arithmetic average, ASTM, Calculating embrittlement, cancer, catastrophic failure, catastrophic nuclear accident, clean water, conservative, corrosion, corruption, dangers of nuclear, democracy, embrittlement, environment, hydrogen attack, LWSMR, MASLWR, median average, neutron bombardment, nuclear accident, nuclear disaster, nuclear energy, nuclear reactor pressure vessels, nuclear safety, NuScale, PWR, reactor pressure vessels, risk management, RPV, Shippingport Nuclear power station, Small Modular Reactors, SMR, sudden failure, thermal shock, US NRC
Comment Now! https://www.regulations.gov/comment?D=NRC-2019-0180-0003 Deadline Dec 19 2019, at 11:59 PM ET
NuScale nuclear claims that the old rules for calculating embrittlement of nuclear reactor pressure vessels are outdated and they want to replace them with new rules. They say that the old rules are too conservative, and they want the rules relaxed. Furthermore, NuScale reactor pressure vessels are apparently more at risk than regular nuclear reactors for sudden catastrophic pressure vessel failure, and thus catastrophic nuclear disaster.
According to a study commissioned by the US DOE, NuScale, and similar designs, have thinner nuclear reactor pressure vessel shells, but “significant radiation damage occurs through a greater fraction of wall thickness“. Thus, they suffer from more embrittlement and therefore would be more at risk for sudden through wall cracking and pressure vessel failure.
And, yet, Thomas A. Bergman, on behalf of NuScale Power, LLC “requests that the NRC amend 10 CFR part 50 to alleviate a requirement for calculating the embrittlement for advanced reactor designs and add the embrittlement trend curve formula for calculating the mean value of the transition temperature shift described in American Society for Testing and Materials (ASTM) E900-15…” https://www.regulations.gov/document?D=NRC-2019-0180-0003 The earlier examples are of differing designs from NuScale. A mean value is the arithmetic average and doesn’t take into consideration scatter. Furthermore, existing nuclear reactors vary, amongst themselves, in design, construction, materials, operating experience, and hence damage. If you add Bill Gates’ wealth with your own, and divide by two, it probably doesn’t reflect your wealth. That’s an arithmetic average. That’s the mean. In many cases we want the median average – half above and half below. However, when it comes to nuclear disaster, we want the value which is the most safe and conservative. The safest, of course, is no more nuclear reactors. They are unnecessary and the risks are too high.
Shippingport was a PWR (Pressurized light water reactor) with around the same output as NuScale and had a reactor pressure vessel thickness of over 8 inches — roughly twice as thick as the figure we found for NuScale. It only ran for 25 years, meaning that less embrittlement would occur.
In “Assessment of Materials Issues for Light-Water Small Modular Reactors“, Sandusky, et al. for the US DOE: “The primary objective of this report is to evaluate materials degradation issue unique to the operational environments of LWSMR. Concerns for specific primary system components and materials are identified based on the review of design information shared by mPower and NuScale… A less obvious example of a new design configuration relates to vessel fabrication practices. Vessel fabrication will certainly be more complicated due to the integration of all of the primary system components from a traditional PWR into a single vessel enclosure.
Examples of new environmental exposure conditions include reactor vessel fluence and CRD operating environment. The smaller diameter and lower operating pressures used by LWSMR designs allow for significantly thinner vessel shells, but with higher EOL neutron fluence. As a consequence, significant radiation damage occurs through a greater fraction of the wall thickness. With regard to CRDs and CRD penetrations, some LWSMRs will locate the CRDs at the top of the integrated vessel, causing them to be exposed to steam at higher pressurizer temperatures.
As significant changes in material selection are unlikely for LWSMR designs, research to resolve key materials degradation concerns identified for large advanced PWRs remains of high importance and expanded activities are needed in many areas. Significant benefit for LWSMRs can be gained by R&D to characterize the effects of component fabrication processes and promotes application of advanced fabrication processes that cost-effectively provide increased confidence in long-term primary system performance…“. See: “Assessment of Materials Issues for Light-Water Small Modular Reactors ” Primary Authors: Dave Sandusky, XGEN Engineering Wayne Lunceford, Alliance Engineering Contributing Authors: S. M. Bruemmer and M. A. Catalan Pacific Northwest National Laboratory February 2013 Prepared for the U.S. Department of Energy under Contract DE-AC05-76RL01830 Pacific Northwest National Laboratory Richland, Washington 99352 https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-22290.pdf
A lot of pressure appears to have been exerted to get the new ASTM embrittlement vote pushed through, and the final voters appear to be a biased pro-nuclear group. And, the data appears to have been massaged to get what they wanted. In fact, both the data and members appear to have been manipulated in an attempt to get the result that they wanted. See especially p. 15: https://www.nrc.gov/docs/ML1530/ML15309A007.pdf Some of the things included and excluded by ASTM E900-15e1, which may or may not be applicable to NuScale (e.g. operating temperature): “Standard Guide for Predicting Radiation-Induced Transition Temperature Shift in Reactor Vessel Materials“, ASTM International https://archive.li/wKDse (Beware that the ASTM summary is poorly written and so must be read carefully.) Regardless, NuScale is apparently at a higher risk of failure due to design.
Update Note. This statement was based on an expert opinion: “NuScale claims that the old rules for calculating embrittlement are outdated and they want to replace them with new rules. They say that the old rules are too conservative, they want to relax the rules. The original rules were based on basic science. The new rules are based on empirical data collected. The data collected is subject to fraud and cheating. [Using the mean is but one example.] Furthermore, there is no reason to change the old rules.” However, we are not certain that the current rules are based on basic science, though they should be. When it comes to the nuclear industry what is and what should be are not necessarily the same. The chances are that “the original rules were based on basic science“, however. The NRC appears to have mostly weakened standards in recent decades. What we do know is that NuScale apparently wants to weaken the rules, or they would not be complaining about their “conservative” nature being a burden. Additionally, using an average of historic data is inappropriate, because of differences in design, construction, materials, operating experience, and hence material damage.
NOT ONLY DO NEUTRONS CAUSE EMBRITTLEMENT, WHICH CAN LEAD TO REACTOR PRESSURE VESSEL FAILURE, HYDROGEN ATTACK CAN ALSO LEAD TO REACTOR PRESSURE VESSEL FAILURE, AS CAN CORROSION. THEY ALL WORK TOGETHER TO WEAKEN THE NUCLEAR REACTOR PRESSURE VESSEL. THEY MUST BE EVALUATED TOGETHER. EFFECTS WOULD BE SYNERGISTIC. THESE FAILURES CAN OCCUR AT ANY TIME IN BWR OR PWR THEY ARE JUST MORE LIKELY TO OCCUR IN PRESSURIZED REACTORS (PWR) (LIKE NUSCALE). THEY ARE ALSO MORE LIKELY TO OCCUR DUE TO THERMAL SHOCK BUT COULD FAIL WITHOUT IT.
Shippingport GAO https://www.gao.gov/assets/220/213114.pdf
These earlier reactor pressure vessels were 7 to 11 inches thick. Shippingport was a PWR of around the same output as NuScale and had a reactor pressure vessel thickness of over 8 inches. It only ran for 25 years, and the others discussed in the above report ran even fewer hours.
NuScale 16 years ago when it was called MASLWR and still an official government project, 2003, INEEL/EXT-04-01626. Now it’s a private company but still receiving government (taxpayer) funding. This is an image of a single reactor. However, NuScale want to clump them together, in a common pool of water.
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