The main nonproliferation and safeguards challenges facing the small modular reactors

Alexey Lankevich, PUBLISHED 26.04.2020

Abstract

In recent years, the not yet very familiar acronym SMR (small modular reactor) has become a new development trend for nuclear power around the world.

The advantages of SMRs are quite obvious - there are fewer requirements to the power systems, in which they will work, lower cost, they can be built much faster, and the whole set of equipment will be manufactured in factory conditions.

Since a fundamental objective for the development of this technology is newcomer countries, the principal requirement for all designs of small modular reactors will be to minimize the potential for proliferation and terrorist activities through proliferation-resistant design approaches in combination with IAEA and other safeguards.

Despite the benefits, small modular reactors also have disadvantages. In this paper we want to highlight and explore how SMRs challenge the existing nonproliferation regime. And how various aspects of SMR designs such as: enrichment, fissile material inventory, burnup, breeders, core-life, refueling, digital instrumentation and controls, underground designs, sealed designs, and sea-based nuclear plants are discussed in the context of proliferation concerns.

Finally, we draw conclusions from the analysis.

Article

In recent years, the not yet very familiar acronym SMR (small modular reactor) has become a new development trend for nuclear power around the world.

SMR projects are being developed in the Russia, USA, China, Canada, Great Britain, and other countries, and a real technological race is gradually unfolding. There are 55 designs of such reactors in the world. Six form them are the most acceptable to use.

The advantages of SMRs are quite obvious - there are fewer requirements to the power systems, in which they will work, lower cost, they can be built much faster, and the whole set of equipment will be manufactured in factory conditions.

Prepare the site and the substation, during this time at the plant, will have time to fully complete the SMR, and the only thing left is to move the structure to the site and connect to the grid. The number of professionally trained personnel is several times smaller and the amount of spent nuclear fuel is much more modest.

All SMR projects are modular design and provide for the possibility to increase the number of ready-made units at one site if the customer needs it.

Who has a better chance of winning this race? Everything is quite traditional - the developer who will be the first to provide a reference operating power unit.

If we recall the history of nuclear energy, the development process went from small to large. This was justified by the economic benefits and, above all, the innovation of the technology. In the beginning, you need to test on a prototype, and only then run in a series. Now we are trying to find a justification for the need to return to where we started again.

Since a fundamental objective for the development of this technology is newcomer countries, the principal requirement for all designs of small modular reactors will be to minimize the potential for proliferation and terrorist activities through proliferation-resistant design approaches in combination with IAEA and other safeguards.

The main goal of the IAEA is to monitor and verify member States to ensure that they fulfill their obligations and also with the nation's safeguards to implement material control and accounting.

Because SMRs can be widely deployed if they become economically viable, it becomes necessary to study the nonproliferation problems that they present and the benefits they offer (O'Meara and Sapsted, 2013).

Despite the benefits, small modular reactors also have disadvantages.

Now we want to highlight and explore how SMRs challenge the existing nonproliferation regime. Also, we will try to show the most important tasks that will be faced by the developers SMRs.

Fuel enrichment of the most SMRs being significantly higher than that of modern reactors the most crucial, from the point of view specialists, will be to solve regulatory and procedural tasks related to this.

Many SMR designs have enrichment of the fuel of about 20%. It is the low-enriched uranium limit established by the IAEA.

If we compare the number of separative work units (SWU) and resources to rich which need to obtain weapons-grade uranium from fuel enriched 20% or 5%, we can see that it is nearly three times easier.

Although highly enriched fuel offers some operational advantages. Transition to it represents one of the most politically and institutionally sensitive solutions. Thus, at present, there is no developed and well-established regulatory framework for high enriched fuel (above 5%) in the world, and there are no regulations for interstate transportation of such fuel.

An increase in the number of nuclear reactors, the total amount of nuclear material in circulation, or the remote distribution of these sites would greatly expand the amount of work under the IAEA's safeguards.

It would also increase the number of potential goals for sabotage and terrorist acts or the possibility of errors in accounting for an increase in the volume of nuclear material in circulation.

If we are talking about small quantities of fissile material, it should be recalled that the critical mass required to build a nuclear weapon device without support is 52 kg of U-235 (94% enriched) or 10 kg of Pu-239. And if we look at breeder reactors such as the Toshiba 4S and SVBR-100, we see that there are more fissile materials in these reactors than in a significant quantity. Thus they will be given the same attention as large reactors in terms of verification of nuclear materials.

Many SMRs being had fast-neutron reactor designs we can suggest that they can be particularly useful for conversion U-238 in the fuel to Pu-239, which could be used for the production of a weapons-material.

Therefore, fast spectrum SMRs must be designed with technical solutions that rule out the possibility of plutonium production.

Some SMRs designs (for example Toshiba 4S, SVBR-100) are designed in such a way that they do not have a reproduction zone around the core. However, the absence of such a zone is not a reliable measure, it is always possible to find some free space around the core and secretly turn it into a conversion zone.

Thus it becomes important that the conversion factor at different core configurations remains less than one, and the possibility of reproduction in the reflector is eliminated. Such limits will require careful independent assessments.

Now about the high burnup, sealed design, and refueling of small modular reactors.

Burnup nuclear fuel is a measure of the amount of energy that has been released during the use or "burning" of fuel in the reactor. Thus, the longer the fuel is used to generate energy, the higher its burnup. As burnup increases, the reliability of spent nuclear fuel for weapons purposes decreases.

Higher burnup of uranium fuel leads to more Pu-240 isotope in spent fuel. And this isotope leads to the preliminary detonation of nuclear weapons due to spontaneous fission. If a chain reaction starts before maximum compression (preinitiation), the expected yield will be reduced from about 20 kilotons to one kiloton. For this reason, the Pu-240 content of the plutonium used in the Nagasaki bomb has been minimized. However, the absence of a level of spontaneous neutron emission will not reduce the yield below about 1 kiloton. An explosive device weighing one kiloton would still be a destructive weapon.

From a nonproliferation and safeguards point of view, sealed reactors that are loaded and sealed by the supplier, and are only unloaded, unsealed at secure fuel handling facilities at the end of their core lifetimes, would clearly be acceptable. For not spreading we have heard a lot of compliments about this solution.

But let's look at this issue from a different side. First of all, it is the possibility of sabotage or terrorist attacks against them. And even if they do not lead to serious consequences, especially in developing countries, one can imagine the panic in the entire world community on this matter.

Secondly, the lack of access for inspections, i.e., how nuclear materials will be controlled and verified. Thirdly, there is the possibility of plutonium production for such a design, especially for SMRs highly enriched. In the end, there are many technical barriers that must be overcome if this vision is to be realized.

Bumping and vibration during transportation could lead to weaknesses, cracking or displacement of the fuel. Handling and transportation of sealed reactors after their operation needs to be carefully designed in order to withstand the decay heat. This issue greatly limits the size of the reactors. If without any improvements the design of the SMRs will need to be at least 30 times smaller than AP-1000. There are two ways to address this issue. The first is in the image of large reactors, in which case we reduce the size and no additional cooling systems are needed. The second is to look for a way to mechanically cool spent fuel during transportation back to the plant. But this method will be more expensive.

Most SMRs being developed are characterized by longer core lives than existing nuclear reactors (for example Toshiba 4S and GA EM-2 which have core life as long as 30 years or more). There are a number of problems that need to be addressed. Firstly, the issue of maintenance of equipment will be solved with such a long core life, secondly, how to account for and control nuclear materials without access to the core.

In short, a core lifetime of more than 4 years will not necessarily reduce the frequency of core handling unless it is accompanied by other design features that address regular maintenance and material inspection tasks.

Remote monitoring of nuclear materials, which is implemented for large reactors, is not suitable for SMRs. Since SMRs have a modular sealed design, it will be necessary to develop inside the vessel sensors for monitoring all systems of LWRs.

Another feature of LWRs is a large amount of water between the core and the vessel. Thus, very slow neutron signals will limit the use of neutron chambers for measuring neutron fields and power located outside the vessel. Thus, strongly delayed neutron signals will limit the use of neutron chambers to measure neutron fields and power located outside the vessel. More sensitive neutron detectors will need to be designed and tested to withstand high temperatures and extended radiation exposure.

For fast spectrum reactors, high-energy neutron-resistant detectors will need to be provided. Also in the case of remote monitoring, high reliability of wireless communication against cyber attacks and protection against unauthorized information transfer should be ensured.

An underground location can increase the load on safeguards and reduce the ease of access for unannounced inspections. If you look at them from a physical protection perspective, you will also have questions. When terrorists take such installations and take hostages, it will be very difficult for external forces to influence the situation. A possible solution to this problem would be to place a control room above ground, as in the Toshiba 4S project.

And at the end, as sea-based technologies, such as KLT-40S, are already in operation, it becomes necessary to develop the necessary safeguards and non-proliferation standards regarding the various aspects, vulnerabilities and natural benefits of a sea-based nuclear reactor.

Conclusion

Since there is so much interest in small modular reactors, and only praise for this promising area can be found in the press, we decided to conduct a critical analysis of SMR issues from the perspective of safeguards and non-proliferation.

The SMR constructions can boast many advantages and improvements, in some cases even in the area of non-proliferation. However, as we can see from our analysis, there are a rather impressive number of identified challenges that will have to be overcome before this technology can be deployed, especially in new countries.

These include:

      - development of a legal framework for highly enriched fuel and its inter-State transportation;

      - development of technically sound solutions for fast spectrum SMRs that would eliminate the possibility of plutonium production;

      - consideration of possible areas of sabotage and terrorist attacks on SMRs with different types of deployment and development of plans and instructions for their prevention;

      - development of new approaches, as well as new external detectors and inside body detectors for monitoring, accounting and remote monitoring of nuclear materials;

      - development of methods for cooling spent nuclear fuel during its transportation to the manufacturing plant;

      - development of equipment that can operate without maintenance for a commensurate time with core lifetime.

The solutions and improvements made in the light of the above proposals will give us greater assurance in the area of safeguards and non-proliferation when deploying SMRs around the world, providing us with a sustainable and safe alternative to renewable energy sources.

References

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Topics: Small NPP, Opinions

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