Heavy metal cooled reactors

Wider, H., Carlsson, J., Dietze, K., Konys, J., 2003. Heavy-metal cooled reactors—pros and cons. In Proceedings of GLOBAL 03, New Orleans, USA. 

Step by step solution to the project on long-term storage of spent fuel from nuclear submarines with heavy liquid metal cooled reactors... 

There are many different types of reactors. In the United States, the majority of the reactors are pressurized water reactors with graphite moderators. The Canadians built the CANDU reactor using heavy water as both moderator and coolant. Naval ship reactors are graphite moderated liquid metal cooled reactors. The detailed differences between the reactor types will not be examined, but the operating principal common to all will be discussed. 

This order applies to all varieties of reactors including, but not limited to light water moderated reactors, heavy water moderated reactors, liquid metal cooled reactors, gas cooled reactors and short-pulse transient reactors. Space reactor power and propulsion systems and critical facilities require special design criteria. Attachment 4 is reserved for Nuclear Safety Design for critical facilities and space reactors. 

Some passive decay heat removal systems, such as a water tank surrounding the reactor vessel of a lead-bismuth cooled SVBR-75/100, could be effective for many heavy metal cooled SMRs. They are also quite common to many innovative water cooled SMRs. To abandon the off-site emergency planning it may be important to develop passive heat removal systems that are effective over the whole run of a design basis accident or even an anticipated transient without scram. This may be a task important for many SMR designs representing several reactor lines. 

This applies, for instance, to heavy water moderated reactors, for which special attention should be paid to the production of (tritium), including its monitoring. This also applies to liquid metal cooled reactors, for which special precautions should be prescribed for coping with incidental leaks of coolant. Another example is that of light water reactors, for which gamma radiation dose rates from Ar and should be taken into consideration. 

With a purpose of probing a commercially feasible fast reactor system, a feasibility study on commercialized fast reactor cycle systems (FS) was initiated in 1999 (Aizawa, 2001). In the FS, survey studies were made to identify the most promising concept among various systems such as sodium-cooled fast reactors, gas-cooled fast reactors, heavy metal-cooled fast reactors (lead-cooled fast reactors and lead-bismuth cooled fast reactors), and water-cooled fast reactors with various fuels types such as oxide, nitride, and metal fuels. The FS concluded to select an advanced loop-type SFR with mixed oxide fuel named Japan sodium-cooled fast reactor (JSFR Kotake et al., 2005). 

HLMR Heavy liquid metal-cooled reactors... 

Uranium fuel preparation takes the yellow cake, sodium diuranate, from milling to plants where it is converted to either (a) aluminum-clad metal for the weapons plutonium production reactors (and in the future for the liquid metal cooled reactors) or (b) to Zircaloy-clad UO2 for electricity production in the light and heavy water power reactors (see Fig. 31.11). 

This report provides the presented papers and summarizes the discussions at an IAEA Technical Committee Meeting (TCM) on Natural Circulation Data and Methods for Innovative Nuclear Power Plant Design. While the planned scope of the TCM involved all types of reactor designs (light water reactors, heavy water reactors, gas-cooled reactors and liquid metal-cooled reactors), the meeting participants and papers addressed only light water reactors (LWRs) and heavy water reactors (HWRs). Furthermore, the papers and discussion addressed both evolutionary and innovative water cooled reactors, as defined by the IAEA. ... 

Heavy metal (lead alloy)-cooled reactor (HMCR), with an indirect power cycle ... 

The fuel elements are held in position by grid plates in the reactor core. The fuel burnup to which a reactor may be operated is expressed as megawatt-days per kilogram (MWd/kg), where MWd is the thermal output and kg is the total uranium (sum of U-235 and U-238). In light-water power reactors the core may be operated to about 35 MWd/kg (about 3.5% burnup) before fuel elements have to be replaced. In liquid metal fast breeder reactors (LMFBRs) and high temperature helium gas-cooled reactors (HTGRs), the burnups may exceed 100 MWd/kg ( 10% burnup of the heavy metal atoms). 

Uranium dioxide UO2 is the form in which uranium is most commonly used as a reactor fuel for light-water, heavy-water, and fast-breeder reactors. It is a stable ceramic that can be heated almost to its melting point, around 2760°C, without serious mechanical deterioration. It does not react with water, so that it is not affected by leakage of cladding in water-cooled reactors. Its principal disadvantages compared with uranium metal are its lower uranium atom density and lower thermal conductivity. At 100°C, thermal conductivities are metal, 0.25 UO2, 0.09 W/(cm-°C). 

Techniques to counter the heavy metal coolant disadvantages are being developed, but in spite of this work and the apparent disadvantages of sodium, the consensus in favour of sodium remains strong. This is demonstrated by fact that before lead-cooled fast reactor BREST-300 is built, MINATOM will first build a sodium-cooled LMFR BN-800 (E. Adamov, NW, 23 September 1999). Moreover, in the last few years sodium has been chosen in both China and the Republic of Korea for the respective fast reactor development project. This is a significant endorsement for sodium as a fast reactor coolant. 

Several candidate materials are available for possible use as a moderator in the gas-cooled reactor. These materials include light water, heavy water, metallic hydrides (e.g., zirconium hydride), beryllium metal, beryllium oxide, and graphite. Of these, the most commonly proposed moderator materials are graphite, heavy water, and beryllium oxide. 

Studies on the gas-cooled, fast-spectrum reactor have shown that a potential advantage of carbide fuel over oxide is derived from its increased conductivity, increased heavy metal density, and decreased moderating effect. The improved conductivity of the carbide over the oxide may allow the maximum heat removal per foot of fuel element to be raised from 20 to about 40 kW/ft. Increased heavy metal density and decreased moderating effect of the carbide allow the possibility of a harder neutron spectrum and therefore an increase of about 10% in the breeding ratio. 

These three main lines, as defined by their primary coolant are water cooled, gas cooled, and liquid metal cooled. Water cooled reactors can be fiirther categorized as heavy water or light water moderated reactors. The design approach for a given system can be substantially different from another system within the same technology line. The small and medium reactor area has to deal with all technological lines and all varying approaches. The relevant reactor information for the purpose of this TECDOC has been divided into six parts ... 

Includes gas-cooled, heavy water, graphite-moderated light water, and liquid metal-cooled fast-breeder reactors. Includes reactors of all types planned or under construction. 

Because of the small reactivity margin available for breeding in a thermal reactor, the use of the thorium cycle has mainly been associated with reactors with very good neutron economy based on low parasitic absorption, such as the high-temperature gas-cooled reactor, where graphite is used in place of metal for the fuel cladding, or heavy water reactors, with very low moderator absorption. A special case is the molten salt breeder reactor, where circulation of the fissile and fertile materials allows continuous removal not only of Pa but also of fission products. 

Recently, work toward elaboration of the RBEC-M concept was also motivated by an exchange of scientific and technical information with the organizations in Russia and abroad, especially those involved earlier in the development and/or those developing new reactors cooled by heavy metals. In particular, the French Commissariat a I Energie Atomique (CEA) and the Japan Nuclear Cycle Development Institute (INC) should be mentioned. In 2001, the RBEC concept description in the format for the Generation IV programme was submitted to the US DOE and included in the final document on concepts of reactors cooled with liquid metals [XXm-14]. 

From the history of the development of marine reactors cooled by heavy metals, it is known that problems of fuel and coolant compatibility were basically solved by large-scale experimental testing and by observing the experience of several operating installations consequently constructed. 

After approximately 3 years of permanence inside of the reactor core, the spent fuel of an LWR of 1000 MWg (typical bum-up of 40,000 MWd/tHM, initial enrichment to 4% U 5 years cooling) is transferred to cooling pools (note MWd/tHM, megaWatt-days per ton of heavy metal). 

The development of heavy liquid metal reactors (HLMRs) in Russia stems from its experience with Pb—Bi eutectic coolants in Soviet Alpha-class submarines. Altogether, USSR had eight nuclear submarines and two on-the-ground Pb—Bi-cooled reactor prototypes. Details of the submarine experience are extensively presented... 

This appendix provides additional materials (schematics, layouts, T—s diagrams, basic parameters, and photos) on advanced thermal (combined cycle and supercritical pressure Rankine steam turbine cycle) power plants and nuclear power plants with modern nuclear power reactors [pressurized water reactors (PWRs), boiling water reactors (BWRs), pressurized heavy water reactors (PHWRs), advanced gas-cooled reactors (AGRs), gas-cooled reactors (OCRs), light water-cooled graphitemoderated reactors (LGRs) (RBMKs and EGPs), and liquid metal fast-breeder reactors (LMFBRs) (BN-600 and BN-800)]. 

The second class of innovative concepts is liqnid metal-cooled fast-spectrum reactors ( fast-spectrum refers to the energy of the neutrons in the reactor core). In a typical reactor, a moderator (usually water, which pulls double-duty as both neutron moderator and reactor coolant) is nsed to slow down neutrons because slower neutrons are more efficient at causing fission in U-235. In a fast-spectrum reactor, there is no moderator. Instead, it relies on higher energy neutrons, which are less effective at causing uranium to fission but are more effective at causing fission in plutonium and other heavy elements. For this reason, these reactors are not ideal for a uranium-based fuel cycle but they are quite suitable for use with a fuel cycle based on plutonium and the other heavy... 

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