ML20237L804

Testimony of Cd Sellers Re Contention 6.* Related Correspondence

ML20237L804
Person / Time
Site:	Turkey Point
Issue date:	08/31/1987
From:	Sellers C Office of Nuclear Reactor Regulation
To:
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ML20237L782	List: ML20237L780 ML20237L799 ML20237L804
References
OLA-2, NUDOCS 8709090082
Download: ML20237L804 (16)

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UNITED STATES OF AMEP,1CA NUCLEAR REGULATORY COMMISSION j i

l BEFORE Tile ATOMIC SAFETY AND LICENSING BOARD '

in the Matter of )

) Docket Nos. 50-250 OLA-2 FLORIDA POWER AND LIGHT COMPANY ) 50-251 OLA-2

)

(Turkey Point Plant, Units 3 & 4) ) (SFP Expansion)

TESTIMONY OF CLIFFORD DAVID SELLERS REGARDING CONTENTION 6 Q1. Please state your name and place of employment.

A1. My name is Clifford David Sellers. I am employed by the U.S. Nu-clear Regulatory Commission as a Senior Metallurgist in the Materials Engineering Branch of the Office of Nuclear Reactor Regulation. A copy of my professional qualifications is attached.

02. PMase explain the purpose of your testimony, A2. The purpose of my testimony is to address Contention 6 with regard to degradation of spent fuel pool materials other than Boraflex.

Contention 6 states:

The Licensee and Staff have not adequately considered or analyzed materials deterioration or failure in materials integrity resulting from the increased generation and

[ sic] heat and radioactivity, as a result of increased capacity and long term storage, in the spent fuel pool.

The Licensing Board found in its March 27, 1987 Order that, while there would not be appreciable deterioration of spent fuel pool ma-terials in the near term (Order at 33), a question remained 8709090082 870831 PDR ADDCK 05000250 T pop

' i' i concerning spent fuel pool integrity over the extended storage peri-od authorized by the amendments. Order at 33. The question was -

raised by: publ. Plons by A. B. Johnson entitled " Behavior ~ of 1

Spent Nuclear Fuel in Water Storage"- (BNWL 2256,_ September,1977) and " Spent Fuel Storage: Experience" 4 Nuclear Technology, Volume 43, mid-April,1979) .

The Board ' noted -that statements in two publications by- Johnson Indicated that the longest l water storage of Zircaloy-clad' fuel and stainless steel-clad fuel is about 19 years and 12 years, respective--

ly. Order at 32. While Johnson stated that : the technology for handling spent fuel has developed over 35 years and has largely been satisfactory, Johnson concluded that expected spent fuel stor-age of 20 to-100 years would be an incentive to determine whether any slow degradation mechanisms are operative.

Order at 33. The Board also acknowledged the Intervenor's observation that spent fuel presently stored at Turkey Point did not exceed 39,000 MWD /MT but that the plant may now operate until burnup of 55,000

.. MWD /MT. Order at 32. Consequently, the Board asked the parties to " address the matter of the' modes and effectiveness of survell-lance of materlats and the monitoring of the fuel storage pool and contents to provide a measured basis for safety during the extend- ,

i ed period of use." Order at 33.

Q3. What is the purpose and effect of the rerack program?

A3. Redesign of the spent fuel pool racks increases only the storage j l

capacity of the pool and not the frequency or the amount of newly I discharged fuel to be placed in the pool during each fuel reload 1

cycle. The rerack design does not change the radioactivity of the l l

newly discharged fuel placed in the storage pool. The proposed

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pool storage densification will equip each pool with sufficient stor- j 1

age locations and provide adequate storace with full core discharge )

capacity well into the next century based on a conservatively esti- j mated 18-month fuel cycle. As a result of the expanded storage capacity, there will be an increase in radiation exposure to spent {

fuel pool materials.

Q4. What are the materials to be considered within the spent fuel pool structures?

A4. The new spent fuel storage racks are constructed of Type 304 stainless steel as the load carrying structure and use sheets of Boraflex (held in place by a thin-walled stainless steel wrapper) on the outer surface of the storage cells and between the cells as a neutron absorbing material. ' Type 304 stainless steel is also used in the pool liner. For the rack feet 17-4 PH stainless steel is used.

The pool structure is concrete composed of cement and aggregate and uses reinforcing bars of carbon steel. The fuel assemblies are constructed of Zircaloy fuel cladding, inconel 718 springs, and ,

i stair.less steel nozzles and bands.

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05. Has there' been to the best of your knowledge, any service induced.

degradation observed in any spent fuel storage racks? ,

i A5. No service induced defects have been observed'in spent fuel stor-age ' racks that have ' been removed at other plants involved in reracking programs. Some of these racks had been in service more than ten years.

06. What is the industry's experience with wet fuel storage and the performance of spent fuel pool materials? l A6. The 40 years of industry experience with wet storage illustrates that it is 'a fully-developed technology with no associated major technological problems. Spent fuel storage pools are operated with-out significant risk to the public or the plant personnel. There is substantial technical basis for allowing spent fuel to remain in wet storage for several decades beyond the expiration of the reactor operation license. There is no evidence that Zircaloy-clad fuel or stainless steel structural elements degrade significantly during wet i storage. This is demonstrated by continuous storage of fuel ele-ments for as many as 25 years and ' irradiation of fuel in reactors for as long as 22 years. Cladding defects have had little' impact during wet storage. Experience to date with handling operations at spent fuel ' storage pools indicates that failed fuel rods can be ac-4 commodated. Furthermore, very few fuel assemblies have suffered major mechanical damage as a result of handling operations at spent .

fuel storage pools. I l

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What is - the anticipated maximum radiation exposure of fuel pool

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structural materials as a rnsult cf the expanded storage? ,

I A7. As calculated by Westinghouse, the materials in the spent fuel can .

be expected to be exposed to e maximum neutron fluence of 4.8 x 2

10" neutrons /cm . Of the materials in the spent fuel pool, only the racks containing the first discharged fuel assemblies can be expected to receive this amount of radiation. .The pool liner and 4

pool concrete structure, while in place in the pool for the entire storage period, will have the radiation attenuated by distance from '

the radiation sources (the aged fuel assemblies) and the shielding afforded by the water. Such attenuated exposure would be well below the threshold for radiation damage to the carbon steel in the pool structure and the stainless steel, which is in the order of 10 17 '",

and 10 18 . respectively.

Q8. What corrosion do you expect the fuel pool materials to experience as a result of the expanded storage? -

AB. Although fuel assemblies will be stored for a longer period of time, the Staff does not anticipate a significant increase in the corrosion occurring in the pool because the rates of most corrosion reactions ,

tend to decraase with time as protective oxide films form on the metals.

Corrosion can also cause microstructural change, the reaction of corrosion products with the material to change the structure of the material, but this would more likely occur during reactor operation ,

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rather than storage. Microstructural change can occur with ,

Zircaloy-clad fuel when the hydrogen produced by the reaction be- l tween zirconium and water diffuses into metal, forming hydride par- i ticles or a hydride phase within the Zircaloy cladding. With stainless steel fuel cladding, such microstructural changes are not likely to occur because no known hydride or hydriding problems have ever been observed with stainless steels. In fact, stainless j steels are often considered one of the better barriers to hydrogen diffusion. Further, microstructural changes from solid state diffu-slon processes do not occur below 500 F in stainless steels. There-fore, ilttle or no microstructural changes would occur in the spent fuel pool materials which is attributable to the extended storage.

C9. What other long term mechanisms of degradation or corrosion could affect stainless steel in the pool liner and storage racks?

A9. Stress corrosion cracking and intergranular corrosion of austenitic stainless steels that are sensitized (e.g. , adjacent to welds) are conceivable mechanisms of degradation of components in spent fuel storage pools. Specimens with welds of the type used in the Tur-key Point racks have been subjected to accelerated environmental i

tests. Stress corrosion cracking of sensitized steels adjacent to )

I welds in the fuel pool liner or in the fuel storage racks is a possi- l I

bility, but, should it occur, it would be highly localized (usually with an aspect ratio of less than 10) and confined to specific areas of the rack or liner structure and would not lead to gross degrada-l tion of the spent fuel storage pool components. Stress corrosion l

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cracking is less likely to result from the oxygenated, borated water than from chlorides in the water. Chloride stress corrosion of the i stainless steels : is effectively prevented at Turkey Point by the tight controls on chiaride levels in the fuel pools practiced by the ,

i licensee. . Stress corrosion cracking of 17-rl PH stainless steel when ]

used in the H-1100 heat treatment has not been a problem because the internal stresses (from the transformation processes that result.

In the; hardening of this materiel) are not high enough- to make it prone to stress corrosion cracking in service. Test reactors use  !

Type 17-4 PH in the Il-1100 heat trf.etment in control rod drive mechanisms, and ir. service survelliance has shown no degradation at all of this material after many years of service in. water of similar quality to- that in the Turkey Point pools, and a temperature of 1

145'F. I i

01C. What effect does the increase in amount of spent fuel stored in a fuel pool have on the radioactive particulate release to the fuel pool 4

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environment?

A10. The primary source of radioactivity release to the spent fuel pool 1

environment is crud that enters the pool with the freshly dis- i I

charged fuel, where it is subsequently removed by the pool water j purification system. I know of no evidence that these crud depos-its influence the corrosion of stainless steel. The increased spent fuel storage should not increase the crud burden on the demineralizers, since crud release oc. curs primarily within the first )

i few weeks after the fresh fuel is placed in the pool, and is removed

i by the fl!ter-demineralizers in the water purification well before the next refueling. Therefore there is no mechanism for the Increased j i

storage of spent fuel in spent fuel pools to result in any serious l degradation to the spent fuel poo! components . or the fuel itself.

011. What is the likollhood and effect of leskage and deterioration of spent fuel during long term storage?

A11. Leakage and disintegration of spent fuel and its cladding while in pool storage is highly unlikely. In the Battelle Pacific Northwest Laboratories report BNWL-2256, Dr. Johnson has surveyed the in-formation on behavior of spent fuel in pool storage and has found no ev!dence of degradation of spent nuclear fuel during pool stor-age after times up to 18 years for Zircaloy-clad fuel and 12 years for stainless steel-clad fuel (as of 1977). In surveys for the Nu-clear Regulatory Commission, performed by Dr. J.R. Weeks of Brookhaven National Labs, since the issuance of Dr. Johnson's re- I port, utilities were contacted that have stainless steel-clad fuel in i

storage. At the Connecticut Yankee and San Onofre nuclear plants , stainless steel-clad fuel has been continuously stored in their pools since the early 1970's with no evidence of any failures developing in fuel cladding.

Leaking fuel has been stored in a number of fuel pools both in this country and elsewhere as described by Dr. Johnson. In all cases, the excellent corrosion resistance of the uranium oxide fuel pellets has prevented any noticeable additional degradation of these fuel

i pellets in the pool environment both in the high purity water BWR type pools, or In' the boric acid pools such as exist at most PWR.

sites. Should a defect develop in a fuel cladding ~ in the reactor, the volatile and soluble fission products, normally the alkalis and the halogens, would be released to the reactor coolant and removed l by the reactor coolant purification system. Thus, the majority of them would 'not enter the fuel pool. Some small amounts of these materials may enter the pool from fuel that developed defects in the reactor, during the first few months after the fuel enters the pool.

These (except for the inert gases) would readily be removed by the spent fuci pool water purification system. Fuel elements are tested for their leak tightness before being placed in the pool. Thus the plant staff is aware which fuel elements to be placed in the pool contain defects.

In the highly unlikely event that a defect should develop in the fuel cladding during the first few months of pool storace, gaseous j l

and alkall fission products could be released to the pool and the pool environment. The spent fuel pool monitors, which are used to monitor the spent fuel pool area, and the cleanup system monitors would detect such a release. Should a leak develop in a fuel clad-ding several months after it has been placed in the pool (an unlike-I ly occurence) and after most of the gaseous fission product activity has decayed , the activity which would provide detection of this  ;

Sreach of the cladding would be less. However, the consequences 1

would also be less, and the situation would differ ilttle from that 1 i

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1 for fuel elements containing known defects which are stored in the I i

same pool. Therefore, the proposed long-term storage does not j affect the. probability that degradation of the fuel will occur in the pool or that significant amounts of fission products would be re-leased to the pool.

From this discussion, I conclude that the possibility of leakage of the spent fuel element cladding and/or the disintegration of the spent fuel during storage is remote because of the excellent corro-sion resistance of the spent fuel pellets snd the zircoloy cladding in the spent fuel pool environment.

012. Will the increase in spent fuel poct storage capacity result in in-creased deterioration of the concrete pool structures?

A12. No. The performance of the concrete in the cpent fuel pools and the dismantling of many concrete structures used as shielding has not produced any evidence of degradation due to radiation heating or radiation. Therefore, because the expanded storage only results in small increases in radiation and radiation heating, no significant degradation of the concrete structure of the Turkey Point spent fuel pools will occur.

Q13. Does the increased capacity of the spent fuel pool affect the heat load of the spent fuel pool?

l A13. Fuel assemblies stored for a period sufficient to fill the originally 1

approved Turkey Point fuel storage rack capacity would contribute

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'little to the heat load of the spent fuel storage pool. -These assem-

, biles cause a small increase in maximum pool temperature when new-ly discharged fuel is added to the pool. ' As these old elements i continue to age, they contribute less and less to the heat load of l

the pool. The heat load contribution of ell the aged elements 'dur- j ing the last 3 refuelings (calculated by Westinghouse) only raises the maximum pool temperature after refueling to 143oF and decreas-es thereafter. This maximum pool temperature is within NRC gulde-lines for maximum exposure temperature to concrete.

o Q14. What is the impact of increased capacity on stored fuel assemblies?

A14. The increased capacity will increase the storage period of the as-semblies. Stainless steel clad spent fuel has been stored in PWR spent fuel pools more than 18 years. The exposure in the reactor, which is much greater than radiation levels in the storage pools, l represents the maximum radiation exposure any stainless steel can accumulate in a spent fuel pool since the steel is directly against the fuel as the cladding material. Destructive and visual examina-tion of this material produced no evidence of significant degradation of the stainless steel. Relating these observations to the materials of construction for the storage racks, demonstrates that they would also not be subject to any significant degradation over long term use, far beyond the present storage time.

l Zircaloy-clad rods were examined after nearly 21 years of water storage. A comparison of cladding properties with those measured i

. 20 years earlier on rods from the ,same fuel asrombly showed that no detectable changes had occurred in corrosion film thickness, cladding mechanical properties and fission gas thickness, cladding mechanical properties and fission gas release. Zircaloy-clad fuel elements which were loaded into Canada's NPD reactor in 1962 are i continuing to operate satisfactorily (i.e. with no apparent degrada-tion) after 22 years of exposure to far greater radiation than any element in the Turkey Point spent fuel pools will receive during residence in the pools.

Q15. What assurance do surveillance of materials and monitoring of the spent fuel pool provide?

A15. Surveillance, as used in the context of meterials engineering, means the installation of specifically prepared test specimens which are i non destructively removable for test after exposure to an environ-ment which may degrade certain n.aterial properties. In this narrow l k

context, no surveillance of spent fuel pool. materials is planned. {

i That is, no removable test specimens representing spent fuel pool {

l materials are installed. j However, in the broad (dictionary) sense, spent fuel pool materials are subject to surveillance. There is monitoring of activity in the spent fuel pool buildino atmosphere and the spent fuel pool cleanup j system. Therefore, the capability to detect leaking fuel is adequate I i

for determining the condition of the spent fuel in the spent fuel )

storage pool for an indefinite number of years. The Licensee )

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E performs routine visual observations on periodic rounds inside the fuel storage building and the fuel. Is subjected to periodic inventory 1

by underwater- television. The condition of the liner is monitored by l the installed leak chase system. in addition, the Licensee maintains 1

spent fuel pool area monitors to continuously monitor the pool areas- ]

1 and the plant's vent monitoring . system . to monitor total plant air- l 1

borne radioactivity released (noble gas, Iodine and particulate).  :

Further, the water chemistry specifications provided by the licensee end the water chemistry purity as currently practiced in the pool, '

1 while not performed for the purpose of monitoring corrosion, are .

quite acceptable for preventing corrosion of materials in this pool, r

This routine surveillance or monitoring currently performed by the Licensee is adequate to assure safety of the fuel storege pool and its contents during the extended storage period authcrized by the amendments.

Qi6. Would you please summarize your testimony?

- A16. In summary, for the reasons explained previously, the materials in the spent . fuel pools will not degrade significantly because of the Increased pool storage capacity over any term of years foreseeable for storage at individual plants. The stainless steel storage racks will not be degraded because' of increased radiation by aged fuel elements. . The contribution of radiation to the adjacent structure decreases as the elements age. The Staff has evaluated the use of stainless steels in storage racks in approving rerack amendments

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for other plants and has concluded that the stainless steel racks can be used to the end of life of the plant. Many experiments have

. shown that . stainless steel, as well as the inconel and Zircaloy in l the aged fuel assemblies can be exposed to many orders of magni-tude .of radiation greater than can be reasonably expected in spent i fue' pool racks without significant degradatl'on. In addition, there is' no evidence that degradation would occur due to the small in-creases in radiation or heat to storage pool !!ners or the-concrete structure in spent fuel pools as a result of the increased storage.

While the Staff guidelines suggest a maximum pool water temperature of 140oF after normal discharge, any of the meterials in the pool can be exposed to much higher temperatures (145 F to 180 F) for extended periods without detectable degradation. Accordingly, the Staff has adequately considered and analyzed degradation in materi-als integrity resulting from increased generation of heat and radio-activity, as a result of the Increased capacity and the extended storage time of aged fuel elements in the Turkey Point spent fuel pools and has concluded that the extended storage authorized by the amendments raises no question of materials integrity.

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1 l'I During the'yeprs 1964'to 1968. I was employed as a Quality Engineer at.the

. Naval Reactors Facility located near Idaho Falls,LIdaho and served as site.

materials engineer. . In my capacity of. quality assurance engineer I prepared 3

procedures and specification supplements reviewed procurement documents and L , .perfonned audits. My. major accomplishments were the. establishment of

,; materials receiving; inspection and materials verification programs.

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' Fro i.1961 through 1963 I was a senior metallurgical engineer at the Bettis

. Atomic Power' Laboratory. .In this position I was a " cognizant engineer" for l

various hiah strength structural alloys such as 17-4 PH; 12% chromium steels; low'. alloy'(bolting) steels;InconelX;Haynes25,etc.,withresponsibility for specification preparation and. troubleshooting. Additionally, I was

. involved in. failure analysis of components fabricated from these alloys. I

'also performed field and in-plant inspection of 17-4 PH control rod drive mechanism components. Additionally, I was al .

irradiation programs of high strength bolting,so materialsinvolved in preparation and in testing of of  !

specimens prepared for irradiated components. This led to the presentation of.a paper on irradiated stainless steel at the 1963 ANS meeting.

From. graduation in 1951 I was employed in various levels of increasing responsibilityattheWestinghouseElectricCorporationAviationGasTurbine Division until.that Division s dissolution at the end of 1960 I initially was responsible'for the radiographic inspection of and shop contact on aluminum and magnesium alloy castings and investment cast refractory alloys and fabrications. Subsequently.I was involved in shop contact and trouble-shooting of in-house casting and forging shops. Later I was responsible for development of and applications for improved light-alloy and refractory alloys, including ~ preparation of design data and testing of engine hardware.

.Ne6r the end'of my service with this division I performed extensive failure analysis work on both engine and test rig failures, both in-house and in the field. During my period of employment in this division I received 13 patent

^ disclosure awards and was also involved in training of-personnel in the areas of physical metallurgy and failure analysis.

In my last' year of college and the preceeding summer I work at Penn State in

'the Metallurgy Department as an undergraduate lab technician with responsibi-11 ties for fabrication, testing, and photography of equipment and specimens and for the metallography of test specimens. The project was a joint Metallurgy / Ceramics Department project on the vitreous enameling of steel.

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CLIFFORD DAVID SELLERS METALLURGIST MATERIALS ENGINEERING BRANCH

.. . PROFESSIONAL QUALIFICATIONS In my.preseht position as Senior Materials Engineer in the Materials Engineering Branch;I am involved.in safety review and evaluation and inservice

' inspection of mater'ials.used .in the construction and maintenance of nuclear

. power plents'and investigation of materials problems.

The Materials Engineering Branch is responsible for materials application, I metallurgical investigate studies including thbrication problems, and inservice degradation processes such as stress corrosion and radiation.

effects.. Other responsibi?ities of this branch includes various aspects of i materials integrity, fracture toughness criteria, for the wide range of l materials used in the construction of nuclear power plant components. In addition to the' normal casework review responsibilities I have been involved in problems in many of the areas enumerated above. I was also previously involved in work leading to in NRC position.of bolting application requirements. . Recently, much of my work involves steam generator problems.

My current work involves. inservice inspection and evaluation of operating plant problems. i IhaveaBSdegreeinMetallurgy(PennState1951)andhavedonegraduatework  !

at the Ur,1versity of Delaware and University of Idaho.

I have been in the Materials Engineering Branch or Section continuously since starting )

with the AEC late in 1973 except for a brief assignment to Division of Operating Reactors, Engineering Branch. Much of my effort with Operating Reactors was with low pressure steam turbine disc cracking and primary components support structures. )

, From 1968 to 1973 I was a Senior Engineer with Westinghouse Nuclear Energy i Systems-PWR Systems Division, Monroeville, Pennsylvania. In this position m j dutiesinvolveddesignassistanceandtroubleshooting(bothshopandfield)ycn reactor ~ internals, control rods, instrumentation, and reactor pressure vessels. These duties and other field problem investigatory activities led to preparation and use of field kits to perform in-situ metallography. In this and other connections I have involved in various: activities at Beaver Valley, Cook, Zion Turkey Point, San Onofre, Ginna, Yankee Rowe, Haddam Neck, Indian

. Point, Salem, and SENA.

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