atw - International Journal for Nuclear Power | 03.2024

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32 Research and Innovation Fig. 1. Hypothetical layout of a reactor site with typical Nuclear Island/Balance of Nuclear Island and Conventional Island Balance of Plant buildings, including HES (on site) and SEF (off site) for hydrogen production. primary circuit is normally transferred to the secondary circuit through boilers or steam generators which raise steam to drive turbines for electricity production. However, hydrogen production could be enabled by separating the primary and secondary circuits with an Intermediate Heat Exchanger (IHX). This would allow process heat to be transferred to a hydrogen pro duction facility using diverse coolant fluids in the secondary circuit through heat exchanger(s). A nuclear enabled co-generation site for hydrogen prodcution would therefore require additional systems which are not in current nucelar power plant arrangements, this includes: ⁃ a Heat Extraction System (HES), ⁃ a Steam Electrolysis Facility (SEF). Figure 1 provides an overview of the main systems and the nuclear site boundary. It is argued that for the safety of the reactor the HES, which includes heat exchangers and safety isolation equipment, must be situated within the nuclear site boundary to enable control of isolation in case of an accident scenario. This means that control of systems which can directly impact the performance and response of the reactor remains with the licensee or reactor duty holder for the nuclear licensed site. This control, essential for halting and isolating heat extraction, is vital to ensure safe response to reactor design basis transients and would be treated in a similar way to other steam bypass systems, like those found in the turbine on the conventional island of current nuclear power plants. In contrast, the SEF which is using the steam energy for electrolysis is not strictly required to be within the licensed site. Once the SEF is supplied with hightemperature steam and electricity it can operate autonomously as a standalone chemical processing plant. It may be intuitively assumed that the SEF would also be located on the nuclear site, in fact, locating the SEF off site may present many notable advantages, such as: ⁃ The off-site arrangement allows for flexible modifications and experimentation with the SEF, which currently relies on innovative technology. ⁃ Initial demonstrations may prompt adjustments as operational experience is gained. ⁃ Locating the SEF off the nuclear licensed site is anticipated to reduce deployment costs in construction, operation, and decommissioning phases. ⁃ It facilitates simpler plant modifications since it operates outside nuclear site license regulations which are more onerous than other high hazard industries due to the long-lived consequences if an accident did occur. This approach allows for consideration and risk assessment of the SEF which is in line with the chemical industry and avoids added time, costs and per missioning requirements associated with nuclear site licensing. This approach may offer the opportunity to achieve any necessary approvals for the SEF in less time. Previous experience has shown that a chemical processing plant will generally make many evolutionary changes over just a few years. This is in total contrast to a nuclear licensed site where changes occur over much longer periods due to the safety demonstration, approvals and permissioning required. As such existing arrangements in the site license, like the 10 yearly Periodic Safety Review, would have too long a periodicity and the SEF would require something more frequent. It is also noted that effective management arrangements and a clear understanding of operational changes downstream of the IHX and off-site are crucial for the reactor site to demonstrate safety. Establishing a mechanism to share information between the different facilities which are part of the co-generation arrangement is essential. This would include notifying the reactor site of operational and system changes that might affect nuclear safety or challenge any of the protection systems. It is important that there is an understanding of dynamic hazards or changes in the production process that might impact radiological safety, but may not be immediately visible to the nuclear site. Whilst there are benefits in location of the hydrogen production facility offsite, the final location will require Ausgabe 3 › Mai
Research and Innovation 33 detailed consideration within the design and optioneering processes. This will ensure the risks are appropriately managed, whilst optimising the practicality and efficiency of the cogeneration installation. Regulatory Considerations A fundamental principle of legislation within the UK is that risk is to be reduced to As Low As Reasonably Practicable (ALARP). This principle places a requirement on the duty holder of a site to implement measures to reduce risk, wherever doing so is considered reasonable and it is proportionate. The principle is often demonstrated by implementing safety measures which are recognised as industry Relevant Good Practice (RGP). However, in novel applications or situations where this is absent, then it must be shown that sufficient measures have been put in place up to a point where the reduction in risk (i.e. benefit gained form the measure(s)) compared to the additional cost of implementing more measures has become grossly disproportionate. The ALARP principle applies to all industrial activities in the UK. Within the nuclear industry radiological and nuclear safety assessments are used to evaluate risk. These assessments follow a well-established and rigorous process to meet the requirement of the nuclear installation’s Site Licence Conditions (SLCs). License holders typically have procedures, standards and guidance which are based on their interpretation of the regulator’s Safety Assessment Principles (SAPs). Numerical risk assessment criteria will be contained in these guides for purposes of assessing radiological hazards to workers and members of the public during normal operations and fault conditions. The concept of Defence in Depth (DiD) is very important in the design and operation of a nuclear facility. DiD ensures that there are multiple levels or layers of suitable defence so that if one were to fail another layer would be on hand to prevent a situation developing into an accident. This philosophy means that reactor designs provide appropriate levels of diversity, independence, and redundancy in the safety systems which respond to different postulated fault scenarios, so that even if an accident were to occur there are additional layers which can mitigate the consequences. The aspiration of operating a nuclear reactor as the principal energy source to enable hydrogen production in a cogeneration arrangement provides great opportunities to improve energy efficiencies whilst also de-carbonising both energy production and industrial processes. However, the introduction of significant quantities of flammable materials increases the hazards and therefore overall risk. Experience has shown that fire and explosion hazards tend to dominate the risk associated with production and storage of large quantities of flammable gases (including hydrogen), with explosions due to their nature often resulting in unacceptably high consequences. In theory, mitigation of hazards associated with hydrogen can be achieved by placing the hydrogen production facilities at the greatest possible distance from the nuclear licenced site, which would reduce the associated risk to ALARP. However, in practice when heat assisted technologies are placed closer to the heat source, they offer significantly improved efficiency due to the improved steam quality which is lost during transportation of the steam. Therefore, the location of the SEF will need to be based on a balance between the required efficiencies for the hydrogen production versus an acceptable increased level of risk to the nuclear licensed site. As such consideration of how to effectively manage this risk as part of the Safety Case for a co-generation site arrangement needs to be undertaken and demonstrated to regulators. There are additional widely acknowledged concerns associated with coupling a nuclear reactor and chemical process, which although will require con sideration within any design and safety case, are not considered as significant as the hydrogen explosion hazard. Co-generation also presents the potential for cross contamination to occur. This could result in either radioactivity transfer, in particular tritium, from the reactor to the chemical process and product or chemicals and contaminants from the industrial process entering the reactor systems. Whilst these scenarios present a potential safety challenge and regulatory concerns, they can readily be managed either through the use of an intermediate circuit, or the use of a high integrity heat exchanger system. The former is generally preferred since it provides the potential to utilise different heat transfer fluids. Detection within the intermediate circuit provides a strategy to identify if contamination occurs and allow for appropriate action to be taken. A final consideration is associated with the potential for increased design basis transients for the reactor, such as a sudden loss of load. This scenario is expected to occur more frequently within a chemical process compared to a turbine trip which is a well understood fault for a conventional reactor solely generating electricity. Transients during operation need to be understood and modelled to ensure that the reactor remains in the safe operating envelope, and would form part of the design basis for the equipment and protection systems. Safety Case Considerations The principal safety requirement of a nuclear plant is that radioactive material is completely retained inside the plant, even during extreme accidents, with no severe consequences outside the site fence. There is already a wealth of knowledge and experience in the nuclear industry for managing the hazards associated with using and storing hydrogen gas at a nuclear licensed site. Although the management of specific hazards can vary between different sites it should be noted that the general approach to safety and the safety management strategies are usually the same. This is Vol. 69 (2024)
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Page 3 and 4: Editorial 3 Zu teuer und zu langsam
Page 5 and 6: Did you know? 5 Did you know? Zukun
Page 7 and 8: Feature: Environment and Safety 7 V
Page 9 and 10: Feature: Environment and Safety 9 (
Page 11 and 12: Feature: Environment and Safety 11
Page 23 and 24: Interview 23 Die Sicherheit steht a
Page 25 and 26: Interview 25 Endlagerung in der Sch
Page 27 and 28: Energy Policy, Economy and Law 27 Z
Page 29 and 30: Energy Policy, Economy and Law 29 A
Page 31: Research and Innovation 31 Nuclear
Page 35 and 36: Research and Innovation 35 Fig. 3.
Page 37 and 38: Fuel 37 Progress in ceramic technol
Page 39 and 40: Fuel 39 The laser bonding technolog
Page 41 and 42: Die Digitalisierung Ihrer Gebäudef
Page 43 and 44: Spotlight on Nuclear Law 43 Verzög
Page 45 and 46: Spotlight on Nuclear Law 45 IV Folg
Page 47 and 48: Environment and Safety 47 Abb. 1. F
Page 49 and 50: Environment and Safety Anzeige 49 T
Page 51 and 52: Environment and Safety 51 Fazit Zus
Page 53 and 54: At a Glance 53 Kontakt Timo Knoll G
Page 55 and 56: Vor 66 Jahren 55 Vol. 69 (2024)
Page 61 and 62: Buchbesprechung 61 Neuerscheinung z
Page 63 and 64: KTG-Fachinfo 63 rund 5,6 Milliarden
Page 65 and 66: KTG-Fachinfo 65 Investitionen, Stru
Page 67 and 68: KTG-Fachinfo 67 aktuellen Diskussio
Page 69 and 70: Kerntechnik 2024 69 Programmvorscha
Page 71 and 72: Kerntechnik 2024 71 Technical Sessi
Page 73 and 74: Kerntechnik 2024 73 Poster Session
Page 75 and 76: Kerntechnik 2024 75 Unsere Partner
Page 77 and 78: KTG Inside 77 Mitgliederversammlung
Page 79: SEMINARPROGRAMM 2024 Grundlagenschu

atw - International Journal for Nuclear Power | 03.2024

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