The last 5 Apollo missions that landed on the moon (starting from Apollo-12) deployed Apollo Lunar Surface Experiments Package (ALSEP) which was powered by radioisotope thermoelectric generators (RTG)
RTG assembly (on the ground) and the fuel element part inside the fuel cask (which Alan Bean is trying to retrieve with a special tool, prior to inserting it into the assembly) are shown in the cropped AS12-46-6790 image below:
Alan Bean (Apollo 12) claims he could feel the heat from the RTG through his gloves:
116:50:05 Bean: That cask's going (in?). Okay, Houston. The fuel element is in the RTG. I can feel it radiate heat already! (To Pete) Put your hand over here.
116:50:54 Bean: Hey, feel the heat off that machine. That's amazing.
116:50:59 Conrad: 1400 degrees (Fahrenheit or about 760 Celsius). (In a conspiratorial tone) Almost as hot as the Sun! (Chuckles)
Some more quotes and comments:
117:07:05 Bean: Use your tongs to hold this (probably ALSEP package 2 which is the base for the RTG) up a minute. It (the RTG)'s a little hot, and I don't want to touch it. Watch (out for) this.
[Bean - (From the 1969 Technical Debrief) "We had no trouble putting down the RTG. I did notice, however, that you could feel the heat radiating from the RTG. When I removed the bracket that carried the power cable that ran from the RTG to the Central Station, it felt warm to the touch. I didn't want to keep my fingers there too long, so I handled it with the ALSEP tool (UHT) as opposed to just my gloved hands, as I had been doing in practice. Apparently that bracket can get pretty hot, although we only had the element in it a short time."]
[Readers will note that anything that can be felt as 'warm' through the gloves, must be quite hot and a potential threat to the gloves. It has been about 17 minutes since they fueled the RTG.]
From the context of Conrad's phrase, it seems (to me, at least) he was either exaggerating the temperature figure in an attempt to joke, or quoted the temperature of plutonium sitting in the very inside of the fuel element. 760 degC seems a bit too hot for the actual radiator surface.
As the above crop from AS12-46-6790 photo shows, the front surface of the fuel element part (that is visible in front of the fuel cask) doesn't glow red, which it should have if it was above 525 °C, according to this source:
In practice, virtually all solid or liquid substances start to glow around 798 K (525 °C) (977 ˚F), with a mildly dull red color, whether or not a chemical reaction takes place that produces light as a result of an exothermic process. This limit is called the Draper point.
This source lists the figure for the RTG thermal power:
The energy source for each device was a rod of plutonium-238 providing a thermal power of approximately 1250 W.
Question: How hot would surface of the RTG radiator (deployed by Apollo-12 crew) have gotten (I assume the radiator surface as Bean did not touch the actual power element with bare gloves), so that it was possible to feel it through thermally insulated gloves? Was Conrad's estimate a joke, or was it close to reality?
Bonus question: what temperature Apollo gloves could withstand before they get damaged?