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18 March 2010

Answer to Question #1314 Submitted to "Ask the Experts"

Category: Doses and Dose Calculations — External dose calculations

The following question was answered by an expert in the appropriate field:

How can I estimate the dose to a worker due to gamma radiation emanating from a small crack in the shielding of a storage cask for spent nuclear fuel, say 1 cm thick or less?

What is needed is the gamma dose rate. The gamma dose rate will depend on:

the past history of the fuel (Unused fuel, easy, no dose rate. Very recently used fuel has a huge dose rate at the surface, but this fuel will be stored on site and not be placed in a container),
the number of fuel elements, and
the configuration of the shielding of the storage or transport container.

It's very hard for such a container to crack. It would require some drastic action. If this is a 1 cm long hair-line crack (and the container is probably 10 cm thick), the gamma dose rate will be the same as in the case of no crack.The quantity of shielding material between the fuel element and the outside of the container in the region of the crack will be the same. You could check this with a portable monitor. If this is a 1 cm open hole (how do you manage that?), you will have a collimated beam of high intensity gamma radiation, and the best thing you can do is put a lot of lead over the hole as soon as possible. Don't even think of measuring or calculating it. If a worker has been working in the region of a container which contains a suspected crack, evaluate his personal dosimeter as soon as possible and do area monitoring. John Hunt, PhD

Answer posted on 31 October 2001. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.