Can Russia Produce the World's Best Modular Nuclear Reactor?
The SVBR-100 is the first in a class of “fast-breeder” power reactors that use a bootstrapping or breed/burn approach to multiply the energy extracted from a pound of uranium ore by a factor of 100 [Amer_Nuclear_Soc, 1]. Inside “heavy metal” reactors, the plentiful, fertile isotope U-238 is progressively converted to fissile Pu-239 which is then burned. As the U-238 gradually becomes depleted from the fuel mixture, more U-238 is added from stocks of un-enriched uranium. _SVBR-100
Small modular nuclear reactors (SMRs) promise safe, affordable, abundant heat and electricity at all scales from community to city. A wide range of reactor designs are being considered, from the highly experimental to the well tested and proven. The largest test bed for small nuclear power reactors has been the militaries of the US and Russia / former USSR.
The SVBR-100 reactor was developed by a group of Russian nuclear scientists and engineers after the Chernobyl disaster, with the goal of developing a safer, lower risk molten metal cooled reactor. Here are some of the safety features of the design:
The reactor system development project had a conservative approach to engineering design; the project has mainly included off-the-shelf or scaled engineering solutions with reasonable best practices proven by operational experience in nuclear power station reactors and other reactor facilities. This approach includes basic items, assemblies and pieces of reactor equipment: fuel pellets, fuel cladding, fuel assemblies, control rods, vessel internals, control rod actuators, LBC system components, steam generators with coaxial (fild) tubes, separators, self-contained cooldown condensers, gas system condensers, refuelling system equipment, and so on. The operating parameters of the primary and secondary cooling circuit were also developed conservatively.
Such an approach has considerably decreased technical and financial risks by reducing the likelihood of errors peculiar to innovative nuclear projects, and decreased the scope, terms and costs of R&D.
The combination of a fast reactor design with heavy metal coolant operating in an integral reactor layout ensures that the SVBR 100 reactor system meets IAEA international project safety levels for prevention of severe accidents and inherent safety, according to analysis and studies (5).
The reactor is typified by negative feedback and a negative void reactivity effect; the effect of the strongest absorber rod does not exceed Beff. Those tendencies, along with the control and protection system engineering design, prevents instantaneous neutron excursion.
The coolant's high boiling point improves core heat removal reliability and safety since there is no departure from nucleate boiling. That property, plus the unit's protective enclosure, prevents loss of coolant accidents (LOCA) and high-pressure radioactive release.
Low operating primary pressure reduces the risk of air leaks into the system, and allows a thinner reactor pressure vessel. Low operating pressure also lessens the limits on the speed of temperature changes under thermal cyclic strength.
Nuclear steam supply systems are free of components that release hydrogen as a result of thermal, radiation and chemical reactions with coolant, water and air. Therefore, a case of a primary-circuit depressurisation should not result in a fire or chemical explosion.
Nuclear steam system supply (NSSS) safety is independent of the status of turbine-generator set systems and equipment, which may be designed and manufactured to general industry rules and regulations.
The existence of inherent NSSS safety features allow safety functions to be combined with normal-operation systems. Safety systems exclude components whose failure-or deliberate malicious actuation-could disable the system.
Decay heat removal (independent of the steam generators) occurs passively through the natural circulation of lead-bismuth coolant in the primary circuit by heat transfer from the single-unit reactor vessel to the Passive Heat Removal System (PHRS) tank water. It continues further by boiling tank water passing through the steam dump into the atmosphere. The reactor's safe non-intervention period is about three days during which time no temperature limit is exceeded.
Steam generator leaks are confined passively, with the steam pressure in the gas system exceeding 1 MPa. If some steam generator tubes are ruptured, or if the gas system condenser breaks down, the burst rupture diaphragm is broken and leaked steam is dumped into the PHRS tank used as a bubbler (under normal circumstances, it serves a neutron protection function). Operational experience has found that a small SG leak need not cause an immediate NSSS shutdown.
Auxiliary protection system rods installed in dry channels are passively actuated by gravitational force. The rods, which have no drives on the reactor pressure vessel head, are held fixed in the raised position under normal temperature regimes by retainers made of an alloy with a particular melting point. When the lead-bismuth coolant temperature exceeds the specified value, it melts the retainers, and the rods drop.
Even with the combination of postulated initiating events such as damage to the containment, damage to the reinforced concrete slab above the reactor, depressurisation of the primary gas system with the direct contact of lead-bismuth coolant reflector in the single unit vessel with atmospheric air, and major plant blackout, there will be no reactor runaway, explosion, fire, nor environmental radioactive release exceeding the limits of NPP site population evacuation. Analysis suggests the probability of severe core damage is considerably lower than regulatory limits.
One of the main factors determining the high safety level of the reactor is the low potential energy stored in the coolant under operating parameters: 1 GJ/m3 for lead-bismuth coolant, versus 10 GJ/m3 and 20 GJ/m3 for sodium and water (6). This feature explains the tolerance of the NSSS to not only equipment failures, human error or factors overlapping the two, but also to malicious actions in which all of the special safety systems are wilfully disabled. _Power-Engineering
Here is a brief summary listing the basic features of the SVBR-100:
- It incorporates a fast reactor with non-reactive lead-bismuth coolant (LBC), a eutectic lead-bismuth alloy in the primary circuit. Its melting point is 123.5 deg C and its boiling point is 1670 deg C.
- The entire primary equipment circuit is contained within a robust single reactor vessel; LBC valves and pipelines are all exterior.
- A protective enclosure surrounds the single-unit reactor vessel.
- The reactor passes heat to a two-circuit heat-removal system and steam generator with multiple-circulation secondary coolant system.
- Natural circulation of coolant in the reactor heat removal circuits is sufficient to passively cool down the reactor and prevent hazardous superheating of the core.
- Compared to other reactors, the SVBR 100 reactor system has a dramatic reduction in the number of active safety systems; normal-operation systems ensure the performance of safety functions.
- Main components in the single-unit reactor and reactor system are built as modules, and so can be replaced or maintained.
- At the end of a core cycle, provision has been made for a single refuelling operation in which the entire fuel core is replaced as a single assembly.
- Without design change, the reactor can use various types of fuel (uranium dioxide, MOX, nitride fuel). When using the latter two, the core conversion ratio is greater than zero, so it is possible to operate a self-supported closed fuel cycle.
- Primary loop equipment repairs and fuel reloading can be performed without having to drain the LBC, whose liquid state is maintained by core decay heat and heating system operation.
...On 15 June 2006, Rosatom scientific and engineering council no. 1 recommended that a detailed design of a SVBR 100 reactor trial unit would be pursued with reference to a specific site. The project is managed by AKME-Engineering, a 50-50 joint venture between state corporation Rosatom and JSC EuroSibEnergo.
As of May 2011, siting licence works are underway, pilot plant specifications and key reactor and reactor core research and development works have begun. A complete reactor and power plant design is expected to be completed by 2013, along with a preliminary safety report. In 2013 a construction licence is also expected to be obtained.
The trial unit is expected to be commissioned by 2017 at the Russian state Atomic Reactor Research Institute, Dimitrovgrad, in the region of Ulyanovsk. Total investment is estimated at RUR 16-18 billion ($500-600 million).
V. V. Petrochenko, Director General JSC AKME-engineering, 24 Bolshaya Ordynka Street, Moscow 119017, Russia. _Power-Engineering
References for the Power-Engineering article above
Pockets of competence still exist within the fading industrial infrastructure of Russia. The design team for the SVBR-100 has taken a large number of factors into consideration. If Rosatom follows through on this commitment, it would mark a turning point of sorts for Putin's Russia -- away from dead-end cronyism and fossil fuels dependency. If Russia can mass produce the first safe, high-quality, widely available SMR, the country might conceivably control the global market -- unless China gets there first or comes up with a viable copy fairly quickly. The US NRC under Obama has apparently chosen to forfeit the race, due to its foot-dragging approach to the licensing process.
The global need for such an affordable and safe scalable reactor system is immense.