2018 - 12 - 28 Letter to Gavin Newsom about embrittlement problem at Diablo Canyon

San Luis Obispo Mothers for Peace informs California Governor- Elect Gavin Newsom about serious problems posed by embrittlement at the Diablo Canyon plant. Safety and environmental concerns as well as grid reliability are at risk.

December 28, 2018

Hon.Governor-Elect Gavin Newsom

California State Capitol, Suite 1114

Sacramento, CA 95814

Dear Governor-Elect Newsom,

San Luis Obispo Mothers for Peace (SLOMFP), a 501c3 nonprofit organization, has

been the legal intervenor in matters regarding Diablo Canyon nuclear plant since 1973.

Unit 1 at Diablo Canyon is scheduled to permanently shut down in 2024, and Unit 2 in

2025. There is a matter of great importance that SLOMFP believes you have the power

to influence and thereby promote greater grid reliability and safety in the State of


In 2003, the Unit 1 reactor vessel at Diablo Canyon was identified by the NRC as one of

the five most embrittled reactor vessels in the United States’ fleet. What this means is

that, if a “cold shutdown” were necessary, meaning that emergency cooling water had to

be poured into the reactor, the vessel has the potential to crack open due to thermal

shock, causing a Category 9 Accident, the worst possible scenario at a nuclear power


The Unit 1 reactor vessel was manufactured in 1972, and in retrospect, engineers

realized that excessive copper had been used in the welds. Copper becomes embrittled

more rapidly than other metals that are used in newer reactor vessels, but this old vessel

continues to operate – 46 years after its manufacture. Because it is so old, and because

it is so embrittled already, it only makes sense to do an inspection now.

Two possible problems with this reactor vessel are excessive embrittlement (changes in

the metals’ atomic structure that are not visible) and interior cracking (visible on

ultrasound examination).

There is just one way to check for embrittlement. “Coupons” (bits of metal that are

composed of the exact same material as the welds inside the reactor vessel) can be

destructively tested. The last time a coupon was tested was in 2003. During the

upcoming outage, a coupon could be pulled from the reactor vessel and tested.

Remotely-controlled ultrasound can check for cracks in the vessel walls. PG&E was

scheduled to check for cracks in the welds by using ultrasound in 2015, but they applied

for and received an exemption from the Nuclear Regulatory Commission (NRC) until

2025. The vessel has not been inspected since 2005, despite the NRC regulation that

reactor vessels must be checked for cracks every ten years.

Unit 1 is due to go offline in February of 2019 for refueling. Ultrasonic testing for cracks

in the interior of the reactor vessel will be possible. During the outage, PG&E can also

remove a coupon and send it to a “hot” lab for testing. SLOMFP requests that you urge

the California Public Utilities Commission to order a full inspection at that time. If the test

results are positive, it can reassure the public that this reactor vessel can safely tolerate

another six years of operation. If not, Unit 1 can be taken offline permanently.

SLOMFP understands that authority regarding safety at nuclear power plants rests with

the NRC; however, the State of California would feel the enormous economic,

environmental, and public health consequences, as well as the loss of grid reliability, that

a reactor vessel accident would inflict on the State and its citizens.

We are available to meet with you to clarify any questions that you may have regarding

embrittlement and cracking at the Diablo Canyon Unit 1 reactor vessel.


San Luis Obispo Mothers for Peace Board of Directors

Liz Apfelberg

Elizabeth Brousse

Elaine Holder

Molly Johnson

Sherry Lewis

Linda Seeley

Jane Swanson

Jill ZamEk

cc: Governor Jerry Brown

Chairman Michael Picker, CPUC

Secretary John Laird, CA Dept. of Natural Resources

Assemblyman Jordan Cunningham

Senator Bill Monning

Congressman Salud Carbajal


Here is SLOMFP’s attorney Sabrina Venskus in her Response to the Joint Proposal,

filed on 8/20/16:

“The atomic reactor for Unit 1 was designed over 50 years ago, and delivered to the

Diablo Canyon site in 1973, approximately 20 years prior to the startup of the Plant. The

reactor vessel was one of the first ever manufactured for the nuclear power industry, by

a company with no previous experience manufacturing such a vessel. Because at that

time the nuclear industry was in its infancy, it was not yet known that the material used

to weld the Diablo Canyon Unit 1 reactor vessel is highly susceptible to radiation


Ultimately, it was realized that reactor vessels damaged by radiation become embrittled

and are susceptible to cracking and vessel failure. This phenomenon is known as

embrittlement and is the subject of a lengthy analysis by Fairewinds Associates, Inc.,

attached to SLOMFP’s expert witness Arnold Gundersen’s prepared testimony as

Appendix A.

What the analysis demonstrates is that “irradiation embrittlement” is a significant issue

for the type of reactor vessels such as Unit 1. The NRC has labeled Diablo Canyon Unit

1 as one of the five most embrittled reactor vessels in the United States. Due to

degradation and loss of integrity in this major component for the Unit 1 reactor, the

reactor vessel poses a risk of what the NRC calls a Class 9 Accident, which is the worst

nuclear catastrophe presently acknowledged by the NRC.

While the NRC has waived the reactor vessel inspection requirements until 2025 (the

last inspection was conducted in 2005), despite acknowledging that Unit 1 is in the top 5

worst embrittled reactors in the country (out of a total of 99 remaining operational

reactors), the glaring fact remains that Unit 1 reactor vessel embrittlement poses a risk

of a significant accident. Reactor embrittlement can cause an atomic reactor to shatter

like glass. Then the nuclear core leaves the atomic reactor and melts down into the

containment, as it did at three of the atomic reactors at the Fukushima Daiichi site in

Japan on March 11, 2011.

A near-miss at California’s Rancho Seco atomic reactor in 1978 provides an object

lesson that pressurized water reactors, such as that at Diablo Canyon, are susceptible to

abrupt changes in temperature and pressure that can be catastrophic for embrittled


In the case of Rancho Seco, while the welds on the reactor were severely stressed by

the pressure and temperature changes that resulted from a cascade of electrical faults

that started when a worker dropped a light bulb on the control room floor, the

Pressurized Thermal Shock and vessel failure was avoided because the reactor was

new and the welds had not yet experienced embrittlement by long-term neutron


Unfortunately, Diablo Canyon Unit 1 is particularly susceptible to a similar PTS

(Pressurized Thermal Shock) like the one experienced at Rancho Seco, both because of

its severely embrittled condition and because of its location in one of the most

seismically active areas of the United States. An earthquake would cause a sudden

emergency shutdown that could defeat the safety systems causing control room

instruments to become unreliable due to “instrument chatter”. The resulting lack of

accurate operator data due to instrument chatter was what ultimately caused the Rancho

Seco mishap and the triple meltdown disaster at Fukushima Daiichi.

More recent analyses now show that the atomic reactor vessel can crack even when it is

not under pressure.

Unfortunately, the feasibility of repairing an embrittled nuclear reactor of the kind at

Diablo Canyon Unit 1 has never been proven.

Despite knowing that unit 1 reactor vessel’s neutron embrittlement increases with each

passing year, PG&E has elected not to inspect the embrittled welds before the end of

unit 1’s operating license in 2024. This constitutes a deviation from industry standards,

which require 10-year weld inspection intervals. PG&E has now elected to inspect on a

20-year interval basis instead, meaning that the next time it plans to inspect the welds

will be after its current operating license expires. While PG&E is perfectly entitled to

request a waiver from complying with industry standards, it certainly cannot then confirm

with certainty that flaws are not developing in the reactor vessel welds. Absence of

evidence is not evidence of absence.

Because PG&E has formally adopted an argumentum ex silentio approach, it cannot be

concluded that embrittlement of unit 1 reactor vessel will not lead to a class 9 accident

between now and 2025. Thus, when contemplating its ultimate decision on the

Application before it, the Commission must take into account the financial and

environmental risks associated with Diablo Canyon’s unaddressed reactor embrittlement

which increase with each passing day that the Plant is in operation.”



Nuclear expert Arnold Gundersen testified before the CPUC during the Joint Proposal

proceedings. Here is a link to his testimony:



Testimony regarding embrittlement of the Unit 1 reactor vessel begins on Page 3 of

Appendix A.