I want to know the answer to the following question:
Which weapon did Feynman found to not be feasible?
All the background I'm provided with is that "On completing this work he was transferred to the Oak Ridge facility, where he aided engineers in devising safety procedures for material storage so that criticality accidents (for example, due to sub-critical amounts of fissile material inadvertently stored in proximity on opposite sides of a wall) could be avoided.". Is that enough to answer the question?
Answer: no