# Presentation: 107994

## Industry Perspective of Requirements for Basic Research in Support of Understanding Chemistry under Extreme Conditions 

**John Elliot**
**Reactor Chemistry and Corrosion Branch**
**AECL-Chalk River Laboratories**
**Ontario, CANADA, K0J 1J0**

## Setting the Stage

**Original nuclear power reactors were build by knowledgeable engineers using materials within their chemistry comfort zone – lots of margin.**
**Probably not a lot of qualification work - except within the US Navy programme – more after-the-fact tests.**
**Had the advantage of prototype/demonstration reactors to learn from.**
**	****New reactor designs will be closer to full scale. Materials will be pushed to edge of the comfort zone under extreme chemistry conditions.**

## Ideas to Walk Away With!

**Chemistry Control - Establish what the extreme chemistry conditions are.**
**develop ‘tools’ to monitor chemistry at operating conditions. **
**concentrate on issues that allow the chemistry to be controlled.**
**Material degradation test programmes.**
**must be done under the correct chemistry conditions.**
**will entail long term test programmes & should use a number of complimentary techniques.**
**Radio-activity transport is the sleeper issue.  **
**needs to be defined and understood early in the design process.**
**modest capital investment up front will save many operational dollars later.**

## Perspective: Systems chemist operating a ‘yet-to-be-defined’ nuclear plant.

_**Objectives of Chemistry Control are:**_
**Minimise the degradation of the **_***diverse ***_**system materials – includes fuel, in- and out-of-core components.**
**Minimise transport of radioactivity to areas where inspection and maintenance are required.**
_***Chemistry Control in a Nuclear Reactor is a COMPROMISE***_

## 
Examples given this presentation are based on 
water-cooled reactor experience .......

	but the perspective is same for other designs.

**Examples given this presentation are based on **
**water-cooled reactor experience .......**
**	****	**
**	****but the perspective is same for other designs.**

## Control of Chemistry

**Requirement:**
**Need to be able to measure the chemistry of the coolant medium at the operating conditions of the reactor.**
***	******Currently, samples are analysed at 25******o******C after passage down long sample lines from reactor circuits operating at >300******o******C.  Not representative if looking at concentrations of sparingly soluble or reactive species.******  ***
***	******(Some BWRs now using ECP probes.)***
**Solution:**
**Develop probes of various sorts which can undertake these measurements at operating conditions. **

## Chemistry Control‘A Slightly Extreme View’

**The System Chemist ‘does not care’ about chemistry he cannot control!**
**Example:**
**Radiolysis of water in current water-cooled reactors.**
**Events before ~1 ********s are of little interest as additives (e.g. H****2****) to the coolant cannot influence chemistry (i.e. scavenge) in this time zone.**

## Chemistry Control con’t.

**	****Modelling electrochemical potentials around a HTS circuit requires:**
**Yields at ~1********s:**
**H****2****O ****-radn******** **_***e***__***aq***__***-***__***, H, OH, HO***__***2***_**, ****H****2****, H****2****O****2**
**Rate constants of subsequent reactions, e.g.,**
**OH ****+ ****H****2**** ******** ****H**** + H****2****O**
**H (e****aq****-****)**** **** ****+ ****H****2****O****2**** ******** ****OH**** + H****2****O**
**	****at the temperatures of interest.**
**Mass transfer of species to system surfaces.**
**No need to know about the ‘physical’ phase or what happens in the spur/tracks (i.e. pico-second regime).**
**(Waste management chemists may be interested – but not station chemists)**

## Breakdown of Research

_***Using water radiolysis as an example:***_
** ****Fundamental (Pointy Head)**
**Covers events that occur before ~1********s – ionisation, thermalisation,  diffusion out-of-track/spur. Tends to be ‘exotic’.**
** ****Basic Research (Nuts & Bolts)**
**Yields of primary species, rate constants. Tends to use ‘low’ tech methods****.**
** ****Applied (Real Situation)**
**Tests which follow steady-state concentrations of products – often in larger facilities – in-reactor loops.  Used to understand the chemistry environment that materials of construction are really exposed to. **
**Provide reality check for modelling calculations.**
**Research to understand extreme chemistry for new reactors needs to focus initially on last two areas.**

## Example of Reality CheckNet radiolysis: H2O -radn H2  + 1⁄2O2Suppressed radiolysis:  H2O + H2 added -radn H2 added

**Base radiolysis model is collection of ‘best’ values of yields & rate constants from literature.**
**Radiolysis model had to be adjusted. Rate constant  for**
**OH**** + ****H****2**** ******** H****2****O + ****H**
**	****lowered by 70% to get approximate fit!**

## Material Degradation under Extreme Chemistry Environments

**Any new reactor design will be:**
**Pushing existing materials to the edge of the comfort zone.**
**Using unproven new materials, surface coatings, etc.**
**	****New reactors will have a design life ~60 years.  **
**	****Short-term, accelerated degradation tests over**
** ‘****a month’ is not the way to go to qualify materials.**
**(Okay – for scoping studies)**

## Material Degradation under Extreme Chemistry Environments, con’t.

**	**_***Identify the relevant issues and then design the appropriate test programme, e.g.:***_
**Simple material loss to general corrosion leading to loss of wall thickness. ****(Relatively easy)**
**Initiation and propagation of cracks due to chemistry environment (includes normal and off-normal chemistry). ****(Difficult)**
**Potential synergistic effects of one degradation mechanism on another.  ****(Very Difficult)**
**	****Example, corrosion-produced hydrogen can lower material properties to make cracking more facile.  Hydrides in Zr-alloys, hydrogen assisted creep cracking in steels.**

## Material Degradation under Extreme Chemistry Environments, con’t.

**There must be a commitment to fund long-term, realistic experimental programmes which may involve tests which will have the duration of ‘years’! **
***These types of tests tend to fall within the mandate of National Laboratories and Reactor Vendors.***
**Experiments must be done under the appropriate ‘extreme’ chemistry conditions for long enough to provide valid answers for ~60 year reactor.**
***Short-term tests can some times be misleading.***

## Importance of Using Appropriate Chemistry 

**Flow Accelerated Corrosion of carbon steel feeder pipes downstream of CANDU core is now an issue. Wall thinning rates up to ~120 ********m/year are observed.**
***	******Chemistry conditions are reducing and coolant is unsaturated in dissolved iron species with respect to magnetite.***
**Large scale out-reactor loop tests in early ’80s noted physical erosion above flow velocities of 23 m/s **_**BUT**_** corrosion rate was ~4 ********m/year in range 8-15 m/s relevant to CANDU for feeder pipes.   **
**	*****Hindsight shows chemistry conditions were inappropriate: trace oxygen present (no hydrogen added) and no purification system leading to water being saturated in dissolved iron.*****  **
**	****Moral:  Test should be performed under appropriate chemistry!**

## Importance of Longer Tests.

**Industry experience (BoP) indicated increasing Cr content of steel reduces Flow Accelerated Corrosion. **
** **
**Need to verify increased Cr would work under CANDU HTS chemistry conditions.**
**Carbon steel used for feeder pipes in original CANDU reactors had a very low Cr content - because of a low Co content requirement (to minimise Co-60 production.)**
**AECL has added a minimum 0.30 wt% Cr content for feeder carbon steel for replacement feeders and for new reactors.**

## Importance of Longer Tests

**Initially 0.33wt% Cr steel corroded faster than 0.02 wt% Cr steel.**
**After ~50 days effect of Cr builds in – probably due to Cr accumulation in oxide surface layer.**
**Other longer term tests confirm continued benefit of Cr in reducing FAC**

## Importance of doing tests in different facilities to minimise risk

**One corrosion test rarely captures all the conditions appropriately, e.g. galvanic couples may be unavoidable in some, not in others; radiolysis products present or absent, etc.**
**Prudent to use complimentary experiments in different facilities to provide confidence in results.**
**Test the same material but from different sources/heats.**
** **

## Chemistry & Material DegradationFuture Reactors

**Important to identify all possible chemistry conditions – both operating, maintenance and accident.**
**Important to focus on understanding the chemistry so that it can be ‘controlled’. **
**Important to develop ‘tools’ to monitor the chemistry at operating conditions. **
**Important to choose materials that are robust in all the chemistries.**
**Material degradation tests must be realistic and cover the chemistry conditions.   **

## Radioactivity Transport

_**Like it or Not:**_
**All Reactors generate radioactive products in the core, e.g., Co-60, Sb-122 & -124, Fission products, N-16.**
**Radioactivity is transported around the Heat Transport Circuit, e.g., high radiation fields where iron oxides deposit, N-16 shine in turbine halls under Hydrogen Water Chemistry.**
_**All Reactors have to be inspected and maintained.**_

## Costs Associated with Radiation Dose

**Cost is estimated as high as $100,000 per person-rem. **
**Currently dose per outage are in 14-40 rem range.**
**‘****Burning out’ critical personnel leads to loss of schedule during outages which is operating $$$$$$.**
**Easier at design stage to reduce activity transport than do remedial actions **
_***e.g., a full system decontamination cost ~$20M.***_
***Upfront capital vs. Operating costs later.***** **

## Radioactivity Transport

_**Universal Requirement:**_**    ****ALARA Principle in effect!**
***AT THE DESIGN STAGE!***
_***Activity transport can be minimised through:***_
**Understanding the chemical behaviour of corrosion products in the circulating heat transport medium.**
**Material (trace) specifications set to minimise species that can be activated, e.g. Cobalt-59.**
**Chemistry conditions set to minimise the deposition of corrosion products in-core where they can be activated and transport back to out-of-core location.**

## Radioactivity Transport Antimony Example 

**Under **_***reducing***_** chemistry Sb can deposit on fuel surfaces in-core and be activated to Sb-122 and Sb-124 during operation.**
**Under **_***oxidizing***_** conditions during outages, Sb is mobilized from the core and is absorbed on iron oxide surfaces out of core – increases maintenance worker dose significantly.**
**Sb Removal Process involves adding H****2****O****2**** to coolant to oxidize ‘immobilized’ Sb(0-III) to ‘mobilized’ Sb(V) quickly and remove immediately on IX resin before absorption on surfaces.**
**Source of Sb – pump seals and bearings, trace impurity in materials.  **

## Radioactivity TransportNitrogen-16 Shine in BWR

**Nitrogen-16 formed from Oxygen-16 (n,p reaction).**
**Normal water chemistry (****Oxidizing ****-no H****2**** added) – N-16 exists as water soluble nitrates, nitrites – stays in liquid phase in containment.**
**Hydrogen water chemistry (****Reducing**** - H****2**** added) – **
**	****N-16 exists as a volatile species such as NH****3**** – carried over to turbine hall in the steam.**

## Radioactivity TransportFuture Reactors

**Important to identify potential activation products and set material specifications to minimise impact **_***- at design stage.***_
**Need to understand the transport behaviour of both the precursors and activated species **_***under all possible chemistries***_** in the new design reactors.**
**Need to plan for any mitigating strategies before detail design of the reactor begins.**

## Situation to Avoid in New Reactors 

## My Personal Impression

**Roles:**
**National Laboratories and Reactor Vendor establishments are best facilities for longer term material/chemistry testing.  They have the staying power.  **
**Academic institutions rarely have the infrastructure or funding for long term testing. They are best for short term testing & developing mechanistic understandings – corrosion and activity transport.**
** **_***Well suited for training future scientists & engineers.***_**  **

## Ideas to Walk Away With!

**Chemistry Control - Establish what the extreme chemistry conditions are.**
**develop ‘tools’ to monitor chemistry at operating conditions. **
**concentrate on issues that allow the chemistry to be controlled.**
**Material degradation test programmes.**
**must be done under the correct chemistry conditions.**
**will entail long term test programmes & should use a number of complimentary techniques.**
**Radio-activity transport is the sleeper issue.  **
**needs to be defined and understood early in the design process.**
**modest capital investment up front will save many operational dollars later.**

## The Legacy

**40 years from now, an engineer is going to be operating the ‘new’ reactor based on this ‘basic research’!**
**What will the legacy be?**
**Wow – those guys back then were really smart and  knew what they were doing. **
** **
**Man-o-Man – what were those guys thinking when they designed this pile of scrap metal. **

## Acknowledgements

**Glenn Glowa**
**Dave Guzonas**
**David Mancey**
**Ian Muir**
**Craig Stuart**
**Zane Walker**
**Mike Wright**