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Interim Dry Storage – Creep (ZIRAT29/IZNA24)

Fuel Material, Interim Dry Storage

Dry storage of commercial spent nuclear fuel (CSNF) is a well-established technology. As of 2024, spent nuclear fuel elements from commercial power plants and from research reactors have been stored in a dry state for nearly 40 years and 50 years, respectively. The overarching goal is preventing CSNF degradation that would result in multiple fuel rod failures during dry storage, at least through post-storage retrieval for reprocessing or placement and sealing in a container at a final disposal repository. Since performance with dry storage has already been shown acceptable for tens of years, the emphasis is presently on any changes that may occur during extensions of the dry-storage time periods to a hundred years. This Special Topic Report addresses Thermal Creep. It is shown that thermal creep under normal conditions of storage is unlikely to result in cladding rupture for present, as well as later.

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Loss of Coolant Accident (ZIRAT29/IZNA24)

Fuel Material, LOCA and RIA Fuel Performance

During and after a Loss Of Coolant Accident, the core must be coolable, and structural integrity must be maintained. The fuel cladding temperatures during a LOCA may increase over 1 000°C, resulting in:

• Steam oxidation of the cladding
• Cladding embrittlement,
• Ballooning and burst if the rod internal pressure is large enough and,
• Finally, if the high temperatures are maintained long enough, the Zr oxidation reaction may become so exothermic that fuel rod cannot be cooled.

Fuel safety criteria in most countries are based on the United States Nuclear Regulatory Commission (USNRC) criteria. The Japanese and the French criterion are not based on zero ductility of cladding, but on the failure threshold value determined in the integral thermal shock tests under restrained conditions. The idea of this report is to tell the “LOCA story”, from physics to acceptance criteria including a short background to the LOCA phenomenon focusing on the data and information which are used in the current design approaches focusing on BWRs, PWRs, VVERs.

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Fuel Reliability Assessment Through Radiochemistry and Poolside Examinations (LCC20)

Coolant Chemistry & Corrosion, PWR/VVER Chemistry

Nuclear power plants are capable of operating safely with leaking fuel in their cores and have done so on many occasions. Fuel failures affect three principal areas:  radiological safety, core and plant operation, and costs. With increased fuel reliability, the effects of leaking fuel on each these areas are heightened. The issue of secondary degradation is particularly severe because of the large increases in radiation exposure that such events can cause in the primary coolant and clean-up systems.  

The use of radiochemistry for the detection and tracking of leaking fuel will obviously not prevent failures from occurring, but can provide information for mitigating the radiation exposure, operational and economic consequences. The objective of this report is to identify methods for detecting failed fuel and assessing conditions associated with leaking rod(s) during operation in an NPP.  The report provides background for understanding the capabilities and limitations of the tracking and assessment methods. 

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Zinc Chemistry in BWRs, PWRs and VVERs (LCC20)

Coolant Chemistry & Corrosion, PWR/VVER Chemistry

This report describes the use of zinc injection technology in BWRs, PWRs and VVERs plants worldwide. Zinc addition is a mature technology applied both in PWR and BWR reactors while its implementation in VVER plants is still waiting to the commissioning of new reactor designs. It has been a crucial milestone in coolant chemistry for controlling and reducing radiation build-up, operational radiation as well as IGSCC mitigation in BWRs and mitigation of Primary Water Stress Corrosion Cracking (PWSCC).

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Key Emerging Issues and Recent Progress Related to Plant Chemistry/Corrosion (PWR, CANDU, and BWR Nuclear Power Plants) (LCC19)

Coolant Chemistry & Corrosion, PWR/VVER Chemistry

Safety and reliability of power plants are becoming increasingly important factors since many plants are aging and have obtained license renewal for continued power operation and also for new reactors using different technologies that are or will be in design, construction, commissioning, or start-up stage. Therefore, sharing plant operating experiences, sharing lessons learned, and sharing new industry research are all crucial in order to maintain the nuclear power plant fleet in a healthy condition as well as for new reactors using different technologies that are or will be in design, construction, commissioning or start-up stages.

This report on Key Emerging Issues and Recent Progress, ANT International has collected the most relevant experiences and advanced research exposed at the Nuclear Plant Chemistry Conference NPC-2023 that took place in Antibes Juan-les Pins, France in September.

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PWRs Operation and Maintenance Raw Water Systems (LCC19)

Degradation of Different Types of Structural Materials, Structural Material Degradation

Raw water has a major safety role as acting as cold source for plants. Raw water is used for:

  • Cooling the condenser, either in open or in closed circuits;
  • Providing water for service water systems;
  • Providing water to the Fire Fighting System;
  • Providing water to the Auxiliary Feedwater Tank in case of emergency (earlier units).

The report covers the following topics: design consideration, raw water chemical treatments, operating experience along with the maintenance programmes of raw water systems.

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STR on Interim Dry Storage of Commercial Spent Nuclear Fuel – An Update (ZIRAT28/IZNA 23)

Fuel Material, Interim Dry Storage

Except for a few countries (Finland, Sweden, France, and possibly Canada), the timing for establishing a geologic repository has been shown to be unpredictable. Therefore, spent fuel storage will remain the last backend operation for the foreseeable future in many countries. With proper attention, the radiological impact of storage is very low, but regulatory agencies have placed a heavy burden on licensees because of concerns related to the highly negative public perception related to the presence of spent fuel storage facilities in our biological environment. Therefore, locations where spent nuclear fuel (SNF) is or will be stored and their chosen storage technologies are the subjects of much scrutiny.

The focus of this review is on the spent nuclear fuel rods, and not on the storage system components such as the casks or the canisters  and their internal hardware elements. More specifically, the following topics are treated in the report: 

  • Update of “Back-end” issues
  • Thermal creep behaviour in relation to hydride reorientation
  • PWR fuel rod cladding failure due to the hydrogen migration in spent fuel
  • Update on any work on storage, transportation, long term issues
  • Correlation between cooling rate and hydride reorientation. In particular, the case of fast cooling when the cask containing SNF is flooded with water, from a cladding temperature of ~350°C to ~30°C, is examined.

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Accident Tolerant Fuel: an update report 2020-2023 (ZIRAT28/IZNA 23)

Accident Tolerant Fuel, Fuel Material

During the last decade the development of various Accident Tolerant Fuel (ATF) concepts has come into focus of both research and industry communities in the USA, Europe and Asia. The accident tolerant fuel program is aiming towards improving the safety of nuclear energy by investigating materials that can replace or modify the current uranium-dioxide nuclear fuel and zirconium-based cladding. This research programs are being supported by all major nuclear countries since 2011.

This updated version of the previously issued ANT International 2021 ATF report will provide the reader with a useful, quick but comprehensive overview of the latest ATF technical developments. It will give relevant information about ATF cladding and fuel, appropriate warnings and useful insights to nuclear fuel engineers and designers as well as to the fuel buyers.

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Nuclear Fuel Behaviour Under RIA Conditions

Fuel Material, LOCA and RIA Fuel Performance

(ZIRAT27/IZNA22)

The content of the Updated RIA is basically the same as the original report (Nuclear Fuel Behaviour under RIA conditions published within the ZIRAT21/IZNA Programmes), see information below. 

The main focus of this report is to give an update on two major subjects: (1) new RIA tests and the interpretation of the results and (2) new RIA related regulations. New RIA tests will complete the existing data base and their potential significance for RIA modelling or for RIA ruling. New acceptance criteria for RIA issued by US NRC are briefly described as well as some national approaches, different from the US NRC

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