Los Alamos National Laboratory Advanced Simulation and Computing (ASC) Program
Ensuring the safety and reliability of the nation's nuclear weapons stockpile

Study determines additional water is available to cool supercomputers at LANL

A sustainable solution supporting future supercomputing at LANL

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Trinity water cooling installation

To support the Advanced Simulation and Computing (ASC) Program in 2025 and beyond, Los Alamos National Laboratory (LANL) is preparing for future generations of high performance computers used to analyze and predict the performance, safety, and reliability of the nation’s nuclear stockpile and certify its functionality.

Computer simulations are an important part of that mission. As the need for simulations increases, so too does the computing power needed to achieve the necessary fidelity in those simulations. This increase in computing power also demands more computer cooling capability.

In keeping with its commitment to act as stewards of the environment, LANL is exploring sustainable options to meet this demand. ASC recently conducted a feasibility study to explore the option of getting non-potable wastewater from Los Alamos County. The study showed promising results.

Water cooling operation

The Strategic Computing Complex (SCC) houses several generations of supercomputer, including Trinity. To keep the systems running efficiently, the SCC uses two types of cooling: air cooling and water cooling. Auxiliary systems and smaller supercomputers, such as Fire and Ice, are cooled by a 4,800-ton air cooling system. Larger systems with increasing circuit densities, such as Trinity, are cooled using a 4,200-ton water cooling system. An additional 5,040 tons of water cooling capability is being added by the Exascale Class Computer Cooling Equipment project to support future supercomputers.

Cooling towers are a type of heat exchanger in which water and air interact to lower the temperature of the warmer water. As water evaporates, heat is released and the temperature of the remaining water decreases. The cooled water is then pumped back to cool the computers. As the water cycles through, it is warmed again before it makes its way back to the cooling towers to repeat the process.

The SCC uses warm water cooling towers, a more energy efficient system that does not require refrigerated water. The water used to cool the computer systems is relatively warm (around 75 °F). The supercomputing equipment will heat this water nearly 10 °F, still quite cold compared to the equipment.

The current systems at the SCC are mainly cooled using water from LANL’s Sanitary Effluent Reclamation Facility (SERF). SERF collects treated wastewater from the Laboratory (water that is already suitable for discharge) and further purifies it for reuse in operations to support our mission rather than immediately discharging it to the environment.

Because Los Alamos sits at the edge of an extinct volcano, ground water is high in silica. “One of the primary functions of SERF,” says Andy Erickson, facility operations director at LANL, “is to remove silica so that we can reuse the water in other applications.” By reusing wastewater, the Laboratory is reducing its environmental impact and working towards its goals for potable water usage reduction.

“It’s really a double benefit for the Laboratory,” continues Erickson. “It helps reduce our total potable water usage and helps improve our energy efficiency.”

Feasibility study

SERF’s reclaimed water production is nearing its upper capacity limit. To meet the demand and avoid increasing potable water usage, ASC recently completed a feasibility study to examine whether there is adequate volume, available delivery, and acceptable water quality from the Los Alamos County wastewater treatment plant (WWTP) to operate new cooling towers as part of a future supercomputing infrastructure.

The Los Alamos County WWTP can provide approximately 96 million-gallons of non-potable reuse water each year. The study showed that the county water, combined with the reuse water from SERF, could provide enough water to cool an 80 MW supercomputer for most of the year. In June and July, when the sum of water provided from SERF and the county is not sufficient, potable water (or stored water) will need to be used to make up the difference (see graph above).

The additional county water volume is beyond SERF’s current capacity. With additional capacity and other improvements, such as improving SERF’s chemical process, LANL will have the volume of water and quality of water necessary for future supercomputing.

Modeling was completed for the existing county reuse infrastructure with respect to the water available each month as well as the demands at LANL. For most of the year, the existing piping is able to supply the available and desired water to LANL property. Improvements will be necessary to meet demands for the entire year. It is important to formally explore the options identified in the feasibility study: county reuse infrastructure improvements to provide more capacity, new non-potable water pipes to improve delivery, or alternative water treatment techniques to improve operations.

The study concluded that the use of Los Alamos County non-potable reuse water is feasible. There is a sufficient volume of water available for use, delivery of the water is practical, and the quality of water is close to what is necessary for future supercomputing.

“SERF has already been instrumental in reducing the Laboratory’s potable water usage,” said Monica Witt, LANL’s Sustainability Officer. “Now we’re talking about reusing a second wastewater stream that would otherwise be discharged to the environment. That’s a big deal.”

The new water availability will enhance LANL’s multi-year strategy to support future supercomputing for ASC at LANL while achieving water sustainability goals.