ML20205Q542

Evaluation of Matl Performance Suitability of New Vermont Yankee Spent Fuel Storage Rack Design

ML20205Q542
Person / Time
Site:	Vermont Yankee
Issue date:	03/31/1987
From:	Hoffman J YANKEE ATOMIC ELECTRIC CO.
To:
Shared Package
ML20205P635	List: ML20205P631 ML20205P793 ML20205Q542
References
NUDOCS 8704030564
Download: ML20205Q542 (10)

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• AN EVALUATION OF THE MATERIAL PERFORMANCE SUITABILITY OF THE NEW VERMONT YANITE SPENT FUEL STORAGE RACK DESIGN By J. R. Hoffman, P.E.

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• BACKGROUND Vermont Yankee is proposing to revise the design of its spent fuel storage racks. The rack design currently in use is an anodized aluminum j structure containing aluminum clad poison material encapsulated in sealed

cans. The racks are electrically insulated from the stainless steel pool i liner to preclude the possibility of galvanic corrosion.

The new design is fabricated from stainless steel containing aluminum clad poison material in vented cans.

This report will evaluate the suitability of the materials in the new f design for service in the Vermont Yankee spent fuel pool.

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SPENT FUEL POOL ENVIRONMENT The spent fuel pool is nominally pure demineralized water. No special additives are used for chemistry control purposes. The water chemistry l

I control limits are as follows (Reference 1):

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pH 5.8 - 7.5 Conductivity <1.0 micro-mho/cm

! Chloride <500 ppb i Silica <1,000 ppb l Bulk Temperature <150 F MATERIAL PERFORMANCE j The first consideration is suitability of the rack structure for the intended environment. The fuel racks are fabricated from Type 304L stainless i

steel with a controlled maximum carbon content of 0.030 w/o. This material i j has demonstrated outstanding general and localized corrosion resistance in the as-welded condition under the Electric Power Research Institute (EPRI) BWR 1 Alternate Materials Program (Reference (6)). Since the fuel storage pool f environment is considerably less aggressive than the test qualification j conditions, equal or better performance is expected.

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The next consideration is exposure of the poison material to the pool environment. The poison material is a boron carbide matrix clad with Type

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1100 aluminum, known by the trademark BORAL. This poison material has been

! -used for many years as a poison material in test reactors. Referende (2) discusses tests performed on BORAL that had been exposed for over 19 years to i

! reactor coolant at the Brookhaven National Laboratory test reactor. No 4-degradation of the BORAL was seen. The surface exposed to the reactor coolant I was covered with a tightly adhering, thin corrosion product.

f Reference (2) also reported the results of testing which exposed BORAL

for 360 days in water at a pH of 4.1 and 10.4, which brackets the pH range of l the fuel storage pool. No effect due to pH was observed.

Reference (3) reports that corrosion of aluminum is affected by pH, as shown in Figure 1. The Reference (2) results are not necessarily in conflict j with this. It is possible that the corrosion-rate at a pH of.4.1 is sim'ilar j to the rate at a pH of 10.4, both of which are significantly greater than.the f rate at the pH range of the fuel storage pool water.

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1 Reference (4) reports the results of testing and literature research by I

i a manufacturer of similar design fuel storage racks (the rack manufacturer, f Brooks and Perkins, is also the manufacturer of BORAL).

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j The results of this testing are in agreement with-the literature -

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corrosion at 150 F is negligible.

b a i The vented cavity design results in the BORAL and stainless steel being f

j in contact in the water environment, raising the possibility of galvanic and/or crevice corrosion. This condition was evaluated in Reference (4) at  ;

I temperatures as high as 356 F. The reported corrosion rate of the aluminum was 0.1 mils per year. Assuming the thinnest piece of BORAL with the thickest 4

l section of B C matrix, a clad thickness of .007 inches will result. Thus, 4

j the BORAL clad is satisfactory for well over 40 years of life. No corrosion j of the stainless steel was noted.

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• CONCLUSION The general literature and special test reports were reviewed to determine the suitability for service of the Vermont Yankee spent fdel storage racks.

The data show that stainless steel, BORAL, and stainless steel /BORAL couples have been tested in conditions more severe than the fuel storage pool environment with no deleterious effect.

I Weeks, et.al., in Reference 5 report similar finding.

Thus, it is concluded that no technical concerns exist from the standpoint of material serviceability.

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i . Iost solutions contained 1-10 X 10-8 N 1I:02, 68 ppm CaSO., 30 ppm MgSO.,

T '; l 1-2 ppm Nacl (Draley and Ruther).  !!!

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11 Al + NaOH + H2O - NaAIO: + }H: (1) ['

This reaction proceeds rapidly at room temperature, whereas for iron -] j a similar reaction forming NaFeO2and Na:FeO, requires concentrated ti i alkali and high temperatures. 'l i

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Corrosion Characteristics ,'

As mentioned previously, aluminum is characterized by (1) sensitivity to corrosion by alkalies and (2) pronounced attack by traces of Cu ,

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j G . I REFERENCES

1. Vermont Yankee Procedure RP-4624, Revision 8 September 29, 1986.

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2. General Electric Company Report 78-212-0079, "BORAL From Long-Term Exposure at BNL and Brooks and Perkins," December 14, 1978. '

3. Uhlig, Herbert H., Corrosion and Corrosion Control, John Wiley and Sons, 1971.

4 ~. Brooks and Perkins Report No. 577, "The Suitability of Brooks and Perkins Spent Fuel Storage Module for Use in BWR Storage Pool," July 21, 1978.

5. Czajkowski, C., J. R. Weeks, and S. R. Potter, " Corrosion of Structural and Poison Material in Spent Fuel Storage Pools." Paper No. 163, National Association of Corrosion Engineers, Corrosion /81 Conference, April 6-10, 1986.

6. EPRI NP-2671-LD, " Alternative Alloys for BWR Piping," October 1982.

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APPENDIX A EXCERPT FROM VERMONT YANKEE Procedure RP4624

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. SAWLING A@ TREATWNT OF THE FLEL POOL $YSTEK -- -

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Purpose:

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y' To enable the Chemistry and Health Pnysics' personnel to analyze. and control Fuel Pool chemical parameters, y ,4 i l

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% s Fuel Pool water will be sampled to ?nable a. variety of analyses to be '

performed. Table I .provides a listing of"tne chemical parameters that'will t be monitored, operating limits on the palsmeter, and the governing operating '

a procedure for each.

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The following tables are included's  : I

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Table I Fuel Pool Parameters _ . t, s '

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l Table II Precoat Data for Fuel Pool camineralizers ,

References i l .,

l \p A. Tech. Specs. '

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B. Admin. Limits ..

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1. See Table I [ l C. Other '~ ,  ?

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1. 0.P. 0630, Water Chemistry

2. D.P. 2631, Radiochemical Instrumentation; s

3. 0.P. 0640, Chemistry and Health Physics Department Schst:11ng

4. D.P. 0641, Procedure for Logging Results of Chemical Analysis ,

5. D.P. 0633, Control of Non-Tecn Spec Lab Procedures , . i'; * -r

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6. A.P. 6807, Collection and Temporary Storage of @ Records { > N ,

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'} Precautions; q .., /g o I n ...i ",3 m.-

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' l. Appropriate protective clothing should be worn when'. sampling." ,

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( 2. A radiation monitor shou be.NNdduh.ngsahlir.g. ( , j f f ,

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3. Avoid spraying Fuel Pool water over the sides of'L% sab5tirsink wnen

! drawing a sangle. '

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, - 'Rzv. 8 j TABLE I FLEL POOL PAR 4ETERS With Aluminum Fuel Pool eter Parameter Equip. In Pool Procedure Domineralizer inlet conductivity at 25'C <1 mo/cm OP 0630 Demineralizer effluent conductivity at 25'C < inlet cond OP 0630 Demineralizer inlet and outlet pH at 25'C Neutral (5.8-7.5) OP 0630 Chloride <0.5 ppm OP 0630 Silica <1 ppm' DP 0633 Heavy Elements (dissolved Fe, Cu, N1) <0.1 ppm OP 0633 Total Solids (insoluble) Influent only <1 ppm DP 0633 Domineralizer activity Effluent < influent OP 2631 Using lab conductivity meter and flow cell, check panel conductivity readings daily.

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APPENDIX B GENERAL ELECTRIC COMPANY Report 78-212-0079 s

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