Works for conversion of ruined ChNPP Unit 4

into an ecologically safe system: possible use

in Fukushima Daiichi Units 1-4 works

Viktor Krasnov Head of Division, Institute for Safety

Problems of Nuclear Power Plants National Academy of

Sciences of Ukraine (ISP NPP)

15-th Meeting of Joint Ukrainian-Japanese Committee for issues of cooperation in area

of improvement of post-accident response to emergency situations

at Nuclear Power Plants

In Chernobyl, like at Fukushima Daiichi, as result of explosion, outer reactor containments

were destroyed with producing huge amount of radioactive materials. In Chernobyl it

was as regards: reactor core fragments, high-level lavas containing nuclear fuel,

radioactive dust, radioactive water, destroyed building structures.

Radioactive materials in destroyed ChNPP Unit 4: high-level lavas with nuclear fuel and melted and solidified metal,

fragments of reactor core, building structures, radioactive water and radioactive dust.

Destruction of all protective safety barriers.

Generation of fuel-containing materials

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Generation and spreading of high-level lavas

with irradiated nuclear fuel

Scheme of lava spreading and generation of LFCM local

clusters (a):

(b) - room 304/3 (black LFCM);

(c) - steam distributing corridor, room 210/7 (brown LFCM);

(d) - PSP-2, room 012/15 (brown LFCM);

(e) - PSP-1, room 012/7 (brown LFCM);

(f) - room 305/2 (black & brown LFCM);

(g) - room 217/2 (“Elephant foot”, black LFCM);

(h) - molten and solidified metal with high activity.

(b)

(d)

(e)

The main portion of nuclear fuel had come to

bottom marks of Reactor Department, where due

to afterheat and exothermal reactions the

Chernobyl lavas were produced and had a wide

range: from 1100 С and probably before UO2

grain melting temperature (~2800 С).

Produced lava was spreading along rooms,

corridors, cable passages and other free

channels with producing LFCM clusters.

(а)

(с)

(f)

(g)

(d)(h)

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(b)

(e)

Currently, destroyed ChNPP Unit 4 contains around 180 t of irradiated nuclear fuel of primary reactor charge (190,2 t),

whose activity makes approximately 2,1∙109 Bq/g uranium.

On the survivor fragments of building structures, “Shelter” object’ protective

structure was built:

1. Southward. New structures of “Mammoth” (a) and “Octopus” beams (b)

were installed. They served as supports for southern roofing (с).

2. Northward. Cascade wall was erected as metal formwork filled by concrete

and containers with radioactive materials released from destroyed Unit during

accident moment.

3. From above. New structures were installed - B1/B2 beams (а).

Pipe sheathing was laid on them (b), and light roofing rests upon it (с).

4. Westward. Buttress wall was erected.

5. And at last, erection of protective building - “Shelter” Object.

(а) (b

)

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3

2

4

(а)(b) (c)

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Erection of protective structure «Shelter» object

The priority tasks at this stage

were as regards:

- organization of dosimeter reconnaissance and dosimetry control.

- works to define the state of building structures.

- organization of works for sampling and analyzing aerosols, radioactive

water and specimens of core fragments of ruined reactor, including the

melt; as well as with involving remote-controlled gears.

- organization of monitoring of nuclear and radiation hazard of melt of

reactor core fragments, and arrangement of systems for automated

monitoring of neutrons, gamma- field, temperature and moisture -

«Shater» and «Finish».1

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Works to convert destroyed ChNPP Unit 4 into an ecologically safe system

Shelter Implementation Plan, as a guaranty for NPP staff, public and environmental

protection from potential nuclear and radiation hazard

Remove the fuel containing materials and long-lived radioactive waste from

the SO, perform its conditioning with the following storage and disposal in the

RAW storage facilities in accordance with the effective standards; complete

the SO decommissioning

Stage 3

Create additional protective barriers, primarily the New Safe Confinement in order to

provide required conditions for a technical activity at Stage 3, and ensure the personnel,

public and environment safety; preparatory and engineering activities intended to develop a

technology for fuel containing materials (FCM) removal from the Object Shelter at Stage 3;

create the infrastructure for the management of Shelter Object radioactive waste

Stage 2

Stabilize the existing facility, enhance its operational reliability and longevity

of structures and systems ensuring stabilization and monitoring of SO safety

parameters

Stage 1

SO conversion into an Ecologically Safe System shall be achieved through implementation of 3 stages:

Stabilization

Preparation for Conversion

Conversion

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The works for SO building structures’

stabilization were aimed at excluding of

probability of potential accidents associated with

destruction of building structures and prolonging

the lifetime of «Shelter» safe operation (15 years)

before the completion of New Safe Confinement’s

erection. Realization of this project has allowed

reducing the scope of work for Ukrainian entities,

including also for our Institute.

Western fragment of “Shelter” Object

(a) – Southern roofing. Connection of southern boards and clubs.

(b) - Northern cascade wall. Connection of northern boards and clubs.

«Shelter» object areas, in which the measures to

stabilize building structures were realized

Stabilization of building structures of Shelter Object

Strengthening of

western

foundation

Connection of northern

buttress wall with

northern boards-clubs

Replacement of sheets

on light roofing

Strengthening of B1

support beam on

ventilation shafts

Strengthening of western

and eastern «Mammoth»

beam

Connection of southern

boards with southern

boards-clubs

Stabilization of

Deaerating Stack

framework

(a) (b)

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The main functions of NSC are as regards:

1. Reduction of radiation impact onto public, personnel and environment by establishing the limits under conditions of normal operation of

"Shelter“ object, and in case of violation of normal operation and emergency situations, including the incidents during the dismantling of

unstable structures and future management of fuel-containing materials (FCM) and radwaste (RAW).

2. Reduction of spreading of ionizing radiation and radioactive substances located inside the SO.

3. Technological support - creation of conditions for dismantling unstable structures, future retrieval of FCM and RAW, removal of accumulated

radioactive water, realization of monitoring and technical maintenance of "Shelter“ object .

4. Monitoring of main parameters of "Shelter" object status and control of technological processes.

5. Protection on unauthorized access to FCM and RAW and provision of IAEA safeguard system’ functioning.

NSC provides as follows:

• improvement in radiation safety level; integrity of NSC confinement limits the radiation impact onto public, personnel and environment for 100-

year operation period;

• reduction of probability of emergency collapse due to dismantling of unstable structures;

• reduction of aftermath of emergency collapse due to enclosing and bearing structures and monitoring systems inside the NSC;

• possibility of realization of strategy aimed at SO conversion into an ecologically safe system: possibility to realize dismantling of unstable

structures of existing "Shelter" and retrieval of fuel-containing materials.

Main parameters:

Span – 257 m, Length – 150 m; Height – 108 m; Mass – 38000 t, Cranes – 4 x 50 t, Life time – 100 years

Construction of New Safe Confinement - NSC

Complex «New Safe Confinement - Shelter Object»

In November 2016, New Safe Confinement was installed in its design position. With the all above mentioned, our problems are not

terminated. The erection of New Safe Confinement (NSC) has brought to appearance of already new quality complex – «New Safe

Confinement - Shelter Object», in which, due to changes in temperature and moisture mode, the processes occurring in the

Shelter Object would change and, with high probability, could destabilize status quo of nuclear and radiation safety.

That is why we continue today our researches

already within the complex NSC-SO, which are

aimed at monitoring of:

• Nuclear safety of fuel-containing materials in

SO, which can produce high-criticality areas.

• Radiation safety due to presence of

radioactively contaminated water and radioactive

dust.

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Severe accidents of NPP reactors accompanied by high temperatures entail the fuel melt, fusion penetration in reactor vessel and

origination of nuclearly hazardous areas. In such areas, a high probability of self-sustained chain reaction (SCR) exists, as it was in

Chornobyl in 1990 year. So, the priority task – creation of systems for monitoring nuclear safety and countermeasures to prevent the SCR.

(а)- State of nuclear fuel melt in ChNPP Unit 4 – sub-reactor rooms.

(b)- State of nuclear fuel melt at F-1 –reactor №1 (on TEPCO data)

(а)

Destruction of internal protective safety barriers. Problems of nuclear hazard.

Кef

Effective multiplication factor (Кef) dependence on the level of volumetric water

content when the modeling's lattice spacing is 0.5, 2.0, 4.0 cm and FCM cluster’s

temperature is 270C and 800C

(b)

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Graphs of neutron flux density of detectors of nuclear safety monitoring system

within localization area of nuclear hazardous LFCM

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One of the main dust migration mechanisms inside the SO is carry-over of radioactive aerosols by airflows existing in SO internal

space as result of natural ventilation. Airflow intensity is defined by differences in pressure inside and outside the building, wind velocity

and difference in air temperature inside and outside the building. A part of dust is released beyond the SO limits by means of air carry-over

as releases through the ventilation stack (b), and through the openings in SO walls and roofing. Monitoring of RA releases (their volumes,

radionuclide and dispersion content) is made today as follows:

(1) - monitoring of RA releases through leakage in SO roofing;

(2) - monitoring of RA releases over breakup via “Bypass” system;

(3) - monitoring of activity and content of aerosol radionuclide fallouts inside “Shelter” object;

(4) - monitoring of RA in near-surface air layer at industrial site of “Shelter” object;

(5) - monitoring of RA generation from open clusters of lava-like fuel-containing materials (LFCM)

Monitoring of radioactive aerosols (RA)

SO DS

Bypass

RA monitoring in

near-surface air layer

under NSC

(1)

(2)

(3)

(4)

(3)

(5)

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Monitoring of radioactive aerosols in near-surface layer at SO industrial site

and territories adjacent to it

Dynamics of annual average concentrations of aerosols-carriers of

beta-emitting nuclides (Σβ) sum (137Cs, 90Sr, 241Am) in 1998 - 2017 y.

Layout of facilities for aerosol situation monitoring:

- aspiration facility; - filtering facility; - horizontal pad;

- horizontal gauze pad

Dynamics of -emitting aerosol concentrations in near-surface air layer in 2001-2017 years at

monitoring points AF 1 ( ) , AF2 ( ), AF3 ( ) at individual stages of NSC Arch

erection:

1 – stabilization measures; 2 – berm dismantling; 3 – ground excavation for foundation strips;

4 – collapse of Turbine Hall roofing; 5 - erection of enclosing contour walls;

6- NSC Arch pushing. 11

Reference levels

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Degradation of fuel-containing materials – generation in of radioactive water clusters

One of the main factors able to destabilize the both existing currently level of radiation and ecological safety of “Shelter” object (SO), and in the future after

NSC commission is availability of radioactive water clusters in “Shelter” object rooms, including: non-controlled radioactivity carry-over in SO rooms;

possible increase in fuel-containing mass criticality; leaching of FCM and carry-over of uranium soluble forms with their accumulation in bottom sediments.

(a)

Main flows of radioactive water in SO (a) and (b) volumes of main water clusters (as of 2017)

т.о. 31

т.о. 6

т.о. 18

т.о. 32 т.о. 7

т.о. 36

т.о. 30

Average concentrations of radionuclides and uranium in radioactive water samples on elevations 0,00 and +3,0 m

made as regards: 137Cs – 4,9∙1010 Bq/m3, 90Sr – 1,6∙1010 Bq/m3, 238+239+240Pu – 2,1∙107 Bq/m3, uranium – 160 g/m3.

Monthly, radioactive water is sampled from SO rooms and are defined as follows: uranium concentration (mg/dm3), volumetric activity of fission products (90Sr, 137Cs) and transuranium elements (238Pu, 239+240Pu, 241Am and 244Cm) (Bq/dm3), stable components: gadolinium (neutron absorber), HPO4

2-, HCO3-, CO3

2- (mg/dm3).

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1. «Decontamination and analysis of penetration depth of radioactive

contamination in concrete surfaces of Shelter Object rooms

2. «Research of low dose impact of Chornobyl radioactivity spectrum

onto human cell mutations»

3. «Study of changes in Shelter Object’s radwaste

activities under neutron irradiation»source

Cs

Sr

Tc

Eu Am Cm 13

Research & development work with Japanese specialists of Nuclear

Safety Research Association (NSRA) in 2002-2004 years

Cooperation with Japanese institutes and entities.

Japan’s Parliament. Fukushima Nuclear Accident

Independent Investigation Commission

Tokyo, January 2011

Tokyo University

The Cabinet of Japan

YASUHIRO SONODA

Tokyo, February 2011

Ministry of Environment

YOKOMITSU KATSUHIKO

Ministry of Economy

SEISHU MAKINO

Ministry of Foreign Affairs

KOICHIRO GEMBA

Meeting with representatives of Fukushima prefecture

in Koriyama and Tomioka 14

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ISTC/STCU Technical Working Group

Meeting. February 2012, Fukushima

ISTC/STCU Technical Working Group Meeting

on the environmental assessment for

long term monitoring and remediation in and around

Fukushima. December 2012, Tokyo.

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5th Meeting of the OECD/NEA BSAF Project – Phase 2 Joint Session on

Status of Fukushima Daiichi NPPs & Decommissioning Activities

«The 2nd International Forum on the Decommissioning of the Fukushima

Daiichi Nuclear Power Station», Hеrono- Iwaki -Tomiokа

1st CLADS Workshop “Advanced Science toward

Decommissioning of FDNPP” Nov. 10, 2015, Tokai- Mura

Scientific & technical cooperation with

Collaborative Laboratories for Advanced Decommissioning Science (CLADS),

Japan Atomic Energy Agency (JAEA)

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A PROPOSAL FOR THE NEAREST FUTURE –

IS THE CREATION IN TOWN OF CHORNOBYL OF

JOINT SCIENTIFIC AND TECHNICAL CENTER

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It will allow conducting:

1. Research and development and pilot and design works associated with

conversion of NPP «Fukushima» and Chornobyl NPP into an ecologically safe

system;

2. Fundamental and applied researches in nuclear and radiation safety area of

emergency objects of nuclear power engineering;

3. Study, development and implementation of new procedures for management of

fuel-containing materials and radioactive wastes;

4. Experience exchange and training of young scientists for above fields.

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Available resources-1

Research site in Chornobyl. Qualified scientific staff.

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Available resources-2

Research laboratories of 2-nd and 3-rd radiation hazard class

and special equipment in Chornobyl.

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Available resources-3

Laboratory of 1-st radiation hazard class with high-level melt samples of

irradiated nuclear fuel from ruined ChNPP Unit 4.

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Available resources-4

In November 2016, between Japan Atomic Energy Agency and our Institute for NPP safety problems of Ukraine’s

National Academy of Sciences, a MEMORANDUM was signed on scientific and technical cooperation. This

MEMORANDUM can become a basement for arranging a research site in the town of Chornobyl for realization of needed

research programs of joint research studies.

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