Potential for Recriticality of the Relocated Core

Knowledge of the effective multiplication factor (k_eff) of variously configured damaged fuel at Three Mile Island Unit 2 (TMI-2) has greatly affected ongoing defueling operations. A recent DOT 4.3 discrete ordinates analysis has extended prior postaccident analyses of k_eff to “best-estimate”predictions of criticality at several crucial periods during the progression of the accident. Results from the current analysis show that the TMI-2 fuel was most likely in a highly subcritical configuration at all times during the accident. In addition, conservative calculations have shown that during the crucial initial coolant boiloff period of the accident, the conditions necessary for criticality are extremely unlikely.