The flow of groundwater often plagues construction of tunnels and other underground systems. One way of preventing it is with an ice seal—freezing the water in the soil so that the ice formed is a barrier to water movement. Such a structure was planned for the Fukushima TEPCO nuclear power plant, which was severely damaged by a 2011 tsunami that created a tremendous environmental challenge. A major concern was potential contamination with radioactive isotopes of groundwater flowing under the plant and into the ocean. A proposal under consideration was to channel the flow around the plant by forming an ice dam with a 1,400-meter perimeter, a depth of 30 m, and a thickness of approximately 2 m. This was to be done by pumping a brine solution at a temperature of -40°C though vertical pipes spaced at 1-m intervals. The brine would exit at a temperature no greater than -25°C. To keep ambient temperature fluctuations from causing occasional melting, the dam was to have a mean temperature of about  -20°C. 

(a) Estimate the average cooling rate (kW) and associated flow rate of brine (L/min) required to complete formation of the dam within 60 days of starting the refrigeration system. State and give your rationale for each of the assumptions and/or approximations necessary to obtain your result. 

(b) From a suitable reference, for which you must provide a citation, find an estimate of the ratio of the heat removed to the work done by a refrigeration system. Use the value to estimate the power usage during the time the dam is being created. 

(c) It is expected that substantially less power will be used once the dam has been formed. Explain. 

Exploratory Exercises—Research and Discover

(d) Identify the primary radioactive species that were of greatest concern regarding contamination of the groundwater. (e) Explosions of hydrogen occurred in the power plants after the cooling water system was shut down upon being flooded by the tsunami. What was the source of the hydrogen? Describe the scenario that led to hydrogen formation.