Entombment requires removal of RPV head – could introduce more problems than it solves

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From: Hrabal, Craig
Sent: Wednesday, March 23, 2011 6:00 PM
To: Rahimi, Meraj; Davis, Jack; Sippel, Timothy; Guttmann, Jack; Tripp, Christopher; Barto, Andrew; Call, Michel; Forsyth, Daniel; Jordan, Natreon; Li, Zhian; Smith, Jeremy; Wilson, Veronica
Subject: RE: any comments on the proposed response?

You should emphasize that any entombment involving pouring borated concrete or and will require removing the pressure vessel head, which could introduce more problems e.g., radioactive release) than it solves

Also, any borated water added to the core must be via pumping


From: Li, Zhian
Sent: Wednesday, March 23, 2011 5:35 PM
To: Rahimi, Meraj; Davis, Jack; Sippel, Timothy; Guttmann, Jack; Tripp, Christopher; Barto, Andrew; Call, Michel; Forsyth, Daniel; Hrabal, Craig; Jordan, Natreon; Smith, Jeremy; Wilson, Veronica
Subject: RE: any comments on the proposed response?
Meraj,
I would suggest to make the recommended actions into two phases. The first phase is to switch from seawater to borated to continue cooling the reactor core and spent fuel to sufficiently low temperatures so that entombment or removal of the damaged fuels becomes possible.

In the second phase, a decision is made to either entombed the core at the reactor site or remove the core to a; remote ISFSI. Environmental impact and city rebuilding should be the two most primary concerns. Once decision is made, practical limit such as enclosure of the reactor with passive heat removal should be considered. However, the word of caution is that the phase II decision should not be done in a rush.

Zhian


From: Rahimi, Meraj
Sent: Wednesday, March 23, 2011 5:23 PM
To: Davis, Jack; Sippel, Timothy; Guttmann, Jack; Tripp, Christopher; Barto, Andrew; Call,
Michel; Forsyth, Daniel; Hrabal, Craig; Jordan, Natreon; Li, Zhian; Smith, Jeremy; Wilson,
Veronica
Subject: any comments on the proposed response?

Any comments?

The first action is to pour borated water into core or the spent fuel pool. If the entombment is to build a structure around the molten core or pool, there should not be any
impact on the system reactivity.

With respect to heat transfer, the entombment should be built in such a way that lower and upper vents would.allow heat removal through air convection. If the entombment is to pour some type of materials directly on the molten core or spent fuel in dried pool, it depends on the material. The staff believes, the environment is probably too hot for the concrete to cure. The other option may be the use of sand with boron frits which could turn into glass if added at the appropriate temperature. This would immobilize the radionuclides but longer cooling time might be required.

The staff believes it might be prudent to wait for longer cooling time in order to allow the removal of core and spent fuel debris in the pool similar to the TMI recovery.

Another option might be the use of a filtered flexible confinement barrier around the core and the spent fuel pool.

Meraj Rahimi
Chief of Criticality, Shielding, and Dose Assessment Branch Division of Spent Fuel Storage and Transportation Office of Nuclear Materials Safety and Safeguard U.S. Nuclear Regulatory Commission
6003 Executive Blvd., Suite 301
Rockville, MD 20852
Phone: 301-492-3338
Fax: 301-492-3348
e-mail: meral.rahimi(@nrc.gov


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