Estimated safety assessment of spent nuclear fuel transportation
When transporting spent nuclear fuel in transport packages, it is required to confirm compliance with the requirements of nuclear and radiation safety established in regulatory documents. A comprehensive safety justification includes carrying out a complex of non-trivial, time-consuming calculations from different subject areas of physics. The calculation evaluation is carried out within the framework of complex computational codes (programs), the use of which requires highly qualified users, assumes high-performance computing equipment and, as a rule, the availability of a license to operate a software product. It is obvious that the decision-making procedure, within the framework of the described technology of calculation assessment, takes considerable time and is not always available. In part, this problem is solved by the industry standard OST 95 745-2005 currently in force. It conservatively sets ranges of known fuel characteristics for spent fuel assemblies (SFAS) of VVER-440 and VVER-1000 type reactors: initial enrichment, burnout depth, etc., in accordance with which the requirements of regulatory documents are provided unconditionally. At the same time, there is no need for labor-intensive calculations, and the justification for the safety of SFAS transportation is reduced to confirming compliance with the requirements of the industry standard. However, the degree of conservatism of this approach seems excessive. In addition, the transition of nuclear power with VVER-type reactors to new fuel cycles is currently underway. This transition is accompanied by an increase in initial enrichment and an increase in the depth of fuel burnout. In this case, the characteristics of the fuel assemblies assigned to transportation go beyond the limits of the values given in the regulatory document, which requires a full calculation justification for the safety of transportation of a batch of SFAS. This problem requires the development of a methodology for calculating the safety of transportation, taking into account, on the one hand, the main factors affecting the safety characteristics, and on the other - implemented in the framework of fairly simple computational codes. The article presents the main provisions of simplified methods for assessing the nuclear and radiation safety of SFAS transportation, as well as the results of control calculations.