ENS 47258
ENS Event | |
|---|---|
00:45 Sep 13, 2011 | |
| Title | Control Room Envelope Declared Inoperable |
| Event Description | On September 12, 2011, at 1745 PDT operators declared the control room envelope (CRE) inoperable and entered Technical Specification (TS) 3.7.10 Action B. This was due to discovery of inadequately documented CRE in-leakage test data.
On September 12, 2011, DCPP [Diablo Canyon Power Plant] personnel reviewing the CRE testing dated February 3, 2005 determined that the test report provided inadequate information to conclude that the most limiting alignment for control room pressurization would result in zero cubic feet per minute (CFM) in-leakage into the CRE, contrary to the Final Safety Analysis Report (FSAR) accident analysis for the most limiting design basis accident. Three of the four ventilation alignments tested had reported values of in-leakage greater than zero CFM. Plant staff implemented compensatory measures by placing the control room ventilation system into its pressurization accident alignment at 1828 PDT using the alignment from the test which had a reported value of zero CFM in-leakage. Additionally, administrative controls are being established to maintain post-Loss of Coolant Accident Emergency Core Cooling System leakage at a rate that would ensure operator doses are maintained less than the FSAR accident analysis results for the highest in-leakage rate reported by the test. Plant personnel notified the NRC Resident Inspector.
On 9/13/11 procedure revisions were approved with reduced limits for post-Loss of Coolant Accident Emergency Core Cooling System (ECCS) leakage. These reduced limits ensure operator doses are maintained less than the FSAR accident analysis results for the highest in-leakage rate reported by the CRE in-leakage test. Plant staff have since determined that the potential benefit of operating the control room ventilation system in its pressurization alignment was unnecessary with the ECCS leakage restriction and on 9/16/11 operators restored the control room ventilation system into its normal operating alignment. The licensee has notified the NRC Resident Inspector. Notified R4DO (Greg Pick)
This is an update to EN #47258 reported on 9/13/11 where it was reported that operators had declared the Control Room Envelope inoperable. [This report was subsequently] updated on 9/16/2011. On 10/18/11 at 16:45 PDT, plant staff determined that the CRE testing dated February 3, 2005 was not performed using a bounding configuration which would result in greatest consequence to the control room operators. The recorded in-leakage from the test was therefore considered to be non-bounding. [As a result of this determination, plant staff have] implemented additional compensatory measures by issuing a shift order requiring the use of self-contained breathing apparatus and potassium iodide tablets under certain accident conditions in accordance with Regulatory Guide 1.196 and NEI 99-03. Plant personnel notified the NRC Resident Inspector. Notified R4DO (Campbell). |
| Where | |
|---|---|
Diablo Canyon  California (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+1.2 h0.05 days <br />0.00714 weeks <br />0.00164 months <br />) | |
| Opened: | Bob Kline 01:57 Sep 13, 2011 |
| NRC Officer: | Charles Teal |
| Last Updated: | Oct 19, 2011 |
| 47258 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 544172019-11-30T19:00:00030 November 2019 19:00:00
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