Make that ultra-high pressure. And our team is up to the task. At the recent Nuclear Energy Assembly in Scottsdale, Ariz., AREVA NP’s utility customer Exelon won a Top Innovative Practice award for application of AREVA NP’s ultra-high pressure cavitation peening (UHPCP) at two of its plants in 2016.
What we did
In 2016, AREVA NP and Exelon performed the first-of-a-kind application of ultra-high pressure cavitation peening on an in-service reactor vessel closure head (RVCH) in the world – and the first-of-a-kind implementation in the U.S. specifically aimed at addressing primary water stress corrosion cracking (PWSCC) in RVCH penetrations.
On top of that, each of the four implementations of RVCH cavitation peening to-date has been completed in outages lasting less than 30 days. Nothing like adding a little deadline pressure to the job! Overall, a total of 305 control rod drive mechanism (CRDM) nozzle penetrations were peened on the outer surface of the head, and 309 CRDM nozzle and vent line penetrations were peened from the inner surface. That’s a whole LOT of peening!
Why it matters
This strategic project was the culmination of the U.S. nuclear industry’s pressurized water reactor (PWR) experience since December 2000, including over 180 repairs of Alloy 600 reactor vessel head penetrations due to PWSCC-induced flaws. These emergent repairs have cost the nuclear industry millions of dollars due to outage delays, repair costs and subsequent increased inspection frequencies. The unpredictability and consequences of emergent flaws have led many PWR utilities to replace their reactor vessel heads with improved PWSCC-resistant alloy reactor vessel heads.
Working together, AREVA NP and Exelon teams found that proactively performing cavitation peening mitigates the nozzle penetrations’ susceptibility to PWSCC, eliminating the need to perform costly emergent repairs or completely replace the reactor vessel closure head.
What it means for our customer
Exelon was able to achieve long-term preservation of critical nuclear power plant assets (Alloy 600 RVCHs) through the employment of innovative strategies (UHPCP) that resulted in savings of more than $370 million, avoiding over 580 rem of radioactive dose to workers, and reducing outage duration by over 150 days (400 man-months of emergent work) due to projected emergent repairs spanning the service life of four reactors at the Byron and Braidwood Nuclear Generating Stations in Illinois.
Specifically, the customer was able to realize benefits such as:
- Preservation of the RVCH asset by reduced risk from PWSCC initiation.
- Avoidance of head replacement at four reactors (Byron Unit 2 and Braidwood Unit 1 were completed first in 2016, Byron Unit 1 was completed in March 2017, and Braidwood Unit 2 was completed May 2017); replacing a single PWR Alloy 600 head with a new Alloy 690 head can cost approximately $100-$120 million, plus added time to refueling outage activity.
- Optimized inspection relief is in queue in the NRC relief request approval process. This will provide a savings from the multi-million dollar head inspection activity during each refueling outage with costs of approximately $2 million per outage. Inspection relief will also provide a reduction of worker cumulative dose of approximately 1000 mrem during each outage.
- Reduced contingency planning for emergent nozzle repairs during a refueling outage that saves approximately 10 rem of radiation worker occupational dose and $2-$5 million per repair.
- Initiation of a proactive stance on aging management of a key nuclear safety significant component that protects the health and safety of the public.
Learn more about UHPCP
To see how cavitation peening works and how it’s delivered in the plant, check out these AREVA peening videos.
For more information on cavitation peening, visit us.areva.com/crr.