Abstract
The criticality safety control technique is required for the fuel debris removal from the Fukushima Dai-Ichi Nuclear Power Station which experienced a severe accident. The subcriticality estimation is expected to be done with only limited information about the fuel debris while the primary containment vessel internal survey work is ongoing. The purpose of this study is to develop the subcriticality estimation method called the virtual neutron capture method. The neutrons from the surface of the fuel debris represent a major portion of detector counts. The method consists of two evaluations: the evaluation at the surface of the fuel debris for which the isotope compositions are known by fuel debris sampling and the evaluation at the region of the fuel debris for which these compositions are unknown. For the unknown composition region, the average isotope composition with arbitrary water content is given. The method surveys the relationship with the detector count and the neutron multiplication factor with any size of the unknown composition region and any ratio of the water content before the on-site evaluation. The method is verified by experiments done in the Kyoto University Critical Assembly. The method shows that the maximum difference from the reference neutron multiplication factor is 4.5 %dk. As a result, the virtual neutron capture method can be adopted to the subcriticality monitoring if the method includes the estimation margin of 4.5 %dk within the neutron multiplication factor range from 0.70 to 0.95.
Highlights
The criticality safety control technique is required for the fuel debris removal from the Fukushima DaiIchi Nuclear Power Station which experienced a severe accident
The purpose of this study is to develop a subcriticality estimation method, called the virtual neutron capture (VNC) method, using limited information consisting of the position of the fuel debris and the isotope composition at the surface of the fuel debris
A subcriticality estimation method, which is called the virtual neutron capture method, was proposed using only limited information consisting of the position of the fuel debris and the isotope composition at the surface of the fuel debris
Summary
The criticality safety control technique is required for the fuel debris removal from the Fukushima DaiIchi Nuclear Power Station which experienced a severe accident. One of the criticality safety control techniques is the subcriticality monitoring by a subcriticality estimation method. Several subcriticality estimation methods have been proposed. Two examples are the neutron source multiplication method (NSM) [1] and the Feynman-D method which is known as a stochastic method [2]. The developed method is based on the NSM method because the detector count is time-averaged value, not stochastic.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
