I definitely get burnt out on occasion but frankly far less than other jobs I've had (and definitely far less than school!). The department offers alternative workweek schedules for my classification, so I work 10-hour days Tue-Fri and get a three-day weekend every week. On top of the already pretty good time off packages from the state, my classification gets 92 hours of paid professional development / continuing education hours every fiscal year. My work/life balance is grand compared to most social work jobs.
Another perk of working with inmates is: they're not going anywhere and their needs are being met. A lot of social work jobs come with added stress of worrying about clients' needs while away from work, and in many case being constantly on-call to respond to those needs for clients on your caseload. There is an on-call clinician at each prison for very rare crisis situations, but this is an optional, rotating duty that people volunteer for for the extra income. You don't have to do it. In short: Unlike most social work jobs, you can leave work at work.