webmaster Posted July 2, 2005 Share Posted July 2, 2005 From: Andrew L. Scott Subject: ACT2 and REACT not in agreement I have been trying to model the Yucca Mountain J-13 well water in preparation for performing a sensitivity analysis for U speciation. Attached you will find the Statement of the Problem, some REACT output, the thermo dB, scripts for ACT2 and REACT and some calculation macros. I updated the thermo.com.v8.r6+ dB with the NEA 2003 numbers for U species only at 25 deg C. I hope someone is able to understand and help with my problem. I have tried to be as complete as possible with the materials I have provided, but if there is anything that I have not included or you do not understand something I have done, please feel free to ask. [A note from the admin: The files are not available From: Mark Logsdon Subject: Re: ACT2 and REACT not in agreement You certainly have been complete in your information. I regret that I don't have time to go throuygh all your calculations, but I have a quick question on the two bases you use. Your REACT basis gives Na at 2 mmolar and Cl at 0.2 mmolar. But the ACT2 basis has log a Na at - 3.5 and log a Cl at -2.8. Are you sure you are calculating the acivities properly? If you just take log C (as a quick consistency check) I get -2.7 and -3.7, respectively, so the log a values look funny to me - and in fact, their order doesn't look right either. I haven't tried to do this for other components or to check your spreadsheet. From: Tom Meuzelaar Subject: Re: ACT2 and REACT not in agreement I think I see the problem. If you allow NO3- to speciate over your activity diagram (in Act2, Basis tab, click the right-most arrow for the NO3- entry, and choose "Speciate over X-Y"), you'll get a very similar diagram to your Act2 plot (the "correct" plot) without NO3- (if you additionally suppress Coffinite, the diagrams look even more similar). In your original "incorrect" activity diagram, there is an implicit assumption that NO3- is stable over your entire Eh-pH range- React predicts, however, that most of your NO3- component will occur as the N2(aq) species- you can confirm this by looking at your React output file. By choosing the "speciate" option in Act2, you're allowing the program to predict which nitrogen species is stable- the outcome greatly effects the final diagram. From: Andrew L. Scott Subject: RE: ACT2 and REACT not in agreement Thanks for the feedback, particularly Tom Meuzlaar and Mark Logsdon. Based on their comments, I recalculated the basis and allowed speciation over the X-Y axis in ACT2, and now have perfect agreement (and a greater understanding of process) between ACT2 and REACT. ............... view attachments ........... http://gwb.eligeos.org/attachments/al-scott1.jpg http://gwb.eligeos.org/attachments/al-scott2.jpg ................................................... If the silicon species is not allowed to speciate, quartz will not precipitate, and allows the precipitation of Haiweeite, a uranyl silicate mineral, at equilibrium. This calls into question the kinetics of the two processes (quartz and Haiweeite precipitation/dissolution) with regard to the mobility of the U in the Yucca Mountain J-13 water (represented by the top-most green dot). ............... view attachments ........... http://gwb.eligeos.org/attachments/al-scott3.jpg http://gwb.eligeos.org/attachments/al-scott4.jpg ................................................... Quote Link to comment Share on other sites More sharing options...
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.