By Thomas L. Englert, Ph.D., P.E. and John A.D. Burnett, §316 Practice Leaders for HDR, Inc.
In roughly six months, owners and operators of nuclear generating facilities will have a new regulation to address. After a hiatus of more than four years, the U.S. Environmental Protection Agency (EPA) will issue a new version of the 316(b) Phase II rule, which regulates fish impingement and entrainment at cooling water intakes.
At most nuclear facilities the rule will require costly monitoring and reporting, and many will have to make expensive changes to their intakes and operations to minimize organism losses. In April 2011, EPA published a draft of the new rule and is committed via a settlement agreement with environmental groups to publish a final version by July 2012.
EPA has received comments on the draft rule from many industry groups and stakeholders including the Nuclear Energy Institute (NEI), which is responsible for establishing unified nuclear industry policy on matters affecting the nuclear energy industry.
A Brief History
Section 316(b) requires that the location, design, construction, and capacity of cooling water intake structures reflect the best technology available (BTA) for minimizing adverse environmental impact (equated by EPA with entrainment and impingement of fish and shellfish).
It was enacted in 1972. In 1976, EPA published §316(b) regulations, which were successfully challenged by a group of utilities. In 1979, EPA formally withdrew the regulations, and states then adopted their own cooling water intake regulations, varying widely in scope and rigor. In the mid- 1990s, a coalition of environmental groups filed suit against EPA over failure to re-enact §316(b) regulations. In October 1995, the U.S. District Southern District of New York entered a Consent Decree between the parties, directing EPA to take final action.
As part of its response, EPA issued the Phase II Rule in July 2004, covering existing electric generating plants that withdraw at least 50 million gallons of cooling water per day. This rule included waterbody-based performance standards for reducing organism loss due to entrainment and impingement relative to a baseline intake and flow condition. In March 2007, the Phase II Rule, was remanded to EPA for reconsideration as a result of legal proceedings.
The proposed §316(b) rule for existing facilities issued in April of this year and the subject of this article is EPA’s response to the remand and combines Phase II and the existing facility portion of Phase III into one rule.
The proposed rule, which was published in the Federal Register on April 20, 2011, applies to existing power plants and industrial and manufacturing facilities that withdraw at least 2 million gallons per day (MGD) of cooling water and use at least 25 percent of that water exclusively for cooling purposes. Nearly all nuclear facilities will meet this criterion because even those with cooling towers likely require more than 2 MGD in make-up water.
The proposed rule provides two impingement compliance options (1) the use of modified travelling screens with fish buckets and a fish handling and return system and (2) reduction of through-screen velocity to less than 0.5 feet per second. With respect to entrainment, the proposed rule requires that the permitting authority maximize entrainment protections.
Facilities that withdraw large amounts of water, at least 125 million gallons per day, are to conduct studies to help their permitting authority determine what site-specific controls, if any, would be required to reduce entrainment mortality.
What sets the nuclear industry apart
Nuclear power plants, like other steam electric generation facilities, heat water to create steam to turn a turbine that generates electricity. These plants depend on effective cooling water systems to cool steam back to water so the process can continue. In addition, some nuclear facilities derive their safety-system cooling water from the same intake structure that supplies cooling water for the condenser. Thus, cooling water intake structures are vital to the electric generation process itself and can be essential to ensuring safe nuclear energy production.
|Figure 1 CLEAN WATER ACT §316(b) MILESTONES|
There are currently 104 operating nuclear units generating 20 percent of the nation’s electricity. Of these, 39 plants, 62 units (60 percent), use once-through cooling systems. Nuclear plants and the technology they use in their cooling water systems vary substantially based on waterbody type and time of construction, among other factors, with different plants demonstrating different technological needs and potential environmental impacts.
Nuclear plants are built on a variety of waterbody types with different flow and surge characteristics, and different species compositions.
In some ways, the site-specific characteristics of nuclear facilities are much different from those of other entities regulated under this rulemaking. For example, the nature of nuclear power generation requires nuclear facilities to have a larger cooling water flow than non-nuclear generators. Nuclear facilities are more likely to be sited near the Great Lakes or oceans than are non-nuclear facilities, and waterbody location and type affect the fish and shellfish species that are present.
Nuclear facilities have other differences. For example, implementing technologies that may be installed to meet the proposed impingement standard are likely to create longer downtimes and present unique safety challenges. Because nuclear generators typically have large flow requirements, simply reducing intake water volume may not be an option. And since they do not emit criteria pollutants or greenhouse gases, extended downtime or decreases in plant efficiency due to BTA installment may mean replacing nuclear power generation with technology that is less carbon-friendly.
Where NEI and EPA Part Ways
In comments on the proposed 316(b) rule provided in August, 2011, NEI stated that it agrees with EPA’s decision not to require power plants to adopt closed-cycle cooling technology. NEI also agrees with EPA’s decision not to adopt a national best technology available (BTA) to address entrainment mortality. Selecting BTA requires considering many site-specific factors such as those mentioned above.
In the same comments, NEI stated that EPA should offer the same flexibility for impingement that it offers for entrainment. The proposed rule allows BTA for entrainment mortality to be determined based on site-specific criteria, but is proposing a national BTA standard for impingement mortality.
NEI contends that the proposed “one size fits all” criterion for impingement is a departure from the site-by-site criteria used for the past 30 years and is unworkable, given the great variability in the waterbodies and species found at nuclear sites. Instead of national criteria, NEI recommends that the same site-specific approach proposed for entrainment mortality be applied to impingement mortality.
|Aquatic filter barriers prevent both impingement and entrainment by filtering the cooling water before it enters the intake. All photos courtesy of HRD, Inc.|
With regard to entrainment, while NEI agrees with EPA’s site-specific approach to entrainment controls, it feels the agency should specify that permitting authorities should impose such controls only if the quantifiable benefits are comparable to the quantifiable costs.
Overall, NEI takes issue with the 316(b) cost-benefit analysis provided by EPA, contending that the costs are 21 times the monetized benefit, with the rule resulting in a negative net benefit of $366 million annually.
A look at compliance technologies
The compliance technology that is considered for installation at a facility is dependent on the compliance alternative chosen.
If modified traveling screens are selected for compliance, the proposed rule requires that the annual average and monthly maximum mortality of impinged fish be less than 12 and 31 percent, respectively. If this technology is paired with fine-mesh screens, the numbers of organisms entrained can be reduced. However, the excluded organisms are now impinged on the screens and only those that survive impingement will actually contribute to a reduction in losses due to entrainment. Variants on the traveling screen that may also warrant consideration include dual-flow screens that can reduce through-screen velocities, and drum screens and Geiger screens that can reduce screen carry over.
|Fish handling and return systems, such as the one shown here, are part of one of the impingement compliance options EPA is considering.|
Fixed panel screens with sufficient screen surface area to achieve a through-screen velocity of less than 0.5 feet per second can be used to satisfy the reduced intake velocity requirement. Retrofitting fixed panel screens at most facilities involves significant, costly modifications to the cooling water intake because at most nuclear facilities the intake would have to be doubled or even tripled in size.
Wedgewire screens are considered a promising technology for reducing both impingement and entrainment. They have a “v” or wedge-shaped cross-section wire welded to a framing system that forms a slotted screen. The through-slot velocity needs to be low enough to minimize potential impingement of weak swimmers, yet sufficient “sweeping” speed must be present in the source water body to carry excluded organisms safely away from the screen. This technology would achieve impingement compliance by reducing through-slot velocities to less than 0.5 feet per second and potentially provide entrainment protection by using narrow slot sizes. Some studies indicate that narrower slot sizes may lead to increased avoidance of the screens by entrainable-size larvae.
|Impingement occurs when aquatic organisms too large to be entrained are trapped against intake screens.|
Barrier nets are constructed of wide-mesh fabric panels and configured to completely surround the cooling water intake structure. Their mesh sizes are typically relatively large (3/8 inch) and they have had the most success in locations where seasonal migrations create high impingement events. This technology would achieve impingement compliance by reducing through-net velocities to less than 0.5 feet per second but would not generally protect against entrainment.
Aquatic filter barriers such as the Gunderboom Marine Life Exclusion System are water-permeable barriers that reduce both impingement and entrainment by completely surrounding the intake structure and preventing organisms from entering. A curtain formed by two layers of treated fabric is either suspended by flotation billets and anchored in place, or integrated into existing shoreline intake structures. This technology would achieve impingement compliance by reducing through-fabric velocities to less than 0.5 feet per second and provide substantial entrainment reductions to the extent early life stages are excluded from entering the intake.
Closed-cycle cooling may have limited application as a full or partial retrofit depending on the existing configuration and many other factors. Closed-cycle systems such as cooling towers typically use only 2 to 5 percent of the water used in a once-through system. The closed-cycle cooling option is not recognized explicitly by the proposed rule; however, if 0.5 feet per second through-screen velocities are achieved as a result of the reduced water use, impingement compliance would be achieved and the reduced intake flows would also reduce entrainment.
The list of potential operational measures to be considered for compliance is smaller than that for technologies but also worthy of mention. For example, if capacity factor reductions or unit mothballing result in through-screen velocities that are less than 0.5 feet per second, impingement compliance would be achieved and entrainment losses would be reduced. Variable speed drives, flow optimization, and targeted outages may also be considered to the extent they provide impingement and entrainment protections that will be recognized by permitting authorities. Safety and reliability considerations can limit the application of operational measures at nuclear facilities
|Entrainment occurs when small aquatic organisms such as eggs and larvae are drawn through the intake screens and into the cooling water intake system.|
The extent to which a particular technology or suite of technologies and operational measures may be appropriate depends on the permit director’s objectives for entrainment reductions as well as site-specific biological and engineering considerations. For some technologies, performance in terms of impingement and entrainment reductions can be largely driven by the robustness or fragility of specific species subject to withdrawal at the facility and the extent of debris loading and biofouling. Costs will be driven by these same site-specific factors, as well as the existing intake configuration, space availability, and potentially many other factors. Other technologies and combinations of technologies and operational measures may be worthy of consideration depending on how the final rule differs from what EPA has proposed.
EPA will be reviewing and responding to all comments received on the draft rule. When the final rule goes into effect, scheduled to be no later than July 27, 2012, technologies to meet impingement requirements would need to be implemented as soon as possible but within eight years, i.e., no later than 2020. Existing electrical generation facilities with a design intake flow of 50 million gallons per day or more would be on an expedited compliance schedule, presumably because EPA believes these former Phase II facilities already performed certain related studies based on requirements in the 2004 version of the rule. Of particular interest to these facilities is the large number of application requirements due within just six months of rule promulgation. All other facilities, including electrical generation facilities that withdraw between 2 and 50 million gallons per day, have a more lenient schedule of three years. Also important is the requirement that all existing facilities with actual intake flows of 125MGD and greater perform additional entrainment studies.
|Ristroph traveling screens are part of an impingement compliance option EPA is considering.|
The proposed rule has important implications for nuclear power plant owners and managers. Available compliance strategies for impingement mortality require either costly upgrades of traveling screens to include fish protection, or reducing intake velocity to less than 0.5 feet per second. The latter could be achieved by expanding the intake or installing one of a number of screen or barrier options discussed above – all of which can be very costly and in many cases not feasible. The approach plant owners should take toward planning for compliance will depend to a large extent on their individual permitting authority’s approach, given that entrainment requirements are based on the permit director’s best professional judgment.
What should owners/operators be doing?
Nuclear facility owners should be talking to their permitting authorities and developing compliance strategies, considering the economic and operational impact of the alternatives. They should evaluate the proposed rule’s impact on operations and potential cost implications, which will depend to some extent on the individual state’s approach. They should also consider the implications within the larger context of other regulations. Nuclear facility owners also will need to evaluate the rule’s impact on issues such as liability and safety.
Nuclear Energy Institute comments provided to U.S. Environmental Protection Agency in reference to EPA’s Proposed Phase II 316(b) Rule, May 29, 2004.
Nuclear Energy Institute comments provided to U.S. Environmental Protection Agency in reference to EPA’s Proposed Phase II 316 (b) Rule, August 18, 2011.
Power Engineerng Issue Archives
View Power Generation Articles on PennEnergy.com