 1100 aluminum and a core of boron carbide uniformly dispersed in a matrix of type 1100 aluminum.

J A group of SFSM's are assembled into a tightly packed array called a high-density storage rack. A network of horizontal and diagonal members separate 3 the modules within the rack and provide the necessary lateral support. The racks stand in a vertical position on the bottom of a 40-foot deep storage pool.

The water in the storage pools is constantly circulated through a series of filters which causes a constant water flow within the pool. The water is monitored and controlled for pH and temperature within specific limits depending on the type

i. of nuclear reactor.

Environment of SFSM: In a BWR, the high density storage rack is exposed to the

.J following conditions.

Radiation Exposure ,10" rads gamma total. ,

-104 neutrons /cm2 /sec average flux.

r Water Type demineralized.

, Water Temperature 700 to 1500F (210 to 660C).

pH at 770F (250C) 5. 8 to 7. 5 I l Chloride ion, ppm, max. O. 5

- ISO

l Rcport 577 h Brooks &Perkins, Incorporated Total Heavy Element, ppm, max. O.1 Total Suspended Solids, ppm, max. 1. 0

• Solids Filtration, Microns, max. 25.0 The storage racks are expectedto withstand these conditions over a 40-year

, period.

Shielding Capability of Boral: The shielding capability of a Boral panel is due to its ability to capture thermal neutrons. The capture of thermal neutrons is L ' accomplished by the B 10 (boron-ten) isotopes that are contained within the boron carbide particles. These boron carbide particles are chemically inert (unreac-1 tive), heat-resistant, highly crystalline and nearly equivalent to diamond in hardness.

In order for corrosion to cause a reduction in the shielding capability of a Boral panel, the boron carbide particles have to be physically displaced from the panel. A displacement of the boron carbide particles to occur would require the following sequence of events.

J (1) The complete removal of the outer protective aluminum surfaces on 7 the Boral panel.

~

(2) The complete removal of the aluminum matrix surrounding each boron carbide particle.

(3) The physical displacement of the boron carbide particles.

TESTING AND RESEARCH

. .i Testing and research were conducted to substantiate the ability of the Brooks &

Perkins SFSM to satisfactorily resist the environment of a boiling water reactor spent fuel storage pool. The following is an outline of the investigation. ,

1. Corrosion Resistance Testing and Research .

1.1 SFSM Without Leak in Stainless Steel Covering: The corrosion resist-ance of the stainless steel covering of the SFSM has been investigated i through research of published data. The following information indicates I

that the Brooks & Perkins SFSM (namely 304 stainless steel) provides adequate corrosion resistance to achieve a life expectancy of 40 years when used in a BWR storage pool.

I f

O t 300

- . Report 577

' $h Brooks &Perkins, Incorporated 1.1.1 Stainless Steel - Type 304:

A. General CorrosionI Water Type BWR. -

pH 7. 0 to 11 Temperature 5720F (3000C)

L Oxygen, ppm < . 01 to 2 Chlorides, ppm 4.1 Corrosion Rate, mpy <2-

"I i Estimated Corrosion Rate

@ 1500 F, mpy <.6

]J Expected Life (at 36 mils ~-

thickness) > 60 years B. General Corrosion After 3000 Hours 2 L1

, Water Type high purity, demineralized j Hydrazine, ppm . 01 to . 0 7

, Oxygen, ppm < .005 Chlorine, ppm < . 05 pH 6. 95 to 9. 58

= Flow Rate, gal /hr 3. 5 Temperature 320 F _(1600C)

Corrosion Rate, mpy .01 Expected Life (at 36 mils ,

6 thickness) > 60 years .

I National Assoc. of Corrosion Engineers, Corrosion Data Survey,1974, i pp. 34 and 252 l

2 A. P. Larrick, Corrosion Studies in Simulated N-Reactor Secondary System Water Environment. Atomic Energy Commission Research and Development, i

Report HW-76358, Hanford Atomic Products Operation, May 1963, pp.7,10 and 22.

• 100

Repert 577

& Brooks &Perkins. Incorporated C. . Stress-Corrosion-Cracking after 3000 hours0.0347 days <br />0.833 hours <br />0.00496 weeks <br />0.00114 months <br /> water quality same as "B" above Stress % of .2% yield 120 4

[a re sulta "Metallographic r

examination of selected samples also failed to

. reveal any cracking."

expected life (at .36 mils thickness) > 60 years -

1. 2 'SFSM With A Leak'In The Stainless Steel Covering

~

1. 2.1 Resistance to Corrosion From Published Data The corrosion resistance of BORAL and of Stainless Steel

[ (Type 304) coupled with Aluminum (Type 1100F) has been investigated to determine the corrosion resistance of the SFSM under conditions of the stainless steel covering con-l taining a leak during use in a BWR Storage Pool. The published data reviewed indicates the materials used in the Brooks at i

' ' Perkins' SFSM (namely BORAL, 304 Stainless Steel and 1100F Aluminum) provide adequate corrosion resistance to achieve a life expectancy of forty years without a reduction of neutron absorbing capability when used in a BWR Storage Pool with.

, a leak in the stainless steel covering.

l j CORROSION DATA -

BORAL A. 2000 Hour Test Results Il ,

i

{

water type e BWR .

! PH 7. 0

'I lI temp. 190 F (88 C) 1 L. Marti-Balaguer and W. R. Smalley, " Evaluation of Control Rod Materials; CVTR Project", CVNA-86. Carolinas-Virginia Nuclear -

Power Associates, Inc. (1960) l l

g - se

.. ..u. .. . . . . .

~

Rspart 577 4

- &h Brooks &Perkins. Incorporated corrosion rate, mpy 1. 2 to 2.1 estimated corrosion rate

@ 70 to 150 F. , mpy -

.18 to .12 expected life (at 15 mils thickne s s)* .> 45 years STAINLESS STEEL (type 304) coupled with ALUMINUM (type 1100F)

A. Crevice and Galvanic Corrosion rg water type high purity, demineralized oxygen, ppm 4 to 5 ,,

pH ,

5. 0 to 6. 0

flow rate, fpm 0. 5 l-temp. ,

194 to 356 F (90 to 180 C)

L time, hrs. 1100 1775 2000 Al max. pit depth, mils 2 <3 <5 Al corrosion rate, mpy 0.1 0.1 0.1 S.S. Corrosion rate, mpy 0 0 0 expected life (at 15 mils > 60 yrs >60 yrs'760 yrs thickness of A1)

CONCLUSION: A thorough review of the published test data indicates the .'

materials used in the Brooks and Perkins, Inc. spent fuel storage module -

~

7 (namely 304 Stainless Steel and 1100F Aluminum) provide adequate corrosion -

resistance to achieve a life expectancy of forty years without a reduction of neutron absorbing capability when used in a BWR storage pool with a rupture in the stainless steel covering.

f

• 10 mils of Clad plus 5 mils of Matrix Holding Boundary Layers of B4C.

4J

.L. English and J.C. Griess, Dynamic Corrosion for the High - Flux

! Isotope Reactor, ORNL -TM - 1030, September, 1966, pg. 1,2,3,3,2 3,

! 26,27,31.

9 l- I

'M =100

l Report 577 b @~+p Brooks &Perkins, Incorporated \

i i i

l '- '

[ 1. 2. 2 Corrosion Resistance of BORAL l

A test was conducted to determine the physical changes to ~ ,

l unprotected samples of BORAL after one year of exposure i g

to an aqueous solution representing a BWR Storage Pool water.

Test Method: Three bare and unclad samples of BORAL were

placed in a covered beaker containing demineralized water.

ig The samples were the standard 35% B4C type BORAL panels L ,

- that measured .177 x 2 x 2 inches. The samples and the solution were periodically examined and the progression of n - the changes were recorded. The samples were carefully left undisturbed during the test period without any change or alteration being made to the water solution.

~~

Results: The BORAL samples experienced weight losses through general corrosion with no evidence of pitting, galvanic or intergranular types of corrosion. The average rate of weight a loss after one year of exposure was 1.91 milligrams per square centimeter per year or .28 mils per. year.

The pH reaction and other test data are included in Appendix 1.

i The test concluded that the period of time necessary for the total

, loss of the outer cladding of the BORAL by general corrosion at i the corrosion rate after one year would be considerably more 5

than 40 years.

j 2. Irradiation Resistance Testing and Research

-. 2.1 Gas Generation Tests of BORON CARBIDE / ALUMINUM MATRIX BLEND ,

L An experiment was conducted to determine if gas would be evolved .

by the matrix material utilized in BORAL with hygroscopic moisture'.

j* during neutron and gamma irradiation. -

ie I

The experiment consisted of irradiating a 26 gram granular boron

} carbide / aluminum sample containing 2,673 ppm moisture.

s The samples were exposed to radiation over 5 minute and 75 hour8.680556e-4 days <br />0.0208 hours <br />1.240079e-4 weeks <br />2.85375e-5 months <br /> periods. The radiation exposure of these tests is listed i I in Table 1.

' i

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, . - , Report 577' h Brooks &Perkins, Incorporated i

TABLE 1 40 YEAR AND TEST CUMULATIVE i

RADIATION EXPOSURE _

u 40 Year 5 Min. Test 75 Hr. Test Radiation Type Exposure Exposure Exposure 4 ,., Neutron (n/cm )

13 13

4. 50 x 10 4. 05 x 10 16' Thermal ( .1 Mev) 4. 29 x 10 Epithe rmal - 1. 38 x 10 1. 24 x'10 I

Fast ( 1 Mev) - 6. 00 x 10 12 5. 40 x 10 6

Gamma (rad) 8. 00 x 10 1. 67 x 10 1. 50 x 10 i Test resulted in no gas evolution detected during or following the 5 minute ,

j and 75 hour8.680556e-4 days <br />0.0208 hours <br />1.240079e-4 weeks <br />2.85375e-5 months <br /> irradiation.

A complete description of the experiment is included in Appendix 2.

! 2. 2 Irradiation of SFSM with and without leak in Stainless Steel Covering Experimental observations were made of BORAL plates encased in stainless steel jackets. Samples were tested dry and with 25 ml distilled water injected within the stainless steel jacket. .

Under irradiation fluxes and water conditions expected in ,

a power reactor spent fuel pool, the BORAL samples exhibited '

T no detectable gas evolution, pressure buildup or damage due to .

temperature or other effects.

A listing of the experimental results is given in Table 2. -

A description of the experiment is included in Appendix 3.

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SAMPLE 1 SAMPLE 2 --

4 9" x 9" Boral Plate 9 Stainless Steel Jacket !Stainless

" x 9" Boral SteelPlate Jacket l L

Dry .25 ml Distilled Water I

L CONDITION 1 42 Hours 25 Hours I

j Spent Fuel No Detectable Effect No Detectable Effect

- 2 x 105 Rad h/ r -

I N - Negligible i.

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j CONDITION 2 24 Hours 6 Hours f Reactor at 2 MW No Detectable Effect No Detectable Effect

- 4 x 107Rad /hr i

7 i N - 1 x 10 Rad /hr l  !

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! CONDITION 3 4 Hours 4 Hours i

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Reactor Shutdown No Detectable Effect No Detectable Effect '

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- 1. 2 x 10 Rad /hr -

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1 TABLE 2 l Observed Effects of Irradiation Conditions on BORAL Samples

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hh Brooks &Perkins,In:cipara:ed il

2. 3 Helium Generation The previously discussed irradiation tests have-shown no detectable gas generation by BORAL, but concern has been expressed due to the well known reaction oN I

+5 BM 3Li +2 He 4

and the possibility of pressure-build-up in an enclosed

"' environment. This concern may be satisfied by considering

• that all neutrons which strike the BORAL are thermal neutrons and are absorbed by boron-10 and considering the following calculations.

4

{ = 10 n/cm /sec Average Flux 4

LI BORAL Area / tube = 3.4 x 10 cm2

Void between BORAL and tube = 130cc Void in BORAL core / tube = 300cc Seconds in 40 years = 1.26 x 109 4 9 13 molecule s/cm2 over 40 years

{ = 10 x 1. 26 x 10 = 1. 26 x 10

~*

13 23 -11 mole s/cm 2of He over 40 yrs

1. 26 x 10 4 6. 023 x 10 = 2.1 x 10

,. 2.1 x 10*II x 3. 4 x 104 = 7 x 10-7 moles / tube of He over 40 yrs 7 x 10" x 22. 4 x 10 =3 1. 6 x 10-2 cc/ tube @ STP of He in 40 yrs i

Pressure @ 150 F = 1 atm x 1.6 x 10-2 x (273 + 66) (273 x 430) -

= 4. 6 x 10-5 atm i

The pressure rise for the 40 year period of 4.6 x 10-5 atmospheres i or . 0007 pounds per square inch is insignificant when considering 8 the internal gauge pressure to cause a buckling of the tube walls is in excess of 5 pounds per square inch and that the. pool water exerts an external pressure of 17 psi under 40 feet of water.

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.3 Report 577  !

Brooks & Perkins, Incorporated a

A PPENDIX 1 Test Data from Brooks at Perkins Report 511 " Corrosion Resistance of BORAL Tm to One Year of Exposure to BWR Storage Pool Water."

Total Unit Wt.

Surface Area Iritial Final Weight Loss lhetrabon Size  % git Weight Loss Per Yeap Fbr Yar Sample (cm) Two (cmSp)6s (gms ) (gms) (gms) (rrgrns / cm /yr) (mils /yr)

L A .45x4.92x4.92 48.4 29.8564 29.7612 .0952 1.97 .29 B .45x5.08x5.08 51.6 31.2759 31.2042 .0717 1.39 .20 C .45x5.08x5.24 53.2 32.3222 32.1962 .1261 2.37 .34 Average 1.91 ,

.276 Observation of pH of Test Solution The pH of the solution increased in number from the original 5. 6 to 7. 7 in the first two and one-half months and remained at that approximate level for

h. the remainder of the year. A graph of this observation follows.

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+y Brooks &Perkins. Incorporated APPENDIX 2 Gas Generation Tests of Boron Carbide / Aluminum Matrix Blend -

Test Description Sample material was tightly packed, but not compressed, into a cylindrical-aluminum container as illustrated in the following figure of the BORAL L- irradiation container. Minimum lengths of tubing and connectors were attached to a threaded fitting at the top of the cylinder to enable: 1) Attachment of a pressure relief valve set at 30 psig and 2) Attachment of a valved gage tapoff for pressure measurement. The total volume of tubing and connectors was approximately O. Sec. The in line relief valve relieved to a long aluminum tube that extended from the irradiation position to the pool surface. A_ gage j was attached to the tube above the pool surface.

If gas pressure built up during irradiation above the point of lifting the relief

!J valve, the pressure would have been detected on the surface gage. Following irradiation, a gage was attached to the container to measure pressure built up by gas evolution during irradiation.

I Samples were subjected to gamma and neutron fluxes in the Ford Nuclear Reactor at the University of Michigan, Ann Arbor, Michigan.

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Relief 6.2

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Rsport 577 hh Brooks &Perkins. Incorporated APPENDIX 3 Irradiation of Boral Plates encased in Stainless Steel-

% Test

Description:

Each BORAL sample was a 9_ inch x. 9 inch plate of 0. 26 inch thickne s s. Each plate was encased in a thin, watertight jacket of stainless steel .

welded around the edges. A threaded connection was welded in the upper right

[ corner of the face on one side of the stainless steel jacket. Irradiations were conducted in the Ford Nuclear Reactor pool at depths of 12 and 20 feet.

An aluminum tube was run from the connection to the surface of the reactor pool for pressure measurements and gas collection.

Prior to testing, each sample plate was baked at 2000C for seven hours,in a vacuum oven to remove moisture.

Each sample was tested to 10 P SIG internal pressure. Experimental pressure s J were limited to 5 P SIG as a reactor safety precaution.

Experimental measurements were made of pressure within each sample. Gas evolved during the tests was collected and analyzed. It was decided that temperature would not be measured. Each sample was observed after irradiation for damage due to pressure, temperature, or other effects.

Each sample was pressurized momentarily to 10 P SIG as it was inserted into the reactor pool to verify watertightness. Once each sample was placed in

, its experimental position, a 30 inch Hg vacuum was drawn to evacuate as much air as possible. The starting pressure for each test was the 30 inch Hg vacuum.

J Experimental Conditions: The two samples were subjected to two different irradiation conditions. Sample I was a sealed, dry sample vented only through

, the gas collection line to the surface of the reactor pool. Sample 2 was

! identical to Sample 1 except that 25 ml of distilled water was injected within .

4

, r the stainless steel jacket. .

Initially, in Condition 1, each sample was irradiated adjacent to spent reactor fuel in a gamma flux of 2 x 105 rad /hr. In condition 2, each sample was placed in a holder adjacent to the reactor pperating at a power level of 2 MW. The j as 4 x 10 1 Condition 2 gamma approximately 1 x 10 gNw/cm2 /sec, rad or 1/hr x 10 anp thermal rad /hr. Finally neutron flux was 3, in Condition

each sample was left adjacent to the reactor core immediately after shutdown.

Neutron flux was quite low, approximately five orders of maggitude below )

, cperating levels, while gamma flux was measured as 1. 2 x 10 rad /hr. '

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