Tritium retention

Fig. 18. Tritium retention as a function of neutron damage tn graphite and graphite composite.

The extent of retention of tritium is 79 + 2 % in the former case and 21 2 % in the latter 155) complete retention (or complete loss) of tritium is, of course, not to be expected, since the isotope effect for extrusion of deuterium rather than protium in the condensation shown in Fig. 68 is not infinite. The percent tritium retention in the process of dehydration and water exchange (fig. 58) is now generally called the F-value 1491 thus enantiomerically pure CHDTC02H gives an F-value of either 79 (R configuration) or 21 (S configuration) values below 79 or above 21, i.e. closer to 50, indicate that the acid is not enantiomerically pure. The F-value determination... 

Feeding experiments with doubly labeled 3-hydroxy-4-[14C]methoxy-A-meth-yl-(f -[3H]- and -(5)-[3H]A,-benzylamines in King Alfred daffodils produced oduline (186) with high (82-85%) tritium retention (139). This observation suggested that the incorporation of A-methylisovanillamine into 186 occurred by a nonstereospecific process in which hydrogen removal from the benzylic position was governed by a kinetic isotope effect. 

Experimental results indicate that hydrogen isotopes reside in the near surface region as well as in the bulk stainless steel after low energy bombardment. The total retention of hydrogen isotopes is relatively low, indicating that tritium retention in... 

Results obtained on tritium retention during aromatic hydroxylation of the fragment in (118) derived from tryptophan101 appear in full,100 without essentially the addition of new information. 

There are large uncertainties about the tritium retention problem. The most pessimistic extrapolations based on data from co-deposition of tritium with carbon [8] conclude that the allowed maximum of 350 g of T retained in the vessel will be reached after only a few ITER discharges. This is seen as a genuine problem with graphite, whereas other candidate wall materials like W do not show such a strong effect of tritium retention. Therefore, already for ITER it is of paramount importance to clarify this problem and to verify that carbon as a wall material is acceptable at all for tritium operation. 

Layers are formed on many locations of the plasma facing wall tiles but also on areas with no direct plasma ion impact ( remote areas ). It turns out that understanding of the tritium-retention requires the understanding of the erosion of carbon, its local and global transport within the device and the details of the deposition mechanisms being responsible for the layer properties. 

Data needs and issues to be addressed with respect to tritium retention ... 

The requirements for long pulse operation in the next step fusion device ITER and beyond, like acceptable power exhaust, peak load for steady state, transient loads, sufficient target lifetime, limited long term tritium retention in wall surfaces, acceptable impurity contamination in central plasma and efficient helium exhaust, depend on complex processes. The input to the numerical codes, which are used for the optimization of divertor and wall components, relies to a large extend on our understanding of the major processes related to erosion and deposition, tritium retention, impurity sources and erosion processes. The reliability of predictions made with these codes depends crucially on the accuracy of the atomic and plasma-material interaction data available. 

It is evident that the removal of tritium from the torus of ITER-like machines requires the removal of tritium from the co-deposited layers, or perhaps - depending on the technique used - the removal of the co-deposits themselves. Notwithstanding the observation that tritium retention in short-pulse machines will be affected by mechanisms other than co-deposition, the experience gained from TFTR and JET - the only tritium-burning tokamaks in the world - is of paramount importance for gaining some understanding of the T-removal processes. Here we present a brief review of the T-removal experience with TFTR and JET, and then review controlled laboratory and... 

G. Federici, R.A. Anderl, P. Andrew et al., In-vessel tritium retention and removal in ITER, J. Nucl. Mater. 266-269 (1999) 14... 

C.H. Skinner et al., Plasma-wall interactions and tritium retention in TFTR, J. Nucl. Mater. 241-243 (1997) 214... 

D. Mueller, W. Blanchard, B.L. Doyle et al., Tritium retention and removal on TFTR, Proc. 17th IEEE/NPSS Symp. on Fusion Engineering, San Diego, CA, October 6-10, 1997... 

For the time being, one of the most crucial issues for a next-step device such as ITER is tritium retention. The actual ITER design uses beryllium for the main chamber wall and carbon as well as tungsten in the divertor [1, 2], For this choice of materials, tritium co-deposition with eroded carbon is expected to be the dominant tritium retention mechanism. This holds also... 

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