quick answer: Your NUC seems to have an hardware error. There a lot of people having the same NUC-behavior. They never got a running system after this WHEA error. You have to contact your dealer or Intel to get a new NUC. When you get your new NUC, you should upgrade the BIOS to 42 (at the moment).
This message was posted on behalf of Intel Corporation
Intel has confirmed that electrical over-voltage can occur in the voltage regulator circuitry. Intel has observed the NUC “WHEA UNCORRECTABLE ERROR” issue can occur as a result of electrical overstress. Intel has released BIOS version 0042 that improves the electrical overstress protection in the voltage regulator circuitry on the Intel® NUC Kit NUC6i3SYH, Intel® NUC Kit NUC6i3SYK, Intel® NUC Kit NUC6i5SYH, and Intel® NUC Kit NUC6i5SYK products. Intel recommends customers update the Intel NUC to BIOS version 0042.
Users who see “WHEA UNCORRECTABLE ERROR” repeatedly on these products are encouraged to contact Intel Customer Support for assistance.