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[cdn-nucl-l] Pu-238 atmospheric releases
> On the subject of atmospheric plutonium releases, particularly those
> involving accidental releases from radioisotope thermoelectric generators
> (RTGs) carrying the short-lived isotope Pu-238, the book SPACE NUCLEAR
> POWER, by J.A. Angelo Jr. and D. Buden ( Orbit Book Co., 1985 ) is a good
> On p. 244 is the following section (chapter 13) :
> Aerospace Nuclear Incidents
> To date, the United States has launched 19 space missions with
> power sources. After four successful RTG launches, the Transit-5BN-3
> to achieve orbit on 21 April 1964 due to a launch vehicle abort that was
> traced to conflicting guidance controller signals occurring during ascent.
> This guidance malfunction caused the launch vehicle to pitch improperly
> orbital insertion of the payload was not achieved. Despite the ascent
> however, the SNAP-9A RTG on board the spacecraft as designed for a
> launch/mission abort and it burned up on reentry into the earth's
> atmosphere. The RTG's plutonium-238 metal fuel was injected into the
> atmosphere in the Southern Hemisphere at an altitude between 45 and 60
> kilometers. Airborne and surface sampling was initiated following this
> and four months later plutonium dioxide (PuO2) was first positively
> identified at an altitude of 32.9 km at 35 degrees south latitude. It was
> subsequently concluded that, as designed, the radioisotope fuel had
> completely burned up during reentry over the West Indian Ocean north of
> Madagascar [2,6].
> The second U.S. RTG aerospace nuclear incident occurred on 18 May 1968 and
> involved a SNAP-19 generator on board the Nimbus B-1 meteorological
> spacecraft. In this case, erratic behavior of the launch vehicle forced
> intentional destruction by the Range Safety Officer when the vehicle and
> payload were at an altitude of 30 km and traveling downrange from the
> Vandenberg Air Force Base launch site. Tracking data placed the impact
> of the launch vehicle and spacecraft debris in the Santa Barbara Channel
> about 5 km north of San Miguel Island off the California coast. Here, the
> water depth is about 90 meters. The SNAP-19 generator was designed for
> intact reentry and had been tested in a marine environment. Since data
> indicated that the radioisotope fuel capsules were still intact and that
> they posed no immediate environmental or health problem, there was no
> immediate urgency to recover them from the ocean floor. In fact, the
> generator was recovered from the Pacific Ocean five months later (see Fig.
> 13.1). The entire incident verified that the radioisotope fuel capsules of
> this design could remain in a marine environment for long periods of time
> following a launch/mission abort without concern for fuel release.
> Post-incident examination of the fuel capsules revealed that no
> effects were suffered from the destruction of the launch vehicle, impact
> the ocean, or nearly five months residency on the ocean bottom. The
> ablators surrounding the capsule were also intact [2,6].
> A third RTG aerospace nuclear incident involved the aborted Apollo 13
> mission to the Moon in April 1970. In this event, the SNAP-27 fuel
> containing 44,500 curies of plutonium-238 oxide microspheres, reentered
> Earth's atmosphere along with the Aquarius Lunar Module (LM) which had
> served as a translunar trajectory lifeboat for the in-flight stranded
> 13 astronauts. En route to the Moon, an oxygen tank had exploded in the
> Service Module. Following the near fatal explosion, astronauts Lowell,
> Swigert, and Heise powered up the Aquarius, battened down the crippled
> command ship Odyssey, and continued on a course around the Moon and back
> the Earth. For more than 90 hours these three men rode a lunar landing
> designed to accommodate just two astronauts for two days. Then,
> Earth, they again fired the Aquarius (LM) engine to thread themselves
> carefully through a narrow reentry corridor, shifted to the lifeless
> command module (CM), and cut loose both the damaged Service Module and
> LM lifeboat. The three astronauts were recovered within 45 minutes of
> splashdown in the Pacific Ocean .
> The Apollo 13 SNAP-27 fuel capsule, on the other hand, was contained in a
> graphite fuel cask attached to the LM. Both reentered at approximately 122
> km above the South Pacific Ocean. Atmospheric monitoring at several high
> low altitudes in the area indicated that no nuclear fuel was released.
> Consequently, it was assumed that the SNAP-27 capsule impacted intact, as
> designed, in the deep ocean south of the Fiji Islands and now resides near
> the Tonga Trench in some 6 to 9 kilometers of water. There was no
> adverse effect on the biosphere as a consequence of this incident --
> indicating again the efficacy of the U.S. aerospace nuclear safety
> On page 140 :
> Consistent with aerospace nuclear safety philosophy of the day, the fuel
> capsules were designed for intact impact under launch abort conditions and
> for high altitude burnup and dispersal in the event that a mission abort
> caused the spacecraft to reenter the Earth's atmosphere.
> The liner... material accommodated atmospheric burnup.
> The segmented fuel block design permitted separation of the capsules for
> exposure to aerodynamic heating during a reentry abort.
> [ Comment : the metal form of Pu-238 also contributed to the burning up --
> in contrast to the PuO2 used today, which is already oxidized & will
> therefore not support a chemical reaction with oxygen...]
> page 136 :
> The SNAP-3B and -9A systems were designed for nuclear fuel burnup and high
> altitude dispersal in the event of an atmospheric reentry of the
> nuclear-powered spacecraft.
> Tables 8.1, 8.2 and 8.3 give technical details :
> The 12.2 kg SNAP-9A power source [ with 17,000 Ci of Pu-238 METAL (!!) ],
> which was launched on the Transit-5BN-3 Navigational Spacecraft on 21
> 1964 burned up on reentry after the mission was aborted during launch.
> All subsequent RTGs [ SNAP-19 and later models ] used PuO2 rather than
> and were designed to survive reentry intact.
> The SNAP-27 in the Apollo 13 incident had 44.5 kCi of PuO2 - 30.8 kg
> the cask - when it crashed intact into the South Pacific Ocean on 11 April
> In the SNAP RTGs the primary reentry heat shield, consisting of graphite,
> formed an outer cylinder around all the fuel capsules. The larger RTG
> developed for the Galileo and Cassini missions is composed of General
> Purpose Heat Sources (GPHS-RTGs), and is a modular power unit design
> providing flexibility for different spacecraft power demands. Each 250
> watt-thermal module has its own passive safety provisions, including an
> aeroshell serving as the structural element and an ablator.