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Nuclear Power Plant Hydraulics



Containment tank LOCA CFD model

Flow streamlines in a nuclear containment building




Full scale flow modeling

Full scale piping with viewing ports for gas entrainment study.  Courtesy of Duke Energy.




storage tank withdrawal physical flow model

Outlet piping and viewing chamber for tank withdrawal vortexing study


Alden has been performing regulatory hydraulic and environmental analysis work for the nuclear industry since the first major construction boom in the 1970’s. From supporting the Nuclear Regulatory Commission directly with development of NUREG’s to testing of sump strainers for plants to Clean Water Act compliance advising, Alden has become a trusted name in the nuclear community.

A major strength of Alden’s offering is the ability to perform combined physical and numeric modeling (or “hybrid modeling”) on projects. Both types have their strengths and weaknesses, and the ability to leverage them in an integrated fashion provides the best product for our customers at the lowest cost.

Categories of Nuclear Power Projects

 Below is a general classification of projects conducted by Alden for the Nuclear Industry:

Generic Safety Issue (GSI) 191: PWR Emergency Core Cooling System (ECCS) Performance Concerns

High Energy Line Breaks (HELBs) inside nuclear reactor containment lead to shredding of insulation, fireproofing, coatings, and other miscellaneous materials, and the debris can be transported during the event. If washed towards the recirculation pumps, this debris could potentially impede the performance of the Emergency Core Cooling System (ECCS).

Alden has teamed with leaders in the industry to test sump strainers being designed for individual plant retrofits. To evaluate transport of material towards the sump and the potential for degradation in performance of the ECCS, Alden uses Computational Fluid Dynamics (CFD) in collaboration with debris generation modeling to predict the volume of material transported to the sump screens. This debris volume is then used in full scale laboratory tests to determine head loss across the screen under design flow rates. 

BWR Sump Performance Evaluation

The models of reactor containment sumps are designed based on Froude similarity to include the sump and surrounding area with all the structures and piping which would influence the approach flow. Testing to observe flow patterns, formation and type of vortices, and pre-rotation and swirl effects is undertaken for the various operating conditions including restrictions due to screen blockage. Evaluation of inlet loss coefficients for the various conditions is made to verify available NPSH. If necessary, vortex suppressors or other design modifications are derived and tested. 

BWR Suppression Pool Debris Testing

The pool dynamic conditions associated with the high-energy phase of a MLOCA are usually referred to as "chugging." Chugging occurs when water re-enters the down comers as a result of decreasing steam flow, thereby condensing steam. Alden conducted a parametric study sponsored by the NRC to investigate and provide insight into debris transport in a BWR suppression pool following a LOCA.

Intake Structures

There are a number of hydraulics problems related to intake structures at nuclear power plants, including both cooling water intakes and internal storage tank withdrawals.

From an environmental perspective, Alden has performed both partial and full scale testing of traveling water screens under plant specific conditions and channel geometry in order to ensure proper hydraulic performance of these solutions to rule 316 (b) of the Clean Water Act.

Some plants have to struggle with sediment and debris in the body from which they withdraw water. Alden’s combined expertise in physical and numerical modeling has helped plants to improve performance and be more profitable.

Operation of fresh water intakes in northern regions is complicated by the accumulation of frazil ice on the intake which can rapidly and unexpectedly shut down the intake facility. Alden has performed CFD simulations of intakes under warm back-flush conditions to assist in system design.

Another major concern is the hydraulic performance of circulating and /or cooling water intakes. Alden regularly performs physical model studies of circulation and cooling water pump intakes, investigating overall hydraulic performance under varying external conditions as well as looking into the possibility of vortex formation.

Air ingestion must be also carefully avoided during the withdrawal of water in storage tanks for emergency systems. In response to recent Nuclear Regulatory Commission (NRC) Component Design Bases Inspection (CBDI) issues, Alden has performed a series of test programs for plant owners in order to address these concerns.

Plant Discharge Structures – Thermal Discharge Modeling

Rule 316(a) of the Clean Water Act regulates thermal discharge from thermal electric power plants, dictating how much temperature rise can occur over a given surface area of a water body. Alden’s computational modeling, physical modeling, and field service expertise have been used extensively by the nuclear community to design site-specific outfalls and to demonstrate compliance. 

Plant System Hydraulics

Alden’s modeling and design experience has been leveraged for a variety of internal nuclear plant system hydraulics, in addition to the GSI-191 and tank draw-down work described above. These projects include studies of biocide mixing in raw water tube sheets, debris fouling in tube sheets, accumulated gas entrainment in complex piping, and flow and pressure transients.

For further information, please download this nuclear power qualifications statement.