BRIEFING NOTE

DATE: 21/04/2021

Radioactive waste resulting from the Chernobyl accident
Review – March 2021

The accident which occurred on 26 April 1986 at the Chernobyl NPP’s Reactor 4 resulted in a
massive release of radioactive material into the environment in the form of gases, fuelparticles, and aerosols. The hasty decontamination work around the damaged power plant
generated large quantities of radioactive waste (nearly two million cubic metres of plants, soil,construction materials, various equipment, etc.) which were disposed of in the exclusion zonearound the damaged reactor.
Waste was managed according to its radioactivity. Intermediate and high level waste (104 Bq/g toabove 106 Bq/g) was mainly stored in concrete casemates (Podlesny facility, for example, see Figure1) or disposed in sealed-bottom trenches covered with a clay layer (Buriakovka facility, see Figure 1).
Both types of facility are subject to radiation monitoring. Their characteristics and the inventoriesof the waste they contain are presented in Table 1, and their location is indicated in Figure 2.

Figure 1: Podlesny (left) and Buriakovka (right) facilities.

PodlesnyRICS

Chernobyl NPP
Ch NPP Stage IIIVector site

Buryakivka

Figure 2: Map of the various interim storage and final radioactive waste disposal sites in the exclusion zone.
Table 1: Waste treatment facilities for radioactive waste exceeding 10 4 Bq/g.

Facilities

Characteristics

Types and volume of waste

Radiologicalinventory

Buriakovka
disposal

Disposal in sealed-bottom
trenches covered with alayer of clay, operated
since 1987

700,000 m3 of intermediatelevel waste

2.6 1015 Bq

Podlesny storage

Storage in concrete
casemates, operated
between 1986 and 1988

11,000 m3 of remediation
waste generated following
the accident (high-level andlong-lived waste)

2.6 1015 Bq

Storage in concretebuildings, operated
between 1986 and 1988

26,000 m3 of remediation
waste generated during theemergency phase (low- andintermediate-level and longlived), some of which isencapsulated in metaldrums

2.8 1014 Bq

ChNPP stage III
storage, also
calledKompleksny(Cs, Sr, Eu, Pu, Am)(137Cs, 90Sr, 134Cs,
154
Eu, 155Eu, 238Pu,239,240
Pu, 241Pu,241Am)(137Cs, 90Sr, 238Pu,
239,240
Pu, 241Pu,241Am)

Work has recently been carried out on these facilities. For example, a new water drainage
system and eight new groundwater monitoring wells were built around the Podlesny facility in2012, and, in 2018-2019, additional characterisations were undertaken to specify theradiological and physical characteristics of the waste. New engineered barriers were built on
the ChNPP stage III facility and the monitoring system was upgraded in 2016. Finally, theBuriakovka trench disposal facility reached its initial capacity (30 trenches) and anauthorisation was issued in 2019 for the construction of six new trenches.
Further waste treatment facilities are under construction at the Vektor site in the exclusionzone. This is a used sealed source and solid radioactive waste storage facility intended toreceive waste from the Chernobyl NPP currently in operation as well as from other Ukrainian
power plants.

Two other facilities, in the 10 km zone around the Chernobyl NPP, are under construction forthe dry storage of spent fuel assemblies from VVER-1000 and VVER-440 reactors (16,529 fuelassemblies) and for the storage of high-level vitrified waste from the reprocessing of spent
fuel assemblies in Russia.
Low- and intermediate-level waste (between 102 and 104 Bq/g), consisting of contaminatedsoil, wood, and construction materials, was stored as tumuli or, most often, buried in trenches
located on nine sites within a radius of 10 km around the damaged reactor (Yaniv Station,Naftobaza, Pischane Plato, Rudyy Lis, Stara Budbaza, Nova Budbaza, Prypiat, Kopachi, andChystohalivka). These nine sites, called ‘Raw Interim Confinement Sites’ (RICS), are located in theareas shaded pink in Figure 2. Thus, from 1986 to 1987, between 800 and 1,000 trenches weredug in the sand soil and covered with a 20 to 50-cm layer of sand. These trenches are generally
2 to 4 m deep, a few metres wide, and a few hundred metres long. It is estimated that one
million cubic metres of radioactive waste are buried in them, representing a total radioactivityof 2.1015 Bq.
Various works are in progress in these trenches, including census operations to identify thelocations of the trenches and waste inventories, as well as maintenance operations. Sometrenches, those posing the most risk to workers in the exclusion zone and to the environment,
have been emptied. In 2020, 7,700 m3 of waste was removed from the trenches and disposedof at the Buriakovka facility, among others.
Most low-level waste trenches are not airtight or do not have an effective barrier against themigration of radioactive pollutants; as such, a gradual migration of radionuclides into thegroundwater was detected from the 1990s.
IRSN research on the mobility of radionuclides in soil and groundwater on these sites, carriedout from 1999 in cooperation with Ukrainian institutes (IGS1, UIAR2), focused on aninstrumented trench on the Rudyy Lis site (trench T22 of the EPIC pilot project - Experimental
Platform in Chernobyl), located 2.5 kilometres west of the damaged reactor (see Figure 3 andFigure 4). All the data acquired was used as input for models simulating the transfer of 90Sr togroundwater by considering different flow conditions (Bugai et al., 2012a; Nguyen, 2017).
Estimated 90Sr migration speeds were one metre per year in the 1990s which decreased to afew tens of centimetres per year in the 2000s. However, these models fail to reflect someactivity measurements made in groundwater. The impact of seasonal phenomena on the mainprocesses governing the transfer of 90Sr to groundwater could be significant, in particular on
the percolation of water through the trench and on the horizontal movements of water at thebase of the trench in connection with piezometric fluctuations in the groundwater. The
presence of 90Sr in the vegetation on the site also indicates a transfer of 90Sr from the soil tothe vegetation, which could explain certain variations in 90Sr activity observed in thegroundwater.
Other observations and studies show that plutonium migrates through groundwater at a rate
similar to that of strontium. 137Cs, on the other hand, is very slow, due to its attachment to thesubstrate, only travelling at a speed of less than one centimetre per year. However, plant roots
do manage to capture some of this fixed 137Cs, as has been observed and quantified.
Thus, the T22 pilot site appears particularly suitable for studying the activity evolution in thistype of trench in the face of climate change and/or changes in cover due to (i) a characterised

1 Institute of Geological Sciences
2 Ukranian Institute of Agricultural Radiology

source term; (ii) a less complex and widely described hydrogeological context; and (iii) marked
transient phenomena over a relatively short period.
Investigation site

Damaged reactor
Trench and tumulus area

Figure 3: Location of the trench T22 site (investigation site).

Elevation(m above sea level)

Trench T-22

Datum level disturbed layer

Flow direction
Aeolian sand layer
K= 5 m/day, Kd = 3 ml/g

Alluvial sand layer
K = 0.03 m/day, Kd = 10-20 ml/g

Strontium-90 plume fromthe trench

Figure 4: Cross section of trench T22 and extension of the 90Sr plume in the groundwater.