Introduction Legacy waste

Most nuclear nations have generated high level radioactive waste (HLW) from nuclear weapons programs and/or commercial nuclear power genera­tion and most store waste materials from a variety of reprocessing flow­sheets (see Chapters 10-24 in this book). The Plutonium and URanium Extraction (PUREX) process1 is the baseline for spent fuel reprocessing

Ahe PUREX process was developed in the United States in 1950 and the world’s first opera­tional full-scale PUREX separation plant began radioactive operations at the Savannah River Plant (SRP) in 1954. The process has run continuously at SRP since start-up for defense materials only.

for most countries with active fuel cycle programs. France and the UK reprocess spent fuel for electric utilities from other countries using the PUREX process to recover uranium (235U) and plutonium (239Pu). Slight modifications to the PUREX process can be made to recover 235U, 239Pu, 237Np, and 99Tc (if desired) and a number of countries (e. g., France, Japan, China, etc.) are developing solvent extraction processes to recover the minor actinides (Am and Cm) from spent fuel. Elimination of these acti­nides and fission products from the HLW reduces the long-term radio­toxicity and heat generation from an immobilized waste form once it is entombed in a geological repository.

Most high level waste is in one of two forms: either used nuclear fuel that is destined for direct disposal, or waste from the reprocessing of commer­cially generated spent nuclear fuel (SNF or commercial wastes) or from the reprocessing of fuel used to generate 239Pu for weapons (defense wastes). The SNF retains a high inventory of transuranium elements (~1 at%) in its uranium matrix, and the waste from reprocessing is depleted in actinides, mainly 235U and 239Pu (~99% removed), having been recovered during chemical processing.

Liquid HLW streams are stored either as neutralized nitric acid streams in mild steel tanks (US and Russia) or as nitric acid streams in stainless steel tanks (France, UK, Japan, Russia). Although borosilicate glasses have become the preferred waste form for the immobilization of HLW solutions in the majority of the nuclear nations, the chemical variability of the wastes from the different reactor and reprocessing flowsheets coupled with the additional variability imposed by neutralization vs. direct storage or process­ing of acidic wastes has led to a diverse HLW chemistry, e. g. HLW contains about three-quarters of the elements in the periodic table.

Vitrification is currently the most widely used technology for the treat­ment of HLW throughout the world (Table 6.1). In the United States, more than 3,496 canisters of borosilicate glass contain vitrified, high-level waste from the Savannah River Site (defense waste processing facility) and 250 canisters at West Valley, New York. In France, approximately 14,000 canis­ters of HLW glass have been produced at the La Hague facility (Table 6.1).

A variety of other radioactive wastes have been generated during the fuel rod cladding/decladding processes, during chemical separations, from radioactive sources, radioactive mill tailings, medical research applications and other commercial processes such as radium for watches and clocks. Many of the sources of radioactive waste (RAW) generation are captured in other chapters in this book regarding the individual practices in various countries (includes legacy waste, currently generated waste, and anticipated future waste).

In countries where the HLW waste is neutralized before processing, the HLW has segregated into a low activity waste (LAW) fraction which is an

Vitrification plant

Location

Melting process

Waste glass produced (metric tons)

Waste loading range (wt%)

Size of

canisters

(meters)

Number

of

canisters

TBq[10]

Defense Waste Processing Facility (DWPF), Savannah

Aiken, South Carolina, USA

JHCM

6,169*

28-40°

0.6×3

3,496

1.7 x 106

River Site

West Valley Demonstration Project (WVDP)

West Valley, New York, USA

JHCM

-500[11]

-20.4-23.5b

0.6×3

275

8.9 x 105

Waste Vitrification Plant (WVP),

Sellafield, UK

Induction, hot crucible

—2,200d

-25-32“

0.43 x 1.34

5,627bt

2.4 x 107

BNFL

Areva NC (R7/T7P

La Flague, France

Induction, hot crucible

6,642*

12-18“

0.43 x 1

16,334

2.51 x 108

AVM or Atelier de Vitrification

Marcoule, France

Induction, hot crucible

1,138s

12-18“

0.43 x 1

3,159

1.69 x 106

de Marcouled

Pamela

Mol, Belgium

JHCM

500s

15-25“

0.30 x 1.2 0.43 x 1.34

2,200

4.5 x 105

Tokai Vitrification Facility®

Japan

JHCM

>100

20-30“

0.43 x 1

247**

1.5 x 104

(TVF)

Mayak Vitrification Facility

Ural Region, Russia

JHCM

-8,000

33“

0.57 x 1

17,600

3.33 x 10′

(EP-500)

Table 6.1 Data on HLW glass production

Подпись: Published by Woodhead Publishing Limited, 2013

alkali-rich supernate and a viscous HLW sludge fraction over time. The LAW fraction of HLW and other medium and low level wastes (MLW and LLW) can be immobilized into a variety of waste forms, i. e. cements, Ceramicrete, glass, hydroceramics, high temperature ceramic/mineral waste forms (made by a variety of technologies discussed below), glass-ceramics, and geopolymers and land disposed in safe and specially engineered facilities.

The concept of conditioning waste in order to immobilize it in solid nuclear waste forms is over 60 years old [1] . Waste forms can chemically incorporate waste species (glass, glass composite materials (GCMs), crystal­line ceramics or mineral analogs, and metals), encapsulate waste species in a matrix (cement, geopolymers, hydroceramics, bitumen), or be a combina­tion of both. Waste forms can be amorphous (glass, bitumen, geopolymers), or crystalline (crystalline ceramics including minerals and zeolites, metals, cements, hydroceramics), or a combination of forms (glass ceramic materi­als, GCMs; glass beads in a metal matrix; granular crystalline mineral waste — forms in a geopolymer or cement). In particular, GCMs can be formed by controlled cooling, melting above the solubility of certain waste constitu­ents and letting them crystallize out on cooling, or by allowing homogene­ous glasses at the melt temperature to cool naturally where some portion of the cooled glass crystallizes.

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