During computer-controlled cognitive tasks, chimpanzees often look up the food dispenser which activates at the same time as feedback for the correct choice but not for feedback for the incorrect choice. Do these "looking back" behaviors also indicate signs of spontaneous monitoring of their confidence in their choices? To address this question, we delayed the feedback for 1s after their choice responses and observed their look-back behaviors during the delay period. Two chimpanzees looked up the food dispenser significantly less frequently when their choice was incorrect (but the feedback was not given) than when it was correct. These look-back behaviors have not been explicitly trained under experimental contexts. Therefore, these results indicate that chimpanzees spontaneously change the frequency of their look-back behaviors in response to the correctness or incorrectness of their own choices, even without external feedback, suggesting that their look-back behaviors may reflect the level of "confidence" or "uncertainty" of their responses immediately before.

During computer-controlled cognitive tasks, chimpanzees often look up the food dispenser which activates at the same time as feedback for the correct choice but not for feedback for the incorrect choice. Do these "looking back" behaviors also indicate signs of spontaneous monitoring of their confidence in their choices? To address this question, we delayed the feedback for 1s after their choice responses and observed their look-back behaviors during the delay period. Two chimpanzees looked up the food dispenser significantly less frequently when their choice was incorrect (but the feedback was not given) than when it was correct. These look-back behaviors have not been explicitly trained under experimental contexts. Therefore, these results indicate that chimpanzees spontaneously change the frequency of their look-back behaviors in response to the correctness or incorrectness of their own choices, even without external feedback, suggesting that their look-back behaviors may reflect the level of "confidence" or "uncertainty" of their responses immediately before.

The spent control rod assemblies are to be processed as a waste for an underground disposal (depth≥70 m). The spent control rod assemblies (4 m in length) need to be cut into 4 sections in order to be stored in the storage containers (1.6 m x 1.6 m x 1.6 m). When the control rod is cut, the B4C powder contained inside the rod is leaked into the water. Contaminating the surrounding water would increase the secondary treatment cost, and consequently the overall processing cost. In this study, we examined a cutting technology that combines press working and underwater plasma cutting, in order to seal the cut control rods and prevent the B4C from being scattered into the water. We cut the control rods underwater in a vertical upright position, and confirmed the effects of B4C scattering. After cutting, the water ingress of the neutron absorbers was 52.8 mg per control rod. The B4C leaked during cutting was 3.6 g. The ratio diffuse of B4C from per control rod was 0.05 %. In conclusion, the results showed that the cutting technology used in this study is effective, and the B4C can be reduced considerably during processing.