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Review of Dry Storage Evaluation by San Onofre Safety

Citizens Oversight (2017-09-28) Ray Lutz

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More Info: Stop Nuke Dump

Background is a website run by Donna Gilmore with a wealth of good factual information about nuclear "dry cask" storage systems, as well as almost everything else related to San Onofre. This review is not intended in any way to denigrate the good intentions of Donna and others to attempt to understand the tradeoffs between various dry storage systems. I, and Citizens Oversight, do not endorse any of these dry storage systems because in their current design, we find they are all inadequate. For this reason, we have started the 1000 Year Dry Storage Challenge to address the disparity between the dry storage systems which exist today and long-term surface storage which we believe will become the best solution to our nations spent fuel woes.

It is hoped that this point-by-point review will allow a healthy dialog about this topic. We are all trying to fully understand and evaluate what has been done on this topic.

Source Document

For discussion, we will refer to the following document

Comparison is improper

It appears that the primary source of differing views on this topic is due to a slight misunderstanding about how systems should be compared. The Holtec system is a multi-component system while the "thick wall" designs are a single-component system. To compare only the inside layer of a multilayer system with the entire single-wall design is an improper and unfair comparison. It would be like comparing a thin jacket liner of a jacket with two-components with an entire jacket of one layer.

Dry storage systems like the Holtec systems or the Areva NUHOMS systems use a thinner interior canister, which provides the confinement boundary, with an overpack or surrounding concrete enclosure to provide shielding from radiation of Alpha, Beta, and Gamma emissions. The single-layer systems couple both of these function into one multi-function cask. To compare only the interior canister without the associated overpacks or concrete shielding is an improper comparison.

Comparison Chart

The document includes the following comparison chart. Each line item is reviewed below, with focus on the Holtec MPC-37 coupled with the Holtec HI-STAR 190 transportation cask.

The following table
Safety Feature Multi-component Design Single-component Design Comment
Overall Wall Thickness 10 5/8" 10" to 19.5" Here, we provide a fair comparison of with both components of the Holtec design
Dual Layer Yes No The inside canister of the multi-component design is welded closed and in early years, has air flowing over it to cool it. The transportation overpack is bolted closed and provides both containment and shielding.
Crack or Break Yes Yes All systems will eventually crack or break. The single-layer casks are made of ductile cast iron which is more brittle than the stainless steel of the canister. Over many years, and with radiation exposure, the thicker casks may crack open. The single-layer casks look thicker than they really are. The walls of these casks have many cut-outs in their walls which are filled with polymer to help absorb radiation. The Holtec HI-STAR 190 overpack has 9" of lead in their walls which is the best shielding material known.
Inspectable Yes Yes The differ in how they can be inspected. The multi-component systems does seal the canisters and treats them as a unit thereafter. There is no need to inspect the contents, but it necessary, the canister can be cut open and then welded back again. The interior canister can be inspected using high-resolution cameras and eddy current imaging, under development but will likely be available by 2020 at San Onofre. There is always some level which is sealed and difficult to inspect. The single-layer systems with a bolted lid are easier to open, but the drawback is they have seals which have to be replaced periodically
Seals must be replaced In overpack, not in canister Yes This is listed as a safety feature, but it is instead a drawback. Seals that have to be replaced make the system more prone to leaks through the lid
Early warning to detect leaks Feasible Feasible Electronic monitoring is feasible in all systems
Continuous radiation Monitoring Feasible Feasible We admit this can be improved but it is hardly a reason to opt for one or the other.
ASME Container Certification Yes Yes From what I have seen, both comply with this.
Defense in depth (redundancy) Higher Lower The multi-component designs offer opportunity for greater defense in depth.
Stored in Concrete Building Feasible Generally A concrete building can be supplied for both but the problem is it would then require active cooling to extract the hot air. The single-component design is incompatible with high-burnup and high heat loads.
Gamma and Neutron Shielding Yes Yes Single-component cast-iron casks must have cavities drilled out in the walls typically filled with polymer to block radiation. Multi-component systems can have superior shielding with replaceable overpacks and concrete bunkers.
Transportable Yes Some are not All dry storage systems in the US must be dual-purpose and provide transportability
Proven Technology No No These have not been used long enough to know how they will perform in various environments and over many decades
Market Leader Yes Losing ground worldwide Multi-component systems are being rapidly adopted.
Compatible with high-heat loads Yes No Thick-wall designs are not rated for high heat loads and may not be compatible with higher enrichment levels AKA high burn up spent fuel

San Onofre Safety Text Citizens Oversight Comment

Nuclear fuel waste is unsafely stored, maintained and monitored at most U.S. nuclear power facilities, with no adequate plan for cracking, leaking dry storage canisters and no adequate funding. We generally agree with this statement. The dry storage systems in use today were designed with short-term on-site storage in mind, with the expectation that the DOE would start picking up the spent fuel by Jan 1998. We believe these designs should be reviewed to support long-term surface storage. Thus, we have introduced our 1000 Year Dry Storage Challenge
Thin-wall canisters cannot be inspected, repaired, maintained or monitored to prevent leaks – Basic requirements we expect in a car. Instead, proposed Department of Energy (DOE) and private company interim storage plans ignore these problems and assume nothing will go wrong. Nuclear Regulatory Commission (NRC) management approves these inferior dry storage systems by ignoring their own safety regulations. The NRC states the Koeberg nuclear plant in South Africa had a comparable container (a tank) crack and leak in only 17 years. The cracks were deeper than the thickness of most thin-wall canisters. This is largely incorrect. Inspection technology is under development and it looks promising, although we must admit this is a retrofit, due to the fact that these were originally intended for temporary on-site use. Repair is obviously possible by replacing the entire canister, which is more easily possible in the multi-component design, but more costly in the thick canister design. Maintenance is obviously feasible as well and dry storage operators must implement a aging-management plan. Monitoring is also possible by constant monitoring of cooling air temperature differentials and surface thermal and radiation monitors.
TRANSPORT PROBLEMS: Transport of uninspected thin-wall nuclear waste canisters and high burnup nuclear fuel waste is unsafe, yet the NRC approves this by ignoring their own regulations. Proposed DOE and private company interim storage plans assume nothing will go wrong when transporting and storing these aging canisters. They have no adequate plan for radioactive leaks in transport or storage. Transportation of high burnup nuclear spent fuel has similar risks in both designs. Aging canisters can be checked and replaced if needed, and since they are fully encapsulated in the sealed transportation cask, this is largely a red herring.
CONSEQUENCES: Each canister contains as much lethal highly radioactive Cesium-137 and other radionuclides as was released in the Chernobyl nuclear disaster. A failure of only one “Chernobyl canister” could result in permanent evacuation of our communities, permanent contamination of major food and water supplies, destabilization of the U.S. economy, increased security risks, major health and economic consequences to families, farmers, ranchers and other businesses, and permanent genetic damage affecting future generations of people and other living creatures on land and sea. This statement is an exaggeration to be sure. The amount of Cesium 137 "released" at Chernobyl was a small fraction of the total Cesium 137 in the failed reactor. If a canister were to fail with a small crack, it is unlikely that ALL of the Cesium 137 would be released like it was at Chernobyl, which was a full melt down of a reactor with many more tons of nuclear material than is in one dry storage canister. With all that said, we do not wish to minimize the danger of spent fuel and these inadequate dry storage systems for extended storage.
SOLUTIONS: Expedite storage of spent nuclear fuel from inferior thin-wall canisters to thick-wall transportable cask systems, similar to those used in Germany, Japan and most other countries. Existing sites should be assessed for environmental and other risks to determine if fuel needs to be relocated to a different location on-site or to a nearby location without those risks, such as another operating nuclear reactor facility. Transport is a major risk factor, so transport risks should be minimized. States should be given authority to raise minimum safety nuclear waste safety standards and to regulate nuclear waste stored and transported in their states. Adequate funding is needed for these efforts. We find it to be infeasible and inadvisable to replace existing multicomponent systems with single-wall systems as is suggested here. Instead, we suggest that the internal canisters be encapsulated and sealed in a cask system that will endure a 1000 Years design life.
1. Most U.S. nuclear plants store spent nuclear fuel waste in thin walled (1/2” to 5/8” thick) welded shut stainless steel canisters (304/304L or 316/316L SS).
This statement is true but it ignores the fact that these are multi-component systems, and include additional layers of steel, lead, and/or concrete.
2. Thin-wall canisters may prematurely crack and have radioactive leaks due to atmospheric and other corrosion factors and U.S. utilities have no adequate plan to deal with this. This is true but they are working to develop these plans. The nuclear industry must finally admit that dry storage systems must last much longer than originally envisioned.
3. Thin wall canisters cannot be inspected for interior or exterior cracks, and cannot be repaired, maintained or monitored to prevent leaks, yet the NRC continues to approve them. Inspection is being developed, repair is feasible by replacing the canister, and they can be maintained and monitored using electronic monitoring systems
4. High burnup fuel used by reactors can cause fuel cladding to become damaged after dry storage. True but is not different in the various dry storage designs
5. The fuel and other contents (e.g., fuel baskets) in thin-wall canisters cannot be inspected. It is unlikely that these will need to be inspected, but they can be by cutting off the top of the canister and replacing it. Once the canister is dried and they are filled with helium, degradation will be minimized but may occur in any cask or canister design. After a long time, it may not matter if the contents becomes degraded. Inspections and opening of casks and canisters should be minimized.
6. If any of the over 2000 U.S. thin wall canisters have cracks, detection occurs after they leak. The NRC only requires quarterly radiation level testing and assumes nothing will go wrong. If the leaks are slow they may be very inconsequential and detecting after the leak occurs may be the best way to handle it. We are inquiring about the various accident conditions and whether the NRC has planned for these design-basis accidents. The NRC does plan for transportation accidents through drop test criteria.
7. Holtec President states a microscopic through-wall crack will release millions of curies of radionuclides into the air and it’s not feasible to repair cracks even if you could find them. This is obviously a misquote. If a microscopic crack were to develop, only a microscopic release of radioactive materials could leak through the crack. The helium in the canister will slowly be replaced with ambient air. We believe the Holtec president was saying that a person would not be able to walk up to a canister to repair it in the face of the radiation, but that does not mean the entire canister could not be replaced by using a fuel pool or hot cell. Also, the thin interior canister can be encapsulated in a surrounding canister system, which could be virtually identical to the single-component casks.
8. Thin-wall canisters have no early warning monitoring system to prevent leaks, no continuous radiation monitoring system and no defense in depth. Any monitoring systems that can be applied to the single-layer systems could be used on the multi-layer systems, including thermal monitoring and continuous radiation monitoring. The multi layer systems have superior defense in depth due to the multiple layers.
9. Most utilities plan to destroy spent fuel pools after decommissioning. However, the only method utilities currently have to replace containers is to unload fuel into a spent fuel pool. A dry fuel handling facility (hot cell) may be needed due to the explosive nature of high burnup fuel rods or to avoid damaging fuel. However, none exist at utilities and none in the U.S. are large enough. Hot cells can be built. It is apparently true that it is easier to use the hot cell approach because it is difficult to introduce water and then dry the fuel assemblies.
10. There are no adequate emergency plans; entire cities and surrounding areas may be uninhabitable. This is true for either cask or canister system
1. Canisters with even partial cracks are not safe for transport. NRC Regulation 10 CFR § 71.85.
Partial cracks will likely not diminish the structural integrity of the canisters, but if the canisters are inspected prior to transport or transported prior to the onset of cracking this issue can be avoided entirely.
2. High burnup fuel can become damaged after dry storage and in transport, with no way to inspect for damage in thin-wall welded canisters. But once you seal the single-component cask lid, you can't inspect without opening it and pulling out the fuel assemblies, something that you really don't want to have to do at all. So the notion that they are inspectable is hardly true because it takes opening the sealed cask.
3. A transport accident can result in a criticality, making communities permanent exclusion zones. The thin canisters are just the inside component of a multi-component system. After many years of cooling, a criticality event is unlikely, but it would be contained in the transportation overpack. Rail transport can minimize the risk of any accident.
4. Transporting high burnup fuel in thin-wall canisters via trains has not been determined safe. NRC is uncertain if train vibrations will cause the fuel cladding to fail in transit. This can be determined very easily in the first few shipments. Spent fuel has been transported for many years, particularly in France, using the AREVA canister design.
5. Our nation’s crumbling infrastructure and system of highways, roads, and bridges is rated a D+, according to the American Society of Civil Engineers. And less than 1% of rails are inspected (FRA). Any transportation plan can take this into account and is true for either canister design, unless you are advocating for never moving the waste from San Onofre.
6. There is no adequate emergency plan. A truck or railway accident or terrorist attack involving transported nuclear waste would render entire cities and surrounding areas uninhabitable. Yes, a terrorist attack may result in this, but it can also occur right where it is, and moving the waste will result in a much lower overall risk, even though for a short time the risk is higher during the transportation phase.

  • Require all nuclear waste storage systems be transportable and designed to be inspected, maintained and monitored to PREVENT radioactive leaks (they currently are not).
    1. Require transportable storage casks with proven ability to inspect (inside and outside the cask), repair, maintain and monitor to PREVENT leaks. Use materials that do not crack, designed for longer life, and have multiple redundancies to prevent radioactive releases.
    2. Most of the rest of the world uses thick-wall metal casks that meet these requirements. Thick-wall casks survived the Great Earthquake and tsunami in Japan. Germany, France, Australia, Belgium, Italy, Switzerland, Russia, South Africa and most other countries use thick-wall metal casks.
      1. Thick-wall metal transportable storage casks are 10” to almost 20” thick, with two bolted lids and double metal seals in each lid for redundancies. Thick wall transportable storage casks are directly transportable and can be inspected inside and have continuous pressure monitoring to prevent radioactive leaks. Thin-wall canisters are welded shut and cannot be inspected inside or out, and must be loaded into a reusable transport cask for transport. b.Thick-wall transportable storage casks are proven technology for over 40 years. Most U.S. thin-wall canisters have been in use about 10 years or less and cannot be inspected, so are unproven technology. Utilities purchased them based on cost, not lifespan and safety.
    3. Thick wall storage casks are designed for a longer life span. Thin-wall stainless steel canisters are vulnerable to short term cracks. Once a crack starts in a thin-wall canister, cracks continue to grow through the wall of the canister. The NRC states it can take 16 years for cracks to grow through the wall. Holtec canister vendor states even a microscopic through-wall crack will release millions of curies of radionuclides and cracks are not feasible to repair even if you could find them.
    4. Require continuous remote early warning monitoring systems to prevent radioactive leaks.
    5. Require ability to inspect and retrieve spent fuel assemblies without destroying the container. Each thin-wall canister system cost about $4 million (includes materials and labor).
    6. Require an on-site replacement and repair plan.
    7. Keep the spent fuel pools until all nuclear waste is removed from the site.
    8. Evaluate need to build a dry fuel handling facility (hot cell), if returning fuel from dry to wet storage might cause an explosive reaction or damage the fuel.
  • Increase protection from environmental and security risks BEFORE the canisters leak
    1. Store casks in hardened reinforced buildings for additional environmental and security protection.
    2. Require utilities fund state and local emergency planning, and on-line continuous radiation monitoring until all waste is removed from site. Provide on-line public access to this information.
  • Improve safety of existing dry storage nuclear fuel waste BEFORE the canisters leak.
    1. Expedite removal of fuel from thin-wall canisters to safer thick-wall casks, before these “Chernobyl canisters” leak and potentially explode.
    2. For high risk sites, relocate waste to a safer site, while minimizing transport and environment risks (e. g., relocate from areas with high risk of flooding, coastal corrosion, or coastal erosion). Do not relocate waste for the purpose of consolidating waste. This is an unnecessary transport risk.
    3. Permit states to regulate and oversee nuclear waste storage and transport, and allow them to set higher nuclear waste standards. It’s time to end federal preemption of states’ rights for nuclear waste stored in their states.
    4. Allocate funding to address these urgent nuclear waste storage and transport issues.




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Title Review of Dry Storage Evaluation by San Onofre Safety
Publisher Citizens Oversight
Author Ray Lutz
Pub Date 2017-09-28
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Keywords Stop Nuke Dump
Related Keywords Nuclear Energy, Nuclear Waste, Shut San Onofre
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Topic revision: r3 - 2017-09-29, RaymondLutz

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