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UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
WASHINGTON, D.C. 20555-0001
March 1, 1999
NRC INFORMATION NOTICE 99-04: | UNPLANNED RADIATION EXPOSURES TO RADIOGRAPHERS, RESULTING FROM FAILURES TO FOLLOW PROPER RADIATION SAFETY PROCEDURES |
All radiography licensees.
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to remind addressees of the risk of unplanned high radiation exposures from radiography equipment, and the need for proper radiation safety practices to prevent such exposures. The notice was prompted by a series of incidents that have occurred recently and that resulted in unplanned exposures, all of which involved failures to follow proper radiation safety procedures. These incidents did not result in radiation exposures that are expected to lead to serious health effects to the exposed individuals. However, there was the potential, in all cases, for high exposures that could have led to serious health consequences. 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.
An obvious fact about which radiographers should be repeatedly reminded is that, without a suitable instrument such as a survey meter or an alarming rate meter, both of which are required equipment for radiography work, there is no way for them to be sure that the source in a radiography camera is not out of its shield when it should have been shielded. Another fact, maybe not as obvious, that radiographers should be reminded of is that, with a typical radiography source such as 3.7 TBq (100 Ci) of Ir-192, the dose rate at 30.5 cm (1 foot) from the unshielded source is about 4.5 Sv/hr (450 rem/hr). Exposure at a foot from such a source will result in exceeding NRC's annual whole body-dose limit in about 40 seconds. A dose to the whole body of about 2.5 Sv (250 rem) would have a 50 percent chance of being fatal, and could be delivered by a 3.7 TBq (100 Ci) Iridium source a foot away in about half an hour. Such an exposure scenario is unlikely, but it is possible, as for example in a situation where extended preparation work is being done close to a camera with an unshielded source. Another type of severe injury that can result from exposure to such a source is that resulting from localized exposures, such as to the hands. For example, handling the guide tube with the source in it could result in dose rates, to the hand, on the order of 10 gray (Gy) [1,000 rads] per minute. Such dose rates could quickly lead to very serious injury to the skin and underlying tissues.
To avoid serious radiation injury, it is necessary to ensure that people are never close to an unshielded radiography source. Radiography cameras are designed to keep the sources locked in their shields when not in use, but the mechanisms used to accomplish this occasionally fail, either because of mechanical problems or because of improper use. The source may also have been cranked out by one person, without knowledge of another person who may later walk into the work area. In all these cases, there is usually no obvious indication that the source is unshielded. Without the proper instruments, a person would not know that a high radiation field exists in the area, and for this reason good radiation safety practices, as well as NRC's regulations, require the use of radiation detection instruments to ensure that the source is securely in the shielded position after use, or that it is safe to approach a radiography camera or a radiography work area.
The instruments needed for that purpose are ones that give a quick indication that a high radiation field exists. Dosimeters issued to radiographers, such as thermoluminescence dosimeters (TLD), film badges, and pocket dosimeters, do not serve this purpose. TLD and film must be sent away for processing before they can indicate a dose. Pocket dosimeters, although they can be read out in the field, are not suitable because they do not give a sufficiently quick indication of a high radiation field, and also because they are meant to be checked only occasionally during work. The only practical options available to the radiographer in the field are survey instruments and alarming rate meters. A radiation survey instrument is carried by the worker and has a meter that shows the dose rate all the time it is in use. It is the instrument of choice when making sure it is safe to enter an area and to verify that the source is in the shield. At times, however, it may be necessary to set the survey instrument aside to prepare for the next shot, or reposition equipment or barriers. Even though the camera may not be in use at such times, it is still necessary to have an instrument that will continue to monitor for possible high radiation fields without the need to continuously look at a meter. The instrument for this purpose is the alarming ratemeter, usually worn on the worker's belt. It does not require the worker to look at a meter, because it is equipped with an alarm that goes off when the radiation field exceeds a preset level. This alerts the worker to a possible problem.
Survey instruments and alarming ratemeters can fail to work for a variety of reasons, or the meter may appear to be working but may be showing an incorrect dose rate reading. Because of this, and because of the serious dangers involved in using radiography sources, both instruments are required to be used during radiography. They serve different functions, but they also act as backups to each other. Note also that, because these instruments are fairly delicate, they must be checked regularly in the field to make sure they are still working properly. A survey instrument is checked by making sure the batteries have sufficient remaining charge, and also by holding the instrument next to a check source and making sure it reads roughly the dose rate it should read in that position. The user must also be sure the instrument is set to the proper scale. Alarming rate meters are checked by ensuring that the batteries are in good condition, the alarm is set at the proper alarm set point, and the alarm actually sounds when the meter is placed in a sufficiently high test radiation field.
In addition to using ratemeters and alarming dosimeters, radiographers should be reminded to follow proper safety procedures when using radiography equipment. These include, as examples: procedures for properly posting and roping off work area; controlling access to the radiography area during radiography; properly ensuring that the source is actually locked when it is retracted into the camera; periodically checking the camera to make sure that there is no apparent damage, and that moving parts do not show undue wear; and similar actions that ensure that the equipment is in good mechanical condition and that it is operated properly.
This information notice does not require any specific action nor written response. If you have any questions about the information in this information notice, please get in touch with the technical contact listed below, or the appropriate regional office.
Donald A. Cool, Director Division of Industrial and Medical Nuclear Safety Office of Nuclear Material Safety and Safeguards |
Technical Contact: | Bruce Carrico, NMSS 301-415-7826 E-mail:jbc@nrc.gov |
Attachments: | 1. List of Recently Issued NMSS Information Notices 2. List of Recently Issued NRC Information Notices |