Have you tried the steps in this knowlege-base article?
Also, if the application re-opens on restart it's probably because 'resume' is enabled. If you deslect the tick as shown in the image on shutdown/restart it should prevent iPhoto re-launching.
Thanks, but that's not it. If I want/need to restart I have to force stop iPhoto. Even when I uncheck Resume it takes typically up to an hour to restart, making me believe iPhoto damaged something on disk which needs e lengthy recovery by the OS
Have you checked your HD doesn't need repairs using the Recovery HD. Restart holding down Command-r, select Disk Utility, click on Macintosh HD and click 'repair disk'. If anything gets changed click on repair disk again until you get a clear pass and then restart as normal from the Apple menu.
Two ways to get iPhoto to close:
1 - Force quit:
2 - open the Terminal application and enter the following:
The second method is preferred as it will close all files that were open whereas a force quit doesn't.
Now if iPhoto hangs again launch iPhoto with the Option key held down and create a new, test library. Import some photos and test to see if the same problem persists. It the new library does not hang your current library is the culprit and needs to be repaired.
Apply the two fixes below in order as needed:
Launch iPhoto with the Command+Option keys held down and rebuild the library.
Since only one option can be run at a time start with Option #3, followed by #4 and then #1 as needed.
Using iPhoto Library Manager to Rebuild Your iPhoto Library
1 - download iPhoto Library Manager and launch.
2 - click on the Add Library button, navigate to your Home/Pictures folder and select your iPhoto Library folder.
3 - Now that the library is listed in the left hand pane of iPLM, click on your library and go to the File ➙ Rebuild Library menu option.
4 - In the next window name the new library and select the location you want it to be placed.
5 - Click on the Create button.
Note: This creates a new library based on the LIbraryData.xml file in the library and will recover Events, Albums, keywords, titles and comments. However, books, calendars, cards and slideshows will be lost. The original library will be left untouched for further attempts at fixing the problem or in case the rebuilt library is not satisfactory.