Nea/Nsc/Wpncs/Doc(2003)2

NEA/NSC/WPNCS/DOC(2003)2

Working Party on Nuclear Criticality Safety

Second Meeting of the Expert Group on Criticality Excursion Analyses

11 September 2002 NEA Headquarters, Issy-les-Moulineaux, France

SUMMARY RECORD

1. Introduction

Cassiano de Oliveira opened the meeting and welcomed the participants to the second meeting of the Expert Group on Criticality Excursion Analyses. Twenty-five participants from twenty different organisations attended the meeting (see the list of participants in Annex 1).

2. Approval of the agenda

The agenda was approved without changes.

3. Technical Presentations

Yuichi Yamane presented a paper entitled “Evaluation of Criticality Accident Analysis Code – TRACY experiments – Benchmrk Program”. He first presented an overview of the Nuclear Fuel Cycle Safety Engineering Research Facility (NUCEF) in the JAERI site of Tokai-Mura (Japan). The Transient Experiment Critical Facility (TRACY) is an annular cylinder with a central absorber rod. The experiments use a 10% enriched uranyl nitrate solution. The core can be operated in various modes depending on the reactivity insertion method and speed. The reactivity can be inserted by either removing the control rod or by the fuel solution feed into the tank. During the experiment, the power, temperature and pressure are monitored. Yuich Yamane showed a curve of power variation with time during a step reactivity insertion (reactivity ranging between 0.3 $ and 1$). He also showed the configuration of the facility for dosimetry experiments where 9 detectors are displayed at various locations around the core. He also informed the participants that JAERI has recently published a documentation of the whole series of TRACY transient experiments (Reports JAERI-Data/code 2002-005 to 2002-007). Finally, examples of what could later represent a calculation benchmark were discussed.

Mike Westfall asked three questions. The first one was “How is the variation of density with temperature and time monitored?”. Yuich Yamane answered that the density is measured at the initial state and at the end of the experiment. An interpolation with temperature is then performed. The second question concerned the order of magnitude of the total number of fissions per litter. Yuichi Yamane answered that it is about 10e+15 fissions per litter of solution. The last question was whether the temperature reactivity feedback coefficient is measured or calculated. The answer was both.

2 NEA/NSC/WPNCS/DOC(2003)2

Pascal Grivot presented a paper entitled “A Selection of SILENE and CRAC Experiments for Criticality Accident Codes Comparison”. He first presented the main features of the SILENE reactor (an annular cylinder with an absorber rod in the center) which has been in operation since 1974. The fuel is a highly enriched (~93 wt%) uranyl nitrate solution with a concentration varying from 71 g/l to 218 g/l. A typical SILENE run was then presented and examples of the pulse, free evolution and steady state modes were discussed. The first mode (quick removal of the control rod) is the standard one for transient experiment purposes. The free evolution mode (slow removal of the control rod, about 1 cm/s) is often used for training purposes and for the testing of criticality alarms. The steady state mode (very slow removal of the control rod, about 1 mm/s) is essentially used for irradiation and dosimetry purposes. Other applications of the SILENE reactor include the irradiation of reactor fuel samples under transient conditions. Pascal Grivot then presented the CRAC program carried out in Valduc between 1967 and 1972. The core is a full cylindrical tank (two diameters were used, namely 30 cm and 80 cm) and the reactivity insertion is made through the addition of solution (a highly enriched uranyl solution with a uranium concentration between 20 g/l and 340 g/l) into the tank. The flow rate varied from 100 to 1800 l/h. The maximum inserted reactivity was 10 $. Typical CRAC results were showed. Finally, Pascal Grivot informed the participants of the publication of a recent IPSN report compiling both programs.

Yuichi Yamane asked Pascal Grivot to comment on heterogeneous experiments. These experiments were made with a two-layer media: a highly concentrated uranyl nitrate above which a nitrate acid is added. The two-phase media is sub-critical. Injecting air under pressure does the mixing of the two phases and triggers the excursion.

Suzumu Mitake presented a paper entitled: “INCTAC: a criticality Accident Analysis Code for Liquid Fuel Systems - Development status in 2002”. The code is composed of several modules for simulation of thermal- and hydro-dynamics, reactor dynamics and the evaluation of important parameters including fission products release. Several TRACY experiments were used for the validation of the code. There seems to be a systematic difference between the calculation results and experiments at the beginning of the transient which might suggest a problem in the determination of the transient start-up. Improvements to the code and to its users’ interface were made in 2002. This includes the development of analytical models for the simulation of radioactive material and fission products transfer from fuel liquid phase to upper gaseous phase.

4. Discussion of calculation benchmarks based on experimental data

Pascal Grivot and Yuichi Yamane led a discussion on suitable benchmarks for code comparisons. It was suggested to start with simple configurations (the pulse mode seems to be the most appropriate at this stage). Experiments where the boiling of the solution did not occur were believed to be a good staring point. It was however agreed to vary the enrichment and the inserted reactivity. Pascal Grivot and Yuichi Yamane will draft specifications and circulate them for comments. Anderson was asked about the availability of the SHEBA experimental data. He commented that he will investigate the issue and informed that most of the configurations were below prompt critical.

5. Web-based information resources on criticality excursions

Ali Nouri suggested designing a web site where information is provided on experimental programs, accidents and calculation tools. Participants will be solicited to provide electronic versions of the documentation and to comment on the content of the web site. An item of particular interest concerns the description of available computer codes and of their validation status.

6. List of actions

Action number Action holders Description of the action Due dates Cea2002.1 Yamane, Grivot, Define a format for benchmark December 2002 Anderson, Mitake, specifications. Briggs and Nouri Cea2002.2 Nouri Collect the material and set-up the web- Next meeting based information resources on criticality excursions including experimental programs, criticality accidents and summaries of computer codes. Cea2002.3 Anderson Check whether the SHEBA experiments December 2002 can be used as benchmarks. Cea2002.4 Yamane and Grivot Propose a first set of benchmarks with U March 2003 solutions varying the enrichment, inserted reactivity… Cea2002.5 All Calculation of these benchmarks. Next meeting Cea2002.6 All Advertise the activity of this group. October 2003 ICNC'2003 might be a good opportunity. Cea2002.7 Briggs Draft a format for an evaluation of accident December 2002 Experiment

Annex 1

List of participants

CZECH REPUBLIC MARKOVA, Ludmila +420 (2) 6617 2291 Ustav jaderneho vyzkumu Rez [email protected] Theoretical Reactor Physics Nuclear Research Institute 25068 REZ

FRANCE BERGE, Ludovic +33 1 47 65 29 31 EDF - Recherche et Développement, [email protected] 1, av. du Général de Gaulle, 92141 Clamart Cédex,

LAVARENNE, Caroline +33 1 58 35 78 67 IRSN/DPEA/SEC [email protected] B.P. 17 F-92265 FONTENAY AUX ROSES CEDEX

Pascal GRIVOT +33 3 8023 4053 CEA/DAM/DRMN/SRSC [email protected] Centre de Valduc 21120 IS-SUR-TILLE

GERMANY GMAL, Bernhard +49 (0)89 32004 494 Gesellschaft fuer Anlagen- und Reaktorsicherheit [email protected] Postfach 1328 D-85739 GARCHING

JAPAN LIEM, Peng Hong +81 29 270 5000 NAIS Co., Inc. [email protected] 416 Muramatsu Tokai-mura, Naka-gun Ibaraki-ken 319-1112

MITAKE, Susumu +81 (3) 4512 2773 NUPEC [email protected] Institute of Nuclear Safety Fuel Cycle Facility Safety Analysis ec. 17-1 Toranomon 3-chome Minato-ku, TOKYO 105-0001

NAITO, Yoshitaka +81 29 270 5000 President [email protected] NAIS co. inc. 416 Muramatsu, Tokai-mura Naka-gun, Ibaraki-ken 319-1112

NOMURA, Yasushi +81 (0)29 282 5834 Fuel Cycle Safety Evaluation Lab. [email protected] JAERI 2-4 Shirakata-Shirane,Tokai-mura, Naka-gun,Ibaraki-ken 319-1195

YAMANE, Yuichi [email protected] Criticality Safety Laboratory, 2-4 Shirakata Shirane, Tokai-mura Naka-gun Ibaraki-ken,

KOREA (REPUBLIC OF) HWANG, Hae Ryong +82 (42) 868 2214 Radiation Safety Analysis Group [email protected] Korea Power Engr. Co., Inc. P.O. Box 148 Yusong DAEJEON 305-353

SWEDEN MENNERDAHL, Dennis +46 (0) 8 756 58 12 E. Mennerdahl Systems [email protected] Starvägen 12 S-183 57 TAEBY

SWITZERLAND GRIMM, Peter +41 (56) 310 2071 Paul Scherrer Institute [email protected] CH-5232 VILLIGEN PSI

UNITED KINGDOM BROOME, Peter E. +44 (0)1925 833 022 British Nuclear Fuels plc [email protected] R101, Rutherford House BNFL Risley Warrington WA3 6AS

DE OLIVEIRA, Cassiano R.E. +44 (207) 594 9319 Imperial College of Science, [email protected] Technology and Medicine T.H. Huxley School Prince Consort Road LONDON SW7 2BP

GULLIFORD, Jim +44 1925 83 3450 BNFL plc [email protected] R101 Rutherford House Risley WA3 6AS

UNITED STATES OF AMERICA ANDERSON, Richard E. +1 (505) 667 6912 Los Alamos National Laboratory [email protected] NIS-6, MS J562 P.O. Box 1663 LOS ALAMOS, NM 87545

BRADY RAAP, Michaele C. +1 (509) 375-3781 Pacific Northwest National Laboratory (PNNL) [email protected] 902 Battelle Blvd P.O. Box 999, MSIN: K8-34 Richland, Washington 99352

BRIGGS, J. Blair +1 (208) 526 7628 Idaho National Engineering [email protected] & Environmental Laboratory P.O. Box 1625, MS-3860 2525 North Fremont IDAHO FALLS, ID 83415-3860

DEHART, Mark D. +1 (865) 576 3468 Building 6011, MS 6370 [email protected] Oak Ridge National Laboratory Post Office Box 2008 Oak Ridge, TN 37831-6370

FUJITA, Edward K. +1 630 252 4866 Reactor Analysis & Engineering Division [email protected] Argonne National Laboratory 9700 South Cass Avenue, Bldg. 208 ARGONNE, IL 60439-4842

HOPPER, Calvin M. +1 865 576 8617 Oak Ridge National Laboratory [email protected] Building 6011, MS-6370 1 Bethel Valley Road Oak Ridge, TN 37831-6370

WESTFALL, R. Michael +1 (865) 574 5269/80 Oak Ridge National Laboratory [email protected] Building 6011, MS 6370 P.O. Box 2008 Oak Ridge, TN 37831-6370

WITHEE, Carl J. +1 (301) 415 8534 U.S. NRC [email protected] Office of Nuclear Material Safety & Safeguards /SFPO Mail Stop O-13-D13 WASHINGTON, DC 20555

International Organisations NOURI, Ali +33 (0)1 45 24 10 84 OECD Nuclear Energy Agency [email protected] Le Seine St-Germain 12, Boulevard des Iles 92130 Issy-les-Moulineaux

SUYAMA, Kenya +33 (0) 1 4524 1152 OECD/NEA [email protected] Le Seine St-Germain 12, Boulevard des Iles F-92130 Issy-les-Moulineaux