UNITED STATES 

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, D.C. 20555

October 31, 2005

NRC INFORMATION NOTICE 2005-28: INADEQUATE TEST PROCEDURE FAILS TO

DETECT INOPERABLE CRITICALITY ACCIDENT

ALARM HORNS

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 concern related to criticality alarms at fuel fabrication facilities, nuclear power

plants, and other facilities processing, storing, or handling critical masses of fissile material. 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 70.24 and 10 CFR 76.89, certain licensees possessing, storing, or handling

critical masses of fissile material are required to maintain a criticality accident alarm system that

is capable of detecting the minimum accident of concern in fissile material operations and

annunciating a clearly audible signal that will cause the immediate evacuation of affected

persons to a safe location. All areas of fuel cycle facilities licensed under these regulations are

required to be covered by event detection and alarm signaling devices. In addition, certain 10

CFR Part 50 licensees are required, as part of their licensing basis for new and spent fuel

storage, to maintain a criticality accident alarm system in accordance with the 10 CFR Part 70

regulations.

A fuel cycle licensee conducted monthly tests of the site criticality accident alarm system by

sounding the horns while designated employees listened for the alarm. The licensee relied on

all employees to report questionable alarm audibility. Subsequent to a recent routine criticality

alarm system test at the facility, a licensee maintenance manager questioned audibility and

directed maintenance staff to check all criticality accident alarm horns in the system. The horn

operability check resulted in the discovery that eight horns were inoperable and that the

criticality alarm system was inaudible at several exterior locations.

The fuel cycle licensee in this situation used multiple, independent criticality accident alarm

detector/annunciator systems to accomplish coverage of the facility. The licensee facility was

physically large, and used several independent criticality alarm systems. Multiple, independent

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IN 2005-28

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criticality alarm systems were used because the licensee desired that employees only evacuate

if they would be affected by the criticality event detected as defined by horn audibility. Detector

and annunciator (horn) coverage of exterior areas was not fully redundant, resulting in the

necessity for individual systems to be able to annunciate events in their area of coverage

without the assistance of other systems. Four out of five horns on one exterior system became

inoperable over time so that an alarm from that system could not be heard in a large portion of

its area of coverage, including locations with high ambient noise levels and the interior of two

buildings containing non-fissile operations.

DISCUSSION

The criticality alarm concern arises when licensees fail to detect inoperable criticality alarm

system annunciators (horns) during routine testing, and an inaudible criticality alarm situation is

not corrected. Two factors contributed to the problem. First, the test procedure sounded horns

in groups and did not routinely check individual horns for operability. Inoperable horns were not

always detected during the criticality alarm routine tests and, in fact, could go undetected until

many horns were inaudible and a large part of the facility was not receiving an audible alarm. 

Second, the licensee relied on all employees to report inaudibility, but employees did not fully

understand requirements for criticality alarm horn response during system audibility testing. In

fact, employees were trained to react only to audible alarms. The affected buildings involved

intermittent work operations so that, even though the criticality alarm system horns involved

were rated at approximately 100 decibels, employees working in the area did not recognize that

the horns never sounded.

The NRC concern about this issue is that failure to adequately test a criticality alarm system for

audibility may cause an inaudible condition to go undetected for an indefinite amount of time. 

This event likely occurred because licensee training did not result in employees understanding 

that inoperable horns in a work area were required to be reported and testing procedures did

not result in detection and correction of inoperable horns.

Failure to maintain audibility of the criticality alarm system exposes licensees to the possibility

that affected employees will not evacuate during an actual criticality event. NRC inspections of

criticality alarm systems typically include review of criticality accident alarm audibility test

procedures, employee emergency response training, criticality accident alarm detector/

annunciator coverage, and criticality accident alarm outage procedures.
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CONTACT

This information notice does not require any specific action or written response. Please direct

any questions about this matter to the technical contact below, or the appropriate

regional office.

/RA/ /RA/

Patrick L. Hiland, Chief Robert C. Pierson, Director

Reactor Operations Branch Division of Fuel Cycle Safety

Division of Inspection Program Management and Safeguards

Office of Nuclear Reactor Regulation 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 2005-28

 Page 1 of 3

Recently Issued NMSS Generic Communications

Date GC No. Subject Addressees

2/11/05 BL-05-01 Material Control and

Accounting at Reactors and

Wet Spent Fuel Storage

Facilities

All holders of operating licenses

for nuclear power reactors,

decommissioning nuclear power

reactor sites storing spent fuel in

a pool, and wet spent fuel storage

sites.

8/25/05 RIS-05-18 Guidance for Establishing

and Maintaining a Safety

Conscious Work

Environment

All licensees, applicants for

licenses, holders of certificates of

compliance, and their contractors

subject to NRC authority

8/10/05 RIS-05-16 Issuance of NRC

Management Directive 8.17,

“Licensee Complaints

Against NRC Employees”

All licensees and certificate

holders.

8/3/05 RIS-05-15 Reporting Requirements for

Damaged Industrial

Radiographic Equipment

All material licensees possessing

industrial radiographic equipment,

regulated under 10 CFR Part 34.

7/13/05 RIS-05-13 NRC Incident Response and

the National Response Plan

All licensees and certificate

holders.

7/11/05 RIS-05-12 Transportation of

Radioactive Material

Quantities of Concern NRC

Threat Advisory and

Protective Measures System

Licensees authorized to possess

radioactive material that equals or

exceeds the threshold values in

the Additional Security Measures

(ASM) for transportation of

Radioactive Material Quantities of

Concern (RAMQC) under their 10

CFR Part 30, 32, 50, 70, and 71

licenses and Agreement State

licensees similarly authorized to

possess such material in such

quantities under their Agreement

State licenses.

7/11/05 RIS-05-11 Requirements for Power

Reactor Licensees in

Possession of Devices

Subject to the General

License Requirements of 10

CFR 31.5

All holders of operating licenses

for nuclear power reactors and

generally licensed device

vendors.
Attachment

IN 2005-28

Page 2 of 3

Recently Issued NMSS Generic Communications

Date GC No. Subject Addressees

6/10/05 RIS-05-10 Performance-Based

Approach for Associated

Equipment in 10 CFR 34.20

All industrial radiography

licensees and manufacturers and

distributors of industrial

radiography equipment.

4/18/05 RIS-05-06 Reporting Requirements for

Gauges Damaged at

Temporary Job Sites

All material licensees possessing

portable gauges, regulated under

10 CFR Part 30.

4/14/05 RIS-05-04 Guidance on the Protection

of Unattended Openings

that Intersect a Security

Boundary or Area

All holders of operating licenses

or construction permits for nuclear

power reactors,

research and test reactors,

decommissioning reactors with

fuel on site, Category 1 fuel cycle

facilities, critical mass facilities,

uranium conversion facility,

independent spent fuel storage

installations, gaseous diffusion

plants, and certain other material

licensees.

2/28/05 RIS-05-03 10 CFR Part 40 Exemptions

for Uranium Contained in

Aircraft Counterweights -

Storage and Repair

All persons possessing aircraft

counterweights containing

uranium under the exemption in

10 CFR 40.13(c)(5).

10/07/05 IN-05-27 Low Dose-Rate Manual

Brachytheraphy Equipment

Related Medical Events

All medical licensees.

7/29/05 IN-05-22 Inadequate Criticality Safety

Analysis of Ventilation

Systems at Fuel Cycle

Facilities

All licensees authorized to

possess a critical mass of special

nuclear material.

6/23/05 IN-05-17 Manual Brachytherapy

Source Jamming

All medical licensees authorized

to possess a Mick applicator.
Attachment

IN 2005-28

Page 3 of 3

Recently Issued NMSS Generic Communications

Date GC No. Subject Addressees

5/17/05 IN-05-13 Potential Non-conservative

Error in Modeling Geometric

Regions in the

Keno-v.a Criticality Code

All licensees using the Keno-V.a

criticality code module in

Standardized Computer Analyses

for Licensing Evaluation (SCALE)

software developed by Oak Ridge

National Laboratory (ORNL)

5/17/05 IN-05-12 Excessively Large Criticality

Safety Limits Fail to Provide

Double Contingency at Fuel

Cycle Facility

All licensees authorized to

possess a critical mass of special

nuclear material.

4/7/05 IN-05-10 Changes to 10 CFR Part 71

Packages

All 10 CFR Part 71 licensees and

certificate holders.

4/1/05 IN-05-07 Results of HEMYC Electrical

Raceway Fire Barrier

System Full Scale Fire

Testing

All holders of operating licenses

for nuclear power reactors, except

those who have

permanently ceased operations

and have certified that fuel has

been permanently removed

from the reactor vessel, and fuel

facilities licensees.

3/10/05 IN-05-05 Improving Material Control

and Accountability Interface

with Criticality Safety

Activities 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.