Background Long term tritium retention is one of the most critical issues for ITER during the tritium phase. It is mandatory to evaluate the long term fuel retention in the hydrogen (H) phase of ITER, since it gives a basic information for the PFC material choice for the T phase EU PWI Task Force Issue card: H,D,T accountancy V.Philipps, ITPA Div and SOL, Issue card: H,D,T accountancy V. Philipps, E. Tsitrone

Present status: The tritium balance in T phase will be performed by T accounting in the ITER plant by regeneration of the whole gas handling system This procedure will require 1 week of shutdown and can only be performed periodically. It is presently not foreseen to assess the in vessel T inventory on a shot to shot (or day by day ) basis [3]. Refurbishment are necessary to Improve the AGHS system such that H,D T accountancy can be done on a regular (shot by shot or day by day at least) basis. This needs refurbishment of the AGHS system to be able to Measure accurately the pressure (p) and the temperature (T) of the exhaust gas in a well calibrated volume (V) Calculate the gas amount using the gas equation Determine the concentrations of H,D,T by appropriate analytical techniques, such as gas chromatography, mass spectrometry, laser Raman spectroscopy, ionization chambers, etc.). ( classical P-V-T method) EU PWI Task Force Issue card: H,D,T accountancy V.Philipps, ITPA Div and SOL,

The accountancy methods discussed above can be improved by addition of a few percent of deuterium to the protium gas in the ITER H phase and determination of the deuterium amounts injected and exhausted using the (p-V-T ) method as described above. Analysis of the trapped amounts by using hydrogen only could be done but large amounts of protium are ab- and ad-sorbed naturally in many materials and this method may lead to larger errors. EU PWI Task Force Issue card: H,D,T accountancy V.Philipps, ITPA Div and SOL, These simple and in-expensive solutions for improvement of the tritium and deuterium amounts injected into the torus and received from the cryo-pumps on a shot-by-shot basis are proposed in a paper by R. Lässer, D.K. Murdoch and M. Glugla TRITIUM ACCOUNTANCY ISSUES OF THE ITER FUEL CYCLE

EU PWI Task Force Issue card: H,D,T accountancy V.Philipps, ITPA Div and SOL, In addition to the refurbishment of the exhaust system, other diagnostics are important Additional use pressure gauges, which should be redundant and located in different toroidal locations in the sub-divertor for instance, as close as possible to the pumps (to reduce uncertainties due to the conductance of the pumping ducts), and with a sufficient time resolution for transients Calibration procedures should be established (gas injection for calibration of the pressure gauges, determination of effective pumping speeds, confirmation by divertor cryopumps regeneration etc). Laser assisted techniques to measure in situ the amount of retained fuel and deposited material are under development and have been demonstrated 1. LIBS (laser induced spectroscopy, uses the laser plasmato detect spectroscopically the ablated material) ( e.g. Semerok et al, CEA Saclay ) 2. Laser induced desorption and use target plasma to detect desorption (e.g Schweer, PSI Portland)

►Heating of surface layers by long pulse (3 ms), Nd:YAG laser radiation coupled into a fiber (35m); ► Desorption of hydrogen in a single laser shot; ► In situ measurement of released hydrogen by spectroscopic observation ( e.g. H Balmer lines) ► Quantitative determination of H isotopes inventory in surface layers using S/XB conversion factors Surface Tile Spectroscopy H ,  H 2, CH 4 LCFS Incident Laser beam: Fibre-coupled Nd:YAG typ. 40 J / 3 ms, 0.2 cm 2 Set-up at TEXTOR #61038 time=49s Laser beam accessible range of laser Observation Line of sight Proof of principle at JET Has been successfully applied in situ in TEXTOR B. Schweer, V. Philipps, F. Irrek 2. Laser induced desorption and use target plasma to detect desorption JET EU PWI Task Force Issue card: H,D,T accountancy V.Philipps, ITPA Div and SOL,