The France patent FR2553560 was lapsed in 1998, as notification of lapse. The patent is valuable. I think it is used in MOX plant. I would like to know the reason of lapse of the valuable patent. How can I do that?
Short of asking the assignee of the patent: Japan Atomic Energy Research Institute, there is no way to know why they allowed the patent to lapse. Generally the reason for allowing a patent to lapse is that the patent owner no longer feels the patent fees are justified by the income or protection derived by the patent. Perhaps no one in France was "dissolving plutonium dioxide or a mixed oxide of uranium and plutonium" using the described method after 1998? It should be noted that the patent would have expired anyway on October 12th, 2003.