Information Notice 1989-78, Failure of Packing Nuts on One-Inch Uranium Hexafluoride Cylinder Valves

Failure of Packing Nuts on One-Inch Uranium Hexafluoride Cylinder Valves

ML031180771
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, 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:	11/22/1989
From:	Cunningham R NRC/NMSS/IMNS
To:
References
IN-89-078, NUDOCS 8911160028
Download: ML031180771 (6)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, D.C. 20555 November 22, 1989 NRC INFORMATION NOTICE NO. 89-78: FAILURE OF PACKING NUTS ON ONE-INCH

URANIUM HEXAFLUORIDE CYLINDER VALVES

Addressees

All U.S. Nuclear Regulatory Commission (NRC) licensees authorized to possess

and use source material and/or special nuclear material for the heating, emptying, filling, or shipping of uranium hexafluoride in 30- and 48-inch

diameter cylinders.

Purpose

This notice is provided to advise licensees about incidents in which packing

nuts on one-inch uranium hexafluoride cylinder valves were found to be cracked.

It is expected that recipients will review the information for applicability

to their activities, distribute it to responsible operations staff, and consider

actions, if appropriate, to identify and correct similar occurrences at their

facilities. However, suggestions contained in this Notice do not constitute any

new NRC requirements, and no written response is required.

Description of Circumstances

Allied-Signal, Inc., has reported that cracks were observed in packing nuts

on three one-inch valves designed for use in 30- and 48-inch diameter uranium

hexafluoride cylinders. The cracks were discovered when the valves were removed

from storage and visually inspected by the licensee. The affected valves were

unused and had been in storage since receipt in early 1987 from the French firm, Descote. Both the U.S. Department of Energy (DOE) and the Canadian Atomic

Energy Control Board have reported similar cracking in packing nuts on one-inch

valves supplied by Superior Valve Company. However, unlike the Descote valves, the Superior valves were in service at the time the cracks were observed.

Cracked nuts on uranium hexafluoride cylinder valves can result in leakage of

uranium hexafluoride through the packing material and valve stem.

DOE's contractor, Martin Marietta Energy Systems, Inc. (MMES), examined one

of the affected Descote valves to determine possible causes of the cracking.

Its investigation found that the failure mode of the packing nut was inter- granular cracking. The metallographic structure of the examined nut was

different from Descote and Superior nuts produced from other bar stock.

89111

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IN 89-78 November 22, 1989 The cracked packing nuts were produced from material designated heat lot R91.

The MMES investigation also indicated that the nut had significant residual

stresses, possibly resulting from surface finishing operations. These findings

suggest that the packing nuts produced from heat lot R91 and/or subjected to

surface grinding are susceptible to stress corrosion cracking.

Descote has also investigated the cracking problem and concluded that the

cracking is the combined result of the following:

1. Excessive stresses placed on the nut by cold flow and thermal expansion

of the teflon packing rings, resulting from retightening of the nut and

repeated heating of the valve;

2. Mechanical and structural characteristics of the packing nut material are

incompatible with these stresses; and

3. The presence of uranium hexafluoride, hydrofluoric acid, and nascent

hydrogen facilitates cracking.

Based on its findings and those of MMES, Descote has recalled all one-inch

valve packing nuts produced from heat lot R91.

Discussion:

The American National Standards Institute (ANSI) provides criteria or packaging

of uranium hexafluoride for transport. The criteria are found in ANSI

N14.1-1987, NUranium Hexafluoride-Packaging for Transport." This standard

provides, in part, specific information on design, fabrication, and assembly

requirements for the one-inch valve installed in uranium hexafluoride cylinders.

The standard states that the valve packing nut is initially to be torqued in

the range of 120 to 150 foot-pounds, to compact the teflon packing rings. If

leakage at the valve stem occurs, the packing nut may be retightened. However, excessive force is not to be used in an attempt to eliminate the leak. The

maximum torque permitted by the standard for retightening the packing nut is

150 foot-pounds.

Although NRC does not consider the cracked packing nut to be a major safety

issue, licensees should consider actions to identify and reduce the occurrence

of cracking. Licensees should review their retightening procedures to ensure

that operators are not misapplying the ANSI torquing requirement by retightening

packing nuts to the maximum torque with each valve use. Furthermore, since

packing nuts are more likely to crack while in service, licensees should have

operators check for cracked packing nuts before and after each valve use.

I .

IN 89-78 November 22, 1989 No written response is required by this information notice. If you have any

questions about this matter, please direct them to the technical contacts

listed below or to the appropriate NRC regional office.

chard E. Cunningm, Directo /

ivision of Industrial and

Medical Nuclear Safety

Technical Contacts: i. Scott Pennington, HMSS

(301) 492-0693 George H. Bidinger, 1MSS

(301) 492-0683 Attachments:

1. List of Recently Issued NMSS Information Notices

2. List of Recently Issued NRC Information Notices

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UNITED STATES FIRT LAS AI

POSTAGE As FEES PAID

NUCLEAR REGULATORY COMMISSION USSNRC

WASHINGTON, D.C. 20555 OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE, $300

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, DC 20555 NOVEMBER , 1989 NRC INFORMATION NOTICE NO. 89-  : FAILURE OF PACKING NUTS ON ONE-INCH

URANIUM HEXAFLUORIDE CYLINDER VALVES

Addressees

All U. S. Nuclear Regulatory Commission (NRC) licensees authorized to possess

and use source material and/or special nuclear material for the heating, emptying, filling, or shipping of uranium hexafluoride in 30- and 48-inch

diameter cylinders.

Purpose

This Notice is provided to advise licensees about incidents in which packing

nuts on one-inch uranium hexafluoride cylinder valves were found to be cracked.

It is expected that recipients will review the information for applicability to

their activities, distribute it to responsible operations staff, and consider

actions, if appropriate, to identify and correct similar occurrences at their

facilities. However, suggestions contained in this Notice do not constitute any

new NRC requirements, and no written response is required.

Description of Circumstances

Allied-Signal, Inc., has reported that cracks were observed in packing nuts on

three one-inch valves designed for use in 30- and 48-inch diameter uranium

hexafluoride cylinders. The cracks were discovered when the valves were removed

from storage and visually inspected by the licensee. The affected valves were

unused and had been in storage since receipt in early 1987 from the French firm, Descote. Both the U.S. Department of Energy (DOE) and the Canadian Atomic

Energy Control Board have reported similar cracking in packing nuts on one-inch

valves supplied by Superior Valve Company. However, unlike the Descote valves, the Superior valves were in service at the time the cracks were observed.

Cracked nuts on uranium hexafluoride cylinder valves can result in leakage of

uranium hexafluoride through the packing material and valve stem.

DOE's contractor, Martin Marietta Energy Systems, Inc. (MMES), examined one of

the affected Descote valves to determine possible causes of the cracking.

Its investigation found that the failure mode of the packing nut was intergranular

cracking. The metallographic structure of the examined nut was different

from Descote and Superior nuts produced from other bar stock. The cracked

IN 89- November , 1989 No written response is required by this Information Notice. If you have any

questions about this matter, please direct them to the technical contacts listed

below or to the appropriate NRC Regional Office.

Richard E. Cunningham, Director

Division of Industrial and

Medical Nuclear Safety

Technical Contacts: W. Scott Pennington, NMSS

(301) 492-0693 George H. Bidinger, NMSS

(301) 492-0683 Attachments:

1. List of Recently Issued

NMSS Information Notices

2. List of Recently Issued

NRC Information Notices

Editor &

EKraus: 11/9 /89 OFC:IMUF: IMUF IMUF: X

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