UNITED STATES 

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR MATERIALS SAFETY AND SAFEGUARDS

WASHINGTON, DC 20555-001

October 31, 2002

NRC INFORMATION NOTICE 2002-31 POTENTIALLY DEFECTIVE UF6 CYLINDER

VALVES (1-INCH)

Addressees:

All licensees authorized to possess and use source material and/or special nuclear material for

the heating, emptying, filling, or shipping of uranium hexafluoride (UF6) in 30- and 48-inch

cylinders.

Purpose:

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to inform

addressees about safety concerns related to UF6 cylinder valves manufactured by the Hunt

Valve Company, Inc., of Salem, Ohio. The two safety concerns involve (1) cracked packing

nuts and (2) the loss of material traceability and failure to conduct hardness testing of the valve

stems. 

NRC anticipates that recipients will review the information for applicability to their facilities and

consider actions, as appropriate, to avoid similar problems. However, suggestions contained

in this information notice do not constitute new NRC requirements; therefore, no specific action

or written response is required.

Description of Circumstances:

Hunt Valve Company is an approved supplier of one-inch and 3/4-inch UF6 cylinder valves for

the United States Enrichment Corporation (USEC) and others. These valves are required to be

manufactured under NQA-1, “Quality Assurance Requirements for Nuclear Facility

Applications,” and ANSI N14.1, “American National Standard for Nuclear Materials - Uranium

Hexafluoride - Packaging for Transport.” On December 4, 2000, Hunt Valve Company made a

10 CFR Part 21 notification concerning discovery of defective packing nuts for one-inch UF6

valves. During visual inspections, several packing nuts were observed to have surface cracks. 

The cracked packing nuts were originally isolated to heat codes AXP and AFD. Subsequently,

additional defective nuts were identified for the following heat codes:

AFM ATE AFB AFC AXN BXN BXP CCF CCG

The NRC has subsequently been informed of several other possible deviations from the

purchase orders that occurred on UF6 valves. Those deviations allegedly involved the loss of

material traceability and the failure to conduct hardness tests for valve stems. Possible suspect

valve stem heat codes are PEN and PFV. The NRC is continuing to investigate this matter, and

will release additional information when it becomes available.

ML023040090
IN 2002-31

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Discussion:

There are two types of UF6 cylinder valves in use in NRC licensed activities (1) a 3/4-inch valve

designated as cylinder valve 51 (by ANSI N14.1) which are not known to be affected by the

defects addressed in this notice and (2) a one-inch valve designated as cylinder valve 50. 

These UF6 valves form part of the pressure boundary for Model No. 30B (30-inch diameter)

cylinders that contain low enriched uranium (up to 5 percent U235) and various 48-inch diameter 

cylinders containing enriched, natural and depleted (tails) uranium. As such, the valves perform

several safety functions.

First, UF6 is a chemically hazardous material. The related hazards involve soluble uranium

toxicity (a heavy metal health threat to the kidneys) and hydrogen fluoride (exterior chemical

burns, interior lung damage due to inhalation and electrolyte imbalance), which is a chemical

reaction by-product that occurs when UF6 is exposed to moisture in the air. Second, both

natural, depleted and low-enriched uranium are slightly radioactive. In addition, for enriched

uranium, nuclear criticality could occur if a sufficient amount of water was accidentally

introduced into a cylinder. 

The UF6 valves perform their intended safety functions in two ways. Before UF6 cylinders are

filled, emptied or sampled, the UF6 is liquified by heating and pressurizing it to well above

atmospheric pressure. When the valve is open, the packing nut serves as a secondary barrier

to prevent leakage past the valve stem. For emptying and sampling UF6 cylinders, the cylinders

are typically heated in a secondary pressure vessel designed to contain any UF6 leakage. 

However, in some applications, UF6 cylinders may be filled with liquid UF6 while the cylinder is

not in such a secondary pressure vessel. 

When the cylinders are put in storage or transported, the valves are closed and the seated

valve stem provides the primary pressure barrier. The barrier provided by the valve is an

important design safety feature during transport of filled cylinders. Transportation containers

must be capable of withstanding normal transport conditions and accidents, including impact,

fire, and water immersion. Radiological and criticality safety of enriched UF6 in transport relies

on the cylinder and valve preventing the release of material and assuring that there is no water

leakage into the cylinder, even in the event of an accident and immersion in water. 

UF6 valves that could have cracked packing nuts or valve stems that do not meet the purchase

order material traceability or hardness requirements may not be able to fully meet the safety

margins required for certain plant operations and transportation, and routine procurement

receipt inspections may not be able to detect all of these deficiencies.
IN 2002 -31

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Related Generic Communications

• Information Notice No. 89-78: “Failure of Packing Nuts on One-Inch Uranium Hexafluoride

Cylinder Valves” dated November 22, 1989.

• Information Notice No. 97-24: “Failure of Packing Nuts on One-Inch Uranium Hexafluoride

Cylinder Valves” dated May 8, 1997.

This information notice does not require any specific action or written response. If you have

any questions about the information in this notice, please contact one of the technical contacts

listed below or the appropriate project manager in the NRC’s Office of Nuclear Material Safety

and Safeguards (NMSS).

/RA/

Robert C. Pierson, Director

Division of Fuel Cycle Safety and Safeguards

Office of Nuclear Material Safety and Safeguards

Technical Contacts: William Troskoski, NMSS Geoffrey Hornseth, SFPO

(301) 415-8076 (301) 415-2756

E-mail: wmt@nrc.gov E-mail: gph@nrc.gov

Attachments:

1. List of Recently Issued NMSS Information Notices

2. List of Recently Issued NRC Information Notices