UNITED STATES

 NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, DC 20555

March 10, 2005

NRC INFORMATION NOTICE 2005-05: IMPROVING MATERIAL CONTROL AND

ACCOUNTABILITY INTERFACE WITH

CRITICALITY SAFETY ACTIVITIES AT FUEL

CYCLE FACILITIES

ADDRESSEES

All licensees authorized to possess a critical mass of special nuclear material.

PURPOSE

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

addressees of a safety concern related to criticality safety at fuel fabrication and other facilities

processing, storing, or handling critical masses of fissile material. The safety concern arises

when licensees fail to establish and maintain a communication process between criticality safety

staff and material control and accountability (MC&A) staff, in order to support timely

identification of fissile material-related process upsets that challenge the criticality safety basis

for the facility. It is expected that licensees will review this information and consider actions, as

appropriate, to avoid similar problems. Suggestions contained in this IN are not NRC

requirements; therefore, no specific action nor written response is required.

DESCRIPTION OF CIRCUMSTANCES

Under 10 CFR Parts 70 and 76, certain licensees processing, storing, or handling critical

masses of fissile material are required to analyze accident scenarios leading to criticality and

provide reliable controls to assure that inadvertent criticality events are highly unlikely. 

Recently, a licensee reported an event, to the NRC, concerning operation of an incinerator

outside of the approved safety basis. The licensee had performed a criticality safety evaluation

of the incinerator approximately 8 years previously and had concluded that criticality was not

credible outside of the primary combustion chamber. 

The licensee nuclear criticality safety (NCS) analysis focused on accumulation of sufficient

mass in the incinerator system to support criticality. Licensee NCS engineers concluded that

very limited amounts of ash would carry over from the incinerator primary combustion chamber

to the remainder of the incinerator system and that mass controls on the primary combustion

chamber would limit uranium concentration in the ash to less than 21.6 percent throughout the

incinerator system. This led the licensee’s NCS engineers to conclude that criticality outside the

primary combustion chamber was not credible due to normal operations and expected

upsets.

ML050590234
IN 2005-05

Page 2 of 3

At the time that this NCS analysis was approved, licensee MC&A staff possessed sampling data

showing concentration levels above 21.6 percent uranium in some parts of the incinerator

system. In addition, licensee MC&A staff were aware, from approximately 15 years of

operational experience, that substantial amounts of fissile material routinely accumulated in

parts of the incinerator system where criticality analysis assumed minimal accumulation.

The material accumulation event was identified initially when a licensee criticality safety

engineer reviewed MC&A sampling data. Subsequent investigation of the event by the licensee

revealed that ash deposits at various locations in the incinerator routinely exceeded the 

21.6 percent uranium concentration assumed to be bounding for ash and that the mass of ash

deposited also exceeded expectations. Licensee review of MC&A sampling records confirmed

that both concentration and deposit information were known prior to approval of the original

NCS analysis.

The amount of fissile material that accumulated in the uncontrolled parts of the incinerator

system exceeded a critical mass. Extensive investigation by the licensee and the NRC revealed

a poor interface between licensee criticality safety and MC&A staff. This poor interface,

resulting from failing to require routine interaction, apparently was a factor in the failure to

identify the process upset before the event occurred.

Discussion

Two issues from this event are of concern to the NRC. The first issue is that licensee NCS staff

had not ensured that MC&A staff were familiar with the criticality safety basis for the incinerator

system. Specifically, MC&A staff were not aware of the basic assumption that fissile material

would not accumulate in the upper chamber or flue. Had MC&A staff been made aware of this

assumption, they would likely have identified the reality of incinerator ash deposition and

caused the NCS staff to place additional criticality controls on at least those two sections of the

incinerator system.

The second issue is that the MC&A sampling data routinely reported mass and concentration

values that challenged the criticality safety basis, and this fact was not recognized by criticality

safety engineers because the data were not routinely provided to them.

Licensee NCS staff are familiar with the criticality safety basis and underlying assumptions. 

MC&A staff have a general knowledge of where material is currently located and where process

hold-up is likely to occur. Communication between these two organizations is necessary to

assure that the criticality safety basis is not violated.

Failure to establish appropriate interactions between criticality safety and MC&A staff exposes

fuel cycle licensees to this type of programmatic failure. Licensees should consider actions, as

appropriate, to mitigate this vulnerability. NCS staff should be familiar with MC&A sampling

methodology and data reporting and should routinely review MC&A reports for location of

material in relation to the criticality safety basis. MC&A staff should be trained on the criticality
IN 2005-05

Page 3 of 3

safety basis, particularly bounding assumptions about fissile material accumulation, and should

routinely review new or changed NCS analyses.

This IN requires no specific action nor written response. If you have any questions about the

information in this notice, please contact the technical contact listed below.

/RA/

Robert C. Pierson, Director

Division of Fuel Cycle Safety 

 and Safeguards

Office of Nuclear Material Safety 

 and Safeguards

Technical Contact: Dennis Morey, NMSS

301-415-6107

e-mail: dcm@nrc.gov

Attachment: List of Recently Issued NMSS Generic Communications
Attachment 

IN 2005-05

Page 1 of 1

Recently Issued NMSS Generic Comminications

Date GC No. Subject Addressees

12/16/2004 RIS-04-020 NRC Regulatory issue

Summary 2004-20:

Lessons Learned from

Review of 10 CFR Parts 71

and 72 Applications

All holders of, and applicants for,

a (1) 10 CFR Part 71 certificate

of compliance for a radioactive

material transportation package;

(2) 10 CFR Part 72 cretificate of

compliance for a spent fuel

storage cask; and (3) 10 CFR

Part 72 specific license for an

independent spent fuel storage

installation (ISFSI).

12/01/2004 RIS-04-018 NRC Regulatory Issue

Summary 2004-18:

Expiration Date for 10 CFR

Part 71 Quality Assurance

Program Approvals

All holders of U.S. Nuclear

Regulatory Commission (NRC)-

approved 10 CFR Part 71 Quality

Assurance Programs (QAPs).

11/23/2004 RIS-04-017 NRC Regulatory Issue

Summary 2004-17:

Revised Decay-in-Storage

Provisions for the Storage

of Radioactive Waste

Containing Byproduct

Material

All licensees regulated under 10

CFR Parts 30, 32, 33, and 50.

10/26/2004 IN-04-018 Recent Safety-Related

Event at Panoramic

Wet-source-Storage

Irradiator

All licensees authorized to 

possess and use sealed sources

in panoramic wet-source-storage

irradiators, and irradiator

vendors.

07/19/2004 IN-04-014 Use of less than Optimal

Bounding Assumptions

in Criticality Safety Analysis

at Fuel Cycle Facilities

All licensees authorized to

possess a critical mass 

of special nuclear material 

Note: NRC generic communications may be found on the NRC public website,

http://www.nrc.gov, under Electronic Reading Room/Document Collections.