NVARCHAR column as PRIMARY KEY or as UNIQUE column

I'm developing a SQL Server 2012 database and I have a doubt about nvarchar columns as primary keys.

I have this table:

CREATE TABLE [dbo].[CODES]
(
    [ID_CODE] [bigint] IDENTITY(1,1) NOT NULL,
    [CODE_LEVEL] [tinyint] NOT NULL,
    [CODE] [nvarchar](20) NOT NULL,
    [FLAG] [tinyint] NOT NULL,
    [IS_TRANSMITTED] [bit] NOT NULL DEFAULT 0,
     CONSTRAINT [PK_CODES] PRIMARY KEY CLUSTERED 
    (
        [CODE_LEVEL] ASC,
        [CODE] ASC
    )
)

But now I want to use [CODE] column as primary key and remove [ID_CODE] column.

Is there any issue or penalty if I have a NVARCHAR column as PRIMARY KEY?

[CODE] column value must be unique, so I've thought that I can set an UNIQUE constraint to that column.

Any advice?