.NET SDK -- Where is my refresh token?

I keep reading that I am responsible for retrieving and saving a Refresh Token.  And then I read in some posts that the SDK handles that behind the scenes.  So, I'm confused.

Here's what I'm using to test uploading files:

public BoxClient CreateAccessClient(string tokenFilePath)
{
    BoxClient result = null;

    // Open a stream to read and dispose of the automatically created Box configuration file.
    using (FileStream fs = new FileStream(tokenFilePath, FileMode.Open, FileAccess.Read))
    {
        // Initialize the SDK with the Box configuration file and create a client that uses the Service Account.
        var session = new BoxJWTAuth(BoxConfig.CreateFromJsonFile(fs));
        result = session.AdminClient(session.AdminToken());
    }

    return result;
}

I'm using the JSON file I downloaded when I created my App.  I understand I'm using my App's Service Account (on a Developer's account) for access and this appears to be working OK for uploading and getting shared links.  But, I'm not seeing a Refresh Token.  In looking at the debug information for the client I create above, I see a RefreshToken variable in BoxClient.Auth.Session.RefreshToken, but it's null.  And I do see my access token has a lifetime of 60 minutes.

Do I assume correctly that in 60 days from the time I created my App account, I won't be able to connect anymore?  If so, what do I need to change.  Thanks!