TABLE XI PLUTONIUM RELEASE. RATES FROM PMC IN WATER Power Sample PMC-142 PMT-113 PM-148-T Wt (W) (g) 50 50 29 138 135 74 Dimensions (mm) Height Diam 5.5 5.5 3.7 Immersed 54.4 54.4 54.4 100 days after immersion. This is the earliest dis- integration observed for any disk, and it should be compared with 190 days for disk PMT-113 tested in seawater at 10°C for 417 days. As did PMC disks tested in seawater, this disk showed a preferential release of molybdenum compared to plutonium, which indicates that corrosion of the molybdenum coating of individual pressed plutonium particles led to its disintegration. It is surprising that an accelerated plutonium release was not observed. Despite the final decrease, the averagereleaserate is the highest observed for a PMC disk. These data in- Average Days 548 417 326 Release Rate Water sea sea fresh (uCi/m?-s) 10°C 10°C 10°C 2.3 7.0 15.6 1. In Seawater. The plutonium release rate from the 2.5-W pellet HPZ-3 (Table XII) has remained at 20 nCi/m?-s for the last three months, followingits earlier drop from a maximum of 69 nCi/m?-s rate observed nine months ago. Duringthefirst 400 days of immersion, its average release rate was fairly linear at 54 to 75 nCi/m?-s, different from the continually accelerating rates from PMC disks. Since then, the rate has decreased slowly and appears now to haveleveled off. Despite the lengthy immersion, the pellet has not deteriorated visibly pointing to the superior stability of PPO compared to PMC. dicate that freshwater corrosion of PMC disks proceeds more rapidly than saltwater corrosion and produces an average release rate slightly greater than 12 uCi/m2-s. The plutonium release rate from the 2.5-W pellet HPZ-60-3, immersed in 37°C water typical of tropical near-shore shallows, has averaged 2.9 E. PPO Dissolution or Release Rates. second lowest rate from any 2“®8Pu fuel tested thus nCi/m2-s for 544 days, practically unchanged from last quarter’s average of 3.2 nCi/m2-s. This is the These tests are to compare release rates from 2.5- and 25-W PPO pellets in both fresh water and seawater. Because of the remote chance that a heat source may drop into a warm tidal pool, seawater 300}- 3 ~ W pellets. 200/-€ 28 t g —- T r <q 200 8ve2 at|[ é & Large crack oppeore Q : of x r ~ | % moblin ‘Perteds ZZ 109 | a 4 = c: “ 4 E lOO t e 4. © srarted 8Co U +| 8RG Crumbling ™ ’ o | ico | qi tests at 37°C are included. Six experiments are under way, three with 2.5-W pellets and three with 25- I 320 705 | 300 N | 0 | i0G 200 Days of Immersion ! 300 Days of Immersion Fig. 6. Plutonium release from PMC disks in simulated seawater. Fig. 7. Plutonium release from a PMCdisk in fresh water. + iar ray i4 13