SE0100215 March 2001 ISSN 1650-1942 SWEDISH DEFENCE RESEARCH AGENCY Methodology report FOI-R-0054 Hans Tovedal Simulation of Fission Products from Nuclear Weapons Explosions 7500000.00 H + 1 [ mSv / h ] 7050000.00- 7000000.00- 6950000.00- 6900000.00 1400000.00 1500000.00 1600000.00 1700000.00 1800000.00 Division of NBC Defence SE-901 82 UMEA 2/ SWEDISH DEFENCE RESEARCH AGENCY FOI-R--0054-SE Division of NBC Defence March 2001 SE-901 82 UMEA ISSN 1650-1942 Hans Tovedal Simulation of Fission Products from Nuclear Weapons Explosions Issuing organization Document ref. No., ISRN Swedish Defence Research Agency FOI-R—0054-SE Division of NBC Defence Date of issue Project No. SE-901 82 UMEA March 2001 A413 Project name (abbrev. If necessary) SWEDEN Author(s) Initiator or sponsoring organization Hans Tovedal Project manager Goran Agren Scientifically and technically responsible Kenneth Lidstrom Document title in translation Simulation of Fission Products from Nuclear Weapons Explosions Abstract The simulation method MARS, Mathematical Radiac Simulation, is primarily intended for preparedness exercises in nuclear fallout areas and simulates the ionizing radiation doserates from fission products deposited on the ground, i e fallout from a nuclear weapons explosion or from a release of radioactive materia from a nuclear reactor. MARS gives at any time after the fictitious explosion or reactor release the doserates at any position in the fallout area. A special method, in this report called FOSIM, Fallout Simulation, based on MARS values, has also been developed. This is a technique to produce a standardized solution containing fission products of about the same composition as that caused by a nuclear weapons explosion. The MARS method and the FOSIM technique were both applied in a preparedness group exercise in a nuclear weapons scenario, LOTTA, in a northern region of Sweden in March 1998. This report gives a short description of the FOSIM method and a fairly detailed evaluation of the application results. From these, it is obvious that the technique produces a set of fission products that, from a couple of hours after the explosion and further, is quite similar to that expected in the fallout from a nuclear weapons explosion. The samples, taken in the fallout area, and prepared by addition of certain amounts of the FOSIM solution, offers unique opportunities for the preparedness laboratory to check and further develop its analysing methods. Some steps of the FOSIM technique need to be further developed, but already in this exercise it gave very realistic sample conditions for the benefit of the laboratory analyses. Key words MARS, mathematical, radiac, simulation, nuclear, fallout, doserate, fission, explosion, FOSIM Further bibliographic information Language ISSN 1650-1942 ISBN Pages 28 Price Ace. to pricelist Dokumentets utgivare Dokumentbeteckning, ISRN Totalförsvarets forskningsinstitut FOI-R—0054—SE Avdelningen för NBC-skydd Dokumentets datum Uppdragsnummer 901 82 UMEÅ Mars 2001 A413 Projektnamn (ev förkortat) Upphovsman(män) Uppdragsgivare Hans Tovedal Projektansvarig Göran Ågren Fackansvarig Kenneth Lidström Dokumentets titel Simulering av fissionsprodukter från kärnvapenexplosioner Sammanfattning Den tidigare utvecklade simuleringsmetoden MARS, Mathematical Radiac Simulation, är huvudsakligen avsedd för beredskapsövningar i områden med radioaktivt nedfall. Den simulerar den joniserande strålningens dosrat från fallout, dvs markdeponerade fissionsprodukter från en kärnvapenexplosion eller efter ett utsläpp av radioaktiv materia från en kärnreaktor. Mars ger kontinuerligt dosraten i varje enskild del av nedfallsområdet. En speciell metod, i denna rapport kallad FOSIM, Fallout Simulation, baserad på MARS-data, har nyligen utvecklats och tillämpats. Den består av en teknik att producera en standardiserad lösning av fissionsprodukter med samma sammansättning som de som skapas vid kärnvapenexplosioner. MARS- och FOSEVÍ-metoderna har båda tillämpats i samband med en beredskapsövning, LOTTA, Mars 1998, i norra delen av Sverige, med ett kärnvapenscenario. Föreliggande rapport ger en kortfattad beskrivning av FOSIM och en mer detaljerad uvärdering av resultaten och metoden som sådan. Det framgår att FOSIM-tekniken ger en uppsättning fissionsprodukter som, från några timmar efter den tänkta kärnvapenexplosionen och i fortsättningen därefter, överensstämmer mycket väl med den som förväntas i nedfallet efter en verklig kärnvapenexplosion. Mark- och vegetationsprover, tagna inom det simulerade nedfallsområdet och preparerade med FOSEVI-lösningen i enlighet med MARS-värdena, ger unika möjligheter för beredskapslaboratorierna att testa och eventuellt vidareutveckla sina analysmetoder. Vissa delar av FOSIM-metoden behöver förbättras något, men redan vid den genomförda övningen erhölls mycket realistiska prover, till nytta för övningen av analyslaboratorierna. Nyckelord MARS, radioaktiv, nedfall, joniserande strålning, dosrat, fissionsprodukt, kärnvapenexplosion, FOSIM Övriga bibliografiska uppgifter Språk ISSN 1650-1942 ISBN Omfång 28 sidor Pris Enl. prislista Distributör (om annan än ovan) FOI-R--0054--SE Contents Introduction 6 General aspects 6 The fission product simulation method 7 Theoretical basis for the exercise 12 Preparatory test 16 Data and results from the exercise 19 The remaining analyses 21 The remaining nuclides 27 Conclusion 27 References 28 FOI-R--0054--SE Introduction A group for radiac preparedness at the Swedish Defence Research Agency, FOI, has been trained and tested in a simulated nuclear weapons explosion scenario. One important task for the group is to maintain a well-trained and competent preparedness regarding the radiation effects of fallout from nuclear weapons explosions, nuclear reactor accidents and any other incident that may lead to the release of huge amounts of radioactive materia. The measurement of radiation doserates in the environment and laboratory analyses of samples collected in the fallout area, are high priority operations to be performed by the group at an early stage. That would make a basis for decisions of authorities regarding eventual measures in order to reduce the doserate to the population. The exercise was intended to cover all types of preparedness competence in the group, which demanded a high degree of realism in the scenario. Two simulation procedures were applied in order to meet this demand, namely 1. The doserates in the fallout area was simulated by the use of the MARS method 2. The radioactive materia in environmental samples was simulated by fission products from neutron irradiated uranium. This report is a technical description and evaluation of the second procedure, which may be called the FOSIM, Fallout Simulation, method. This is one in a series of reports1>2;3'4'5'6 which are describing the LOTTA exercise from other point of views. General aspects A nuclear weapons explosion in the air creates a big cloud containing a huge amount of radioactive materia, fission and neutron activation products. When the explosion takes place near the ground, a lot of ground material will be sucked up in the cloud, consisting of particles with a size distribution from rather coarse gravel to very fine particles. The radioactive materia will deposit on the particles, which are transported away by the winds and eventually returned to the ground. Big particles will soon leave the cloud while the smaller ones fall down much later and far away from where they were removed. This process creates a fallout area, where the activity per square metre and the ionising radiation doserate may be very high. The content of different radionuclides in the radioactive materia and its distribution on different particle sizes will depend on the size and type of the nuclear load, the altitude of the explosion point and several other factors. While the temperature is still very high, big particles, which will soon fall to the ground, will be contaminated with elements that condense at the prevailing temperature. Smaller particles on the other hand will also carry elements that condense at much lower temperatures. Consequently, the nuclide composition will change in character along the direction of the cloud movement, partly because of these different condense processes, but mainly due to the physical decay of radionuclides with different decay constants. FOI-R--0054--SE The expected mitial radionuclide composition after the splitting of fissile element may be taken from tables7. This report contains tables for individual and cumulative fission yields together with half-lives for occuring, significant isobars. Prediction of the most probable radionuclide composition in the case of a real nuclear weapons explosion is of course not quite feasible. Therefore, for exercise purposes one have to choose a composition among those considered possible to anticipate. The difference between the anticipated set of radionuclides from the splitting of the two common fissile elements, U-235 and Pu-239, is so small that, from the exercise point of view, it has no significance on the choice. The competence requirements for a preparedness group, that has to survey the fallout area for extension and intensity of the radioactive materia, will not be dependent on the fissile element type in the bomb. It is only necessary to choose a scenario that contains the most conceivable and dominating radionuclides. Fission products created by neutron irradiation of natural uranium in a nuclear reactor show in the initial stage approximately