Information Notice 1989-31, Swelling and Cracking of Hafnium Control Rods

Swelling and Cracking of Hafnium Control Rods

ML031180736
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	03/22/1989
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-89-031, NUDOCS 8903160427
Download: ML031180736 (7)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 March 22, 1989 NRC INFORMATION NOTICE NO. 89-31: SWELLING AND CRACKING OF HAFNIUM

CONTROL RODS

Addressees

All holders of operating licenses or construction permits for pressurized water

reactors (PWRs) with Hafnium control rods.

Purpose

This information notice is being provided to alert addressees of swelling and

cracking of Hafnium control rods at several PWRs. It is expected that reci- pients will review the information for applicability to their facilities and

consider actions, as appropriate, to avoid similar problems. However, sug- gestions contained in this information notice do not constitute NRC require- ments; therefore, no specific action or written response is required.

Description of Circumstances

During eddy current and profilometry measurements of the control rods at the

Wolf Creek Generating Station, abnormal wear and swelling were identified in

53 Hafnium rod cluster control assemblies (RCCAs). As a result, the Wolf Creek

licensee informed the RCCA vendor, Westinghouse Electric Corporation, of their

inspection results. Subsequently, Westinghouse examined previous inspection

data from Union Electric Co.'s Callaway Plant and confirmed that Hafnium

control rod swelling was also occurring at Callaway. In addition, there

has been some foreign experience with these Hafnium control rods breaking

due to either swelling or hydriding and fretting.

Discussion:

Westinghouse introduced Hafnium material in RCCAs as a replacement for silver- indium-cadmium (Ag-In-Cd) in the 1970s. Some control rod cladding wear was

expected; however, the extent of swelling and cracking discovered at the Wolf

Creek and Callaway reactors was not.

Westinghouse believes that the Hafnium control rod swelling and cracking are

caused by hydriding of the Hafnium. Hydriding of the control rod occurs when

hydrogen from the reactor coolant diffuses through the stainless steel cladding

and reacts with Hafnium to form Hafnium hydride. The hydriding phenomenon was

addressed by Westinghouse during the development of the Hafnium control rods

8903160427-

IN 89-31 -

March 22, 1989 and was not considered to be significant. During autoclave

control rods In the 1970s, hydriding occurred uniformly over testing of the

length of the rod and resulted in only a very minor volumetricthe entire

increase.

At the Wolf Creek and Callaway reactors, however, the abnormal

ized swelling of the control rods occurred at several locations,wear and local- largest number of swollen sections located in the upper regions with the

rods. According to Westinghouse, Hafnium reacts with air during of the control

process and quickly forms a protective oxide layer on the Hafnium the fabrication

that inhibits the hydriding process. It is postulated that rod surface

of the Hafnium rods with the cladding during the assembly of Initial misalignment

in loose particles or spalling of the stainless steel cladding the RCCAs can result

the inner diameter of the cladding. During thermal cycling, near the top of

the differential

thermal expansion between the Hafnium and the stainless steel

cladding causes

the particles to come in contact with the Hafnium and to penetrate

the protective oxide layer. After the oxide layer is penetrated, or remove

of hydrogen into the Hafnium occurs. Because the Hafnium and the diffusion

the

a constant interface at the bottom of the control rod, the greatestcladding have

movement between the Hafnium and the stainless steel occurs relative

at the top of the

control rod and results in increased hydriding.

The principal safety concern associated with swelling and cracking

hydriding is the inability of a control rod to fully insert caused by

into the core

because of interference between control rods and the guide

analysis prepared by Westinghouse to evaluate the potential cards. The safety

consequences of

control rod swelling and end plug cracking-indicates that-there-is

bility of interference or locking of the control rods. The no possi- maximum

diametrical increase of a control rod due to the hydriding mechanism theoretical

calculated by Westinghouse to be 0.026 inches. In the safety has been

maximum increase was conservatively assumed to be 0.029 inches analysis, the

in a maximum control rod diameter of 0.410 inches. Since the and resulted

passage way In

the guide cards through which the control rods travel has a nominal

diameter of 0.420 inches, Westinghouse has determined that inside

a nominal clearance

of at least 0.010 inches exists between the control rods and

when the maximum diametrical increase rs assumed. the guide cards

Westinghouse has also calculated that operating plants with

Hafnium control

rods will experience only a small increase in control rod drop

than 0.1 seconds) assuming that all 24 RCCA individual absorber times (less

rods are bent.

In addition, no plant is expected to exceed its technical specification

on rod drop time through the end of either a third 18-month limits

cycle or a fourth

12-month cycle.

Although the current information does not suggest the need

the NRC is concerned about the long-term continued operationfor immediate action, with swollen or cracked Hafnium control rods. The NRC staff of nuclear reactors

and Westinghouse

personnel are continuing their evaluations on this issue. In

the interim, it

is important that addressees take whatever actions are necessary

similar problems, if they exist at their facilities, are detected to ensure that

rective actions are taken to preclude any deterioration of early and cor- the safety function

of the control rods.

IN 89-31 March 22, 1989 No specific action or written response is required by this information notice.

If you have any questions regarding this matter, please contact one of the

technical contacts listed below or the Regional Administrator of the appropri- ate regional office.

e EDirector

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: S.L. Wu, NRR

(301) 492-1065 L. Phillips, NRR

(301) 492-3235 Attachment: List of Recently Issued NRC Information Notices

I

Attacl.-

IN 89-31 March 22, 1989 Page I of I

LIST OF RECENTLY ISSUED

NRCINFORMATION NOTICES

Intoirmitlon w;e uT

Notice No. Subinet ttusnrx

.....- .... . I----.

.

-^

o To

89-30 High Teberature 3/15/89 All holders of Ots

Environments at or CPs for nuclear

Nuclear Power Plants power reactors.

89-29 Potential Failure of 3/15/89 All holders of OLs

ASEA BrowmBoveri or CPs for nuclear

Circuit Breakers Power reactors.

During Seismic Event

89-28 Weight and Center of 3/14/89 All holders of OLs

Grav1ty Discrepancies or CPs for nuclear

for Copes-Vulcan power reactors.

Air-Operated Valves

89-27 Limitations on the Use 3/8/89 All holders of OLs

of Waste Forms and High or CPs for nuclear

Integrity Containers for power reactors, fuel

the Disposal of Low-Level cycle licenses and

Radioactive Waste certain by-product

materials licenses.

89-26 Instrument Air Supply to 3/7/89 All holders of OLs

Safety-Related Equipment or CPs for nuclear

power reactors.

89-25 Unauthorized Transfer of 3/7/89 All U.S. NRCsource.

Ownership or Control of byproduct. and special

Licensed Activities nuclear material

licensees.

89-24 Nuclear Criticality Safety 3/6/89 All fuel cycle

licensees and other

licensees possessing

more than critical

mass quantities of

special nuclear

material.

89-23 Environmental Qualification 3/3/89 All holdersof OLs.

of tttton-VIaItrI Series or CPs for nuclear

Electrical Connectors power reactors.

OL

• Operating License

CP

• Construction Permit

UNITED STATES

NUCLEAR REGULATORY COMMISSION FIRST CLASS MAIL

POSTAGE & FEES PAID

WASHINGTON, D.C. 20555 USNRC

PERMIT No. 0G-7 OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE, $300

IN 89-31 March 22, 1989 No specific action or written response is required by this information notice.

If you have any questions regarding this matter, please contact one of the

technical contacts listed below or the Regional Administrator of the appropri- ate regional office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: S.L. Wu, NRR

(301) 492-1065 L. Phillips, NRR

(301) 492-3235 Attachment: List of Recently Issued NRC Information Notices

• SEE PREVIOUS PAGE FOR CO RENC;

• IP *C/OGCB:DOEA:NRR *RPB:ARM *D/DEST:NRR

R l RHaLiber CHBerlinger TechEd LCShao

-31/7/89 03/ /89 03/9/89 02/28/89 03/8/89

• O'CB:DOEA:NRR *SR)(B:DEST:NRR *SRXB:DEST:NRR *C/SRXB: DEST: NRR *AD/SAD:DEST:NRR

JGuillen SLWLu LPhillips WHodges AThadani

03/10/89 03/1l/89 03/1/89 03/2/89 03/6/89

IN 89-XX

March xx, 1989 No specific action or written response is required by this information notice.

If you have any questions regarding this matter, please contact one of the

technical contacts listed below or the Regional Administrator of the appropri- ate regional office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: S.L. Wu, NRR

(301) 492-1065 L. Phillips, NRR

(301) 492-3235 Attachment: List of Recently Issued NRC Information Noticesx

D/DOEA:NRR C/OGCB:DOEA:NRR Rie,M DR

CERossi CHBerlinger TechEd L hao

03/ /89 03/ q/p

I on 03/ /89 O s EANRR SRXB:DEST:NRR SRXBI R C/SRXB:.4D£EIRR AD/ AD:D NRR

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03/ W/89 03/i 03 /1 /89 03//89 03/ /89 IPF

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V'3/ 7 /89

March 17, 19B?

NRC INFORMATION NOTICE NO. 89-XX: SWELLING AND CRACKING OF HAFNIUM

CONTROL RODS

Purpose

...

Description of Circumstances

... In addition, there has been

some foreign experience with these hafnium control rods breaking

due to either swelling or hydriding and fretting.