ML20079L312

Forwards Rept Providing Update of in-reactor Surveillance Programs & Overall GE BWR Fuel Experience Through Dec 1990

ML20079L312
Person / Time
Site:	05000605
Issue date:	10/25/1991
From:	Charnley J GENERAL ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
JSC-91-037, JSC-91-37, NUDOCS 9111060207
Download: ML20079L312 (13)

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SrN - fd- '#I October 25,199I JSC 91037 Document Control Desk US Nuclear Regulatory Commission Washi:igton, DC 20555

SUBJECT:

GE EXPERIENCE WITil llWk FUEL TIIROUGli DECEMllER 19M)

. Attached is the subject report you requested. This report provides an update of the in-reactor surveillance programs as well as overall GE BWR fuel exnerience. Please call Gary Jones of my staff en (cf.) 9251417 if you have any questions relative to this report.

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.JSC:z Attachraeut CC: ?W Marriott LS Gifford RC Jones, Jr. (NRC) 9111060207 911o25 PDR A

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BCC: GO Jones Fuel Engineering Managers FLE M

GE EXPERIENCE WITil BWR FUEL THROUGH DECEMBER 1990 1

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1. Intmdurlien This infonnation report provides an updated review of GE experience with production and developmental BWR Zircaloy-clad UO 2fuel rods through December 1990. This experience includes successr ul commercial reactor operation of fuel bundles to greater than 45,000 mwd /MTU bundle average exposure (approximately 60,000 mwd /MTU peak pellet expo-sure).

The perfornumee of GE 8X8 fuel types continues to be highly successful as demonstrated by an over.dl fuel rod reliability rate from 1974 to the end of 1990 of greater than 99.98%

11. (lE BWR FucLEApericace Base As of December 31,1990, over 4.0 million GE 8X8 fuel type production Zircaloy-clad UO2 fuel rods were in, or had completed, operation in commercial BWRs. Figure i shows cumu-lative 8X8 fuel rods loaded as a function of' calendar year. As of December 31,1990, over 1.5 million GE fuel rods were in operation Figure 2 illustrates GE's core loadings at the end of 1990 by fuel type. As of December 31,1990, GE had loaded approximately 1.37 million pellet-clad interaction (PCI) resistant barrier fuel rods in conunercial BWR's. The GE fuel manufacturing facility in Wilmington, North Carolina, is producing 100% of its 1991 load as barrier fuel.

In 1990, sixteen domestic and six overseas GE BWR plants containing GE fuel had refueling outages with over 3300 new GE 8X8 fuel bundles loaded. Nearly 80% of this new fuel loaded was GE's latest production fuel desis GE8X8EB and GE8X8NB.

1 11 . In-Reactor Surveillanccfmstams and Sunuuy_9lS.urveillance Resuhs One of the most important aspects of the GE fuel design pmcess is the in-reactor pufomi-ance monitoring of a design before and after its introduction. In keeping with the GE philos-ophy of test-beforeasse, lead use assemblies (LUA's) containing selected key design features are used to demonstrate the satisfactory perfonnance of these features and to provide lead experience for future production fuel. The fuel surveillance program adopted by GE and ac-cepted by the NRC is descriled in References I through 4.

A summary of GE's lead use assembly surveillance program is comained in Table 1. Exami-nation results are provided below:

A. Barrier FucLEIDgram The goal of this program was the demonstration of a Pellet-Cladding Interaction (PCI) resistant fuel under conditions which would provide statistically significant results. The PCI-resistant fuel features the barrier concept to protect the fuel cladding from failure caused by PCI. The barrier fuel ' program consisted of four lead use e:semblies, loaded into Quad Cities-1 in 1979 at the beginning of cycle 5, and a demonstration reload of 144 bundles with Zr-lined cladding placed into the core of Quad Citiew2 in 1981 at the beginning of cycle 6.

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The barrier LUA's at Quad Cities-1 operated for up to 5 cycles and underwent five pool-side examinations consisting of visual inspections and non-destru:tive testing of se-lected fuel rods. These examinations revealed that the bundles and individual fuel rods exhibited characteristics typical of nomud operation.

Six rods were removed from one of the discharged t UA's (at 43000 mwd /MTU) and were then exchanged with 6 iods from a bundle that had completed two cycles of opera-tion. The reload bundle cornaining the 6 barrier LUA tods was reinserted in Quad Cities I for Cycle 11. In November 1990, at the end of Cycle 11, examination of these six rods showed that they continued to exhibit nomial perfonnance. They were re-inserted la Cycle 12 for an additiomd cycle of irradiation.

The Quad Cities,-2 barrier fuel program was designed to subject the barrier cladding fuel to significant power increases in order to demonstrate the PCI retistance of barrier fuel.

Two power increase demonstrations were perfonned; the first in 1983 at the end of cycle 6 and the second in 1985 at the end of cycle 7. Sixteen barrier bundles were involved in each demonstration. During the following plant outage, all demonstration barrier bundles were evaluated by vacuum offgas sipping and detennined to be sound. Subse-quent to the power increase demonstrations, nli PCIOMR operating restrictions were re-moved from the barrier fuel bundles in the core. Plant offgas surveillance indicates that all fuel bundles in the core continue to operate reliably. Of the 144 bundles in the reload, 32 operated for 3 cycles,80 operated for 4 cycles,32 for 5 cycles and 16 bundles are operating in their 6th cycle.

B. Improved Design Feature Lead Use Assemblics Several Lead Use Assemblies have been Asigned and placed in operation for the pur-pose of obtaining experience and perfonnance data on new product design features.

These LUAs have undergone extensive preirradiation characterization, with plans for interim poolside examinations. These improved Design Feature LUAs include:

1. 1983 Lead Use Assemblies Four LUAs were loaded into a BWR 4 in 1983. The first poolside examination of these bundles was complved in August 1985, after one cycle of operation, and showe i characteristics typical of nonnal operation. The second poolside examina-tion w as completed in November 1987, after two cycles of operation, and showed characteristics typical of two cycles of normal operation. The LUAs retumed to service in December 1989. The third poolside examination is planned for October 1991.

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2. 1914.ltadif ci Assemblics Five LUAs were loaded into a llWR 4 in 1985. Four of the LUAs were loaded in central core locations and one LUA was loaded at the edge of the core.The first

. poolside examination of these bundles was completed in April 1987, after one cycle of operation, and showed characteristics typical of nonnal operation. The second poolside examination was completed in October 1988, after two cycles of operation, and showed characteristics typical of two cycles of nonnal operation. The third cycle of operation ended in July 1990. The four central LUAs achieved bundle ex-posures of about 40000 htWd/hiTU. The edge LUA achieved about 25000 h1Wd/

h1TU and was re-inserted for continued operation.

3. 1987 LeaLUstAssemb!its Four LUAs were loaded into a BWR 4 in 1987. These fuel assemblies represent lead use GE8X8NB fuel. The first poolside examination of these bundles was com-pleted in October 1988, after one cycle of operation, and showed characteristics typ.

ical of nonnal operation. The second poolside examination of these bundles was completed in h1 arch 1990, after two cycles of operation, and showed characteristics typical of nonnal operation. The next poolside examination is scheduled in 1991 after the third cycle of operation.

A second group of four LUAs were loaded into another BWR 4 in 1989 at the be-ginning of cycle 8. The first poolside examination of these bundles is scheduled in 1991 after the first cycle of operation.

4. Cindding Corrosion Perfonnanct1UAs Six LUAs were loaded into a BWR 4 in early 1988 and six LUAs were loaded into another BWR 4 in late 1988. Features tested include cladding material, heat treat-ment, and surface conditioning and the most recent corrosion improvement pro-cesses. These two reactors have historically exhibited highly variable cladding cor-rosion perfonnance, even for cladding material taken from the same tubing lot but irradiated in the two different reactors. Three LUAs were examined in the first BWR 4 reactor in late 1989, after one cycle of operation. Another three LUAs were examined in the second BWR 4 reactor in early 1990, also after one cycle of opera-tion. These LUAs reflected bundle average exposures up to 13,000 mwd /h1TU.

Visual inspection revealed excellent corrosion resistance along the full length of the fuel rods. He second poolside examination of the LUAs is scheduled in h1 arch 1991 and in October 1991.

5. GE8X8NB-1 Channel Lead UstAssemblics Four LUAs were loaded into a BWR 4 in 1988. These LUAs represent lead use of GE8X8NB-1 design features. The first poolside examination of these bundles was completed in April 1989, after one cycle of operatbn, and ahowed characteristics 4 l

typical of nonnal operation. The second poolside examination of these bundles was completed in March 1990, after two cycles of operation, and showed characteristics typical of nomial op-ration.

6, gel 1 Lead Use Assemblies In 1990 four GEli LUAs were loaded in each of three reactors ( Two BWR 4s and one BWR 5). Poolside examinations of these bundles are scheduled to begin in 1991.

IV. Gsnetic_ Fuel Perfonnance Mechanisms Pellet-cladding interaction (PCI) a .d crud-induced localized corrosion (CILC) are the pri-mary cladding perforation mechanisms that have affected fuel perfonnance in recent periods.

As described below, product improvements have been developed that wW ev entially elimi-nate these two fuel rod failure mechanisms.

A. Ec]let-Cladding Interaction l Light Water Reactor (LWR) nuclear fuel is susceptible to fuel rod cladding perforation, commonly called pellet-cladding interaction (PCI) failure, when subjected to fast power increases at moderate to high exposures. Operational procedures (PCIOMRs), whir.h in-volve slow approaches to power, have essentially, but not completely, elimin7ted PCI failures in LWRs, but at the cost of reactor capacity factor losses. 2.ltconium barrier fuel was invented by GE as a material saluaou to the PCI failure problem. Extensive test reactor and laboratory tests along with successful in-core power ramp demonstrations in the Quad Cities Unit 2 power reactor have shown that Zr-barrier fuel is convincingly failure resistant. Barrier fuel was commerchlly introduced by GE in 1983. With the succesful completion of the Quad Cities-2 barrier demonstration program, GE recom-mended the removal of all PCIOMR operating restrictions on GE barrier fuel. Over 50 reactor cycles of operation have been succesfully completed by GE barrier fuel without restrictive PCIOMR controls. The effectiveness of the GE barrier cladding design fea-ture has been confirmed by the extensive commercial reactor experience where not a single barrier fuel rod failure due to PCI has been observed in over 920,000 GE barrier fuel rods completing at least one cycle of operation. PCI failures are expected to tw eliminated within the next few years as the population of non-barrier fuel (29% of all GE fuel currently in operation is non-barrier) is discharged.

B. Crud-Induced Localized Corrosion

. In 1979, an unexpected failure mechanism of localized fuel rod cladding conosion was j revealed m some BWRs. Poolside examination of the failed fuel rods revealed plant l corrosion product (crud) scale deposits with high copper concentrations. The nature of l= the failures led to identification of special conditions of environment, operational histo-ry, and material-susceptibility that must occur simultaneously to cause failure. These crud-induced loenlized corrosion (CILC) failures have been limited to plants with cop-per alloy condenser tubes and filter demineralizer condensate cleanup systems.

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Fuel examinations, surveillance, and extensive research have led to a practical under-standing of this mechanism. A reproducible out-ef-reactor test for measuring the sus-ceptibility of Zircaloy to in-leactor nodular corrosion was developed by GB and corte-lated to in-reactor perfonnance (Reference 5). This test confinned a previously undetected variability in the susceptibility of Zircaloy to in-reactor nodular corrosion.

This test has been patented and made available to the industry on a non-profit basis through the ASTM.

Manufacturing processes have been developed that both improve the corrosion resis-tance of the incoming material produced by the Zircaloy vendors and further ensure that improved corrosion resistance is maintained throughout the fabrication processing to

' yield final size fuel rod cladding that is more resistant to in-reactor nodular corrosion.

-These processes have been implemented in the production of all GE fuel to provide a high degree of assurance that adequate corrosion resistant propenies are achieved.

.V. Conclusions GE has developed a substantial fuel experience base that, coupled with an aggressive fuel surveillance program, has provided significant feedback on statistically significant numbers

. of fuel rods with regard to the perfonnance effectiveness of design, operational and manufac-turing changes. It is concluded that the experience gained with GE product ion and develop- ,

mental fuel continues to demonstrate the high reliability of the GE designed BWR fuel.

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VI Refurnces

1. J. S. Chamley (GB) to C.11. Berlinger (NRC), " Post Irradiation Fuel Surveil'ance Pro-gram", November 23,1983.

2. J. S. Chamley (GE) to L. S. Rubenstein (NRC), " Fuel Surveillance Program", February 29,1985.

3. J. S. Chamley (GE) to L. S. Rubenstein (NRC), " Additional Details Regarding Fuel Sur-veillance Program". May 25,1984.

4. L, S, Rubenstein (NRC) to R. L. Gridley (GE), " Acceptance of GE Proposed Fuel Sur- _

veillance Program", June 27,1984.

5. B. Cheng,11. A. Levin, R. B. Adamson, M. O. Marlowe, V. L. Monroe, " Development of a Sensitive and Reproducible Steam Test for Zircaloy Nodular Cormsion", ASTM 7th Intemational Conference on Zirconium in the Nuclear Industry, Strasbourg, France, June 24-27,1985.

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l Table 1 Summary of Ongoing Lead Use Assembly Surveillance Programs Bundle Number of Average Number Completed Exposure At Reactor of Cycles of Last Outage Eragnun Class Ihuldic Operation i LGWdthillD Oh,iettirn Barrier LUA's BWR3 2 5* 43 Barrier Cladding 1983 LUA's BWR4 4 2 24 Improved design features 1984 LUA's BWR4 1 3 25 Improved design features 1987 LUA's BWR4 4 1 12 Lead Use GE8X8NB Corrosion BWR4 6 1 13 Clad hiat'l Performance Process Variables GE8X8NB-1 BWR4 4 2 15 Lead Use Clumnel GE8X8NB-1 LUA's Features Corrosion BWR4 6 1 12 Clad hiat'l Performance Process Variables (1) As of December 1990

• Six fuel rods have been reirradiated for a 6th cycle to average exposures of 50 GWd/h1TU 8

4 Table 1. Continued Sununary of Ongoing Lead Use Assembly Surveillance Programs Bundle Number of Average Number Completed Exposure At Reactor of Cycles of Last Outage "Icuam Class Bundles Opnation LGEdthELD OldectiYts 1987 LUA's BWR4 4 - -

Lead Use GE8X8NB GEli LUA's BWR4 4 - -

Lead Use BWR4 4 - -

GEli BWR5 4 - -

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