UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, DC 20555

 October 26, 2004

NRC INFORMATION NOTICE 2004-18: RECENT SAFETY-RELATED EVENT AT

PANORAMIC WET-SOURCE-STORAGE

IRRADIATOR

Addressees:

All licensees authorized to possess and use sealed sources in panoramic wet-source-storage

irradiators, and irradiator vendors.

Purpose:

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

addressees of a recent safety-related incident at a panoramic wet-source-storage irradiator. It

is expected that recipients will review this notice for applicability to their facilities and consider

actions, if appropriate, to avoid similar problems. However, suggestions contained in this IN are

not new NRC requirements; therefore, no specific action nor written response is required.

Description of Circumstances:

On April 21, 2004, an event occurred at an NRC-licensed panoramic wet-source-storage pool

irradiator used for sterilization of medical supplies. The irradiator contains two source racks that

operate simultaneously, each containing approximately 74 petabecquerel (2 million curies) of

cobalt-60, for a total of 148 petabecquerel (4 million curies). The irradiator operator was

experiencing problems with the source rack upper-limit switch (up-switch) and attempted to

repair it. The up-switch’s function is to signal when the source racks are in the raised, exposed

position. Faults occurred after repeated attempts to fix the switch when the sources were raised

to test the repair, causing the safety interlocks to prevent access to the irradiation room. The

alternate radiation safety officer (ARSO) authorized the irradiator operator to defeat the safety

interlocks; enter the irradiator via the product exit barrier door; walk through the irradiation room

(e.g., room where source racks and pool are located); and open the locked personnel access

maze door from inside the room. Defeating safety interlocks to enter the irradiator had been a

practice at this facility for a number of years. The repair required the use of a ladder, which was

placed over the source pool (adjacent to the rack hoist mechanism). After multiple repair

attempts failed during a 6-hour period, the operator forgot to remove the ladder, and with the

supervision of the ARSO, raised and lowered the source racks to test the repairs that had been

made. However, unknown to the operator or ARSO, the ladder jammed against one of the

source racks, preventing it from lowering into the pool and into the safe, shielded position. The

operator and ARSO incorrectly assumed that the control panel indication of an exposed source

rack was a continuation of the source rack switch problem. They believed it was yet another

false indication. Based on this incorrect understanding, the ARSO again authorized the

irradiator operator to defeat safety interlocks and enter the irradiator via the product exit barrier

door. 

ML042950687
IN 2004-18

Page 2 of 4

The operator enlisted the assistance of a materials handler and they entered the irradiator. The

materials handler was not wearing required dosimetry for this entry. On entering the irradiator,

with only one wall of concrete separating them from direct exposure to the stuck source rack,

the operator noticed an unexpectedly high reading on the survey meter and told the material

handler to leave immediately. After leaving the irradiator, the operator informed the ARSO of

the unexpected radiation levels. The two workers received doses of 44 and 28 millisievert (4.4

and 2.8 rem), respectively, in a matter of seconds. 

NRC conducted a special inspection to respond to this event and, upon learning of the potential

for occupational exposure significantly in excess of regulatory limits, dispatched an Augmented

Inspection Team (AIT) to the site. The team was charged with reviewing the circumstances of

the event and determining root causes. Documentation of these inspections can be found in

NRC Inspection Reports 03019882/2004002 [Agencywide Documents Access and Management

System (ADAMS) Accession No. ML041820011] and 03019882/2004003 [ADAMS Accession

No. ML0420300490]. 

The NRC AIT identified the following:

The licensee did not implement its emergency procedures under conditions that required

them to be implemented.

The licensee did not perform surveys that were adequate to ensure that sources were in

a safe storage condition before defeating safety interlocks and entering the irradiator,

although the emergency procedures required this. The irradiator operator did perform a

survey, but did not identify elevated radiation levels before entering the product exit

barrier door. Elevated levels were detected inside the interim area, with only a concrete

wall separating the operator and assistant from the room with the stuck source rack.

Even without implementing the emergency procedure, good radiation safety practices

would have required appropriate radiation surveys before entering the room.

Defeating safety interlocks and entering the irradiation room via the product exit barrier

door and into the interim area of the irradiator had become common practice at this

facility.

Persistent maintenance problems may have existed with the switch systems; however,

problems were repaired individually and the licensee did not identify trends nor

determine if underlying causes existed for the problems, nor if preventive maintenance

would have reduced the number of problems.

Licensee personnel did not have a complete understanding of the operation and use of

the irradiation room’s radiation monitor. For instance, when the source rack is in the

exposed position, the operator could have depressed the monitor test switch on the

control console to verify if the source racks were exposed or shielded. During this event,

the licensee did not use this feature, which could have prevented personnel from

entering the interim area and receiving an unnecessary dose. 
IN 2004-18

Page 3 of 4

There was no clear guidance in the licensee’s operating procedures as to when to

engage the emergency procedures, except during start-up. 

Annual safety training did not always include performance of a drill. When a drill was

done, the same exit maze scenario was used each time. Therefore, the operators were

not drilled on any of the other nine emergency conditions, such as a stuck source 

rack event.

Discussion:

At irradiators, adherence to requirements is critical, because the sources of radiation involved

are capable of delivering life-threatening exposures. If the two employees had continued on

their intended path instead of turning around when they identified elevated radiation levels, each

individual could have received a dose of at least 4.5 gray (450 rad), a potentially lethal

exposure. To be properly protective of health and safety, it is important that licensee

management strongly emphasize safety as the highest priority, accompanied by training,

adherence to procedures, attention to detail, critical self-assessment, and a questioning attitude

toward safety. 

Events regarding exposure of personnel and source rack jams, like the ones just described, are

preventable. NRC expects licensees to train their personnel to recognize an emergency, when

to engage their emergency procedures, and how to prevent a stuck source rack from occurring. 

NRC also expects that licensees will not defeat safety interlocks. Safety interlocks are designed

to ensure the safety of personnel from the intense radiation fields at irradiators. If the access

door(s) are locked, it is important to engage your emergency procedures to verify the location of

the source racks and associated irradiation room dose rates. For this type of irradiator, this

could have been done by: (a) checking the position of the source hoist cables from inside the

penthouse area; (b) verifying known “hot spots” around the irradiator with an operable survey

meter; and/or (c) depressing the monitor test switch on the control console to check for elevated

radiation levels inside the cell.

If appropriate actions, such as the above, indicate that the source racks are in their safe

shielded position, but the interlocks still continue to prevent access, licensees should contact

the irradiator manufacturer to: (1) determine the cause of the interlock activation and (2) to

discuss proper actions to pursue maintenance and repair. The irradiator manufacturer may

provide detailed instructions for entering the irradiator if safety interlocks must be defeated. 

However, this manner of entry is only to be used when absolutely necessary and is not an

accepted routine. As noted above, entry into the irradiator in this case delivered unintended

doses to two individuals because the above steps were not completed, and could have resulted

in lethal doses. 

Although individual licensees are not required to take specific action, they should consider

reviewing the contents of this IN with those responsible for irradiator operations, to reinforce the

need and importance of a fully functional radiation safety program that ensures the safety of 

its employees. 
IN 2004-18

Page 4 of 4

This IN requires no specific action nor 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 regional office.

/RA/

Charles L. Miller, Director

Division of Industrial and 

 Medical Nuclear Safety

Office of Nuclear Material Safety 

 and Safeguards

Technical Contacts: Kathy Modes, RI Betsy Ullrich, RI 

 (610) 337-5251 (610) 337-5040 

 E-mail: kad@nrc.gov E-mail: exu@nrc.gov 

Tom Decker, RI - Atlanta Office

(404) 562-4721

E-mail: trd@nrc.gov

Attachments:

1. List of Recently Issued NRC Information Notices

2. List of Recently Issued NMSS Information Notices
______________________________________________________________________________________

OL = Operating License

CP = Construction Permit

Attachment 1

IN 2004-18

Page 1 of 1

LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

____________________________________________________________________________________

Information Date of 

Notice No. Subject Issuance Issued to

____________________________________________________________________________________

2004-17 Loose Part Detection and 

Computerized Eddy Current

Data Analysis in Steam

Generators

08/25/2004 All holders of operating licenses

for pressurized-water reactors

(PWRs), except those who have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor.

2004-16 Tube Leakage Due to a

Fabrication Flaw in a

Replacement Steam Generator

08/03/2004 All holders of operating licenses

for pressurized-water reactors

(PWRs), except those who have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor.

2004-15 Dual-Unit Scram at Peach

Bottom Units 2 and 3

07/22/2004 All holders of operating licenses

for nuclear power reactors except

those who have permanently

ceased operation and have

certified that fuel has been

permanently removed from the

reactor vessel.

2004-14 Use of less than Optimal

Bounding Assumptions in

Criticality Safety Analysis at

Fuel Cycle Facilities

07/19/2004 All licensees authorized to

possess a critical mass of special

nuclear material.

2004-13 Registration, Use, and Quality

Assurance Requirements for

NRC-Certified Transportation

Packages

06/30/2004 All materials and

decommissioning reactor

licensees.

Note: NRC generic communications may be received in electronic format shortly after they are

issued by subscribing to the NRC listserver as follows:

To subscribe send an e-mail to <listproc@nrc.gov >, no subject, and the following

command in the message portion:

subscribe gc-nrr firstname lastname
______________________________________________________________________________________

OL = Operating License

CP = Construction Permit

Attachment 2

IN 2004-18

Page 1 of 1

LIST OF RECENTLY ISSUED

NMSS INFORMATION NOTICES

____________________________________________________________________________________

Information Date of 

Notice No. Subject Issuance Issued to

____________________________________________________________________________________

2004-14 Use of less than Optimal

Bounding Assumptions in

Criticality Safety Analysis at

Fuel Cycle Facilities

07/19/2004 All licensees authorized to

possess a critical mass of special

nuclear material.

2004-13 Registration, Use, and Quality

Assurance Requirements for

NRC-Certified Transportation

Packages

06/30/2004 All materials and

decommissioning reactor

licensees.

2004-03 Radiation Exposures to

Members of the Public in

Excess of Regulatory Limits

Caused by Failures to Perform

Appropriate Radiation Surveys

During Well-logging Operations

02/24/2004 All well-logging licensees.

2004-02 Strontium-90 Eye Applicators

New Calibration Values and

Use

02/05/2004 All U.S. Nuclear Regulatory

Commission (NRC) medical-use

licensees and NRC master

materials license medical-use

permittees.

2003-22 Heightened Awareness for

Patients Containing Detectable

Amounts of Radiation from

Medical Administrations

12/09/2003 All medical licensees and NRC

Master Materials License medical

use permittees.

2003-21 High-Dose-Rate-RemoteAfterloader Equipment Failure11/24/2003 All medical licensees.

Note: NRC generic communications may be received in electronic format shortly after they are issued by

subscribing to the NRC listserver as follows:

To subscribe send an e-mail to <listproc@nrc.gov >, no subject, and the following command in the

message portion:

subscribe gc-nrr firstname lastname