All Holtec thin-wall stainless steel canisters (only 1/2″ to 5/8″ thick) are likely damaged from Holtec’s inferior canister downloading system. The downloading system lacks precision, resulting in metal to metal scraping and gouging of canister walls.  This significantly shortens the lifespan of Holtec thin-wall canisters. There are hundreds of these Holtec canisters installed around the U.S. 

In spite of this, the Nuclear Regulatory Commission (NRC) continues to approve Holtec thin-wall canisters. The canisters are not designed to be inspected or repaired (inside or out), so the full extent of the gouging of the walls is unknown. Once cracks start in these canisters, they can grow through the wall in about 16 years, according to the NRC.  Cracks grow faster in hotter canisters.  In spite of knowing this, the NRC continues to approve hotter fuel in these canisters.

Holtec HI-STORM 100 above ground system

Both the below ground and above ground Holtec thin-wall storage systems have inferior canister downloading problems that scrape and gouge canister walls.

A carbon steel MPC (canister) guide ring, located inside the cavity of each below ground HI-STORM UMAX storage hole, unavoidably gouges the walls of the thin-wall stainless steel canisters the entire length of the canister (per the NRC).  The HI-STORM UMAX system is used at San Onofre and Callaway. It is also proposed for the New Mexico Holtec Consolidated “Interim” Storage facility, pending NRC approval.

The above ground Holtec HI-STORM 100 system uses a series of carbon steel vertical MPC guide channels instead of a guide ring. These channels scrape the canister walls the entire length of the canister.  See figure of vertical channels located inside each concrete shell of the HI-STORM 100 system.

PDF page 822:  Figure 3.A.12 inner shell and vertical channels finite-element model (3-D view)

The NRC refuses to cite Holtec for the UMAX HI-STORM canister wall damage in spite of admitting the NRC would not have approved the system if they had known there would be metal to metal contact between the canisters and the MPC guide rings.  

Also, the NRC states the carbon steel guides deposit carbon particles on the stainless steel canister walls, resulting in pit corrosion cracking. This is one more of many conditions that can cause early failure of these thin-wall nuclear pressure vessels.  

Holtec HI-STORM 100 vertical MPC guide channels attach to interior of carbon steel lined concrete cask. Channels scrape stainless steel canister walls and embed corrosive carbon particles as canister is lowered into cask (due to inferior Holtec loading system design). Cutaway shows only partial length of channels (near bottom).

The HI-STORM 100 Final Safety Analysis Report (FSAR) – ML16138A100 shows there is only 9/16th of an inch clearance between the thin-wall canister and the vertical MPC (canister) guide channels. Due to the lack of a precision downloading system, the canister walls are unavoidably scraped the entire length of the canister walls.  The inside channel diameter is 69-4/8 inches and the outer MPC (canister) diameter is 68-3/8 inches, leaving only only 1-1/8 inches difference. This results in only 9/16th of an inch clearance around the canister.

Recommendation

All nuclear waste legislation should be halted until this critical safety issue is resolved. Proposed legislation that promises to transport waste to consolidated interim storage (CIS) facilities will no more solve the nation’s nuclear waste storage problem that rearranging the deck chairs on the Titanic would have stopped it from sinking.

All thin-wall canister systems must be replaced with thick-wall metal cask systems that have ASME N3 Nuclear Pressure Vessel certification. Instead, the NRC approves numerous exemptions to these minimum American Mechanical Standards and to NRC nuclear storage and transport regulations.

• Share handout: Spent Nuclear Fuel Management Recommendations, May 12, 2019
• Sign and share Petition to recall and replace defective thin-wall nuclear waste canisters with proven thick-wall transportable storage casks. Holtec thin-wall canister systems are lemons.

Details and additional references at SanOnofreSafety.org and SOS Holtec Nuclear Waste webpage.

Reference:  HI-STORM 100 Final Safety Analysis Report (FSAR), Non-Proprietary Revision 13, March 31, 2016, NRC Docket No.: 72-1014  Holtec Report No.: HI-20024444 (ML16138A100)  

FSAR PDF page 78:   All MPCs [canisters] have identical external diameters. The outer diameter of the MPC is 68-3/8 inches and the maximum overall length is approximately 190-1/2 inches. See Section 1.5 for the MPC drawings. Due to the differing storage contents of each MPC, the maximum loaded weight differs among MPCs. See Table 3.2.1 for each MPC weight. However, the maximum weight of a loaded MPC is approximately 44-1/2 tons. Tables 1.2.1 and 1.2.2 contain the key system data and parameters for the MPCs. Dimensions discussed in this section are considered nominal values…

FSAR PDF page 79: Channels.  A single, base HI-STORM overpack design is provided which is capable of storing each type of MPC. The overpack inner cavity is sized to accommodate the MPCs. The inner diameter of the overpack inner shell is 73-1/2 inches and the height of the cavity is 191-1/2 inches. The overpack inner shell is provided with channels distributed around the inner cavity to present an inside diameter of 69-1/2 inches. The channels are intended to offer a flexible medium to absorb some of the impact during a non-mechanistic tip-over, while still allowing the cooling air flow through the ventilated overpack. The outer diameter of the overpack is 132-1/2 inches. The overall height of the HI-STORM 100 overpack is 239-1/2 inches…

FSAR PDF page 85: Channels.  The storage overpack provides an internal cylindrical cavity of sufficient height and diameter for housing an MPC. The inner shell of the overpack has channels attached to its inner diameter. The channels provide guidance for MPC insertion and removal and a flexible medium to absorb impact loads during the non-mechanistic tip-over, while still allowing the cooling air flow to circulate through the overpack. Shims may be attached to channels to allow the proper inner diameter dimension to be obtained…

FSAR PDF page 700: During fabrication the channels are attached to the inner shell by one of two methods, either the channels are welded directly to the inner shell or they are welded to a pair of L-shaped angles (i.e., channel mounts) that are pre-fastened to the inner shell. The results presented in Figures 3.4.16a [PDF page 741] and 3.4.16b [PDF page 742] bound the results from both methods of attachment…