Irradiation time [dj ——•
3.5. GAS EXPLOSION RESEARCH PROGRAMS
3.5.2. The German PNP Program
Delivery of process heat implies the coexistence of nuclear reactor and chemical plant, e.g., coal gasification, hydrogen production, ADAM-EVA transportation system. The main goals of the PNP gas explosion program were, in general, to improve understanding of the complex process of chemical explosions and its effect on the environment, and in particular, to demonstrate that a power station for nuclear coal gasification or process steam production is safely designed against explosions from outside, if the BMI guideline is applied. This is deemed true for explosions of transported hydrocarbons and minimum distance rules applied. However, some experimental studies on gas explosions under conditions typical for process gases inside the plant have revealed that under unfavorable circumstances, overpressures can exceed the respective maximum figures from the guideline. Experimental results were often complex and difficult to interpret. The experimental data base for the phase of flame acceleration is sufficient for a qualitative understanding of the phenomena and sound statements on flame speed and pressure within the frame of a safety analysis for an industrial complex. The transition to detonation itself, however, is strongly and decisively dependent on the turbulence structure which can only insufficiently be simulated in numerical models. It allows a derivation of specific DDT boundary conditions only in very concrete accident scenarios.
The PNP safety program [41] focused on the formation and explosion of clouds of the process gases Hk, CO, air and other representative combustible gases such as acetylene, ethylene, propane, methane, and the damage caused by the blast wave to simple structural elements (window pane, brick wall) after fast deflagration and detonation. Areas of investigations were
(i) flame front velocity in given scenarios and respective mechanisms of flame acce-leration,
(ii) criteria for the transition to detonation, and (iii) criteria for a passing on of a detonation.
Tasks within the study were dealing with deflagration damage analysis, mechanisms of combustion, regulations and limits comprising subtasks about
• identification of PNP specific accident scenarios which result in the release of flammable gas mixtures and assessment of corresponding gas masses to be expec-ted,
• material-specific aspects such as burning velocity, flammability limits, flame sprea-ding,
• the effects of a chemical explosion on building structures in relation to different degrees of partial confinement,
• evaluation and analysis of process gas cloud explosion accidents and experiments,
• derivation of the relation between a deflagrative pressure wave and characteristic destruction lines, upper limits of destruction, "design pressure wave",
• deduction of a load function by a damage analysis of the accident in Beek10,
• experimental investigation of deflagrative combustion and its enhancement in the presence of initial turbulence in a channel with open top,
• Balloon explosion tests, and
• development of a computer code for the spherical spreading of a flame according to the piston model.
Experimental studies within the PNP gas cloud program were conducted and eva-luated by the Fraunhofer Institute for Chemical Technology using flammable mixtures of hydrogen and other fuels with air in different shapes (sphere, hemisphere, tube), confined or unconfined. They are described in more detail in section 8.5.2. Experimental results from other test programs in the USA (explosion series in "FLAME") or Norway (jet ignition with transition to detonation in acetylene-air mixtures) were also taken into account. All tests were close to the go - no go boundary between deflagration and detonation.
An overall statement concerning the deflagration - detonation transition (DDT) was made within the frame of the PNP gas cloud program saying that the mechanisms and flame acceleration are qualitatively understood, however, they cannot be described on a quantitative basis, a statement that is, in principle, still valid today [6, 30, 41], although computational efforts are progressing tremendously.
REFERENCES TO CHAPTER 3
[1] AEA TECHNOLOGY, CFX 4.1: User Guide, AEA Technology (1995).
[2] BERMAN, M., CUMMINGS, J.C., Hydrogen Behavior in Light-Water Reactors, Nuclear Safety 25 (1984) 53-74.
[3] BREITUNG, W., REDLINGER, R., A Model for Structural Response to Hydrogen Combustion Loads in Severe Accidents, Nucl. Tech. Ill (1995) 420-425.
[4] BREITUNG, W., KOTCHOURKO, A., Numerische Simulation von turbulenten Wasserstoff-Verbrennungen bei schweren Kemreaktorunfallen, FZK-Nachrichten 28 (1996) 175-191.
[5] BURGHOLZ, L.M., Das Zwischenkreislaufexperiment - Theorie und Praxis, Re-port Jul-2230, Research Center Julich (1988).
[6] CHAN, C.K., TENNANKORE, K.N., A State-of-the-Art Report on Flame Acce-leration and Transition to Detonation in Hydrogen / Air / Diluent Mixtures, Draft Report, NEA Committee on the Safety of Nuclear Installations (CSNI) (1991).
[7] EDESKUTY, F.J., HAUGH, J.J., THOMPSON, R.T., Safety Aspects of Large-Scale Combustion of Hydrogen, (6th World Hydrogen Energy Conf., Vienna, Aus-tria, 1986), VEZIROGLU, T.N., et al., Hydrogen Energy Progress VI, International Association for Hydrogen Energy (1986) 147-158.
10 In 1975, a violent vapor cloud explosion occurred in Beek, The Netherlands. The accident in a naphta cracker installation was caused by a leakage of the product gases hydrogen, ethylene, and other hydrocarbons. A vapor cloud of an estimated 5500 kg of gas drifted into the plant where it eventually ignited. The accident claimed several fatalities; damage was found up to a distance of 4.5 km.
[8] EICHLER, R., Reinigung inerter Gaskreisläufe nuklearer Energieerzeugungsanla-gen von Tritium und Wasserstoff - Auslegung eines Gasreinigungssystems, Report Jül-2008, Research Center Jülich (1985).
[9] FINESCHI, F., Defense in Depth against the Hydrogen Risk - A European Research Programme, Proc. 34th Annual Conf. of the Canadian Nuclear Association (1994).
[10] FRÖHLING, W., et al., Safety Concept and Operational Criteria of a Nuclear Process Heat Plant, Nucl. Eng. Des. 78 (1984) 167-177.
[11] FUJIMOTO, N., et al., Safety Analysis and Considerations for HTTR Steam Reforming Hydrogen / Methanol Co-Production System, (TCM, Oarai, 1992), High Temperature Applications of Nuclear Energy, Report IAEA-TECDOC-761, International Atomic Energy Agency, Vienna (1994) 86-91.
[12] FUMIZAWA, M., Safety Concept of Heat Application Systems in JAERI - Fire and Explosion Accidents, Presentation at the Research Center Jülich, March 11 (1997).
[13] GHT/HRB, Prozeßgasaustritt und zündfähige Gemische, PNP Quarterly Report H/79, PNP Project (1979).
[14] GESELLSCHAFT FÜR REAKTORSICHERHEIT, Deutsche Risikostudie Kern-kraftwerke, Fachband 4: Einwirkungen von außen (einschließlich anlagenintemer Brände), Verlag TÜV Rheinland, Köln (1980).
[15] KICKEN, E.F., Passive Safety Systems, a Possibility of Enhancing Reactor Safety, Kerntechnik 61 (1996) 207-209.
[16] IAEA, Hydrogen in Water-Cooled Nuclear Power Reactors, International Atomic Energy Agency and Commission of the European Communities, Vienna (1990).
[17] IAEA, Development of Safety Principles for the Design of Future Nuclear Power Plants, IAEA-TECDOC-801, International Atomic Energy Agency, Vienna (1995).
[18] IAEA, Design and Development Status of Small and Medium Reactor Systems 1995, IAEA-TECDOC-881, International Atomic Energy Agency, Vienna (1996).
[19] IAEA, Fuel Performance and Fission Product Behavior in Gas-Cooled Reactors - A Compilation Produced within the IAEA Coordinated research program on Validation of Predictive Methods for Fuel and Fission Product Behavior in Gas-Cooled Reac-tors, IAEA-TECDOC-978, International Atomic Energy Agency, Vienna (1997).
[20] JÄGER, W., WEISBRODT, L, HORNING, H., Nuclear Process Heat Applications for the Modular HTR, Nucl. Eng. Des. 78 (1984) 137-145.
[21] JAHN, H., HÜTTERMANN, B., SCHWINGES, B., Analytical Methods for the Prediction of Hydrogen Distributions in Reactor Containments, Kerntechnik 54 (1989) 153-158.
[22] KANZLEITER, T., Modellcontainment-Versuche zum Wasserstoffabbau bei ausle-gungsüberschreitenden Ereignissen, (Proc. Jahrestagung Kerntechnik '92, Karls-ruhe, 1992), Inforum GmbH, Bonn (1992) 207-210.
[23] KARWAT, H., Hydrogen Mitigation in Steel Shell Containments of Pressurized Water Reactors, Kerntechnik 59 (1994) 171-177.
[24] KATZENMEIER, G., MÜLLER-DIETSCHE, W., Großversuche am ehemaligen Kernkraftwerk HDR, Atomwirtschaft 36 (1991) March 134-137.
[25] KÖNIG, S., BARNERT, H., SINGH, J., Prinzip-Auslegung und sicherheitstechni-sche Untersuchung der Wasserdampf-Kohle-Vergasung von Braunkohle mit HTR-Wärme, Internal Report KFA-ISR-IB-5/91, Research Center Jülich (1991).
[26] KUGELER, K., et al., The Pebble-Bed High-Temperature Reactor as a Source of Nuclear Process Heat, Vol 4: System Considerations on Nuclear-Heated Steam Reformers, Report Jul-1116-RG, Research Center Jiilich (1974).
[27] KUGELER, K., PHLIPPEN, P.-W., The Potential of the Self-Acting Safety Features of High Temperature Reactors, Kerntechnik 61 (1996) 239-244.
[28] LANGER, G., STOCK, M., Experimental Investigations on Hydrogen Behavior in Reactor Containments, Kerntechnik 53 (1988) 39-46.
[29] MERTENS, J. (Ed.), Nukleare ProzeBwarmeanlage AVR-U, Sicherheitstechnische Untersuchungen, Report Jul-Spez-199, Research Center Jiilich (1983).
[30] MOEN, I.O., Transition to Detonation in Fuel-Air Explosive Clouds, J. Hazardous Materials 33 (1993) 159-192.
[31] MURPHY, B., Japanese Industry Turns to Sandia to Test Nuclear Reactor Contain-ment Building Safety, Sandia LabNews, December 20, 1996.
[32] NABIELEK, H., FUKUDA, K., KANIA, M.J., Fuels Technology, Closed-Cycle Gas-Turbine Modular High-Temperature Gas-Cooled Reactor, (Int. Workshop, Cambridge MA, 1991), PENFIELD, S.R., KASTEN, P.R., Massachusetts Institute of Technology (1991) 4-8 - 4-16.
[33] NISHIHARA, T., et al., Safety Considerations and Countermeasures Against Fire and Explosion at an HTGR-Hydrogen Production System (Proposal of Safety Design Concept), (3rd JAERI Symp., Oarai, 1996), Proc. JAERI-Conf 96-010, Japan Atomic Energy Research Institute (1996) 264-271.
[34] NISHIHARA, T., HADA, K., SHIOZAWA, S., Proposal of Safety Design Metho-dologies for an HTGR-Hydrogen Production System (Mainly on Countermeasures against Fire and Explosion), Report JAERI-Research-97-022, Japan Atomic Energy Research Institute (1997) (in Japanese).
[35] PFORTNER, H., Zundverhalten von Erdgas/Luft-Gemischen in freien Wolken, gwf-gas/erdgas 120 (1979) 19-24.
[36] PLYS, M.G., Hydrogen Production and Combustion in Severe Reactor Accidents:
An Integral Assessment Perspective, Nucl. Tech. 101 (1993) 400-410.
[37] PONG, L.T., Assessment of the Combustion Model in the HECTR Code, Re-port NUREG/CR-5590 and SAND90-7080, U.S. Nuclear Regulatory Commission, Washington (1990).
[38] PREUSSER, G., The Multi-Compartment Code WAVCO, Kerntechnik 53 (1988) 47-52.
[39] ROYL, P., et al., Dreidimensionale Simulationen von Wasserstoffverteilung und -verbrennung im auBeren Sicherheitsbehalter eines Druckwasserreaktors, FZK-Nachrichten 28 (1996) 192-208.
[40] SAWA, K., et al., A Study of Silver Behavior in Gas-Turbine High Temperature Gas-Cooled Reactor, (TCM, Beijing, 1995), Design and Development of Gas Cooled Reactors with Closed Cycle Gas Turbines, Report IAEA-TECDOC-899, International Atomic Energy Agency, Vienna (1996) 131-143.
[41] SCHILDKNECHT, M., STOCK, M., Statusbericht zum Kenntnisstand des tlbergangs Deflagration-Detonation unter besonderer Berucksichtigung der Ziel-setzung des PNP-Gaswolkenprogramms, Final Report BF-R-66.459-2, Battelle Institute, Frankfurt (1987).
[42] SCHMTTT, R.E., et al., Experimentelle Untersuchung fiber das Verhalten von Csl bei H2-Verbrennung, (Proc. Jahrestagung Kerntechnik '94, Stuttgart, 1994), Inforum GmbH, Bonn (1994) 179-182.
[43] SCHODEL, J.P., Hydrogen - A Safety Risk?, Hydrogen as an Energy Vector Its Production, Use and Transportation, (CEC Sem., Brussels, 1978), Report EUR 6085, Commission of the European Communities (1978) 567-581.
[44] SHIBATA, T., et al., Availability of Steam Generator Against Thermal Disturbance of Hydrogen Production System Coupled to HTGR, (3rd JAERI Symp., Oarai, 1996), Proc. JAERI-Conf 96-010, Japan Atomic Energy Research Institute (1996) 289-293.
[45] SINGH, Y., et al., The Nuclear Heated Steam Reformer - Design and Semitechnical Operating Experiences, Nucl. Eng. Des. 78 (1984) 179-194.
[46] SINGH, J., HADA, K., JAERI/KFA Cooperation on Nuclear Heat Utilization System Design and Safety, Internal Report KFA-ISR-IB-16/94, Research Center Julich (1994).
[47] STEINWARZ, W., et al., Distribution of Tritium in a Nuclear Process Heat Plant with HTR, Nucl. Eng. Des. 78 (1984) 267-272.
[48] STOCK, M., GEIGER, W., Teilforschungsprogramm Gasexplosionen: Zusammen-fassende Darstellung und Auswertung, Final Report BIeV-R-64.181-4, Battelle In-stitute, Frankfurt (1984).
[49] STOVER, D., et al., Zusammenfassende Darstellung von Experimenten und Er-gebnissen zur Permeationsproblematik an In Situ oxidierten Hochtemperaturlegie-rungen, in: SCHAFER, J. (Ed.), Permeation der Wasserstoffisotope durch metalli-sche Werkstoffe bei hohen Temperaturen, Report Jul-1747, Research Center Julich (1981) 1-21.
[50] TAMANINI, F., URAL, E.A., CHAFFEE, J.L., Hydrogen Combustion Experiments in a 1/4-Scale Model of a Nuclear Power Plant Containment, (22nd Int. Symp. on Combustion, Seattle, 1988) The Combustion Institute (1988) 1715-1722.
[51 ] THOMPSON, L., EPRI Research on Hydrogen Combustion and Control for Nuclear Reactor Safety, (4th World Hydrogen Energy Conf., Pasadena, FRG, 1982), Hy-drogen Energy Progress IV (1982) 1675-1684.
[52] US DEPARTMENT OF ENERGY, Selected Technology Profiles, in: INTER-NATIONAL ENERGY AGENCY, Comparing Energy Technologies, OECD/IEA (1996) 237-296.
[53] VERNA, B.J., Off-Gas System Explosions - Part 1, Nuclear News 19 (1976) No.
14 53-54, - Part 2, Nuclear News 20 (1977) No. 1 43-44, - Part 3, Nuclear News 20 (1977) No. 4 41-42.
[54] WISCHNEWSKI, R., Untersuchungen zur Wassergasbildung bei Storfallen an HTR-Reaktoren am Beispiel einer geplanten HeiBgastemperaturerhohung auf 950
°C am AVR-Reaktor, AVR Report, Arbeitsgemeinschaft Versuchs-Reaktor (1974).
[55] WOLTERS, J. (Ed.), Probabilistic Safety Analysis and Assessment on Possible Urban Siting of the Modular HTR for Process Heat Application, Internal Report KFA-ISR-IB-3/90, Research Center Julich (1990).
[56] YANG, J.W., MUSICKI, Z., NIMNUAL, S., Hydrogen Combustion, Control, and Value-Impact Analysis for PWR Dry Containments, Report NUREG/CR-5662, U.S.
Nuclear Regulatory Commission, Washington (1991).
NEXT PAGE(S)