Information Notice 2000-02, Failure of Criticality Safety Control to Prevent Uranium Dioxide UO2 Powder Accumulation

Failure of Criticality Safety Control to Prevent Uranium Dioxide UO2 Powder Accumulation

ML003685215
Person / Time
Issue date:	02/22/2000
From:	Weber M NRC/NMSS/FCSS/FCOB
To:
Burrows S
References
IN-00-002
Download: ML003685215 (6)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, D.C. 20555 February 22, 2000

NRC INFORMATION NOTICE 2000-02: FAILURE OF CRITICALITY SAFETY CONTROL TO

PREVENT URANIUM DIOXIDE (UO2) POWDER

ACCUMULATION

Addressees

All Nuclear Regulatory Commission (NRC) licensed fuel-cycle conversion, enrichment, and

fabrication facilities.

Purpose

The NRC is issuing this information notice to alert addressees to a problem recently noted with

safety-significant level probes that are not self-checking. A level probe in a uranium dioxide

(UO2) powder hopper failed without indicating a failed condition due to a broken connector in

the level-probe circuit. This allowed UO2 powder to accumulate in a hopper and approach the

criticality safety mass limit before discovery. Recipients are expected to review this information

for applicability to their facilities and consider actions, as appropriate, to avoid similar problems.

Suggestions contained in this information notice are not NRC requirements. Therefore, no

specific action nor written response is required.

Description of Circumstances

On August 5, 1999, a fuel cycle facility operator noticed that dry UO2 powder was not coming

out of a granulator while the granulator was operating. Powder was being automatically fed to

the equipment at the time and a level probe was monitoring the powder level in the feed hopper

as a primary nuclear criticality safety control. The licensee determined that powder had blocked

the compaction section of the granulator and an unusual amount of dry UO2 powder had

accumulated in the powder hopper. The powder accumulation was not detected by the level- probe on the feed hopper because the probe had failed due to a broken connector in the level- probe circuit.

Discussion:

A fuel cycle licensee achieves uniform fuel particle size with equipment that compacts UO2 powder into a ribbon and then grinds up the compacted powder. Powder is added to the

equipment from safe-geometry containers called polypacks. A known difficulty with this

ML003685215 Template: NRR-052

IN 2000-02

2000-02 equipment is that the ribbon of compacted UO2 can jam and block the material flow. The safety

of the operation was assured by limiting mass and moderator in the equipment. Primary

criticality safety controls on mass included operator monitoring of the equipment, an interlock

system limiting the number of polypacks that can be added, and a level-probe in the powder

hopper that feeds the compactor.

An operator assigned to the compactor/granulator equipment observed that powder was not

coming out of the granulator while the equipment was in operation and powder was being

automatically fed to the compactor. The operator subsequently discovered that an unusual

amount of dry UO2 powder had accumulated in the hopper that feeds the compactor. Licensee

investigation revealed that the powder hopper level-probe, which was intended to detect this

type of failure, did not work due to a broken connector in the level-probe circuit. Additionally, the licensee determined that the limit on the number of polypacks that could be added to the

powder hopper was set too high to prevent the mass limit in the hopper from being reached.

Also the licensee determined that required visual checks for powder accumulation were set at

twice per shift without specific instructions on the required interval. Operators were allowed to

perform the checks at the beginning and end of a shift which was too long an interval to ensure

that the mass of UO2 powder did not exceed the mass limit in the hopper.

The primary contributing factor to the event was that the level-probe on the compactor/

granulator powder hopper did not self-indicate failure and alert the licensee to a lost control. A

properly functioning level probe would have indicated the powder accumulation in the hopper

before the powder approached safety limits. A self-indicating circuit would have informed the

licensee of probe failure so that corrective actions could be taken to restore the control.

Additional contributing factors were that the limit on the number of polypacks automatically

added to the hopper was set too high to protect against exceeding the mass limit and that the

interval between required visual checks was allowed to be too long to assure that

accumulations would be seen before the mass limit was exceeded.

This event highlights the need to establish the availability and reliability of safety-significant

controls involving nuclear criticality safety under all credible upsets. Licensees should evaluate

the need for safety-significant electronic equipment to be self-checking. Licensees should also

establish that supporting criticality safety controls will actually perform their intended function.

IN 2000-02

2000-02 It is expected that addressees will evaluate the above information for applicability to licensed

activities. This information notice requires no specific actions nor written response. If you have

any questions about the information in this notice, please contact the technical contact listed

below or the appropriate regional office.

Michael F. Weber, Director

Division of Fuel Cycle Safety

and Safeguards

Office of Nuclear Material Safety

and Safeguards

Sheryl A. Burrows, NMSS

301-415-6667 E-mail: sab2@nrc.gov

Attachments:

1. List of Recently Issued NMSS Information Notices

2. List of Recently Issued NRC Information Notices

IN 2000-02

2000-02 It is expected that addressees will evaluate the above information for applicability to licensed

activities. This information notice requires no specific actions nor written response. If you have

any questions about the information in this notice, please contact the technical contact listed

below or the appropriate regional office.

Michael F. Weber, Director

Division of Fuel Cycle Safety

and Safeguards

Office of Nuclear Material Safety

and Safeguards

Sheryl A. Burrows, NMSS

301-415-6667 E-mail: sab2@nrc.gov

Attachments:

1. List of Recently Issued NMSS Information Notices

2. List of Recently Issued NRC Information Notices

FILE NAME: a:\in2000-02.wpd

• See previous concurrences

OFC TECH ED FCOB FCOB FCOB IMNS FCSS

NAME EKrauss* SBurrows* WSchwink* PTing* KRamsey* MWeber*

DATE 01/21/00 01/3100 02/4/00 02/7/00 02/4/00 02/14/00

C = COVER E = COVER & ENCLOSURE N = NO COPY

OFFICIAL RECORD COPY

Attachment1

IN 2000-02 February 22, 2000 LIST OF RECENTLY ISSUED

NMSS INFORMATION NOTICES

_____________________________________________________________________________________

Information Date of

Notice No. Subject Issuance Issued to

_____________________________________________________________________________________

99-33 Management of Wastes 12/28/99 All medical licensees

Contaminated With

Radioactive Materials

99-32 The Effect of the Year 2000 12/17/99 All NRC medical licensees

Issues on Medical Licensees

99-31 Operational Controls to Guard 11/17/99 All NRC licensed fuel cycle

Against Inadvertent Nuclear conversion, enrichment and

Critically fabrication facilities

99-30 Failure of Double Contingency 11/8/99 All fuel cycle licensees and

Based on Administrative certificates performing laboratory

Controls Involving Laboratory analysis to determine uranium

Sampling and Spectroscopic content, in support of

Analysis of Wet Uranium administrative criticality safety

Waste controls

99-29 Authorized Contents of Spent 10/28/99 All power reactor licensees and

Fuel Casks spent fuel storage licensees and

applicants

99-28 Recall of Star Brand Fire 9/30/99 All holders of licenses for nuclear

Protection Sprinkler Heads power, research and test

reactors, and fuel cycle facilities

99-27 Malfunction of Source 9/2/99 All medical licensees authorized

Retraction Mechanism in to conduct teletherapy treatments

Cobalt-60 Teletherapy

Treatment Units

99-26 Safety and Economic 8/24/99 All Distributors and/or

Consequences of Misleading Manufacturers of Generally

Marketing Information Licensed Products

99-24 Broad-Scope Licensees 7/12/99 All medical licensees of broad- Responsibilities for Reviewing scope and master materials

and Approving Unregistered licensees

Sealed Sources and Devices

Attachment

IN 2000-02 February 22, 2000 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

_____________________________________________________________________________________

Information Date of

Notice No. Subject Issuance Issued to

_____________________________________________________________________________________

2000-01 Operational Issues Identified in 2/11/2000 All holders of licenses for nuclear

Boiling Water Reactor Trip and power reactors

Transient

99-34 Potential Fire Hazard in the 12/28/99 All holders of licenses for nuclear

use of Polyalphaolefin in reactors and fuel cycle facilities

Testing of Air Filters

99-33 Management of Wastes 12/28/99 All medical licensees

Contaminated With

Radioactive Materials

99-32 The Effect of the Year 2000 12/17 All NRC medical licensees

Issues on Medical Licensees

99-31 Operational Controls to Guard 11/17/99 All NRC licensed fuel cycle

Against Inadvertent Nuclear conversion, enrichment and

Criticality fabrication facilities

99-30 Failure of Double Contingency 11/8/99 All fuel cycle licensees and

Based on Administrative certificates performing laboratory

Controls Involving Laboratory analysis to determine uranium

Sampling and Spectroscopic content, in support of

Analysis of Wet Uranium administrative criticality safety

Waste controls

99-29 Authorized Contents of Spent 10/28/99 All power reactor licensees and

Fuel Casks spent fuel storage licensees and

applicants

99-01, Rev. 1 Degradation of Prestressing 10/7/99 All holders of operating licensees

Tendon Systems in for nuclear power reactors

Prestressed Concrete

Constrainments

99-28 Recall of Star Brand Fire 9/30/99 All holders of licenses for nuclear

Protection Sprinkler Heads power, research and test

reactors, and fuel cycle facilities

____________________________________________________________________________________

OL = Operating License

CP = Construction Permit