Junk Plant ANO: Plant Spinning Wildly Out Of Control, Raising Power Level Will Fix It?

Licensee Event Report 50-313/2015-001-00

Manual Reactor Trip Due to Oscillations in the Feedwater System

On December 15, 2015, at approximately 0544, Arkansas Nuclear One, Unit 1 (ANO-1), manually scrammed during a scheduled automatic down power to 35% power for planned maintenance. The Integrated Control System (ICS) (JB) was being utilized for the down power. During the down power, oscillations occurred in the Main Feedwater (MFW) (SJ) system. The ICS was placed in manual and efforts were made to dampen the MFW oscillations. The Operators manually tripped the reactor from approximately 43% power when it became evident that an automatic reactor trip was imminent, based on the observed Reactor Coolant System (RCS) (AB) pressure rise caused by the significant reduction in MFW flow. The direct cause of the manual plant trip is currently considered a result of placing the “B” startup valve in HAND (manual) when the valve was ~36% open, which resulted in a significant underfeed condition of the “B” Once-Through Steam Generator (OTSG). There are currently two root causes considered for this condition: (1) inadequate maintenance practices applied to the ICS modules, and (2) inadequate procedural guidance to address ICS malfunctions.

Event Cause 

The direct cause of the manual plant trip is currently considered a result of placing the “B” startup valve in HAND when the valve was ~36% open, which resulted in a significant underfeed condition of the “B” OTSG. There are currently two root causes considered for this condition: (1) inadequate maintenance practices applied to the ICS modules, and (2) inadequate procedural guidance to address ICS malfunctions.

Just because a licensee says it is the most conservative means to the NRC it is the most conservative. 

So basically nuclear safety relay maintenance problems with poor operator training and poor procedures. They assumed though raising plant power level they understood what was going on in the plant…but it was spinning wildly out of control. It is the certainty/ uncertainty gaming…they assume they knew what was going on, but in actuality the plant was spinning wildly out of control. So it’s the operator’s management in the control room duty to perceive things are out of control…then to conservatively scram. It would have headed off the dangerous feed water flow oscillations.   

Remember the NRC thinks this is the worst plant in the USA. They killed an employee and injured eight others through not following procedures by dropping a 600 ton stater. A pipe broke through this, they (NRC and ANO) then accidentally discovered serous flooding vulnerabilities. These guys had many years since this to get their stuff in one sock…the results of this down power should have never happened. They are still not fixed and dangerous operators of nuclear plants.   

The difference in the RCS cold-leg temperatures continued to build as the plant stabilized. With the “B” MFW low-load control valve considered non-functional, it was determined that the most conservative action would be to raise power slightly so the MFW block valves would re-open and the MFW pumps would shift back to the “Flow Control” mode. A slight power increase using the ICS station in manual was initiated at ~ 0455. Power began to rise as expected and the RCS Tcold condition improved as MFW flows became more evenly matched due to increased feedwater flow to the “A” OTSG.