Two variants of the theory:

Variant 1 - GPHS-RTG fuel pellets (151 grams):

The DOP-26 Iridium cladding protects the GPHS-RTG fuel pellets for the latter part of the drop after the carbon casings have melted.  DOP-26 Iridium has a "dopant" which is a tiny bit of Thorium, Tungsten, and Aluminum to make it ductile and resilient at higher temperatures.  144 of these went into Jupiter on 7-19-2003; 4% survived entry.

Variant 2 - LWRHU fuel pellets (2.7 grams):

Carbon casings also enhance the performance of the Pt-30%Rh (Platinum 70% - Rhodium 30%) clads of LWRHU's which do the real work of holding as a solid throughout the drop.  This alloy of platinum has a very high starting melting point which increases as can be determined by its EOS formula.  The clads are the final barrier protecting the plutonium fuel inside, and the thickness is only 0.875mm.  17 of these went into Jupiter on 12-7-1995; all survived entry.

The 2nd Wave of pellets

A 2nd wave was released into Jupiter on 9-21-2003 (144 RTG pellets and 103 LWRHU's in all). The units in this second wave had a probability of only about 4% survival rate, this still means a few survived intact and the equation of state of Iridium ultimately kept them intact.  The RTG pellets may have been the PRIMARY wave after all that caused the "Wesley mark" almost 6 years later (July 2009).

Cassini at Saturn Information:

NASA has now announced that indeed Cassini will also be plunged into Saturn on September 15, 2017. [1]

Cassini holds the same types of devices that Galileo had, RTG's and LWRHU's in larger amounts on Cassini.

We should expect similar "marks and flashes" activity since Saturn has similar characteristics as Jupiter only 30% of the mass and half as dense.  These factors should contribute to the RTG's (3 groups on Cassini compared to 2 groups on Galileo) and LWRHU's (122) taking a bit shorter time to fall? appropriate depth (gravity is said to be 45% at surface Sat compared to Jup).

Despite the fact that there is no heat shield for the LWRHU fuel units as with the GAEP situation, since there are so many on the Cassini spacecraft [2], SOME will survive the plunge (see notes) 

Either type of unit in the "variants" shown above (RTG units and LWRHU units) could possibly make a multi-year drop to at center or very near center at 1% to 2% radius of Saturn's center (by 2020-2030?).  Saturn is said to NOT have a solid core at 40 to 60 million bars pressure at exact center.  The predicted time range is quite wide because each of the variants requires different drop times and there are other dynamic differences not fully known.  If Saturn reacts similarly to what JOTH theory has predicted at Jupiter, and the mark and flash events are a result there, then we should see some sort of similar sequence (marks and flashes) on Saturn between the years of 2020 and 2025 (rough estimate says 7/14/23 +/- one year either way = July '22 to July '24, range due to Jupiter and Saturn having different variables).

Notes:  With even just an 5+/-% survival rate for each unit to survive intact, almost assuredly a few radioisotope units will survive the fast trip through the upper atmosphere of Saturn and subsequent slow drift to center.

Saturn shows evidence of no solid center, so that's one less obstruction to deal with.  As a result, "closer to center" can be achieved for the "initiation".   As far as "holding" the fusion reaction afterwards, similar pressures would still be available at that lower level (maybe only the last 2% radius); the volume of Saturn viable for fusion would be much smaller even than Jupiter.

Below is an image from NASA showing the predicted location of the plunge in 2017 (red arrow). [3]Just before 6am GMT on September 15, 2017 Cassini will enter into Saturn’s atmosphere to conclude its “Grand Finale” to the Solstice Extended-Extended Mission at Saturn. Above is a screenshot from NASA’s Cassini Tour site which shows the predicted location of the final plunge near the equator after making one last pass over the north pole hexagon of Saturn.

As with Earth satellites that reenter the atmosphere, not all parts burn up in a plunge. The more robust parts actually survive initial atmospheric heat. Which parts of Cassini will likely survive? The GHS-RTG fuel system.

This is the most robust part of the craft especially when referring to the individual plutonium-lad pods, 72 of each in 3 separate fuel booms making 216 altogether. Additionally more than a hundred smaller plutonium-containing fuel pods called LWRHU’s are also sure to survive the initial plunge having similar protection.

1-  (Cassini 2017 tour dates)

2- (Cassini mission LWRHU's = 157 - 35 used on Huygens probe = 122 on Cassini)

3- “Cassini Tour”  Extended-Extended Mission “Grand Finale”