Technical Basis for Revision of Inspection Requirements for Regenerative and Residual Heat Exchangers

2006 ◽  
Author(s):  
Warren Bamford ◽  
Bruce Bishop ◽  
Richard Haessler ◽  
Mark Bowler
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Ultrasonic Inspection ◽  
Regenerative Heat ◽  
Flaw Tolerance ◽  
Nuclear Plants ◽  
History Of ◽  
Technical Basis ◽  
Very High ◽  
Residual Heat

Section XI imposed volumetric inservice inspection requirements on heat exchangers in nuclear plants after most of this equipment was designed and installed. Consequently the equipment was not designed for ultrasonic examination, and in some cases such volumetric examination is not justified. The man-rem dose received from the ultrasonic inspection of some of these components is very high, and there are no known mechanisms of degradation; thus, the volumetric inspection serves no useful purpose. With the use of the newly approved code case, N706, volumetric and surface inspection of the regenerative and residual heat exchangers in PWR plants may be replaced with a visual inspection. These two heat exchangers have high irradiation fields, and both have a number of complicated weld geometries that are difficult to inspect. The regenerative heat exchanger provides preheat for the normal charging water going into the reactor coolant system (RCS). The residual heat exchanger is designed to cool the RCS during plant shut down operations. The technical basis for changing these inspection requirements was derived from four fundamental arguments: 1. The heat exchangers were carefully constructed to nuclear quality requirements. 2. They were inspected during construction, and then during service, and there is no history of degradation. 3. The flaw tolerance of the components is very high, since their duty cycle is mild, and they are constructed of stainless steel. 4. The risk is not significantly changed by replacement of the examinations with visual examinations. This paper will describe in detail the technical arguments under each of these topics, which together form the basis for the code case.

Assessment of ASME Code Examinations on Regenerative, Letdown and Residual Heat Removal Heat Exchangers

2005 ◽  
Author(s):  
S. R. Gosselin ◽  
F. A. Simonen ◽  
S. E. Cumblidge ◽  
G. A. Tinsley ◽  
B. Lydell ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Power Plants ◽  
National Laboratory ◽  
Operating Experience ◽  
Heat Removal ◽  
Pacific Northwest National Laboratory ◽  
Regenerative Heat ◽  
Asme Code ◽  
Residual Heat

Inservice inspection requirements for pressure retaining welds in the regenerative, letdown, and residual heat removal heat exchangers are prescribed in Section XI Articles IWB and IWC of the ASME Boiler and Pressure Vessel Code. Accordingly, volumetric and/or surface examinations are performed on heat exchanger shell, head, nozzle-to-head, and nozzle-to-shell welds. Inspection difficulties associated with the implementation of these Code-required examinations have forced operating nuclear power plants to seek relief from the U.S. Nuclear Regulatory Commission. The nature of these relief requests are generally concerned with metallurgical factors, geometry, accessibility, and radiation burden. Over 60% of licensee requests to the NRC identify significant radiation exposure burden as the principal reason for relief from the ASME Code examinations on regenerative heat exchangers. For the residual heat removal heat exchangers, 90% of the relief requests are associated with geometry and accessibility concerns. Pacific Northwest National Laboratory was funded by the NRC Office of Nuclear Regulatory Research to review current practice with regard to volumetric and/or surface examinations of shell welds of letdown heat exchangers, regenerative heat exchangers, and residual (decay) heat removal heat exchangers. Design, operating, common preventative maintenance practices, and potential degradation mechanisms were reviewed. A detailed survey of domestic and international PWR-specific operating experience was performed to identify pressure boundary failures (or lack of failures) in each heat exchanger type and NSSS design. The service data survey was based on the PIPExp® database and covers PWR plants worldwide for the period 1970–2004. Finally a risk assessment of the current ASME Code inspection requirements for residual heat removal, letdown, and regenerative heat exchangers was performed. The results were then reviewed to discuss the examinations relative to plant safety and occupational radiation exposures.

scholarly journals The influence of main parameters of regenerative heat exchanger on its energy efficiency

2020 ◽  
Vol 178 ◽  
pp. 01024
Author(s):  
Nikolay Monarkin ◽  
Anton Sinitsyn ◽  
Mikhail Pavlov ◽  
Timur Akhmetov
Keyword(s):  
Energy Efficiency ◽  
Heat Capacity ◽  
Heat Exchanger ◽  
Wall Thickness ◽  
Thermal Energy ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Regenerative Heat ◽  
Flow Through ◽  
Geometric Length

The influence of various parameters of stationary switching regenerative heat exchangers used for ventilation on its thermal efficiency was studied. Considered are the geometric (length, diameter and wall thickness of a single equivalent nozzle channel), thermophysical (density and heat capacity of the nozzle material) and operation (air flow through the regenerator and the time of one stage of accumulation/regeneration of thermal energy) parameters.

Mechanical Design and Validation Testing for a High-Performance Supercritical Carbon Dioxide Heat Exchanger

2017 ◽  
Author(s):  
Shaun D. Sullivan ◽  
Jason Farias ◽  
James Kesseli ◽  
James Nash
Keyword(s):  
Carbon Dioxide ◽  
Heat Exchanger ◽  
Supercritical Carbon Dioxide ◽  
Heat Exchangers ◽  
High Performance ◽  
Mechanical Design ◽  
Great Promise ◽  
Heat Rejection ◽  
Very High ◽  
Supercritical Carbon

Supercritical carbon dioxide (sCO2) Brayton cycles hold great promise as they can achieve high efficiencies — in excess of 50% — even at relatively moderate temperatures of 700–800 K. However, this high performance is contingent upon high-effectiveness recuperating and heat rejection heat exchangers within the cycle. A great deal of work has gone into development of these heat exchangers as they must operate not only at elevated temperatures and very high pressures (20–30 MPa), but they must also be compact, low-cost, and long-life components in order to fully leverage the benefits of the sCO2 power cycle. This paper discusses the mechanical design and qualification for a novel plate-fin compact heat exchanger designed for sCO2 cycle recuperators and waste heat rejection heat exchangers, as well as direct sCO2 solar absorber applications. The architecture may furthermore be extended to other very high pressure heat exchanger applications such as pipeline natural gas and transcritical cooling cycles. The basic heat exchanger construction is described, with attention given to those details which have a direct impact on the durability of the unit. Modeling and analysis of various mechanical failure modes — including burst strength, creep, and fatigue — are discussed. The design and construction of test sections, test rigs, and testing procedures are described, along with the test results that demonstrate that the tested design has an operating life well in excess of the 100,000 cycles/90,000 hour targets. Finally, the application of these findings to a set of design tools for future units is demonstrated.

Technical Basis for a Flaw Tolerance Option for Code Case N-770-1 for Large Diameter Cold Leg Piping to Main Coolant Pump Welds, With Obstructions

2010 ◽  
Author(s):  
Warren Bamford ◽  
Reddy Ganta ◽  
Gordon Hall ◽  
Matthew Kelley
Keyword(s):  
Large Diameter ◽  
Coolant Pump ◽  
Dissimilar Metal ◽  
Flaw Tolerance ◽  
Detectable Rate ◽  
Asme Code ◽  
Mitigation Techniques ◽  
Technical Basis ◽  
Flaw Type ◽  
Very High

An extensive series of evaluations have been performed on the Alloy 82/182 dissimilar metal butt welds located at the safe end regions of the CE designed reactor coolant pump suction and discharge nozzles. These nozzles present inspection coverage challenges, which hinder the likelihood of obtaining the required inspection coverage of MRP-139, and the successor document, ASME Code Case N-770. Furthermore, the geometry of the region also contributes to the difficulty of performing standard mitigation techniques. However, these nozzle regions operate at cold leg temperatures, nominally 550°F, and have a very high resistance to the potential for PWSCC, and a low predicted crack growth rate, if such a flaw were to exist in the region. This leads to the suggestion that the required inspection regimen may be too strong for these regions, and the study described herein was structured to investigate that possibility and develop a technical basis for proposing changes to inspection requirements consistent with the flaw tolerance of the region. Specifically, changes to Code Case N-770 are proposed herein, to take advantage of the flaw tolerance of the region. These proposed changes are described in this paper, and the technical basis for them is described in the remainder of the paper. The technical basis rests on three complementary findings: 1. The probability of a flaw existing or initiating in this region is very low; 2. There is a significant margin between the size flaw which would leak at a detectable rate, and the size flaw which would cause the pipe to fail. This provides a significant level of defense in depth for the region; and 3. The flaw tolerance of the region, for both axial and circumferential flaws, is very high, as measured by the size flaw which could grow to the Section XI allowable flaw size for either flaw type.

Roller Profiling for Shaping Corrugated Profiles on the Heat Exchanger Tape for Wind Tunnels

2021 ◽  
pp. 16-27
Author(s):  
Yu.V. Shchipkova ◽  
A.Yu. Popov
Keyword(s):  
Plastic Deformation ◽  
Heat Exchanger ◽  
Contact Pressure ◽  
Heat Exchangers ◽  
Wind Tunnels ◽  
Regenerative Heat ◽  
Elastic Aftereffect ◽  
Study Results ◽  
Profile Correction ◽  
Profiling Techniques

The efficiency of regenerative heat exchangers with heat-accumulating nozzles made of rolled corrugated tapes depends on the profile of their corrugation. It is technologically difficult to obtain corrugations of a given shape by copying --- stamping. It is technically more expedientto form such a profile by rolling between two rollers. The contact area is smaller, and the contact pressure is significantly higher. In this case, the shape and accuracy of the tape profile are determined by the accuracy of calculation and manufacturing of the profile of the rollers. The length of the profiling zone and the contact pressure depend on the diameter of the rollers. To apply the known profiling techniques when calculating the corrugated profile of the rollers, it is necessary to find the position of the centroid. However, the difficulty is in the tape between the rollers whose thickness cannot be neglected. Therefore, the problem is solved by rolling the roller and the rail smooth, where the tape with a profile formed on it is considered as a rail. The paper introduces a technique of roller profiling taking into account the above factors. When profiling the rollers, the springing of the tape, i.e., elastic aftereffect of plastic deformation, is taken into account. The suitable diameter of the rollers has been determined. The study results in a method developed for calculating the rollers corrugation profile, taking into account the established parameters, i.e., diameters of the centroids and rollers, and the rollers teeth profile correction value, depending on the tape springing during rolling

scholarly journals Review of Design and Modeling of Regenerative Heat Exchangers

Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 759
Author(s):  
Bohuslav Kilkovský
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Fixed Bed ◽  
Packed Bed ◽  
Regenerative Heat ◽  
Adequate Accuracy ◽  
Proper Design ◽  
Bed Material ◽  
The Heat Transfer Coefficient

Heat regenerators are simple devices for heat transfer, but their proper design is rather difficult. Their design is based on differential equations that need to be solved. This is one of the reasons why these devices are not widely used. There are several methods for solving them that were developed. However, due to the time demands of calculation, these models did not spread too much. With the development of computer technology, the situation changed, and these methods are now relatively easy to apply, as the calculation does not take a lot of time. Another problem arises when selecting a suitable method for calculating the heat transfer coefficient and pressure drop. Their choice depends on the type of packed bed material, and not all available computational equations also provide adequate accuracy. This paper describes the so-called open Willmott methods and provides a basic overview of equations for calculating the regenerative heat exchanger with a fixed bed. Based on the mentioned computational equations, it is possible to create a tailor-made calculation procedure of regenerative heat exchangers. Since no software was found on the market to design regenerative heat exchangers, it had to be created. An example of software implementation is described at the end of the article. The impulse to create this article was also to broaden the awareness of regenerative heat exchangers, to provide designers with an overview of suitable calculation methods and, thus, to extend the interest and use of this type of heat exchanger.

CFD Study on Counterflow Ceramic Microchannel Heat Exchanger With Different Fins

2013 ◽  
Author(s):  
W. X. Chu ◽  
T. Ma ◽  
M. Zeng ◽  
Q. W. Wang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Heat Transfer Performance ◽  
High Efficiency ◽  
Propulsion Systems ◽  
Microchannel Heat Exchanger ◽  
High Reynolds ◽  
Very High

The conventional heat exchangers cannot satisfy the high efficiency and power requirements due to the low heat transfer performance and large volume. With the development of micro-scale manufacture technology, the ceramic micro-channel heat exchangers are recommended to be used to the highly-efficiency power and propulsion systems, especially the very high temperature conditions. The present paper analyzes the thermal hydraulic performance of the alumina-based ceramic microchannel heat exchangers with four different fins (straight, Z-shaped, airfoil and S-shaped). The numerical results show that the maximal heat transfer rate and heat transfer effectiveness of the heat exchanger with Z-shaped fins reach 90.7 W and 61%, respectively. The temperature distribution of both fluid sides and solid body is predicted. Moreover, the pressure drop and the ratio of E/k are used to evaluate the general heat exchanger performance. The ratio of E/k is smaller than unit of ten at the low Reynolds number and increases greatly at high Reynolds number.

Effect of Face-Area Ratio on Heat-Exchanger Pressure Drops, Size and Weight

2009 ◽  
Author(s):  
David Gordon Wilson
Keyword(s):  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Short Circuit ◽  
Design Guidelines ◽  
Area Ratio ◽  
Regenerative Heat ◽  
Pressure Drops ◽  
Face Area ◽  
Significant Difference

Designers of heat exchangers of all types normally have several degrees of freedom even while meeting the specified effectiveness exactly. One freedom is that of choosing the face-area ratios for the two (or more) fluids. A principal reason for choosing face-area ratio is to arrive at desired pressure drops for the fluids. The lowest pressure drop is not always beneficial: a low pressure drop can produce highly non-uniform flow that would degrade heat-exchanger performance. Obviously a high pressure drop penalizes system performance directly. In this paper it is shown that choosing face-area ratio is a good tool up to a point, one at which penalties in the form of increased size and cost of the overall heat exchanger begin to outweigh the benefits. This paper reports studies on the effects of choosing face-area ratios on rotary regenerative heat exchangers, but most results are applicable to fixed-surface recuperative heat exchangers also. However, one significant difference between the two types is that gas-turbine regenerators have short flow lengths, the thickness of the disk or drum. A short flow length is a virtue, because it reduces the regenerator disk volume and mass. But the disk thickness must not be allowed to be reduced to the point where there is substantial “short-circuit” thermal conduction between the hot and cold faces of a regenerator. These and other aspects of heat-exchanger design are explored in general and by means of examples, and design guidelines are suggested.

Review of Computer Simulations of Regenerative Heat Exchangers

1978 ◽  
Vol 11 (8) ◽  
pp. 309-312
Author(s):  
A. J. Willmott
Keyword(s):  
Heat Exchanger ◽  
Recent Work ◽  
Computer Simulations ◽  
Heat Exchangers ◽  
Operating Conditions ◽  
Design Criteria ◽  
Regenerative Heat ◽  
Regenerative Heat Exchanger ◽  
Fuel Savings

Early models of the stationary performance of the regenerative heat exchanger are discussed together with more recent work in which the behaviour under chronologically varying operating conditions is simulated. The need is presented for better control facilities and possibly new design criteria if fuel savings in regenerative heat exchanger non-stationary operations are to be effected.

scholarly journals Comparing ways of calculation efficiency of regenerative heat exchanger

2021 ◽  
Vol 5 (3) ◽  
pp. 39-44
Author(s):  
A. A. Serov ◽  
◽  
A. V. Tsygankov ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Computational Methods ◽  
Heat Balance ◽  
Heat Exchangers ◽  
Computational Study ◽  
Ventilation System ◽  
Cfd Model ◽  
Regenerative Heat ◽  
Air Ventilation

This article contains information on various methods for calculating the efficiency of regenerative heat exchangers in an air ventilation system. The equations of heat balance and heat transfer are described. The results obtained on the CFD model are compared with the results obtained by various mathematical calculations. The obtained results of the computational study can give an assessment of the accuracy of computational methods to obtain the value of the efficiency of regenerative heat exchangers.

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