Iodine behaviour under LWR accident conditions: Lessons learnt from analyses of the first two Phebus FP tests

N. Girault (Corresponding Author), S. Dickinson, F. Funke, Ari Auvinen, L. Herranz, E. Krausmann

Research output: Contribution to journalArticleScientificpeer-review

50 Citations (Scopus)

Abstract

The International Phebus Fission Product programme, initiated in 1988 and performed by the French “Institut de Radioprotection et de Sûreté Nucléaire” (IRSN), investigates through a series of in-pile integral experiments, key phenomena involved in light water reactor (LWR) severe accidents. The tests cover fuel rod degradation and the behaviour of fission products released via the primary coolant circuit into the containment building.

The results of the first two tests, called FPT0 and FPT1, carried out under low pressure, in a steam rich atmosphere and using fresh fuel for FPT0 and fuel burned in a reactor at 23 GWdt−1 for FPT1, were immensely challenging, especially with regard to the iodine radiochemistry. Some of the most important observed phenomena with regard to the chemistry of iodine were indeed neither predicted nor pre-calculated, which clearly shows the interest and the need for carrying out integral experiments to study the complex phenomena governing fission product behaviour in a PWR in accident conditions. The three most unexpected results in the iodine behaviour related to early detection during fuel degradation of a weak but significant fraction of volatile iodine in the containment, the key role played by silver rapidly binding iodine to form insoluble AgI in the containment sump and the importance of painted surfaces in the containment atmosphere for the formation of a large quantity of volatile organic iodides.

To support the Phebus test interpretation small-scale analytical experiments and computer code analyses were carried out. The former, helping towards a better understanding of overall iodine behaviour, were used to develop or improve models while the latter mainly aimed at identifying relevant key phenomena and at modelling weaknesses. Specific efforts were devoted to exploring the potential origins of the early-detected volatile iodine in the containment building. If a clear explanation has not yet been found, the non-equilibrium chemical processes favoured in the primary coolant circuit and the early radiolytic oxidation of iodides in the condensed water films are at present the most likely explanations. Models that were modified or developed and embodied in the computer codes for organic iodide formation/destruction in the gas phase and Ag–I reactions in the sump lead, in agreement with the Phebus findings respectively to greatly enhanced organic iodide formation kinetics and long term concentration in the containment atmosphere on one hand and, in the conditions of Phebus experiments, to significantly limited molecular iodine volatilisation from the sump in so far as silver was in excess compared to iodine, on the other hand. Organic iodides then quickly gain in importance and become the predominant volatile iodine species at long term.
Original languageEnglish
Pages (from-to)1293-1308
Number of pages16
JournalNuclear Engineering and Design
Volume236
Issue number12
DOIs
Publication statusPublished - 2006
MoE publication typeA1 Journal article-refereed

Fingerprint

light water reactors
Light water reactors
iodine
accidents
Iodine
accident
Accidents
containment
iodide
Iodides
iodides
fission products
Fission products
water
coolants
Silver
atmospheres
Coolants
atmosphere
silver

Keywords

  • nuclear power plants
  • light water reactors
  • LWR
  • accidents
  • LWR accidents
  • nuclear reactor accidents
  • iodine

Cite this

Girault, N. ; Dickinson, S. ; Funke, F. ; Auvinen, Ari ; Herranz, L. ; Krausmann, E. / Iodine behaviour under LWR accident conditions : Lessons learnt from analyses of the first two Phebus FP tests. In: Nuclear Engineering and Design. 2006 ; Vol. 236, No. 12. pp. 1293-1308.
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Iodine behaviour under LWR accident conditions : Lessons learnt from analyses of the first two Phebus FP tests. / Girault, N. (Corresponding Author); Dickinson, S.; Funke, F.; Auvinen, Ari; Herranz, L.; Krausmann, E.

In: Nuclear Engineering and Design, Vol. 236, No. 12, 2006, p. 1293-1308.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Iodine behaviour under LWR accident conditions

T2 - Lessons learnt from analyses of the first two Phebus FP tests

AU - Girault, N.

AU - Dickinson, S.

AU - Funke, F.

AU - Auvinen, Ari

AU - Herranz, L.

AU - Krausmann, E.

PY - 2006

Y1 - 2006

N2 - The International Phebus Fission Product programme, initiated in 1988 and performed by the French “Institut de Radioprotection et de Sûreté Nucléaire” (IRSN), investigates through a series of in-pile integral experiments, key phenomena involved in light water reactor (LWR) severe accidents. The tests cover fuel rod degradation and the behaviour of fission products released via the primary coolant circuit into the containment building.The results of the first two tests, called FPT0 and FPT1, carried out under low pressure, in a steam rich atmosphere and using fresh fuel for FPT0 and fuel burned in a reactor at 23 GWdt−1 for FPT1, were immensely challenging, especially with regard to the iodine radiochemistry. Some of the most important observed phenomena with regard to the chemistry of iodine were indeed neither predicted nor pre-calculated, which clearly shows the interest and the need for carrying out integral experiments to study the complex phenomena governing fission product behaviour in a PWR in accident conditions. The three most unexpected results in the iodine behaviour related to early detection during fuel degradation of a weak but significant fraction of volatile iodine in the containment, the key role played by silver rapidly binding iodine to form insoluble AgI in the containment sump and the importance of painted surfaces in the containment atmosphere for the formation of a large quantity of volatile organic iodides.To support the Phebus test interpretation small-scale analytical experiments and computer code analyses were carried out. The former, helping towards a better understanding of overall iodine behaviour, were used to develop or improve models while the latter mainly aimed at identifying relevant key phenomena and at modelling weaknesses. Specific efforts were devoted to exploring the potential origins of the early-detected volatile iodine in the containment building. If a clear explanation has not yet been found, the non-equilibrium chemical processes favoured in the primary coolant circuit and the early radiolytic oxidation of iodides in the condensed water films are at present the most likely explanations. Models that were modified or developed and embodied in the computer codes for organic iodide formation/destruction in the gas phase and Ag–I reactions in the sump lead, in agreement with the Phebus findings respectively to greatly enhanced organic iodide formation kinetics and long term concentration in the containment atmosphere on one hand and, in the conditions of Phebus experiments, to significantly limited molecular iodine volatilisation from the sump in so far as silver was in excess compared to iodine, on the other hand. Organic iodides then quickly gain in importance and become the predominant volatile iodine species at long term.

AB - The International Phebus Fission Product programme, initiated in 1988 and performed by the French “Institut de Radioprotection et de Sûreté Nucléaire” (IRSN), investigates through a series of in-pile integral experiments, key phenomena involved in light water reactor (LWR) severe accidents. The tests cover fuel rod degradation and the behaviour of fission products released via the primary coolant circuit into the containment building.The results of the first two tests, called FPT0 and FPT1, carried out under low pressure, in a steam rich atmosphere and using fresh fuel for FPT0 and fuel burned in a reactor at 23 GWdt−1 for FPT1, were immensely challenging, especially with regard to the iodine radiochemistry. Some of the most important observed phenomena with regard to the chemistry of iodine were indeed neither predicted nor pre-calculated, which clearly shows the interest and the need for carrying out integral experiments to study the complex phenomena governing fission product behaviour in a PWR in accident conditions. The three most unexpected results in the iodine behaviour related to early detection during fuel degradation of a weak but significant fraction of volatile iodine in the containment, the key role played by silver rapidly binding iodine to form insoluble AgI in the containment sump and the importance of painted surfaces in the containment atmosphere for the formation of a large quantity of volatile organic iodides.To support the Phebus test interpretation small-scale analytical experiments and computer code analyses were carried out. The former, helping towards a better understanding of overall iodine behaviour, were used to develop or improve models while the latter mainly aimed at identifying relevant key phenomena and at modelling weaknesses. Specific efforts were devoted to exploring the potential origins of the early-detected volatile iodine in the containment building. If a clear explanation has not yet been found, the non-equilibrium chemical processes favoured in the primary coolant circuit and the early radiolytic oxidation of iodides in the condensed water films are at present the most likely explanations. Models that were modified or developed and embodied in the computer codes for organic iodide formation/destruction in the gas phase and Ag–I reactions in the sump lead, in agreement with the Phebus findings respectively to greatly enhanced organic iodide formation kinetics and long term concentration in the containment atmosphere on one hand and, in the conditions of Phebus experiments, to significantly limited molecular iodine volatilisation from the sump in so far as silver was in excess compared to iodine, on the other hand. Organic iodides then quickly gain in importance and become the predominant volatile iodine species at long term.

KW - nuclear power plants

KW - light water reactors

KW - LWR

KW - accidents

KW - LWR accidents

KW - nuclear reactor accidents

KW - iodine

U2 - 10.1016/j.nucengdes.2005.12.002

DO - 10.1016/j.nucengdes.2005.12.002

M3 - Article

VL - 236

SP - 1293

EP - 1308

JO - Nuclear Engineering and Design

JF - Nuclear Engineering and Design

SN - 0029-5493

IS - 12

ER -