I have not been to Nepal but my understanding is that most films are ok when it comes to X-Ray scans in airport with the exception of high ASA films in the range of 800 and above. I used to work in a professional lab and have handled many different types of films sent in by pros working in many third world countries. All of them came through nicely except a particular case from Bali. Funny thing is that this is not the first time he sent it in to us. Secondly, of the 40+ rolls of 1600 films that came in, only 2 was fogged by the X-Ray machine. What puzzled me is that why didn't all the films get fogged? Why only 2 rolls?
Now, with the birth of new X-Ray machines capable of higher dosage scans, it is inevitable that some of our films may be fogged. In fact, some advance countries have X-Ray machines capable of increasing dosage automatically when it detected metallic objects so as to "see through". Such machines are a nuisance to photographers who would like to protect their films from X-Rays by placing them in a lead bag. The higher X-Ray dosage would definitely penetrate a lead bag.
On the contrary, I would say worry not because in Nepal, the machines are of the older generation ones which a simple lead bag may be used to protect against. You may purchase them from any major camera stores in Singapore.