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Research programmes

Source term programme

Last update in July 2011
The International Source Term Program (ISTP) aims to reduce uncertainties concerning the evaluation of environmental emissions of radioactive products such as iodine and ruthenium in the event of a core meltdown accident in a pressurized water reactor (PWR).
The experimental data obtained through this program help to develop and validate the numerical simulation tools used to evaluate the consequences of this type of accident and evaluate the effectiveness of the means implemented to prevent them.

This five-year, multiple-partner international program has four experimental segments.

1st topic: Studying iodine chemistry


  • In the primary cooling system Chip programme


Objective: provide experimental data on the physicochemical

Banc expérimental CHIP LP 

transformations of iodine in the core where it is released as gas into the reactor containment. The aim is to determine the quantity of gaseous iodine present in the reactor containment.

This topic has been divided into two parts:

  1. Phenomenological tests involving up to 10 chemical elements that are representative of the products released in large quantities from core at the same time as iodine (elements from the control rods, etc.).
    The aim is to identify the chemical elements likely to react with iodine during its transfer from the core into the containment (short transfer time, fast cooling in the presence of steam and hydrogen);
  2. Analytical tests involving a small number of elements. The aim is to collect kinetic data on the main reactions coming into play.
  • In the reactor containment Epicur & Paris programmes


Objective: provide experimental data on the physicochemical EPICURtransformations of iodine (formation & destruction of volatile iodine species) under the effect of radiation in the reactor containment. The aim is to estimate the quantities of gaseous iodine (especially organic iodine which is difficult to trap with filters) likely to be released into the environment in the event of a containment leak.
PARISResearch specifically focuses on:

  1. Chemistry of iodine in aqueous phase under radiation,;
  2. Iodine interactions with surfaces (especially paints) that result in the formation of organic iodine;
  3. Iodine reactions with radiolytic products from air (including ozone).

This research is carried out within the scope of the EPICUR and PARIS programmes. The EPICUR facility has a gamma spectrometry device that is used for the on-line monitoring of the various gaseous species generated.



2nd topic: Degradation of boron carbide (B4C) control rods

Objective: assess the impact of boron carbide control rod degradation on the core degradation, on the production of hydrogen, and on the volatility of certain radioactive products, especially iodine.
Research specifically focuses on:

  1. Degradation mechanisms of a boron carbide control rod in the presence of steam when heated to more than 1,300°C;
  2. Release of oxidation products, as well as borated and carbonated species.

The programme Becarre includes:INTERMEZZO

  1. Analytical tests to determine the steam oxidation kinetics of pellets made from boron carbide or mixtures of boron steel. These tests will also help to characterise the oxidation products formed;
  2. Semi-analytical tests to determine the degradation mechanisms of a 60 cm long control rod segment and its associated releases.
    These tests are performed in the Verdi, Picollo and Intermezzo facilities.

3rd topic: Consequences of fuel rod heating in air

This situation is likely to occur, for example, during an accident involving reactor vessel rupture or during the uncovering of an irradiated fuel storage pool. Such situations can especially affect cladding degradation mechanisms and ruthenium releases.

  • Mozart experimental programme


Métallographie d'un échantillon de MS oxydé sous air à 950°CObjective: study the oxidation of nuclear fuel cladding in air. This programme is studying several alloys (Zircaloy-4, M5TM and Zirlo) in different initial conditions (fresh, preoxidised or pre-hydrided) to simulate ageing in the eactor. The kinetic data collected from these tests is used to develop an air oxidation model for numerical simulation tools that are designed to assess releases.


  • Experimental programme Ruthenium chemistry in the reactor containment


Objective: provide experimental data on the physicochemical Dispositif général RUO4transformations of ruthenium under radiation in the reactor containment. This particularly involves characterising the mechanisms that lead to the formation or destruction of gaseous ruthenium species.
Research specifically focuses on:

  1. Surface deposition rate leading to the destruction of gaseous ruthenium Ru04;
  2. Formation rate of gaseous ruthenium from surface deposits in particular.

4th topic: Fission product releases from irradiated fuel at high temperature


Verdon experimental programme and microanalysis

Objective: study the release of fission products from samples of highly-irradiated UO2 fuel and Mox fuel, which have been the subject of very VERDONlittle research to date (the VERCORS programme conducted from 1989 to 2002 focused on moderately-irradiated UO2 fuel).
The tests consist in heating several fuel pellets to a very high temperature in steam and hydrogen so as to monitor the release of fission products on-line by means of gamma spectrometry.

The microanalysis programme sets out to characterise the distribution and chemical composition of fission productsin the different phases of fuel having been subjected to thermal transients during VERDON and VERCORS tests.
This characterisation should make it possible to validate the test result interpretations.

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Dates: 2005-2010
Project leader: IRSN
Funding: €30 M, several partners

IRSN units involved:

 Chemistry and Fire Studies and Research Department (Serci)

 Fires, Corium and Containment Department (Semic)

"Source term" partners

Programs of "Source term"

Different programmes constitute the "Source term" general programme. Some are described in the links below:

Program data sheet


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