Information Notice 1996-35, Failure of Safety Systems on Self-Shielded Irradiators Because of Inadequate Maintenance and Training

Failure of Safety Systems on Self-Shielded Irradiators Because of Inadequate Maintenance and Training
	ML031060046
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000442, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	06/11/1996
From:	Cool D; NRC/NMSS/IMNS
To:	;
References
	IN-96-035, NUDOCS 9606060078
	Download: ML031060046 (8)
	v • d • e

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS

WASHINGTON, D.C. 20555 June 11, 1996 NRC INFORMATION NOTICE 96-35: FAILURE OF SAFETY SYSTEMS ON SELF-SHIELDED

IRRADIATORS BECAUSE OF INADEQUATE MAINTENANCE

AND TRAINING

Addressees

All U.S. Nuclear Regulatory Commission irradiator licensees and vendors.

Purpose

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

notice (IN)to alert addressees to two incidents where safety interlocks on

self-shielded irradiators (Category I) failed to prevent inadvertent exposure.

The causes of these exposures stemmed from a lack of appropriate maintenance

and/or worker training. The incidents include a broken spring -- possibly

causing malfunction of the safety interlock -- and a worker who intentionally

bypassed a safety interlock. It is expected 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 are not NRC requirements; therefore, no specific

action nor written response is required.

Description of Circumstances

The first incident occurred when an operator may have been able to open the

shielded door of an irradiator with the sources in the exposed position.

After irradiation of several pocket dosimeters, the operator opened the

shielded door of the irradiator to retrieve the dosimeters, but did not

perform a radiation survey, as required by the facility's internal procedures, before opening the door. Twice, the operator placed one hand inside the

irradiator to retrieve the dosimeters. Subsequently, the operator observed

that the unit timer continued to count, indicating that the sources remained

in the exposed position. The operator checked his personal pocket dosimeter, but did not note an unusual reading. However, the operator did not report the

incident until questioned by the radiation safety officer, who had noted an

unusually high dosimetry report of 3.55 millisievert (355 mrem) deep dose

equivalent for the worker. The dose to the right hand was calculated to be a

maximum of 12.5 millisievert (1.25 rem).

The design of the irradiator includes two interconnected interlock systems, intended to prevent unshielded exposure of the sources. These include a door

interlock system -- designed to allow opening of the shielded door only after

the sources are placed in the fully shielded position -- and a source exposure-.

interlock system -- designed to secure the sources in the fully shielded

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IN 96-35 June 11, 1996 position whenever the shielded door is open or unlocked. The manufacturer of

the irradiator indicated that under normal operations, either system

individually wouldiprevent inadvertent access to the unshielded sources.

Following the incident, the manufacturer of the irradiator was requested to

perform an onsite inspection of the irradiator and facilities. During the

inspection, the manufacturer noted:

(1) the irradiator was located in an area that was not climate- controlled;

(2) internal components of the irradiator were in a degraded state;

(3) maintenance of the irradiator had last been performed approximately

10 years ago; and

(4) a return spring, integral to the source exposure safety interlock

system, was broken. The manufacturer indicated that the lack of

environmental control may have accelerated the degradation of the

internal components of the irradiator, and that the lack of periodic

maintenance of the irradiator may have contributed to the failure of

the return spring.

The broken return spring may have caused the source securing mechanism of the

source exposure interlock system to malfunction, possibly allowing exposure of

the sources after the shielded door was unlocked and opened. However, during

the post-incident investigation, neither the manufacturer nor the licensee

were able to identify a failed component of either interlock system that could

have allowed the shielded door to be opened with the sources in the exposed

position. The manufacturer indicated that the design of the source exposure

mechanism -- the operator must manually move the sources from the shielded to

the exposed position with a lever -- would have provided the operator with a

positive indication of source position even if the interlock systems failed.

Source position would have been further provided by a series of green and red

source position lights on the irradiator.

The operator's actions indicate either a lack of training on the proper

functioning and use of the irradiator, a lack of understanding of the training

provided, and/or a disregard for following the established operating and

safety procedures. The operator indicated that the timer continued to count

when the shielded door was opened. However, the manufacturer reported that

the timer automatically activates whenever the source lever is manually moved

to one of the two source exposed positions and the lever is fully engaged in

the source slot, and stops counting as soon as the lever is moved from the

fully engaged position. The fact that the timer continued to count indicates

that the operator had not moved the sources from the fully exposed and engaged

position. The licensee reported that the operator had been trained in the

operation of the irradiator and was listed as an authorized user, but that the

irradiator was used infrequently and that this was only the operator's second

use of the irradiator since being trained.

The second incident occurred when a maintenance worker preparing to perform

maintenance on an irradiator bypassed the irradiator door interlock system to

observe movement of the inner irradiation chamber. The maintenance was being

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IN 96-35 June 11, 1996 performed to correct previous maintenance that resulted in the irradiator not

functioning properly. The maintenance worker was unaware that, although the

sources remained shielded during movement of the irradiation chamber from the

load to irradiate position, high levels of radiation scatter would be present.

The maintenance worker, upon hearing the in-room monitor alarm, immediately

returned the radiation chamber to the 'load' position (maximum shielding).

Although the maintenance worker was familiar with the operation of the

irradiator and had been responsible for its maintenance for nearly 15 years, the worker apparently had not been given formal training on radiation safety

or the operation and maintenance of the irradiator. The maintenance worker

was not aware of the scatter radiation and assumed that since the sources were

not directly exposed, radiation from the sources would be contained within the

device.

During this incident, another worker, hired to perform contract maintenance on

the irradiator, was also in the room near the irradiator. Neither worker wore

dosimetry nor had any documented training in radiation safety. Therefore, their doses could only be calculated based on their recollection and were

estimated to both be approximately 4 microsievert (0.4 mrem) whole body.

Discussion

Although neither incident resulted in doses in excess of regulatory limits, the doses received in both incidents were unnecessary and possibly could have

been avoided with proper training and routine equipment maintenance. A

similar incident in 1984, where a door interlock failed, resulted in the

operator being exposed to 222 terabequerel (6000 curies) of cesium-137.

The first incident clearly demonstrates the need to perform appropriate

maintenance on these types of units. Even though these units are designed

with interlocks and safety features intended to prevent inadvertent exposures, the components of these systems depend on adequate maintenance to function

properly. Failure to properly maintain these systems and provide appropriate

training could result in unnecessary exposures. Manufacturers of these types

of irradiators frequently provide initial and periodic training on the

operation of their units and, in some cases, training on other manufacturers'

units, as well. Initial training is typically a condition of the license and, therefore, must be provided to all irradiator users and maintenance personnel.

Periodic refresher training is also beneficial as a reminder for working

safely around the irradiator and provides for a means to receive or

disseminate additional or updated information.

In addition, most manufacturers have a recommended schedule of maintenance

and/or recommended preventative/periodic maintenance that should be performed.

Users of these types of irradiators should evaluate their usage to determine

the applicability of the recommended maintenance to their situation and usage.

Users who operate their unit more than usual or who use their units under

harsh conditions should consider the need for stepped-up maintenance or

'-> IN 96-35 June 11, 1996 shortened maintenance intervals. In addition, each manufacturer's recommended

maintenance may vary according to the specific unit or type of use.

Therefore, personis performing maintenance on their unit may require specific

maintenance training for their unit.

Users who are not aware of the required training for their unit, or who wish

to receive information concerning training in general, should consult their

license, licensing authority, or the manufacturer of the unit. Regulatory

Guide 10.9, provides additional guidance in this area and may assist persons

who wish to develop a training and maintenance program. Users who wish to

receive additional information concerning recommended maintenance for their

unit should contact the manufacturer of the unit. In addition, third-party

service companies may also be available for training and maintenance services

for these types of irradiators.

This information notice 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.

I3W¶flstn 8 by9WWstIA

Donald A. Cool, Director

Division of Industrial and

Medical Nuclear Safety

Office of Nuclear Material Safety

and Safeguards

Technical contacts: Douglas Broaddus, NMSS

(301) 415-5847 Internet:dab~nrc.gov

Anthony Kirkwood, NMSS

(301) 415-6140

Internet:ask~nrc.gov

Attachments:

1. List of Recently issued NMSS Information Notices

2. List of Recently issued NRC Information Notices

DOCUMENT NAME: 96-35.IN

To receive a copy of this document, Indicate In the box: C' = Copy without attachment/enclosure *E' - Copy with attachmentjendosure N

No copy

See previous concurrence

OFFICE IIMAB* [ClIMAB* [C Tech Editor* l IMOB* [C IMNS* I C,

NAME IDBroaddus* LCamper lEKraus _KRamsey jDCof'

DATE 14/17/96 5/28/96 4/01/96 5/31/96 6/4 96 11 OFFICIAL RECORD COPY

j;

IN 96-XX

May XX, 1996 Users who are not aware of the required training for their unit, or who wish