Experimental Light Water Reactor (ELWR)
U.S.-based North Korea analysis website, 38 North, on 19 February 2018 cited satellite imagery of the North's Yongbyon nuclear facility showing steady progress on the construction of the 100 MWth/30 MWe light water reactor. Construction began in 2010, and the report said the reactor appeared to be externally complete and that a plutonium production reactor at the site may have been in operation recently.
The purpose of this reactor is not entirely clear, and 19 February 2018 analysis by 38 North provides no insight on the matter. While it could add to the DPRK's stockpile of fissile material, the total output would be only a few bombs per year. While a light-water power reactor can be used to produce plutonium, it is not optimal for this purpose, so it must be assumed that the Experimental Light Water Reactor (ELWR) is intended to develop techniques and train personnel to lay the foundation for much larger reactor program - larger reactors, and more of them. While heavy water reactors are obviously for plutonium production, a light water reactor might arguably have peaceful purposes. This could provide a path for the DPRK and Iran to have their cake and eat it too - an ostensibly peaceful program for electrical power generation that is also producing plutonium for weapons [the Japan option].
The 38 North report said the reactor, having been under construction since 2010, seems to be nearing operational status. It cited improvements made over the past year, including new provisions for a more consistent cooling water supply, installation of internal equipment and the connection of the reactor to the local electrical grid. The report added that the latest imagery from February eleventh shows the reactor is externally complete. The site said that “among the most notable changes over the past year is the construction of an earthen dam with a sluiceway across the Kuryong River” which was constructed just downriver below the second cistern in late December 2017 into January 2018.
South Korea's unification ministry said that it was aware of the latest report by that North Korea's experimental light water reactor appears to be nearing completion. "It is not appropriate to mention information on North Korea's nuclear program in detail for now. But we are closely monitoring the situation of North Korea's light water reactor at Yongbyon with the related ministries."
In April 2013, the General Department of Atomic Energy of the DPRK announced that the DPRK would take measures for “readjusting and restarting all the nuclear facilities in Nyongbyon2 including uranium enrichment plant and 5 MW[(e)] graphite moderated reactor”. In September 2015, the Director of the Atomic Energy Institute of the DPRK announced that “all the nuclear facilities in Nyongbyon including the uranium enrichment plant and 5 MW [(e)] graphite-moderated reactor were rearranged, changed or readjusted and they started normal operation…”.
The DPRK stated in April 2009 that it would build a Light Water Reactor (LWR). On 25 August 2017 the IAEA noted that "There were indications in the LWR construction yard of an increase in activities consistent with the fabrication of certain reactor components. The Agency has not observed indications of the delivery or introduction of major reactor components into the reactor containment building. Work to connect what appears to be the LWR’s electrical switchyard with the electrical distribution network was completed."
On a once-through fuel cycle, heavy-water reactors are somewhat less proliferation resistant than light-water reactors. In particular, heavy-water reactors, which use on-line refueling, require different techniques and are more difficult to safeguard than reactors using batch refueling; in addition, the heavy water can be used with natural uranium in a plutonium production reactor.
Another breeder reactor is the light-water version. Such reactors use the basic plant technology of pressurized water reactors but with a uranium/thorium fuel design. In order to breed, they must have fuel highly enriched in U-233; reprocessing and recycling of the fuel are also required. A light-water breeder reactor has about the same proliferation risk as an advanced converter reactor or light-water reactor, recycling fuel. Resource utilization is somewhat less efficient than with the fast breeder reactor. While the lightwater breeder reactor has the basic advantage of building upon light-water reactor technology (and component reliability).
The most widely used system world-wide does not readily lend itself to the proliferation of nuclear-weapons (or nuclear-explosives) capabilities, it may nonetheless facilitate the acquisition of the materials, facilities and expertise necessary to develop nuclear weapons. This system involves mining and milling uranium ore, enriching uranium to a concentration of about 3 to 5 percent in the fissile U-235 isotope, fabricating the enriched uranium into reactor fuel elements, using this fuel in the light-water reactor in a "once-through" mode, that is, using it to generate power and then discharging the spent fuel into interim storage (also called "stow-away").
Fuel fabrication for light water reactors (LWR) (regular commercial power reactors) typically begins with the receipt of low-enriched uranium, in the chemical form of uranium hexafluoride (UF6), from an enrichment plant. The UF6, in solid form in containers, is heated to gaseous form, and then the UF6 gas is chemically processed to form uranium dioxide (UO2) powder. This powder is then pressed into pellets, sintered into ceramic form, loaded into Zircaloy tubes, and constructed into fuel assemblies. Depending on the type of light water reactor—whether it's a boiling-water reactor or a pressurized-water reactor — a fuel assembly may contain up to 264 fuel rods and have dimensions of 5 to 9 inches square by about 12 to 14 feet long.
The isotopic quality of plutonium discharged from a power reactor is considerably less desirable for weapons use than plutonium from a production reactor, where it is discharged early to prevent the buildup of Pu-238 and Pu-240. In the life cycle of a fuel element, there is only a short time during the reprocessing step that fissile fuel is in either pure or relatively pure form.
If nuclear power is employed to produce electricity, there will always be some potential for fissile materials to be removed from somewhere in the fuel cycle for nonpeaceful purposes. It is important to note, however, that diverting special nuclear material from the back end of the commercial nuclear fuel cycle has not been the route to a weapons state. Rather weapons states have emerged through the use of dedicated facilities or though the abuse of research facilities.
Enrichment and reprocessing are the two vulnerable regions of the fuel cycle, with reprocessing being slightly more vulnerable than enrichment There are a wide number of fuel cycles that might be considered for possible adoption. Four essentially span the space.
- The PUREX/MOX approach for LWRs was adopted in Europe during the late 1970s. Large investments have made by COGEMA in France and by BNFL in the United Kingdom at reprocessing plants at La Hague and Sellafield, respectively. The PUREX approach is based on the historical aqueous process originally developed for the extraction of plutonium from spent fuel for nuclear weapons. When used for LWR MOX recycle, the plutonium separated during reprocessing is combined with uranium and refabricated into oxide pellets. These pellets are then loaded into fuel rods, the fuel rods are combined into fuel assemblies, and the fuel assemblies are reloaded into LWRs. Both Russia and Japan have adopted this cycle as their preferred approach. The Japanese have a large reprocessing plant at Rokkosho. Even though plutonium does exist in a pure state at some points in the separations process, strict safeguards measures are in place in these countries and there has been no diversion of plutonium in any part of this fuel cycle. Opponents argue that such technology is not appropriate for wide global use because of the potential for access to separated plutonium at some points of the fuel cycle.
- The UREX process being developed in the U.S. extracts uranium as a pure stream, with over 99.9% purity having been demonstrated in small pilot scale models. In this process the plutonium is not separated into a pure stream but always contains some neptunium, and the process could be configured such that this stream might include some higher transuranic isotopes as well. The most troublesome high-heat fission products, strontium and cesium, can separated as a separate stream. Technetium and iodine are likewise removable as a separate stream. This technology is currently only at the laboratory scale.
- A process intended to use spent fuel from Light Water Reactors in CANDU reactors is being developed in the Republic of Korea. This process is called Direct Use of Plutonium in CANDU Reactors, or DUPIC. The Republic of Korea is in the unique position of having several Light Water Reactors and several CANDU reactors operating in their power reactor fleet.
- In Switzerland, serious consideration is now being given to significantly reducing the plutonium produced by LWRs. The fundamental philosophy is to develop a fuel system such that the net production of plutonium is either zero or negligible. That has led them to a program based on non-fertile fuels, or fuel without U-238 in it, often called Inert Matrix Fuel (IMF). Stated differently, their approach is to load a fraction of the LWR core with non-fertile fuel that is incapable of producing plutonium.
The proliferation resistance measure of the assembly as it changes while it moves through the various steps of PUREX reprocessing, MOX re-fabrication, reactor burning, and ultimate disposition in a repository, all with traditional safeguards. The proliferation resistance value of the PUREX/MOX cycle is, indeed, the lowest during processing, but not substantially different than either the UREX/MOX cycle or the IMF cycle. Over almost all of the time period, the IMF has the highest proliferation resistance measure because of its ability to burn plutonium without creating more as well as its ability to degrade the plutonium isotopic composition considerably.
Under any realistic deployment schedule for the foreseeable future, the amount of plutonium and the rate of its increase would not be likely to differ very much no matter which fuel cycle was adopted. However, fuel cycles differ greatly in the form in which plutonium appears. The recycle system involves the production and processing of separated plutonium in reprocessing and fabrication facilities, and its presence in storage and transit.
Reactor grade plutonium (RGPu) has a higher percentage than weapon grade plutonium [WGPu] of plutonium isotopes other than Pu-239. Weapon-grade plutonium is defined as plutonium containing no more than 7% plutonium-240. It contains Pu-240 at a level of 10% or greater, which increases the neutron activity. A crude weapon made from RGPu could detonate prematurely due to the excess neutrons, resulting in a “fizzle” yield of only a few percent of the expected yield.
Reactor-grade plutonium is significantly more radioactive which complicates the design, manufacture and stockpiling of weapons. Use of reactor-grade plutonium would require large expenditures for remote manufacturing facilities to minimize radiation exposure to workers. Reactor-grade plutonium use in weapons would cause concern over radiation exposure to personnel. A successful test was conducted by the US in 1962, which used reactor-grade plutonium in the nuclear explosive in place of weapon-grade plutonium. The yield was less than 20 kilotons. This test was conducted to obtain nuclear design information concerning the feasibility of using reactor-grade plutonium as the nuclear explosive material. The test confirmed that reactor-grade plutonium could be used to make a nuclear explosive.
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