Issues Concerning the Security and Continued Use of Cesium-137 Irradiators

Sources of Cs-137 greater than 27 Ci (1 TBq) in activity are classifiedas “Radionuclides of Concern” by the U.S. Nuclear RegulatoryCommission (NRC). They fall under “increased controls”that require the owners of these sources to initiate preventativemeasures to decrease the probability of unauthorized and malevolentuse. These controls have been implemented over thepast several years at some cost to the responsible owners who useCs-137 for radiobiological research, medical and pharmaceuticalresearch, blood irradiation, and agricultural sample sterilization.The use of Cs-137 is advantageous in many of these applicationsand aside from the security concerns, has few negative issues.However, because Cs-137 comes in salt form as the easily dispersiblechloride CsCl, the NRC had been directed by the U.S.Congress to investigate if it could be replaced. The results of aNational Research Council investigation requested by NRC andan NRC-sponsored public workshop provide an interesting insightinto the conflicting needs of source users, regulatory/securityoversight, and the financial implications of replacement withother radiation generating devices. This paper is a summary ofthe security concerns regarding the use of CsCl and the NRC’sapproach to mitigating those concerns based on the 2008 NRCworkshop and subsequent NRC publications.