I wish I knew what right Ms. Pelosi has to go on diplomatic missions. Perhaps rather than being a constitutional right, it is a right granted under "administrative law" for the congress. It is not very easy to find the code of "administrative law" compared with researching "constitutional law". She may have violated the Logan Act.
On April 10, 2997, an article written by Carla Mariunucci appeared in the San Francisco Chronicle, indicating that Ms. Pelosi and Rep. Lantos are interested in making a "diplomatic trip" to Iran.
http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/04/10/BAGV9P6C0S6.DTL
Pelosi, Lantos may be interested in diplomatic trip to Iran
Furthermore, the article quoted Rep Lantos as saying that he co-sponsored legislation with Ms. Pelosi which could pass as early as May that calls for making available to all countries --including Iran -- nuclear fuel for peaceful purposes under international oversight by establishing a "nuclear fuel bank".
I believe that the legislation is:
HR 6 Clean Energy Act of 2007
http://frwebgate.access.gpo.gov/cgi-bin/getdoc.cgi?dbname=110_cong_bills&docid=f:h6ih.txt.pdf
Those who advocate the "nuclear fuel bank" consider that clean nuclear technology would be available to all countries. However, those who argue against the "nuclear fuel bank" point out that the uranium enrichment process (using centrifuges to separate isotopes as in the FEP at Natanz, Iran) can also be used to produce a more pure grade of uranium 235 which may be used in a nuclear bomb.
http://news.bbc.co.uk/2/hi/europe/4416482.stm
http://www.iht.com/articles/2006/09/28/opinion/edbuffett.php
http://www.goodharborreport.com/node/295
The head of the Iranian Nuclear Energy Organization, Gholam-Reza Aghazadeh, explains it thus:
The simple way is to inject 0.7% (uranium) and obtain 3.5%, right? Now, if you take this 3.5% and inject it again into the chain (of centrifuges), the result will be 20%. If you inject the 20% back into the chain, the result will be 60%. If you inject this 60%, the result will be 90%.
http://www.memritv.org/Transcript.asp?P1=1120
http://www.memritv.org/Search.asp?ACT=S6&P1=2,148&P3=4
Since Iran has uranium enrichment capabilities at its FEP (fuel enrichment plant) at Natanz, giving Iran nuclear "fuel" enriched to 3.5% might not be a good idea if Iran does have the agenda to develop a nuclear bomb.
The BBC article (listed below) describes the nuclear fuel process.
http://news.bbc.co.uk/2/shared/spl/hi/sci_nat/05/nuclear_fuel/html/mining.stm