if a person sends a summary of an invention to an invention fair for primary registration before patenting the invention, this will be considered as a subject of public disclosure? If it is so, it will be considered as prior science or it is patentable yet (For PCT or US patent)?
The PCT does not have any "grace period", it leaves that to each Contracting State and the national patent law thereof. If the International Searching Authority finds a disclosure made by the inventor prior to the international filing date, it will add a note either in the Search Report itself or in the Written Opinion. Once you enter national/regional phases, the corresponding national/regional patent offices will use that disclosure against the patentability of your invention if there is no grace period under the corresponding patent law.
You have a summary of national/regional grace periods in this document of the WIPO.
I do not know what that registration you mention entails, and whether it qualifies as public disclosure or not, but I am pretty sure that in Europe it would be prior art that can be cited against your invention. At the EPO you have Art. 55 EPC (most Contracting States of the EPC have something similar in their national patent laws) concerning "non-prejudicial disclosures". According to that Article, an invention displayed by the inventors "at an official, or officially recognised, international exhibition falling within the terms of the Convention on international exhibitions" can be a "non-prejudicial disclosure" if it occurred not earlier than 6 months before the filing date of the European patent application. There are at least two important things to note here:
- There are very few exhibitions that are accepted for non-prejudicial disclosures. In other words, almost every exhibition is not an exhibition that qualifies for such non-prejudicial disclosures.
- The Article mentions that the invention is displayed, so only the displaying of the invention at the exhibition can be made non-prejudicial. The registration that you mention is not the same as displaying the invention, thus it does not qualify as a non-prejudicial disclosure (having an NDA in place, as @Eric Shain indicates, may reduce the likelihood that said registration will become prior art).
As a sidenote, in order to make the exhibition of the invention non-prejudicial, there are many steps that need be taken. There is paperwork that needs to be requested from the organization that makes the exhibition, said paperwork must be issued in a particular time period, and then it must be filed with the EPO. Missing the timeline in any of the steps that need be taken causes the exhibition to be prior art.
I do not know much about these legal aspects in the US, so that part will have to be answered by somebody else.
In the U.S. something becomes prior art under 35 USC section 102
(1) the claimed invention was patented, described in a printed publication, or in public use, on sale, or otherwise available to the public before the effective filing date of the claimed invention; . . .
Sending in the registration would not likely be considered a publication but if/when is printed in a guide to the fair it would be a printed publication - even if only online. Would it be considered available to the public? That is a good question for the patent bar exam so I do not recommend counting on it not being "know to the public".
Of course it depends on the level of detail you put in the disclosure. If you only explain the result or purpose and do not describe the structure that achieves that result you have not disclosed the invention. The U.S. does have an odd 1 year grace period. As another answer mentions you can file a provisional patent application with the USPTO. One idea is to file the exact same thing you use for the fair registration as the text of the provisional.