Pacific Gas and Electric (
PG&E) is supplying this information as a voluntary report. On March 8, 2012, at 1850 PST, Diablo Canyon Power Plant (
DCPP), Unit 1, declared the
steam generator (
SG) 1-1 narrow-range, low-low, water level channels for level transmitters LT-517 and LT-519 inoperable. This resulted from
DCPP determining that the low-low setpoints were non-conservative as a result of its evaluation of the Rosemount Nuclear's
10 CFR Part 21 notification titled 'Notification Under
10 CFR Part 21 on Certain Rosemount Model 1154 Series H Pressure Transmitters,' dated March 2, 2012.
PG&E determined that the following SG narrow-range level transmitters having reactor protection and emergency safeguards actuation functions are affected:
Unit 1:
- two channels on SG 1-1
- one channel each on SGs 1-2 and 1-4
Unit 2:
- one channel each on SGs 2-1, 2-2, 2-3 and 2-4
The Part 21 notification identified that the high temperature/pressure accuracy specification changed for certain transmitters which have higher impedance resistors installed in their temperature compensation circuitry. PG&E's evaluation concluded that narrow range SG low-low level setpoint uncertainty increased by as much as 2 percent of span due to the revised specification. Under the most limiting conditions, this deficiency could result in a short delay in relay actuation.
At 1953 PST, DCPP personnel declared the LT-517 and LT-519 water level low-low channels for SG 1-1 to be operable after adjusting the low-low setpoints from 15 percent to 17 percent on SG 1-1. DCPP also changed the low-low setpoints on SG 1-2 and SG 1-4 on March 8, 2012, and is changing this setpoint on all four of the Unit 2 SGs.
PG&E plans to submit a Licensee Event Report on this issue.
Plant personnel notified the NRC Resident Inspector.
