Holtec Government Services successfully analyzes, designs, constructs, and commissions facilities, systems, structures and components (SSCs) for federal and non-governmental nuclear installations. We also provide operational and field support for diagnosing and resolving operational issues. Our technical and governance procedures ensure that our manufactured products and engineering and analytical services meet the requirements of the respective federal regulations, agency guidance and requirements, and the terms of federal contracts. All projects are performed in compliance with the USNRC and US government entities, such as the USDOE and USDOD.
The design and analysis of new and old SSCs often require multi-disciplinary technical expertise. Our highly-trained engineers have expertise in an array of disciplines including mechanical design, civil design, soil mechanics, structural analysis, thermal-hydraulic analysis, shielding evaluation, reactor physics and criticality safety analysis.
The Department of Energy’s (DOE’s) approach to nuclear safety is defined to Title 10, Code of Federal Regulations Part 830, “Nuclear Safety Management.”Because of the broad diversity of the DOE facilities and their processes, Holtec Government Services develops the safety and design bases of each project in compliance with the DOE’s regulatory framework.Our programs apply applicable DOE requirements for implementing Part 830 such that a typical nuclear design project begins with development of a safety design strategy (SDS) for determining the functional performance and capabilities to be provided by the SSC; the design features to achieve them; and the strategy for assuring the necessary levels of operational safety. In parallel, the hazards associated with the design and its operation are identified, analyzed, safety functions are identified, their significance (safety categories) are determined and, where needed, controls developed to prevent or mitigate adverse consequences. DOE Conceptual Safety Design Reports (CSDRs), Preliminary and final Documented Safety Analysis (PDSAs, DSAs) and Technical Safety Requirements (TSRs) are prepared, iterated with the client, and implemented to control the configuration and operating envelopes of the SSC as the facility or SSCs are commissioned. For the DOE, this is accomplished in accordance with DOE Orders, Directives and guidance such as DOE STD-3009-94, Nuclear Facility Documented Safety Analysis and DOE STD-1189-08, Integrating Safety into Design.
Mechanical design and qualification of a wide range of systems, structures and components including steel structures, pressure vessels, heat exchangers, condensers, valves, pumps, piping, cranes and crawlers.
Mechanical design and qualification of heavy load handling rigs and appurtenances and fluid flow systems that comply with ASME Boiler and Pressure Vessel Codes, TEMA & HEI standards for heat exchange equipment.
Civil and structural design and analysis of structural weldments, reinforced & plain concrete structures including containment builds, storage buildings and foundations. Heat transfer calculations, vibration calculations and CFD analyses.
Mechanical design and qualification of nuclear storage and transport devices. The SMR-160 small modular reactor and its support systems are currently under design for future manufacturing.
Qualifying Static and Dynamic Analyses of Systems, Structures and Components
Design of systems, structures and components (SSCs) are often required to demonstrate satisfaction of Design Basis Loads (DBLs) to complete its safety evaluation. Holtec Government Services excels in qualifying an SSC’s design under the full assortment of loadings and hazards that may arise during its service life. Some examples of loadings and hazards described below illustrate the range of our proven capabilities:
Proven capability to prognosticate the structural response of: Anchored and free-standing structures and components with full recognition of soil/structural interaction effects, where applicable; Under-water (submerged) structures and components (including sloshing effect of the water mass, hydraulic coupling from proximate bodies, etc.); SSCs with geometric or material non-linearity structures vulnerable to instability (such as buckling).
Tornadic Wind and Hurricane
High winds and wind-borne missiles are often significant loadings for large exposed structures and buildings. The object of the analysis is to guide the compliance of the subject structure with the governing codes through suitable modifications to the design. The local damage of the structure from a wind-borne projectile is typically performed on LS-DYNA.
Usually germane to structures located on a river basin, a flooding event may be dynamic (moving water) or static (hydraulic pressure). In heat generating systems, structures and components — such as ventilated casks that hold fissile material — flood has the additional consequence of blocking rejection of heat. Holtec Government Services has performed scores of dynamic and static flood analyses on nuclear installations.
Devices for Heavy Load Handling
Handling of heavy loads is a critically important operation because the consequence of an uncontrolled load lowering event can be so catastrophic. The regulatory literature in this area (such as NOG-1, NUREG-0554, NUREG-0612, ANSI 14.6) is fittingly extensive and highly prescriptive. Holtec Government Services has developed a series of analysis methodologies for qualifying load handling systems and appurtenances such as cranes, crawlers, lift yokes and the like. The expertise includes: Upgrading of cranes to ASME- NOG-1 single-failure-proof (SFP) pedigree; Qualification of lifting devices with consideration of non-conformal yoke-to-hook contact interface; Seismic qualification of suspended heavy load from a crane hook (to check against possible impact with proximate structures as well as stress compliance).
Analysis of Fluid Systems
The analysis mission for fluid systems may be classified into four groups: 1) Simple one-dimensional systems typified by in-pipe flows (single phase and two phase). The main objective is computation of pressure loss and analysis of water hammer, 2) Forced flows in heat exchangers. The object is to compute pressure loss, heat transfer coefficient and to assess the risk of flow induced vibrations. 3) Systems containing complex 3-D flows with laminar, transitional, and turbulent regimes (such flow conditions are encountered in a variety of equipment such as heat exchangers, reactor cores and fuel baskets of casks) that required a refined articulation of the flow field. 4) Systems vulnerable to fluid-elastic whirling, the Strouhal effect, acoustic resonance, turbulent buffeting, and other forms of instability from fluid flows such as transmission lines, large surface condensers, large evaporators and the like.
*Analysis of coupled thermal and hydraulic systems using RELAP
Holtec Government Services utilizes mature private domain (company developed) and public domain computer codes (QA validated) for the above class of problems.
Holtec Government Services performs criticality safety analyses and evaluations of fissile materials such as processes and fuel assemblies used in nuclear reactors, radiation shielding analyses for spent fuel and other radioactive materials, and core design calculations, using state-of-the-art codes such as MCNP, SCALE and CASMO/SIMULATE. Criticality safety analyses cover a large range of condition. They are performed for various fuel designs (PWR, BWR, VVER), for wet storage conditions (spent fuel pool) and dry storage/transportation casks, for fresh fuel and spent fuel (utilizing NRC approved burnup credit methodologies), and include both UO2 and MOX fuel. These calculations are performed as part of safety analyses reports and to optimize existing and new designs of storage and transportation system from a criticality safety perspective. As an example, the figure below shows the neutron flux distribution from fission processes a cross section of a spent fuel transport cask loaded with content of different reactivity in different cells.
Radiological evaluations and dose calculations range from simple shielding geometries for radioactive waste as well as complex geometries such as spent fuel storage and transport casks or reactor cores. Holtec Government Services has performed extremely complex evaluations of entire loaded arrays of nuclear fuel storage systems. Calculations cover both neutron and gamma radiation, at any distance from the source, from the cask surface to site boundaries miles away. Calculations also include occupational dose evaluations that analyze dose to personnel based on the operational steps around spent fuel casks. As an example, the figure below shows the combined neutron and gamma dose field in and around an interim storage facility with a large number of storage casks. Finally, Holtec Government Services has experience in core design for nuclear reactors, optimizing the fuel design and performing design calculations for normal and accident conditions.
Insidious hazards – Fatigue, creep and brittle fracture
Cyclic fatigue is a hazard to any component subject to cyclic thermal and/or pressure loadings. Qualification for cyclic loading is performed using the guidelines of ASME Section III Subsection NB-3222.4 which provides the methodology (Miner’s rule) to compute the cumulative damage factor for components subject to a large number of dissimilar cyclic loadings. Creep is a concern in pressure vessels operating at elevated temperatures such as liquid sodium reactors. The service life of creep-constrained designs is, of necessity, limited by the amount of permissible creep. The ASME code provides a methodology for computing cumulative creep that Holtec Government Services has used in certain applications. Long term settlement of a soil foundation under load is an example of ambient temperature creep. Our methodology for subgrade settlement has been approved by NRC. Brittle fracture is a concern in thick-walled pressure vessels and weldments subjected to thermal or mechanical shock loadings. The ASME Code contains restrictions and required testing to qualify materials for applications vulnerable to brittle fracture.
Material selection and protection from environment-induced degradation
- Environmental attack on exposed surfaces is an important consideration in the design of systems, structures and components (SSCs). The selection of the material of construction is a critical decision to protect the SSC from adverse environmental effects. Typical hazards are: Stress corrosion cracking (in stainless steels), surface corrosion (carbon steels), Galvanic corrosion, pitting corrosion, crack propagation from thermal shock, etc.
- Attack on the internals of an SSC from generation of aggressive species during operation is another form of degradation which is routinely considered as a part of the Company’s design practice. A classic example of severe equipment damage from concentration of solutes produced from operation is the Inconel tubed steam generators in the light water reactor plants.
Holtec Government Services maintains a comprehensive information base of potential environmental damage mechanisms that is utilized in the selection of materials.
In their quest for an effective and economical solution, our specialists are not reluctant to escalate the sophistication of the analysis model. Seismic analysis of SSCs provides a typical example: Upon finding that a static seismic analysis is unable to provide a satisfactory answer, our team can invoke the response spectrum method, and if that does not work, then perform a direct time history analysis of the SSC. Holtec Government Services views many physical modifications made to SSCs in operating plants can be averted (with significant associated savings) by utilizing more advanced and refined analysis techniques. In other words, pragmatic use of advanced analysis methods in the service of safe and economical design is the essence of our technical approach.
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