Queries :: Week Number Query When Year Changes

I analyse things by the date they are ordered by the office.

The date gets put into a spreadsheet and i import this into access for the querying.

I need to summarise it by weeknumber and year.

I use the following queries:

To get the week: Week Number: DatePart("ww",[DateOrdered],0,2)
To get the year: Year: Year([DateOrdered])
To put it together: Weekyear: [Year] & "_" & [Week Number]

The problem is when the year changes.

The dates for week 1 for 2014 are between 30/12/2013 and 05/01/2014 and therefore straddles 2013 and 2014.

Therefore when the year and week number is put together the following results are given for that particular week:

DateOrdered - Result of above query
30/12/2013 - 2013_1
31/12/2013 - 2013_1
01/01/2014 - 2014_1
02/01/2014 - 2014_1
03/01/2014 - 2014_1
04/01/2014 - 2014_1
05/01/2014 - 2014_1

All of the above should all read 2014_1 but some obviously are 2013_1. This causes me problems when doing further analysis and cross tabulations.

How can I amend my query so that the above all show the correct year and week number: 2014_1 ?