Hydrology Support for Estimation of K Basin Leakage Rates
PNNL was asked by Duke Engineering and Services Hanford Inc. (DESH) to estimate the maximum, minimum and best estimate leakage rates from the KE fuel storage basin given hypothetical damage to the transfer (or loadout) pit floor. According to DESH, the critical factors were:
1) The time when the basin water level dropped 7 ft, leaving a 9-ft depth of water in the basin to provide a minimum amount of shielding; and
2) The leakage rate when the water level dropped 7 ft (to be compared to the maximum allowable leakage rate of 3,000 gal/h).
The extent of the damage to the pit floor from a dropped cask was calculated for DESH by Mid Columbia Engineering, Inc. We considered:
- the nature of the floor damage
- The depth of water in the basin
- The presence of constructed features such as drain fields
- The sediment stratigraphy beneath the basin
- The saturated hydraulic conductivity of the sediments and other porous materials beneath the basin
- The depth to the water table, and time./li>
Changes in fluid and sediment properties such as from temperature, solution concentration, or colloid transport were not addressed.
Leak rates to the vadose zone through ruptures in the concrete were less than the maximum allowable rate of 3,000 gal/h when the pool level dropped 7 ft. However, the results showed that leak rates along the gravel layer on the asphalt membrane could exceed the maximum allowable rate.