[en] On September 17, 1980, the Nuclear Regulatory Commission (NRC) issued the facility operating license DPR-77 to the Tennessee Valley Authority for the Sequoyah Nuclear Plant, Unit 1, located in Hamilton County, Tennessee. The license authorized operation of Unit 1 at 100 percent power; however, a license condition regarding the adequacy of the hydrogen control system was included that required resolution by January 31, 1981. The purpose of Supplement No. 4 to the SER is to further update our Safety Evaluation Reports on the hydrogen control measures (Section 22.2, II.B.7), and to comply with the license condition which is as follows: 'By January 31, 1981, TVA shall by testing and analysis show to the satisfaction of the NRC staff that an interim hydrogen control system will provide with reasonable assurance protection against breach of containment in the event that a substantial quantity of hydrogen is generated.' TVA submitted on December 11, 1980, the first quarterly report on the research program for hydrogen control. Also, TVA revised volume 2 of the Sequoyah Core Degradation Program Report to incorporate additional information on the overall program. Section II.B.7 of Supplement No. 4 responds to the license condition. Each section is supplementary to and not in lieu of discussion in the Safety Evaluation Report and Supplements Nos. 1, 2, and 3, except where specifically noted. Supplements No. 2 and 3 to the Safety Evaluation Report provided a basis for concluding that the full-power licensing of Sequoyah Unit 1 need not await completion of ongoing work on hydrogen control measures. This supplement concludes that operation of the IDIS for an interim period of one year is appropriate