Entity Framework 5 HasRequired not works - foreign-keys

Question

I have 2 tables
USERS
[Id] INT NOT NULL PK IDENTITY,
[FirstName] nvarchar,
[LastName] nvarchar
and ACCOUNTS
[Id] INT NOT NULL PK,
[Password] nvarchar,
CONSTRAINT FK_Accounts_Users FOREIGN KEY (Id) REFERENCES [security].[Users] (Id)
I need to add at the same time Users and it's Profile.
Using EF FulentApi I make such models:
public UserConfiguration()
{
ToTable("Users", "Security");
HasKey(i => i.Id);
Property(i => i.Id).HasColumnName("Id");
Property(i => i.FirstName).HasColumnName("FirstName");
Property(i => i.LastName).HasColumnName("LastName");
HasRequired(i => i.Account).WithRequiredPrincipal(i => i.User);
}
public AccountConfiguration()
{
ToTable("Accounts", "Security");
HasKey(i => i.Id);
Property(i => i.Id).HasColumnName("Id");
Property(i => i.Password).HasColumnName("Password");
HasRequired(i => i.User).WithRequiredDependent();
}
Then, when I add User with Account it allows me to add null Acount, i.e. this code will works
using(var db = new SecurityDbContext())
{
var user = db.Users.Add(new User
{
FirstName = "John",
LastName = "Rambo"
});
db.SaveChanges();
}
Why Account is null, if in my UserConfiguration model I set Account as required?
And how then I can make a relationship User to Account 1:1?
Thanks in advance.