Skip to main content

ASSESSMENT OF DECONTAMINATION PROCEDURES FOR WWER-PWRs WITH A VIEW TO MINIMIZE THE GENERATION OF WASTE

Objective

The objective of this project is to verify the efficiency of the chemical, electrochemical and physical decontamination processes for the decommissioning of WWER-type pressurized water reactors. The testing of chemical processes has priority, as only these could be applied in the most important technical task of the programme, the decontamination of an entire coolant loop with a present activity content of 35 Ci.

The concept places special emphasis on minimizing the amount of waste, the principle being that only material which has been removed should have to be stored in a repository.

The investigations will be carried out on components which were previously removed from the reactor coolant system of Rheinsberg Nuclear Power Plant on which the specific contamination is 1E4 Bq/square cm. Selected components of the BR-3 are also to be treated.

These parts, among others, are to be decontaminated in accordance with the requirements to levels permitting unrestricted release or reaching at least remelting conditions.

The most promising processes shall be applied for the decontamination of one of the reactor coolant loops at Rheinsberg Nuclear Power Plant. This treatment will aim at reducing contamination to a release (melting) level without dismantling the loop components.

On the basis of the investigation results, a concept is to be established for the decontamination of WWER-type PWR reactors, illustrated with reference to Rheinsberg Nuclear Power Plant.
A special treatment method was tested for the selection of a decontamination process suited for an application aiming at the minimization of waste. The CORD process was selected for application of a decontamination process to the complete pressurized water reactor (VVER) primary loop. In a special treatment step at the end of each decontamination cycle, the deconchemical was decomposed in passing through a newly developed organics decomposition module where organic acids were decomposed to carbon dioxide by intensive ultraviolet light. The result of the test was the complete decomposition of the organic acid to carbon dioxide and water. By this treatment, a large amount of resin capacity necessary for waste removal was saved as the resins were mainly required for the removal of the oxides and activity removed from the contaminated surfaces of the nuclear power plant systems.

Decontamination was performed at laboratory scale on a small sample of the inlet pipe of the regenerative heat exchanger (RHX); this pipe is a stainless steel 304 1"SCH160. A small 10 cm long sample was used for the decontamination test. The piece was submitted to one oxidation step and to two successive decontamination steps. An extension of the decontamination during 6 additional hours resulted only in a slight improvement of the decontamination. A final decontamination factor of about 109 was reached, leading to a residual activity of 77 Becquerels per square centimetre, which for such a pipe corresponds to a mass activity of about 12 Becquerels per gramme, lower than the regulatory melting limit (200 Becquerels per gramme).
WORK PROGRAMME

1. Process evaluation of decontamination processes permitting subsequent unrestricted release (Siemens): selection of the most effective process for the complementary decontamination of component surfaces after an appropriate pretreatment to remove the oxide layer. The specific aim is to determine which method will permit recycling, without generating excessive amounts of secondary waste.

2. Decontamination of removed components: the decontamination process for separate components selected in 1 shall be tested on laboratory samples and full-sized components.

3. Decontamination on one primary loop of the Rheinsberg NPP (Rheinsberg and Siemens)

The in situ decontamination of one of the 3 primary loops of the reactor will consist of:

pre-treatment with APCE/CORD to remove oxide layer;
succession of oxidation and pickling cycles as determined in 1 and 2;
determination of residual activities;
treatment and conditioning of process waste.

4. Overall concept for the decommissioning of a WWER nuclear power plant (Siemens and Rheinsberg).

Based on the experience and the results of the preceding work programme, a concept for the decommissioning of reactor components for WWER NPPs shall be developed. This concept would determine an optimized scheme for the application of the various in situ and component-specific decontamination processes. The general objective of this study is to establish a treatment scheme which will permit recycling of nonactivated components while generating a minimum of waste. A further important requirement is the minimization of operator exposure.

5. Generation of specific data: Specific data on costs, worker exposure, working time and waste arisings will be derived from the execution of items 2 and 3.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Siemens AG
Address
Hammerbacherstraße 12-14
91050 Erlangen
Germany

Participants (2)

BELGIAN NUCLEAR RESEARCH CENTRE
Belgium
Address
200,Herrmann Debrouxlaan 40-42
1160 Bruxelles
Energiewerke Nord GmbH
Germany
Address

16831 Rheinsberg