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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


  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).

  1. Approval of the agenda

The agenda was approved without changes.

  1. 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.
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.

  1. 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.

  1. 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.

  1. List of actions

Action number

Action holders

Description of the action

Due dates


Yamane, Grivot,

Anderson, Mitake,

Briggs and Nouri

Define a format for benchmark


December 2002



Collect the material and set-up the web-based information resources on criticality excursions including experimental

programs, criticality accidents and

summaries of computer codes.

Next meeting



Check whether the SHEBA experiments can be used as benchmarks.

December 2002


Yamane and Grivot

Propose a first set of benchmarks with U solutions varying the enrichment, inserted reactivity…

March 2003



Calculation of these benchmarks.

Next meeting



Advertise the activity of this group.

ICNC'2003 might be a good opportunity.

October 2003



Draft a format for an evaluation of accident Experiment

December 2002

Annex 1

List of participants


MARKOVA, Ludmila +420 (2) 6617 2291

Ustav jaderneho vyzkumu Rez

Theoretical Reactor Physics

Nuclear Research Institute

25068 REZ


BERGE, Ludovic +33 1 47 65 29 31

   EDF - Recherche et Développement,

1, av. du Général de Gaulle,

92141 Clamart Cédex,

LAVARENNE, Caroline +33 1 58 35 78 67


B.P. 17

Pascal GRIVOT +33 3 8023 4053


   Centre de Valduc



GMAL, Bernhard +49 (0)89 32004 494

Gesellschaft fuer Anlagen- und Reaktorsicherheit

Postfach 1328


LIEM, Peng Hong +81 29 270 5000

NAIS Co., Inc.

416 Muramatsu

Tokai-mura, Naka-gun

Ibaraki-ken 319-1112

MITAKE, Susumu +81 (3) 4512 2773


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


   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.


2-4 Shirakata-Shirane,Tokai-mura,

Naka-gun,Ibaraki-ken 319-1195
YAMANE, Yuichi

Criticality Safety Laboratory,

2-4 Shirakata Shirane,

Tokai-mura Naka-gun Ibaraki-ken,


HWANG, Hae Ryong +82 (42) 868 2214

Radiation Safety Analysis Group

Korea Power Engr. Co., Inc.

P.O. Box 148


DAEJEON 305-353

MENNERDAHL, Dennis +46 (0) 8 756 58 12

E. Mennerdahl Systems

Starvägen 12

S-183 57 TAEBY

GRIMM, Peter +41 (56) 310 2071

Paul Scherrer Institute



BROOME, Peter E. +44 (0)1925 833 022

British Nuclear Fuels plc

R101, Rutherford House

BNFL Risley

Warrington WA3 6AS

DE OLIVEIRA, Cassiano R.E. +44 (207) 594 9319

Imperial College of Science,

Technology and Medicine

T.H. Huxley School

Prince Consort Road


GULLIFORD, Jim +44 1925 83 3450

BNFL plc

R101 Rutherford House

Risley WA3 6AS


ANDERSON, Richard E. +1 (505) 667 6912

Los Alamos National Laboratory

NIS-6, MS J562

P.O. Box 1663


BRADY RAAP, Michaele C. +1 (509) 375-3781

Pacific Northwest National Laboratory (PNNL)

902 Battelle Blvd

P.O. Box 999, MSIN: K8-34

Richland, Washington 99352
BRIGGS, J. Blair +1 (208) 526 7628

Idaho National Engineering

& 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

Oak Ridge National Laboratory

Post Office Box 2008

Oak Ridge, TN 37831-6370
FUJITA, Edward K. +1 630 252 4866

Reactor Analysis & Engineering Division

Argonne National Laboratory

9700 South Cass Avenue, Bldg. 208

ARGONNE, IL 60439-4842
HOPPER, Calvin M. +1 865 576 8617

Oak Ridge National Laboratory

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

Building 6011, MS 6370

P.O. Box 2008

Oak Ridge, TN 37831-6370
WITHEE, Carl J. +1 (301) 415 8534


Office of Nuclear Material

Safety & Safeguards /SFPO

Mail Stop O-13-D13


International Organisations

NOURI, Ali +33 (0)1 45 24 10 84

OECD Nuclear Energy Agency

Le Seine St-Germain

12, Boulevard des Iles

92130 Issy-les-Moulineaux

SUYAMA, Kenya +33 (0) 1 4524 1152


Le Seine St-Germain

12, Boulevard des Iles

F-92130 Issy-les-Moulineaux

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