**********************Yurika's E-mail Pu-Update****************** Herbert Scoville Jr. Peace Fellow Project Physicians for Social Responsibility FISSILE MATERIAL DISPOSITION & CIVIL USE OF PLUTONIUM Issue No. 4 November 26, 1996 ------------------------------------------------------------ CONTENTS Main Story: TECHNICAL ASPECTS OF MOX FUEL IN LIGHT WATER REACTORS/THE REACTOR OPTION 1. How Does It Work ? Major Differences From Conventional LWRs 2. Will MOX Option Really Eliminate Plutonium? 3. Impacts on Radioactive Waste Management? 4. The Health and Environmental Effects of the Use of MOX NEWS BRIEFS *G7 Paris Summit Report *Reprocessing Back in the US? *Plutonium Inventory of the World, Update *International MOX Assessment ***************************************************************** Main Story: TECHNICAL ASPECTS OF MOX FUEL IN LIGHT WATER REACTORS (LWR)/ THE REACTOR OPTION 1. How Does It Work? Major Differences From Conventional LWRs Proponents of burning plutonium in mixed-oxide(MOX) fuel in LWRs often say that since plutonium already exists in the burned uranium fuel and is still burning, there will not be a big difference by increasing the amount of plutonium a little bit. The fact is that great effort is put to make it "not a big difference." In conventional LWRs, the uranium fuel has about 3% fissile uranium-235 and the rest is non-fissile uranium-238. When fissile uranium absorbs a neutron, it starts fissioning and releases energy, emitting several neutrons. One neutron will likely start another fission, creating a chain reaction, but the other neutrons must be controlled so that it will not make a massive reaction which will induce an uncontrolled chain reaction. Control rods are designed to absorb the extra neutrons. But some neutrons are also absorbed by the non-fissile uranium-238 and this decays into fissile plutonium-239. In the beginning, the plutonium content is zero and the fissile uranium is about 3%. The fissile uranium decreases as they burn, creating plutonium at the same time. At the end of one reactor cycle, the content of fissile uranium is about 0.7%-0.8%, approximately equal to the content of fissile plutonium-239 that is created.(1) In the case of MOX fuel used in one-third of a LWR core, the plutonium content is roughly 4% from the beginning, which is approximately 5 times more than that in the end of one cycle of a uranium fuel. This is a significant difference in terms of core nuclear physics.(2) In a fast reactor, plutonium content of MOX fuel can be up to 50%. In the option to burn plutonium in CANDU reactors, the MOX fuel content could be 100% core.(3) But this has not been tested, nor is there any experience at all of burning plutonium fuel in CANDU reactors. All light water reactors are designed to burn uranium fuel. Thus the nuclear physics of MOX fuels must be adapted to be as similar as possible to that of uranium fuel. The MOX fuel assemblies should be able to be operated as uranium assemblies without any restriction to the level of power, performance or safety. #Various Types of Fuel Assemblies Necessary To Burn MOX In order to achieve the same performance as normal LWR, the fuel assemblies are made into various types with different plutonium and uranium contents. Usually, MOX fuel assembly designs for pressurized water reactors use three types of plutonium contents, 1.9%, 2.3% and 3.3%.(4) For boiling water reactors, four to six different plutonium contents designs are used.(5) Another difference is that, because of the intensity of plutonium's thermal energy, plutonium fuel pellets cannot be of the same form as uranium fuel. It could be in the form of a donut where the central part is void to let the heat dissipate. But this type of a fuel pellet is likely to collapse.(6) All these factors make the fuel production extremely complicated and difficult, compared to the one-standard uranium fuel for conventional LWRs. #Reduced Efficacy of Control Rods Control rods work by absorbing neutrons in the reactor core, so maintaining stable power conditions. Criticality depends on the small fraction of neutrons produced in the fission of uranium or plutonium which are generated with a delay of about ten seconds.(7) This time difference makes it possible to control the power level by mechanically inserting additional control rods into the core. However, the fraction of delayed-neutrons in Pu-239 is about one- third that of uranium-235, which means that the reactor is more sensitive to variations in power.(8) In addition, plutonium has a slightly higher propensity to capture thermal neutrons than uranium. Therefore the efficacy of control rods is somewhat reduced, and safety margins are lower. The additional demands on control systems are largest for those plutonium fuels in which plutonium-239 content is highest, as in MOX fuel using weapon- grade plutonium.(9) For these reasons, the MOX fuel assemblies should be placed away from the control rods. The higher average energy of the neutron spectrum of MOX also increases the rate of radiation damage to structural materials in and around the core. This could cause embrittlement of the reactor vessel in the end, which is another factor for safety concerns. #Danger of Losing Control of the Reactor Is Greater with MOX Conventional LWRs are designed to decrease the reactivity when the temperature rises. But when using Pu-239 as fuel, heating of the core from an increase in reaction rate tends to increase the reaction rate still further. This is called the positive temperature coefficient of reactivity, meaning there is a danger of losing control of the reactor by accelerated chain reaction of fissioning.(10) ---------------------------------------------------------------- (1)"Han-Genpatu Demae Shimasu," Jinzaburo Takagi (Nanatsumori- Shokan, 1993, p.216) (2) Ibid. pp.216-217 (3)Draft Nonproliferation and Arms Control Assessment of Weapons- Usable Fissile Material Storage and Plutonium Disposition Alternatives (US Department of Energy, October 1, 1996, p.93) (4)"Options for Plutonium," by E.R. Merz(Research Center Julich) for the International Seminar on MOX Fuel (June, 1996, UK) (5)Ibid (6)Ibid note (1) p.218 (7)"Disposition of Separated Plutonium" Frans Berkhout, Frank von Hippel, et.al. (Science and Global Security, 1993 Vol.3, p.177) (8)"Management and Disposition of Excess Weapons Plutonium, Reactor-Related Options (National Academy of Sciences, 1995,p.41) (9) Ibid (10)Ibid. p.42 ================================================================ 2. Will MOX Option Really Eliminate Plutonium? Three options for the disposition of "excess" plutonium are considered. They are the "reactor option," burning it as MOX fuel in reactors; "immobilization", mixing plutonium with highly radioactive fission products and glassifying it into logs for geological disposal; and "deep borehole," burying plutonium deep enough so that it will be unretrievable. The proponents of the reactor option using MOX fuel often say that the immobilization and the deep borehole options will merely put the plutonium underground and will not eliminate plutonium. They claim that the only way to eliminate plutonium is to burn it in reactors. But this is misleading. It can only be eliminated by repeatedly reprocessing the spent MOX fuel, and reusing the separated plutonium. But plutonium from reprocessed MOX spent fuel is degraded in quality and cannot be used as fuel. The scale of effort required to overcome the economics and the technological difficulties is overwhelming. The objective of burning excess plutonium in reactors is to convert the weapons-grade plutonium into spent fuel, contaminated with other highly radioactive fission products so that it will be difficult to retrieve plutonium without reprocessing. This is called the "spent fuel standard." But even if it becomes "spent fuel standard," plutonium could be retrieved by reprocessing, and studies have shown that nuclear bombs could be made from such separated "reactor-grade" plutonium.(11) The real amount of plutonium will decrease by half by burning it as MOX fuel in LWRs. The MOX fuel starts with 4% plutonium and 96% uranium-238. By the end of one fuel cycle, 2% plutonium will remain in the spent MOX fuel together with 94% uranium and 4% fission products.(12) According to National Academy of Sciences, out of the 50 tons of "excess" weapons plutonium, a substantial amount of plutonium would remain in the spent MOX fuel, between 10 to 40 tons(13) depending on how long the fuel remains in the reactor core and the percentage of MOX the core use. ------------------------------------------------------------- (11) Draft Nonproliferation And Arms Control Assessment of Weapons-Usable Fissile Material Storage and Plutonium Disposition Alternatives (US Department of Energy, October 1, 1996, pp.34-36) (12)Notes by Dr. Arjun Makhijani (IEER, November 20, 1996) (13)Management and Disposition of Excess Weapons Plutonium (National Academy of Sciences, 1994, p.155) =============================================================== 3. Impacts on Radioactive Waste Management MOX spent fuel contains more fission products than uranium spent fuel. The important factor in managing spent fuel is the heat generation caused by the highly radioactive fission products. Since spent MOX fuel contains much more fission products, the heat generation from MOX spent fuel is twice as high as that of spent uranium fuel after 10 years and three times as high after 100 years.(14) What this means is that less spent MOX fuel could be put in a limited repository site, leading to the necessity of more or larger repository sites. Or, longer periods of centuries for interim storage would be necessary. Because of the existence of more plutonium, there is a criticality concern for geologic repository, and requires separate licenses for disposal. This means additional costs and delays. In other words, spent MOX fuel disposal will require more space, more time, and more substantial costs. Another typical argument proponents of plutonium "recycling" raise is that the extent of uranium mining, milling, conversion, enrichment and fabrication will be reduced, and thus curb the amount of related radioactive waste as a whole. This argument ignores the additional waste produced by fabricating MOX fuel, burning in LWRs and the effects of making spent MOX fuel disposal more difficult, not to forget the huge waste produced by reprocessing (which is unnecessary only in the case of disposition of weapons plutonium). ----------------------------------------------------------------- (14)"The MOX Industry or The Civilian Use of Plutonium," C. Kueppers & M. Sailer (IPPNW, 1994, p.64) ================================================================ 4. The Health and Environmental Effects of the Use of MOX #Specific Dangers of Plutonium Plutonium does not exist in the natural environment, and is only produced in nuclear reactors. It is known as one of the most toxic elements. It emits high energy alpha radiation, and has harmful biological effects. Alpha radiation has a very short range but very intense ionization power. If exposed on the surface of the skin, the skin works as a shield and will prevent its penetration into the body, but all of its ionizing power will be focused on the small spot, causing burns and killing the skin tissue. If inhaled into the body, the alpha particle will go in through the respiratory tract, and enter the lung. Due to its long half-life, it will stay in the body permanently, emitting alpha radiation, and killing the surrounding tissues by strong ionization. If plutonium is taken into the body in soluble form (e.g. plutonium nitrate) through food chain, it will enter the blood stream, and into the bones, liver and genital organs where it will be enriched. Alpha radiation leads to reactions in the cells of living things. It can cause damage to the nucleus and DNA of the cell, in effect causing genetic damage in descendants, particularly if germ cells are affected.(15) #Dangers of Resuspension in the Environment In the event of a contamination of the environment with plutonium, the whirling up and inhalation of plutonium particles, known as resuspension, plays an important role. If there is a road traffic, building work or cleaning work at the plutonium contaminated site, plutonium can enter the body through the respiratory tract. Generally, the more whirled up, the greater the dose intake per quantity of plutonium on the ground. If there is fire, and plutonium becomes airborne into fine aerosol particles, plutonium contamination of the environment will extend to a far larger scale, landing on ground, contaminating a vast wider area. Plutonium remains effective over very long periods affecting the health of the people and the environment.(16) #Accident Scenario When Burning MOX Accidents involving overheating and meltdown are possible in any nuclear reactors. In such accidents, not only would readily volatile noble gases, like iodine and caesium be released to the environment, but a small portion of the actinides, including plutonium and neptunium would be released. As the activity of the actinides is substantially higher in the case of MOX, the consequences of such severe accidents become more serious. When MOX fuels are used, the probability of having such serious accidents or trouble would increase due to the high content of plutonium in the fuel. Even if an accident is not a serious one, it could become serious since even a small portion of the inventory of actinides released to the environment could cause significant radiological consequences. According to a comparative analysis of possible consequences of a core meltdown accident in the German Kruemmel nuclear power plant with and without the use of MOX fuel(17): *The radiation exposure from inhalation of radioactive materials during the passage of the radioactive cloud is higher by several dozen percent than if uranium fuel elements were exclusively used. *Radiation exposure through the route of inhalation of remobilized long-lived actinide isotopes is more than doubled. *The land areas to become out of use by long-term contamination increases as the resuspension pathway is a limiting factor and the greater part of the dose resulting from the pathway comes from the actinides.(18) #Accidents at Fabrication Plants Accidents at MOX fuel fabrication plants have occurred. In June, 1991, the storage bunker of the MOX fuel fabrication plant in Hanau, Germany was contaminated with MOX. It occurred after the rupture of a foil for container packaging in the course of an in-plant transportation process. Five workers were exposed to plutonium. This accident was the main reason the fabrication plant at Hanau was shut down.(19) In November, 1992, a rod was broken through a handling error and MOX dust released during the mounting of MOX fuel rods to fuel assemblies in the fuel fabrication facility adjoining the MOX facility in Dessel, Belgium.(20) In event of such accidents, if the International Commission on Radiological Protection (ICRP) recommendations for general public exposure were adhered to, only about 1 mg of plutonium may be released from a MOX facility to the environment. As a comparison, in uranium fabrication facility, 2kg (2,000,000mg)of uranium could be released in the same radiation exposure. A 1 mg release of plutonium from a processing process can easily happen from various smaller incidents.(21) #Worker Hazards The National Academy of Sciences concludes that the main environment, safety and health related issues in weapons plutonium disposition that needs special attention with the addition of weapons plutonium is the occupational risk from fuel preparation. (22) Because plutonium is more radioactive than uranium, greater safety concern is required when handling the material in whatever way. The ICRP sets a standard for occupational exposure to radiation at 100 mSv over 5 years, with a maximum of 50 mSv in any one year. If you interpret this in comparison for workers at an uranium fuel fabrication plant with MOX fuel fabrication plant workers, the standards for protection against inhalation are roughly two Million times stricter in plutonium processing than in uranium processing.(23) Another factor is the gamma radiation exposure which comes from americium, which accumulates as plutonium decays into americium as time lapses. Gamma radiation penetrates through almost anything, so it is very difficult to protect workers from this radiation. -------------------------------------------------------------- (15)"The MOX Industry or The Civilian Use of Plutonium," C. Kueppers & M. Sailer (IPPNW,1994,pp.16-19) (16)Ibid (17)"The Consequences of Severe Accidents in the Kruemmel Nuclear Power Plant for the Territory of the City of Hamburg and the Effects of Disaster Control Measures (Oko Institut, April 1992) (18)Ibid. note (15), pp.48-50 (19) Ibid note (15) p.40 (20) Ibid. (21) Ibid. (22)"Management and Disposition of Excess Weapons Plutonium, Reactor-Related Options"(National Academy of Sciences, 1995, p.97) (23)Ibid. note (15) p.38 ================================================================ NEWS BRIEFS >>G7 Paris Summit Report On October 28-31, government officials and experts of the G7 countries plus Russia, Belgium, Switzerland, International Atomic Energy Agency (IAEA) and European Commission gathered in Paris and discussed military plutonium disposition options. The delegations included nuclear fuel cycle companies such as COGEMA of France, BNFL of UK, Belgonucleaire of Belgium, Atomic Energy of Canada Limited, SIEMENS of Germany, and utilities such as Tokyo Electric of Japan, and Nordostschweizerische Kraftwerke AG of Switzerland. They concluded that both burning in reactors (MOX) and immobilization should be pursued in parallel and they are not mutually exclusive. The proposal from Russia, Germany and France to build a pilot scale MOX fabrication plant in Russia is said to be close to fruition and welcomed by the participants including US. However, it was stressed by the US that the new MOX fabrication facility should not be used for any other purposes except for the disposition mission and that the spent MOX fuel not be recycled. The US maintained that it can support a large-scale Russian MOX program "only on the basis that it's not part of a reprocessing economy in Russia." Russia was obviously adamant in refusing these conditions stating that they did not want to accept any position that could be seen as restricting their options in the future. The New York Times reported on November 22 that the US DOE is ready to announce the Record of Decision to choose the reactor option. On November 12, the Japanese press reported Japan will cooperate in the construction of a MOX fabrication plant in Russia, as the US have approved of the plan as well.(24) The domino effect of endorsing the "reactor option" is already starting. But as the New York Times concluded, the "decisive battle will take place years from now, in localities with electric companies that agree to accept mixed oxide fuels." (Sources: Nuclear Fuel 11/4/96, Nucleonics Week 11/7/96, Spent Fuel 11/4/96) (24) Asahi Shimbun, Nov.12,1996, Denki (Electric) Shimbun, Nov.12, 1996 --------------------------------------------------------------- >>Reprocessing Back in the US? On November 12, Gregg Renkes, a staff director of the Senate Natural Resources Committee of the United States, said during a panel discussion at the American Nuclear Society Convention that a provision advocating overseas reprocessing of US waste will be included in the comprehensive nuclear waste legislation to be introduced in the 105th Congress (beginning in early 1997). Spent nuclear fuel and high level radioactive waste are piling up at reactor sites as well as DOE weapons facilities in the US. Renkes claimed that the waste problem US faces today is the result of an "ostrich nuclear policy," keeping heads in the sand, ignoring that the so-called "nuclear fuel cycle back-end policy" is "broken." A reprocessing option was introduced as vague language in the Senate Waste Bill S1271 of 1995. As an "Emergency Relief" measure, if a utility "has exhausted its existing on-site storage capacity," the utility could contract with "entities qualified to provide interim storage and conditioning." The euphemistic term "conditioning" means "reprocessing." However, when S1271 was revised to S1936 in the early summer of 1996, the Emergency Relief provision was dropped. S1936 passed the Senate on July 31, 1996. The House version of the same bill contained no reprocessing language. But under the threat of a Presidential veto, the Republican leadership in the House declined to push this bill through in the election year. As a result, there is no legislation for interim storage at the moment. (Sources: Nuclear Fuel 7/15/96, Nucleonics Week 11/14/96, "US High-level Waste Management Policy and the Reprocessing Option" by Gregg Renkes, "Long Battle Over Yucca Site May Be Coming to a Close," Government & Commerce, November 18, 1995) ------------------------------------------------------------ >>Plutonium Inventory of the World, Update At the Reprocessing Working Group meeting held on October 4-5, in Washington, DC, Dr. Frans Berkhout of the University of Sussex in England gave the latest figures on world plutonium inventory. It will be announced in the new version of the "World Inventory of Plutonium and Highly Enriched Uranium 1992"(25) scheduled to be published in January 1997. According to Dr. Berkhout, the military stockpile is 250 tons, whereas the civilian plutonium is 990 tons as of end of 1995. Of the civilian plutonium, 800 tons is in spent fuel, 141 tons separated and stockpiled, and 49 tons recycled. Of the 49 tons recycled, 21 tons is in fast reactors and 28 tons in light water reactors in the MOX programs. (25)"Plutonium and Highly Enriched Uranium 1996: World Inventories, Capabilities and Policies," Oxford University Press/Stockholm International Peace Research Institute, 1997 ------------------------------------------------------------ >>International MOX Assessment An International MOX Assessment ("A Comprehensive Social Impact Assessment of MOX Use in Light Water Reactors") is being conducted by experts around the world headed and sponsored by Citizens' Nuclear Information Center in Tokyo. In lack of a comprehensive in-depth assessment focused on MOX use in LWRs, the project is intended to be the first such independent, comprehensive study on MOX. The experts include J. Takagi (Japan), M. Schneider(France), I. Hokimoto (Japan), M. Sailer (Germany) and F. Barnaby(UK). The interim report was published on October 26, 1996 in Kyoto, Japan. The report is available from CNIC (Tel:81-3-5330-9520, Fax:81-3-5330-9530, E-mail:cnic-jp@po.iijnet.or.jp). ***************************************************************** Thanks to Kathryn Schultz of Center for Defense Information, the Pu-Updates are available on CDI's Home Page on the Web at under Fissile Materials in the Issues section. **************************************************************** For information or comments, subscription, or for previous issues, please contact Yurika Ayukawa at 202-898-0150 Ext.226, fax 202-898-0172, or e-mail .