Resolution of Generic Safety Issues: Issue 45: Inoperability of Instrumentation Due to Extreme Cold Weather (Rev. 2) ( NUREG-0933, Main Report with Supplements 1–34 )
Concerns for inoperability of instrumentation due to extreme cold weather were raised502 by AEOD after an event at Arkansas Nuclear One, Unit 2 (ANO-2) in which all four RWST instrumentation channels were lost when the level transmitters froze. The system heat-tracing circuit was de-energized because the main line fuse was removed. This situation would have prevented the automatic change-over of the ECC from injection to recirculation mode under LOCA conditions, i.e., loss of safety function. Prior to the ANO-2 event, IE Bulletin No. 79-24501 was issued after LERs revealed many events involving frozen instrument, sampling, and processing lines. All licensees and CP holders were requested to review their plants to determine that adequate protective measures had been taken to assure that safety-related process, instrument, and sampling lines do not freeze during extremely cold weather. AEOD requested that OIE issue a supplement to Bulletin 79-24501 and that NRR address the adequacy of protective measures for freezing of safety-related instrument lines in the review of OLs.
In an August 14, 1981 memorandum to AEOD,503 NRR advised that a BTP on freeze protection of safety-related instrument lines was being developed and would be included in the appropriate SRP11 Section following its review and approval. NRR further advised that OIE proposed to amend the Inspection and Enforcement Manual247 to include a module which would set forth procedures for inspection of systems and measures for protection against cold weather. This inspection module would require that regional inspectors perform plant site visits prior to the beginning of the cold season to verify the condition of heat-tracing systems and measures taken to protect plant equipment from cold weather conditions.
An amendment to the Inspection and Enforcement Manual (Procedure No. 71714)247 was issued by OIE on January 1, 1982, thus completing the OIE portion of the resolution of this issue. Acceptance criteria for the design of protective measures against freezing in instrument lines of safety-related systems were included in Draft504 Regulatory Guide 1.151, "Instrument Sensing Lines," and further work on a BTP was terminated. The Draft Regulatory Guide was issued for comment in March, 1982. Comments were collected and dispositioned and the Regulatory Guide505 was published in July, 1983. Notice of the issuance of Regulatory Guide 1.151505 was published in the Federal Register506 on August 8, 1983. Implementation of the Guide was limited to all CPs issued after September 1, 1983. However, other licensees or applicants could adopt the use of the Guide on a voluntary basis. As stated in the value/impact statement for the Guide, no backfitting of requirements for freeze protection and alarms was to be accomplished other than those changes effected by IE Bulletin 79-24501 (and the inspection requirements added to the OIE Inspection Manual).
In February 1984, the following SRP11 Sections were revised570,571 to incorporate the changes associated with the resolution of this issue: (1) Section 7.1, Rev. 3; (2) Section 7.1, Appendix A, Rev. 1; (3) Section 7.5, Rev. 3; and (4) Section 7.7, Rev. 3. Thus, this issue was RESOLVED and requirements were issued.