Re: Vermont nuclear plant searching for missing fuel rods

[JGinniver@AOL.COM]

In a message dated 22/4/04 5:30:48 pm, gpblackwood@HOTMAIL.COM writes:





> On average and to the best of my knowledge the spent fuel ponds have about

> 10 times more radioactivity than a reactor core and normally retain a large

> amount cesium 137 isotope, which contain somewhere from 15 to 40 million

> curies with a half life of about 30 years. Anyone please correct me if I am

> wrong. But hopefully this was lousy record keeping......

> 

> 

> 



Given that the original article states that "One of the missing pieces is 

about

the size of a pencil. The other piece is about the thickness of a pencil and

17 inches long." then this clearly can't be an accounting error.   According 

to one of my reference books BWR fuel comes as fuel bundles/assemblies 

consisting of an array of fuel pins (earlier plants were 7 x 7 later plants were 8 

x8) which are quite thin, approximately 1.25 cm in diameter, and have an active 

length of at least 12 feet.   So what the facility may have identified is that 

there are two missing fragments of a fuel pin.



The level of activity remaining within the fuel after 25 years will depend on 

the fuel history, time in the core and it's location and the operating 

history of the plant (no. of effective full power days etc.)   The only information 

I could find easily was for a PWR spent fuel assembly (a 17 x 17 array) after 

33,000 Mwd/MTU burnup.   After 10 years the assembly will contain 4.0 E+05 

Curies, and the surface dose rate will be 23,400 rem/hr.   After 50 years the 

assembly will contain 1.0 E+05 Curies and the surface dose rate will be 8,640 

rem/hr.



So although the fragments are only part of one (?) pin from an assembly with 

64 pins (given that there aren't any gaps for in core components) the contact 

dose rate for the pieces will be significant.



Apologies in advance to any radsafe specialist out there if I have made any 

errors in the above.



Regards,

     Julian