A Review of the Evaluation, Simulation, and Control of the Air Conditioning System in a Nuclear Power Plant

Abstract

This review paper aims to present a comprehensive overview of the evaluation, simulation, and control of heating, ventilation, and air conditioning (HVAC) systems in nuclear power plants (NPPs), specifically highlighting their importance in maintaining operational safety, thermal performance, and energy efficiency. The study’s authors summarize recent developments in HVAC technologies, such as passive cooling systems, data-driven energy management frameworks, and intelligent control strategies, to cope with the specific challenges of NPPs. Various passive cooling systems, including heat pipes, thermosyphons, and loop heat pipes, have proven themselves by their ability to remove residual heat from spent fuel pools and reactors power plants with high efficiency. Through experimental studies, they have shown their ability to eliminate operational vulnerability to accidents or guarantee any desired long-term cooling. Intelligent sensor networks allow a more data-driven approach to HVAC control, enabling online energy management frameworks and advanced intelligent control systems. These exhibit considerable promise for optimizing HVAC performance, decreasing energy consumption, and improving operational flexibility in multi-zone systems. Such capabilities are ideal for addressing the dynamic and safety-critical nature of NPPs. They are first enabled by the use of these technologies for real-time monitoring, predictive maintenance, and adaptive control. When applied with advanced HVAC control systems, passive cooling techniques provide an exciting route to improve safety and energy efficiency. An overview of the key findings is that robust thermal management solutions combined with intelligent control and intelligent adaptation are essential when addressing the rapidly evolving demands of nuclear energy systems. This work highlights the priorities in the next generation of nuclear power plants, which should actively pursue seamless integration of out-of-system technologies into existing NPP infrastructures, enabling scalable, cost-effective, and resilient solutions.

1. Introduction

Nuclear power plants (NPPs) are indispensable in catering to the growing global energy demands while ensuring a reduction in greenhouse gas emissions. However, for these to operate safely and effectively, much care must be taken with the environmental control systems they depend on, most notably HVAC (heating, ventilation, and air conditioning). To this end, HVAC systems in NPPs fulfill two primary roles—they provide and maintain conditions that guarantee the workability of staff, the functioning of their devices, and containment tightness during regular operation and accident conditions. The review is then tailored towards the recent advances in passive cooling systems, thermal management applications, control systems, risk mitigation programs, and sustainability in nuclear power plants, focusing on HVAC simulation, assessment, and management. NPP HVAC design must maintain reliable cooling methods under normal and abnormal conditions. A separate concept describing independently operated water storage systems has been proposed to improve emergency plant safety [1]. This review builds on previous work by incorporating new passive rejection technologies, state-of-the-art thermal management techniques, and intelligent control systems into NPP HVAC design and operation. Experimental studies show that heat pipes are capable of removing residual heat from spent fuel pools in both atmospheric and sub-atmospheric conditions [2]. Novel passive cooling systems, validated using simulations, are developed to complement these efforts to ensure safe operating conditions in spent fuel pools [3]. A passively residual heat removal system is also discussed, highlighting the use of two-phase thermosyphons [4]. Moreover, heat removal efficiency calculations and system performance calculations crucial to confirming the cooling strategies are also effectively described in detail, as outlined in calculations in

Table 1. Heat removal calculations [2].

Equation	Number
$Q=Q_w{c}_{p,w}{\rho }_w\left(T_{w1}-T_{w2}\right)$	(1)
$h_e={\displaystyle \frac{Q}{A_e\Delta T_e}}$	(2)
$∆T_e={\displaystyle \frac{T_{Tw;in}+T_{w;out}}{2}}-T_e$	(3)
$h_C={\displaystyle \frac{Q}{A_C{∆T}_C}}$	(4)
$∆T_c=T_c-{\displaystyle \frac{T_{a1}+T_{a2}}{2}}$	(5)
$m=Q/\left(h_{\mathrm{out}}-h_{\mathrm{in}}\right)$	(6)

. The results of these calculations are used to establish a performance index, which helps optimize various passive and active cooling circuits found in nuclear power plants.

The heat removal rate for the heat pipe is vital to assess its performance and was calculated using the enthalpy variance for the hot water entering the assistant hot water tube, as shown in Equation (1). The average heat transfer coefficient for the evaporator and condenser are important heat pipe parameters that are calculated using Formulas (2) and (4), respectively. Equation (6) yields the R134a mass flow rate within the heat pipe [2].

Past research has not adequately assessed the performance of passive cooling systems for spent fuel pools; in this regard, thorough experimental examinations were carried out. Thermal hydraulics and system resilience also underpin HVAC performance in NPPs. System resilience is demonstrated in experimental studies of the thermal response of spent fuel pools to loss of active heat removal scenarios [5]. Thermal management strategies to mitigate risks in loss-of-active-heat-removal scenarios have not been thoroughly explored until this work. In parallel, simulation models investigating the safety margins of large-scale molten pools after the late-phase in-vessel water phase help inform frameworks used in classifying the etiology of potential accidents [6]. All the studies above indicate the need for well-designed thermal management systems to ensure operational safety and avoid catastrophic failures.

Research on intelligent control systems and numerical modeling can further improve the efficiency and reliability of HVAC systems in nuclear power plants (NPPs). By comparing high-performance HVAC rule-based controls with advanced intelligent controllers, this line of research demonstrates how model-based solutions can lead to enhanced performance for energy optimizations [7]. Moreover, life cycle analyses confirm the broader impact of energy optimization strategies, specifically retrofitting existing buildings with energy-efficient HVAC systems [8]. Such systems rely on objective evaluations of the environmental impact of power plants using an analytic hierarchy process [9], thus underscoring the importance of using sustainable practices in power plant operations.

Maintaining containment integrity and conducting risk assessment are paramount for HVAC design in NPPs. The analysis of the influence of spray systems on containment parameters during severe accidents (LBLOCA and TLOFW) showed that a spray system could reduce the risk of containment failure and ensure people’s safety outside the containment system. Spray systems are used in VVER1000/V446 reactors to mitigate risks stemming from severe accidents and maintain the integrity of the containment [10]. Based on nuclear power unit mechanics of failure assessment, the work has implemented a detailed modeling of cold source blockage investigations. Further research development directly benefits from the current risk assessment frameworks available [11]. Furthermore, sensor fault tolerance methods have been developed to maintain reliable instrumentation in safety-critical conditions [12]. This has become important to ensure robust monitoring systems for enhanced NPP safety.

Sustainable HVAC system design encompasses policy, the environment, and technical improvements. Establishing sustainable operations for coastal NPPs is similar to assessing water resources [13]. Comparably, life cycle analyses on retrofitting existing buildings with energy-conserving systems accentuate the system-wide impact of energy-saving strategies [8]. These initiatives align with objective evaluations of power plant emissions, using methodologies like the analytic hierarchy process to assess environmental impact comprehensively [9].

Corrosion management and material science are also vital to the longevity and reliability of HVAC systems. Research on the buildup of surface corrosion in fuel elements has demonstrated its effects on flow and heat transfer characteristics, offering the possibility for fuel performance improvement [14]. Studies have also been conducted on the corrosion resistance of various materials, including SA106B tubes under high-temperature pressurized water conditions, providing valuable strategies for material selection and heat treatment, radiation-resistant materials, and designs that ensure durability for long-term if used in high radiation zones [15]. Similarly, there is an increasing requirement for a well-integrated corrosion management strategy to alleviate safety issues associated with corrosion and its effects, and this need is reinforced in the context of unidentified deposits in pressurized water reactors [16]. These are based on comparative studies of FeCrAl alloys in pressurized water reactors, which show enhanced fuel cladding performance under severe conditions [17].

The dynamics of precipitate formation in research nuclear reactor evaporators using numerical modeling and experimental validation of heat transfer leads to valuable insights into operational problems [18]. A parallel algorithm—the virtual lattice method—is presented for computationally efficient Monte Carlo transport simulations of dispersion nuclear fuels, leading to a new level of exploration for materials, which should provide computationally expedient approaches for material analysis [19].

The advantages of improving the plant’s overall safety by using a hybrid passive cooling system, for both the reactor and the spent fuel pools, have been discussed [20].

The condensation of steam in the presence of air is analyzed on a local level to develop knowledge about its transfer mechanisms within the containment systems [21]. The performance of quenching meshes for safety assessments in hydrogen combustion scenarios at different pressures is obtained [22]. The work studies life cycle management systems focused on chillers in nuclear power plants with the objective of improving maintenance strategies and increasing equipment life [23].

An overview of the Indian PHWR design, memorable highlights, and achievements is clearly discussed [24]. Using airborne particulate matter to measure 129I, a new approach reconstructs 131I dispersion from the 2011 Fukushima nuclear accident, improving environmental monitoring [25]. For example, loss-of-cooling accident calculations on a wet storage pool give information on key parameters that help define safety margins in emergency conditions [26]. The need to utilize coupled code methodologies for best-estimate safety analysis of nuclear power plants is presented in this article, describing the advantages these simulations can provide in terms of accuracy and reliability [27].

To summarize, this review summarizes recent progress in evaluating, simulating, and controlling heating, ventilation, and air conditioning (HVAC) systems of nuclear power plants. By exercising novel passive cooling approaches, thermal hydraulics, intelligent control systems, or even policy-oriented frameworks, the studies reviewed here appear to represent meaningful steps toward actualizing HVAC operations in NPPs. This body of work sets the groundwork for future advancements in HVAC technology, paving the way for safer, more efficient, and environmentally friendly nuclear energy generation utilizing experimental, numerical, and policy-based knowledge. A holistic conceptual review of these developments is presented in

Table 2. Conceptual analysis.

Plant Section	Primary Function	Role of HVAC	Connection to Other Sections
Nuclear Reactor	Energy generation	Cooling the surrounding environment and preventing overheating	Cooling system, safety systems
Cooling System	Cooling the reactor and spent fuel pools	Coordination with cooling systems to maintain temperature and humidity	Reactor, safety systems
HVAC System	Temperature, humidity, and air quality control	Maintaining environmental conditions, pollution control, and safety support	All sections
Safety Systems	Handling potential accidents	Providing clean and cool air for safety systems and preventing contamination	Reactor, cooling system
Control and Monitoring Systems	Monitoring overall plant performance	Sending temperature and humidity data to control systems	All sections

, which sequentially classifies the main concepts, methods, and results. The systematic examination of approaches not only underlines the relationships among diverse strategies but also pinpoints gaps and areas for additional inquiry, thereby laying the groundwork for the advancing development of HVAC systems in nuclear facilities. Figure 1 illustrates the methods used in the reviewed articles, showcasing the variety of approaches employed in this field.

2. Materials and Methods

Recent studies on passive cooling technologies, thermal management, numerical modeling, multi-physics, and experimental validation approaches for evaluating, simulating, and controlling HVAC systems for nuclear power plants (NPPs) have shown that these methods are very solid and can address the difficulties of assuring fault and quality alongside competent and feasible NPP HVAC systems.

One of the most effective solutions is passive cooling technologies, which improve the safety and reliability of NPPs. They developed and validated a novel passive spent fuel pool cooling system using simulations, demonstrating that it could ensure safe operating conditions in loss-of-cooling scenarios [3]. The investigations of passive residual heat removal systems have focused on using two-phase thermosyphons [4], which provided a comprehensive review of advanced thermal management mechanisms. Nonetheless, the thermal performance of approximately 10 pairs of separated heat pipes with compact structures has been experimentally investigated in thermal properties studies as an intensive approach to spent fuel pool heat transfer characteristics [28].

Thermal management is one of the key challenges for the performance of HVAC systems in NPPs [22]. Safety margins are evaluated in three-layer molten pools (core melt, coolant, and gas layer) using simulation models. During late-phase accidents, injecting water into the vessel creates these pools, which greatly affect the mitigation framework and the whole accident behavior [6]. Thermal schemes combined with numerical optimization of finned tube bundle heat exchangers reveal their potential to effectively dissipate heat to ambient air for passive spent fuel pool cooling [29]. Moreover, for the natural circulation of helium–xenon gas mixtures, experimental studies on flow and heat transfer characteristics are crucial to embed a complex, realistic equation inefficient cooling system design [30].

One of the significant areas involves numerical modeling during the HVAC system operation at varied operating conditions. An integrated design and examination of the pressurized heavy water reactor and spent fuel pool passive cooling system were proposed to require the first two-generation passive safety enhancement for the entire power plant [20]. The data source for nuclear reactor defects under abnormal operating conditions is provided with numerical calculations of typical abnormal conditions in the secondary circuit system of a Hua-long Pressurized Reactor [31]. The multi-physics methodology that couples Monte Carlo with CFD (computational fluid dynamics) can improve the accuracy of reactor core modeling, allowing better analyses of the physics of complex phenomena [32].

Traditional rule-based systems need predefined logic while AI-based systems dynamically change as per the conditions resulting in better energy efficiency. The driving forces in HVAC energy management are data-driven technologies that use machine learning and artificial intelligence. Detailed experimental results of a data-driven online energy management framework for HVAC systems (heating, ventilation, and air conditioning), improving energy efficiency while maintaining comfort levels and reducing operational costs, have been proposed [7]. Energy Conservation technologies for the Supply of Fresh Air to zero-energy buildings have introduced creative solutions that can be considered in the context of NPP [33].

Without proper and effective corrosion management systems, the HVAC systems in NPPs would not perform to their fullest potential. Thus, numerical studies on fuel elements’ corrosion surface deposition show how the mixture of different solids can alter the flow and heat transfer properties [14], providing opportunities to enhance the performance of fuels. Xenon behavior modeling using multiple transport mechanisms for molten salt reactors gives an idea of how the materials behave under extreme conditions [34]. Comparative studies have suggested that FeCrAl alloys may enhance fuel cladding performance under extreme conditions in pressurized water reactors [17].

Simulation models require validation against experimental data to verify their accuracy and reliability. The applicability of hybrid Monte Carlo/deterministic activation calculations was validated based on the thermal shield of Enrico Fermi NPP decommissioning activities [35]. This method driven by AI has been confirmed with simulation and experimental data. Experimental investigations into the transient thermoelectric features of heat pipe-cooled nuclear reactors have been performed, serving as benchmarks for numerical simulations [36]. Markov chain Monte Carlo methods and Gibbs sampler Bayesian calibration and fitting of nuclear thermal-hydraulic models provide powerful tools for model validation and uncertainty quantification [37].

Multi-scale and multi-physics modeling approaches are gaining attention to tackle the coupling between various components in HVAC systems. The characteristics of modeling methods overviewed in several works for spent fuel pools with different system codes reflect the strengths and limitations of multiple models [38]. Integrated modeling approaches have become feasible, as evidenced by numerical simulations of flow and reaction features in helium-heated steam reformers and high-temperature reactors [39].

To improve the understanding of heat transfer mechanisms in containment systems, local phenomena are analyzed instead of steam condensation in the presence of air [21]. Coupled codes are used to conduct best-estimate safety analyses for nuclear power plants and improve the accuracy and reliability of simulations [27]. This work presents calculations of loss-of-cooling accidents in wet storage pools, reflecting some primary variables determining safety margins under emergencies [26]. Containment performances in general seismic events and robust containment designs prevent spent fuel storage accidents in a Mark III upper pool [40].

Developing cold source blockage investigation and risk assessment research activities for Chinese nuclear power stations enables better risk management systems [11]. Spray systems in the VVER1000/V446 NPPs prove their effectiveness in eliminating risks and ensuring containment integrity in accidents: LBLOCA, TLOFW contact condition, passive cooling systems, and containment designs that help mitigate risks during extreme weather or cooling system failures contribute to the framework that keeps this running well [10]. The application of integral effect test data to quantify constituent equation influence on safety analysis provides valuable information for model validation and improvement [41].

The work on life cycle management systems for the chillers of nuclear power plants seeks to minimize the cost of maintenance through optimized strategies along with extended life of the equipment [23]. Thermal modeling of metal hydride hydrogen storage systems shows that operating parameters and reactor geometry can significantly impact hydrogen delivery performance [42].

Figure 2 presents the crucial methods applied in the articles surveyed, reflecting the various experimental, numerical, and policy methods that work together to improve the performance and safety of HVAC systems in nuclear power plants. Such techniques highlight the multidisciplinary context of modern HVAC improvements [43,44,45,46].

The flow of information regarding how to evaluate and perform mathematical calculations for HVAC systems, indicating what aspects need to be modeled and what calculations need to be performed mathematically, is depicted in Figure 3. These methods represent the basis for validating the efficiency and safety of systems [47,48,49].

Table 3. Modeling method.

Modeling Method	Article Title
Dissimilarity-based boosting technique for the modeling of complex HVAC systems	Boosting Technique
Simulation and multi-aspect analysis of a novel waste heat recovery process	Simulation-Based Multi-Aspect
An experimental study on the inherent operational characteristics of a DX unit	Direct Expansion Experimental Analysis
Experimental analysis of an air-to-air heat recovery unit	Air-to-Air Heat Recovery Experiment
Solid Desiccant System Design	Solid Desiccant System Design

presents a summary of the modeling techniques utilized in simulating HVAC system performance, highlighting the various methods and assumptions necessary for improving safety and efficiency in the design, operation, maintenance, and monitoring of nuclear power plants.

3. Discussion

The multidisciplinary approach to evaluating, simulating, and controlling HVAC systems in NPPs integrates advancements in passive cooling technologies, thermal management, numerical modeling, corrosion mitigation, safety assessment, and environmental considerations. We summarize three studies reviewed here that help advance empirical knowledge in this area and highlight the state of the art and research opportunities moving forward.

One of the most essential ways for safety enhancement in NPPs, especially in the spent fuel pool, is through passive cooling technologies. Experimental studies demonstrate the performance of heat pipes for heat removal in loss-of-cooling scenarios in various environments, from atmospheric to sub-atmospheric [2,49]. Experimental studies confirm that heat pipes and thermosyphons could be effectively used to remove residual heat in spent fuel pools and could operate reliably during accidents. Two-phase thermosyphon loops have been investigated for long-term passive spent fuel pool refrigeration [50,51], demonstrating that thermosyphons represent a strong passive safety technology option for both standard and accident conditions. Further investigations through thermal analyses have corroborated the efficacy of heat pipe-assisted passive cooling systems in adequately dissipating heat even during challenging environmental conditions, composed of an analysis of temperature with heat pipe and thermosyphon performance [52]. The results are confirmed by numerical modeling [53], while several analyses using RELAP5/MELCOR coupling can also describe the system behavior under different operational conditions. Passive methods include thermosyphons and heat pipes, often offering effective long-term cooling [54]. Presumably, interacting with these studies on a combination level, the former seven are essential in keeping the system passive to provide thermal stability and remove heating during emergencies [49,54].

NPP HVAC systems consist of complex phenomena requiring numerical modeling for their simulation. In this context, a multi-scale and multi-physics coupling method for analyzing the transient characteristics of space nuclear reactors has been developed to provide valuable means for predicting how the overall system will respond to varying conditions due to the dynamic characteristics of both the reactor itself and the associated systems in space environments [55]. Monte Carlo transport simulations based on virtual lattice methods enable configuration-efficient modeling of the dispersion of nuclear fuels [19]. Steam generators are modeled with a distributed parameter to improve our understanding of heat transfer and fluid flow in nuclear power plants (NPPs) [56]. This feature allows for in-depth examination of the interaction between these systems, facilitating better design and enhanced operation.

Even so, with the effectiveness of corrosion management, owing to its duration and variability in HVAC system service life, handling corrosion in HVAC systems in NPPs remains an ongoing challenge. The investigation of surface corrosion deposition in fuel elements shows that it affects the flow and heat transfer characteristics, leading to the optimization of fuel [16]. Studies have shown that materials such as SA106B tubes under high-temperature pressurized water conditions did exhibit corrosion resistance, providing a useful basis for material selection and heat treatment [15]. The vulnerability to corrosive damage and high-risk implications emphasizes the need for comprehensive corrosion management in existing regulatory frameworks.

Safety evaluation and risk management are paramount parts of the structure and performance of HVAC systems in NPPs. The topic is not a theory as such; heat pipes and thermosyphons have been initiated and validated in practice. Further-loss-of-cooling accident compilations for wet storage pools give essential information on safety margins in emergency situations [57]. Dynamic modeling and control of spent nuclear fuel storage pools in periodic operation and station blackout scenarios illustrate that robust containment designs are vital [58]. Additionally, the aforementioned safeguards consist of corrosion management methods, fault-tolerant sensor systems, and enhanced material choice. The development of fault-tolerant sensor technology also adds to risk mitigation by allowing the functioning of instrumentation in safety-critical environments [12]. Moreover, policies on assessments of overall water resources used by coastal NPPs advocate the necessity of sustainable practices during the operation of plants [13].

Environmental and energy efficiency factors are crucial elements in the sustainable use of HVAC systems in NPPs. High-efficiency air conditioners and fluorescent lamps are observed to save substantial energy and environmental benefits in life cycle analyses of retrofitting existing buildings [8]. Methodologies like the analytic hierarchy process allow for an objective evaluation of the emissions of the power plants, which can serve as a comprehensive framework for the environmental impact assessment [9]. A new approach to reconstructing the spatial distribution 131I due to the 2011 Fukushima nuclear accident helps advance environmental monitoring methods [25]. In combination, these studies add to a more complete picture of the ecological perspective of NPP operation.

Studies focusing on spent fuel pool thermal hydraulics in loss of active heat removal scenarios provide key information about how resilient the system is for transients [5]. Accident mitigation frameworks are also informed by simulation models investigating molten pools’ fracture mechanics safety margins after late-phase in-vessel water injection [54]. Together, these studies highlight the significance of sound thermal management systems for operational safety and avoiding catastrophic mishaps.

Additionally, advanced sensor networks on HVAC systems help improve efficiency through real-time monitoring, predictive maintenance, and adaptive control. The intelligent control system and numerical modeling significantly improve the efficiency and reliability of HVAC systems in NPPs. This section introduces the most recent data-driven, machine learning-based, or active learning methods for modeling complex HVAC systems. Owing to the power of machine learning and the potential of advanced analytics for system optimization, dissimilarity-based boosting methods for active learning are developed for complex HVAC systems modeling. The AI-based systems lead to better energy efficiency over traditional rule-based methods [59]. Dynamic optimization approaches to condenser cleaning cycles can improve the overall performance of the system, decreasing operating costs [60]. In conclusion, the methodologies demonstrated here provide helpful tools for enhancing HVAC system performance and reliability.

HVAC design in NPPs requires appropriate consideration of containment integrity and risk assessment. One such example is the HPR1000 reactor that incorporates passive cooling systems in the spent fuel pools. In terms of severe accidents (such as LBLOCA and TLOFW), studies evaluating the effects of spray systems on containment conditions have shown that they can help mitigate the associated risks and help maintain containment integrity [43].

An investigation into cold source blockage has been conducted to further enhance the risk assessment framework in Chinese nuclear power plants [61]. Furthermore, as effective monitoring in safety-critical environments is increasingly essential, sensor fault tolerance technologies have also been developed and discussed in recent years [12].

Steam superheaters have also been modeled using advanced numerical techniques to obtain information about the thermal and hydraulic behavior of the superheaters over a wide range of operating conditions [62]. Furthermore, as the cooling system is critical to the proper functioning of research reactors, many transient thermal–hydraulic studies of single-channel blockages have been performed [63]. Overall, the intrinsic operational characteristics and dynamic energy efficiency of direct expansion air conditioning units are described experimentally in reference [64]. The potential of a district heat recovery system peering through the air-to-air heat recovery units in the balanced ventilation systems has been found useful in [65,66] and providing energy efficiency for residential and industrial purposes. Several studies have dealt with solid desiccant air-conditioning systems and the problems of design parameters and humidity control, all of which are relevant to NPPs [67].

The design of a new multi-aspect process incorporating an electricity generation unit, heating unit, desalination unit, liquefied carbon dioxide production, natural gas recovery, etc. was simulated to maximize the utilization of energy in NPPs [68]. For this reason, several studies on indirect evaporative cooling systems have reported enhanced cooling performance if condensation phenomena from fresh air streams being vented through the system are taken into consideration [69]. These properties may make waste heat recovery technologies a valuable addition to many HVAC systems, improving overall plant efficiency.

A review of the use of artificial intelligence-based techniques for different styles of anomaly detection in the operational activities of nuclear power plants has also been performed, wherein the importance of real-time data analysis and predictive maintenance strategies has been presented [70]. Hydrogen dispersion studies and airborne radionuclide monitoring indicate that the safety of containment and leak detection systems is critical [71,72].

Other devices, including innovative water purification systems designed for spent nuclear fuel storage pools, are also available, among which improvements in liquid waste decontamination systems minimize contamination risks [73].

They could be applied in pipeline detection robots with radiation-proof material, which helps provide inspection capabilities in high-radiation conditions and pipeline integrity and maintenance-related problems in a high-radiation environment [74]. Nanofluids have been studied in optimizing the performance of heat exchangers in a pillow-plate for organic Rankine cycle systems, indicating the potential of using nanofluids as heat transfer agents in municipal solid waste power plants [75]. This is possible due to the newer materials and technologies that are making HVAC systems more efficient.

Combing through various studies, it can be found that membrane heat exchangers and liquid-to-air membrane energy exchangers both have gained a lot of attention aimed at improving HVAC performance in NPPs and other industrial applications [76,77]. There are new possibilities for this energy storage and saving in the HVAC applications by developing dynamic modeling frameworks of solid–gas sorption systems [78]. Advanced thermal management strategies are utilized [79,80]. Some NPPs already have passive cooling systems in place. The HPR1000 reactor, for example, combines active and passive safety systems—as seen in its use of thermosyphons for the cooling of spent fuel pools, to tackle coolant leakage and hydrogen dispersion topics within advanced reactors, notably fusion–fission hybrid reactors, and supercritical water-cooled fast reactors. Advances in the HPR1000 reactor include the integration of both active and passive safety features and emphasize the role of integrated safety in modern NPPs [81]. Relevant studies on hydrogen dispersion in the metallurgical industry and hydrogen production plants connected with NPPs highlight essential measures to reduce relevant accident risk [82].

Such maintenance of charged colloidal filter material from NPP coolants will provide lasting assurance for the HVAC systems [47]. Nuclear island mechanical equipment technical supervision ensures the sustainability of unit safety operations by monitoring the condition of equipment and performing scientific maintenance [83]. The proposed unidentified leak identifications based on EVR ventilation condensate form a new method that makes it possible to identify leaks in NPPs [84]. The radioactive safety of the industrial steam provided by PWR nuclear power plants has been studied, and it is generally believed that minimizing the radioactive contamination of the steam system is an essential part of the requirements for safe HVAC operation [85].

Overall, these studies present some promising insights into HVAC operations in modern NPPs. These include passive cooling innovations and thermal hydraulics, intelligent control systems, and policy-driven frameworks that serve as steppingstones for future advancements in HVAC technology, ultimately enabling safer, more efficient, and sustainable nuclear energy production. This body of research delivers a robust framework for addressing the challenges of NPP HVAC systems by combining insights from experimental, numerical, and policy perspectives.

4. Conclusions

Epistemic uncertainty constitutes a topical field in this review, focusing on the evaluation, simulation and control of HVACs in nuclear application, revealing the state-of-the-art achievements and difficulties which represent a significant burden on security and operative efficiency in such systems. Notable findings are Tank Storage functions in emergency cooling as well as the passive principle of cooling for spent fuel pools; the necessary parts auxiliary systems include two-phase thermosyphons and spray systems as thermal stabilization. Beyond loss-of-coolant accidents, advanced leak detection and long-term passive cooling systems are also crucial solutions.

Tools such as simulations support this hypothesis, showcasing the performance of passive cooling systems when active heat removal systems are no longer functional Research initiatives involving fork-end heat pipes, compact designs, and data-driven energy management frameworks improve thermal performance and HVAC operations. Possibilities of reactor behavior in abnormal conditions can be studied more numerically, using Monte Carlo and computational fluid dynamics approaches.

Thermal performance analysis of heat exchangers and Bayesian calibration of models highlight the advantages in applications with low heat fluxes and predictive accuracy. These improvements are part of a bigger trend of incorporating advanced technologies for optimizing routine operations and emergency response at nuclear plant sites. Future work will be to reconcile these systems with current and future needs for safety, security, and sustainability.